Petition for Writ of Certiorari — 3M Company, et al., Petitioners v. George Amador

APPENDIX

TABLE OF APPENDICES

Appendix A

Opinion, United States Court of Appeals

for the Eighth Circuit, Amador v. 3M Co.,

No. 19-2899 (Aug. 16, 2021) ........................ App-1

Appendix B

Order, United States Court of Appeals for

the Eighth Circuit, Amador v. 3M Co.,

No. 19-2899 (Nov. 9, 2021) ........................ App-46

Appendix C

Memorandum, United States District

Court for the District of Minnesota, In re

Bair Hugger Forced Air Warming Devices

Prods. Liab. Litig., MDL No. 15-2666

(July 31, 2019) ........................................... App-47

Appendix D

Order, United States District Court for

the District of Minnesota, In re Bair

Hugger Forced Air Warming Devices

Prods. Liab. Litig., MDL No. 15-2666

(Dec. 13, 2017) ......................................... App-101

Appendix E

Relevant Rule .......................................... App-134

Fed. R. Evid. 702 .............................. App-134

App-1

Appendix A

UNITED STATES COURT OF APPEALS

FOR THE EIGHTH CIRCUIT

________________

No. 19-2899

________________

IN RE: BAIR HUGGER FORCED AIR WARMING DEVICES

PRODUCTS LIABILITY LITIGATION

________________

GEORGE AMADOR,

v.

Plaintiff-Appellant,

3M COMPANY; ARIZANT HEALTHCARE, INC.,

Defendants-Appellees.

________________

Submitted: March 16, 2021

Filed: August 16, 2021

________________

Before: GRUENDER, KELLY, and GRASZ,

Circuit Judges.

________________

OPINION

________________

GRUENDER, Circuit Judge.

In December 2015, the Judicial Panel on

Multidistrict Litigation created and centralized the In

re Bair Hugger Forced Air Warming Devices Products

Liability Litigation (“MDL”) in the District of

Minnesota (“MDL court”) for coordinated pretrial

App-2

proceedings. Plaintiffs 1 in the MDL have brought

claims against 3M Company and its now-defunct,

wholly owned subsidiary Arizant Healthcare, Inc.

(collectively, “3M”). Plaintiffs assert that they

contracted periprosthetic joint infections (“PJIs”) due

to the use of 3M’s Bair Hugger, a convective (or

“forced-air”) patient-warming device, during their

orthopedic-implant surgeries. In July 2019, on 3M’s

motion, the MDL court excluded Plaintiffs’ generalcausation medical experts as well as one of their

engineering experts, and it then granted 3M summary

judgment as to all of Plaintiffs’ claims. Subsequently,

the MDL court entered an MDL-wide final judgment.

Plaintiffs appeal. First, they argue that the MDL

court abused its discretion in excluding their generalcausation medical experts and engineering expert.

Second, they argue that the MDL court erred in

granting 3M summary judgment whether or not those

experts were properly excluded. Third, they argue that

the MDL court abused its discretion in denying

Plaintiffs’ request for certain discovery. And fourth,

they argue that the MDL court abused its discretion

in ordering certain filings on its docket to remain

sealed. Additionally, on appeal, Plaintiffs ask us to

unseal those parts of the appellate record that

duplicate the filings whose sealing on the MDL court’s

docket they challenge.

We reverse in full the exclusion of Plaintiffs’

general-causation medical experts and reverse in part

the exclusion of their engineering expert. We reverse

1 Although George Amador is the captioned Plaintiff-Appellant,

this appeal is brought by all Plaintiffs in the MDL to challenge

several MDL-wide rulings.

App-3

the grant of summary judgment in favor of 3M. We

affirm the discovery order that Plaintiffs challenge.

We affirm the MDL court’s decision to seal the filings

Plaintiffs seek to have unsealed. And we deny

Plaintiffs’ motion to unseal those same filings on our

own docket.

I.

In the mid-1980s, Dr. Scott Augustine invented

the Bair Hugger, a forced-air device used to keep

patients warm during surgery so as to stave off

hypothermia-related complications that can arise

during or after surgery. The device consists of a

central heating unit, a hose, and a disposable

perforated blanket that is placed over the patient. The

central unit, which is often situated on or near the

floor when in use, draws in air through a filter, warms

that air (usually to a temperature significantly above

the operating-room temperature), and blows it

through the hose into the perforated blanket. The air

exits the blanket through the perforations and keeps

the patient warm. Typically, both the patient and the

blanket are covered with surgical draping during

operations, and the blanket is placed on a part of the

body away from the surgical site, so the air does not

blow directly onto the surgical site.

Dr. Augustine marketed and sold the Bair Hugger

through Augustine Medical, Inc., the company he

founded and led as CEO until 2004. Around that time,

Dr. Augustine was forced to leave Augustine Medical

while under investigation for Medicare fraud.

Augustine Medical then reorganized, and the division

of the company that retained the Bair Hugger product

line changed its name to Arizant Healthcare. In 2010,

App-4

3M acquired Arizant Healthcare and the Bair Hugger

product line. Arizant Healthcare was dissolved in

December 2014.

After leaving Augustine Medical, Dr. Augustine

developed the HotDog, a patient-warming device that

transfers heat conductively to the patient by direct

contact with the patient’s skin rather than by forced

hot air. He then began a campaign to discredit his old

invention and promote his new one. These efforts bore

fruit. In March 2013, a plaintiff sued 3M and Arizant

Healthcare in Texas state court, claiming that he

contracted a PJI due to the Bair Hugger’s use in his

hip-replacement surgery. Dr. Augustine worked with

the law firm representing that plaintiff to prepare a

“litigation guide” and solicitation letter for the

purpose of fomenting more litigation against 3M. By

December 2015, more than sixty materially similar

cases against 3M had been filed in or removed to

federal district courts around the country. At that

time, the Judicial Panel on Multidistrict Litigation

ordered these cases centralized in the District of

Minnesota for consolidated pretrial proceedings. See

28 U.S.C. § 1407(a). Nearly 6,000 lawsuits have since

been filed as part of the MDL.

In these cases, Plaintiffs allege that they suffered

PJIs from the use of the Bair Hugger during their

orthopedic-implant surgeries. PJIs are frequently

caused by the introduction of microbes into the

surgical site during surgery. Bacterial contamination

is a particularly significant threat in orthopedicimplant surgeries because a PJI can be caused by very

few microbes, possibly even a single bacterium. For

this reason, it is standard for such surgeries to take

App-5

place in “ultra-clean ventilation” operating rooms,

where air is blown into the operating room through

high-efficiency particulate air (“HEPA”) filtration at a

uniform velocity. This HEPA-filtered “laminar”

airflow blows over the patient, reducing the likelihood

that operating-room airflow will carry ambient

bacteria from nonsterile areas of the operating room

into the surgical site.

Plaintiffs advance two theories for how the Bair

Hugger caused their PJIs during their orthopedicimplant surgeries. According to the “airflow

disruption” theory, waste heat from the Bair Hugger

creates convection currents that carry ambient

bacteria from nonsterile areas of the operating room

to the surgical site despite the laminar airflow,

resulting in PJIs. According to the “dirty machine”

theory, the Bair Hugger is internally contaminated

with bacteria, which are blown through the blanket

into the operating room, where they become ambient

and eventually reach the surgical site, resulting in

PJIs.

In the master long-form complaint filed in the

MDL, Plaintiffs asserted fourteen state-law claims

against 3M, including negligence and strict liability

(for failure to warn, defective design, and defective

manufacture), among others.

During discovery, Plaintiffs subpoenaed a third

party, VitaHEAT Medical, LLC, to produce discovery

regarding its “UB3,” a conductive patient-warming

device. Plaintiffs alleged that the UB3 was an

alternative design to the Bair Hugger, making this

discovery ostensibly relevant to their design-defect

claims. See generally 63A Am. Jur. 2d Products

App-6

Liability § 894 (May 2021 update) (“The existence of

an alternative design may be used to establish that a

product was unreasonably dangerous due to a design

defect, and in some jurisdictions may be required.”).

VitaHEAT objected on relevancy grounds, arguing

that the UB3 was too different from the Bair Hugger

to count as an “alternative design” for product-liability

purposes. Plaintiffs then filed what they captioned a

“motion to overrule” this relevancy objection. The

MDL court denied this motion, agreeing that

conductive patient-warming devices like the UB3 are

too dissimilar from the Bair Hugger to qualify as

“alternative designs,” meaning that this discovery was

not relevant. Cf. United States v. One Assortment of 93

NFA Regulated Weapons, 897 F.3d 961, 966 (8th Cir.

2018) (“The Federal Rules of Civil Procedure limit

discovery to that which ‘is relevant to any party’s

claim or defense . . . .’” (quoting Fed. R. Civ. P.

26(b)(1))).

The parties jointly agreed to a protective order to

limit the disclosure of confidential information that

might be contained in filings entered on the MDL

docket. Pursuant to this protective order, the parties

submitted numerous filings under seal over the course

of the litigation. As relevant to this appeal, 3M sought

to keep seven such filings under seal over Plaintiffs’

objection, asserting that it would suffer competitive

harm if any was unsealed. The MDL court agreed and

ordered these files kept under seal.

As the litigation progressed, 3M moved to exclude

Plaintiffs’ general-causation medical experts (Dr.

Jonathan M. Samet, an epidemiologist; Dr. William

Jarvis, an infectious-disease specialist; and Dr.

App-7

Michael J. Stonnington, an orthopedic surgeon) as

well as Plaintiffs’ engineering experts (including Dr.

Said Elghobashi and Michael Buck). 3M also filed a

motion for summary judgment contingent on the

exclusion of Plaintiffs’ general-causation medical

experts. The MDL court denied in pertinent part the

motion to exclude those experts and denied the motion

for summary judgment.

Subsequently, Gareis v. 3M Co. became the first

bellwether trial in the MDL. See generally 156 Am.

Jur. Trials § 219 (May 2021 update) (explaining the

bellwether-trial process in mass-tort litigation).

Ruling on pretrial motions in Gareis, the MDL court

excluded evidence of Plaintiffs’ dirty-machine theory.

The case then proceeded to trial on the airflowdisruption theory, and Plaintiffs’ experts Dr. Jarvis,

Dr. Stonnington, and Dr. Elghobashi (among others)

testified. After an approximately two-week trial, the

jury returned a verdict for 3M.

After the Gareis trial, 3M moved for

reconsideration of the MDL court’s orders refusing to

exclude Plaintiffs’ general-causation medical experts

as well as Dr. Elghobashi and denying 3M summary

judgment. The MDL court granted 3M’s motion,

excluding Plaintiffs’ general-causation medical

experts as well as Dr. Elghobashi and granting 3M

summary judgment on all claims. The MDL court then

entered an MDL-wide final judgment. See In re

Temporomandibular Joint (TMJ) Implants Prods.

Liab. Litig., 97 F.3d 1050, 1055 (8th Cir. 1996) (“A

transferee court has the authority to enter dispositive

orders terminating cases consolidated under 28 U.S.C.

§ 1407.”).

App-8

Plaintiffs appeal, challenging the MDL court’s

exclusion of their general-causation medical experts

and Dr. Elghobashi, the MDL-wide grant of summary

judgment in favor of 3M, the discovery ruling

regarding conductive patient-warming devices, and

the sealing of seven MDL docket entries. Plaintiffs

also ask us on appeal to unseal on our own docket the

records that they argue should have been unsealed on

the MDL court’s docket.

II.

We begin by considering Plaintiffs’ challenge to

the MDL court’s exclusion of their general-causation

medical experts (Dr. Samet, Dr. Jarvis, and Dr.

Stonnington)

and

engineering

expert

(Dr.

Elghobashi). Dr. Samet, Dr. Jarvis, and Dr.

Stonnington

each

offered

general-causation

opinions—that is, opinions that the Bair Hugger “is

capable of causing the [PJIs] from which” Plaintiffs

allegedly suffered, see Junk v. Terminix Int’l Co., 628

F.3d 439, 450 (8th Cir. 2010) 2—based on both the

airflow-disruption theory and the dirty-machine

theory. Dr. Elghobashi created a computational-fluiddynamics (“CFD”) model to support the airflowdisruption theory. The MDL court generally treated

the medical experts as a collective set (their opinions

were essentially the same and were founded on much

of the same evidence), and it excluded their opinions

as unreliable because (1) it concluded there was “too

great an analytical gap between the literature and the

experts’ general causation opinions”; and (2) “the

2 The opinions in question did not address specific causation—

whether the Bair Hugger “in fact caused the harm from which”

any particular MDL plaintiff suffered. See id.

App-9

causal inferences made by the experts have not been

generally accepted by the scientific community.” 3 The

MDL court also excluded Dr. Elghobashi’s model and

opinion because (1) his conclusion about the Bair

Hugger’s effects in real-world operating rooms relied

on an unproven and untested premise, (2) there was

too great an analytical gap between the results of his

CFD and his conclusion about the Bair Hugger’s

effects in real-world operating rooms, and (3) the CFD

model was developed for litigation.

For the following reasons, we reverse in full the

exclusion of the medical experts’ opinions and reverse

in part the exclusion of Dr. Elghobashi’s model and

opinion. We first recite the principles that govern our

analysis. We then analyze the reasons given by the

MDL court for excluding the experts.

A.

As the proponent of the expert testimony in

question, Plaintiffs have the burden to prove its

admissibility by a preponderance of the evidence.

3 The MDL court articulated a third reason; namely, that “the

experts failed to consider obvious alternative explanations.” This

reason applies specifically to the medical experts’ treatment of

the epidemiological study on which they relied, see infra Section

II.B.1, that found an association between forced-air warming and

PJIs, see Federal Judicial Center, Reference Manual on Scientific

Evidence at 597-600 (3d ed. 2011) (explaining that

“[c]onsideration of alternative explanations” is one of nine factors

that “guide epidemiologists in making judgments about [general]

causation” based on a study or studies that find an association).

The MDL court discussed this same issue in its analysis of the

“analytical gaps” between that study and the experts’ opinions.

Accordingly, we consider this point in assessing the MDL court’s

“analytical gaps” analysis.

App-10

Lauzon v. Senco Prods., Inc., 270 F.3d 681, 686 (8th

Cir. 2001). Federal Rule of Evidence 702 governs the

admissibility of expert testimony, and under this rule

the district court is “vested with a gatekeeping

function, ensuring that ‘any and all scientific

testimony or evidence admitted is not only relevant,

but reliable.’” Union Pac. R.R. v. Progress Rail Servs.

Corp., 778 F.3d 704, 709 (8th Cir. 2015) (quoting

Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579,

589 (1993)). In exercising this gatekeeping function,

the district court has “broad discretion,” and “on

appeal we will not disturb a decision concerning the

exclusion of expert testimony absent an abuse of that

discretion.” Wagner v. Hesston Corp., 450 F.3d 756,

758 (8th Cir. 2006).

That said, we have recognized that the “liberal

thrust” of Rule 702 regarding the admissibility of

expert testimony creates “an intriguing juxtaposition

with our oft-repeated abuse-of-discretion standard of

review.” Johnson v. Mead Johnson & Co., 754 F.3d

557, 562 (8th Cir. 2014). “While we adhere to this

discretionary standard for review of the district court’s

Rule 702 gatekeeping decision, cases are legion that,

correctly, under Daubert, call for the liberal admission

of expert testimony.” Id. (collecting authorities).

Rule 702’s “screening requirement” has been

“boiled down to a three-part test.” Id. at 561. First, the

testimony must be useful to the finder of fact in

deciding the ultimate issue of fact, meaning it must be

relevant. See id. Second, the expert must be qualified

to assist the finder of fact. Id. Third, the testimony

must be reliable or trustworthy in an evidentiary

sense. Id. At issue here is the third part of this test—

App-11

whether Plaintiffs’ experts’ proposed testimony meets

Rule 702’s reliability requirement. “The standard for

judging the evidentiary reliability of expert evidence

is ‘lower than the merits standard of correctness.’”

Kuhn v. Wyeth, Inc., 686 F.3d 618, 625 (8th Cir. 2012)

(quoting In re Paoli R.R. Yard PCB Litig., 35 F.3d 717,

744 (3d Cir. 1994)).

The reliability inquiry is a “flexible” one, with

“[m]any factors” bearing on it. Daubert, 509 U.S. at

593-94. In Daubert, the Court articulated “four nonexclusive factors” relevant to this inquiry. Johnson,

754 F.3d at 562. These factors are (1) whether the

expert’s theory or technique can be or has been tested,

(2) whether the theory or technique has been subjected

to peer review or publication, (3) the known or

potential rate of error of the theory or technique, and

(4) whether the technique or theory is generally

accepted. See id.; Peitzmeier v. Hennessy Indus., Inc.,

97 F.3d 293, 297 (8th Cir. 1996). Factors recognized

since Daubert include “whether the experts are

proposing to testify about matters growing naturally

and directly out of research they have conducted

independent of the litigation, or whether they have

developed their opinions expressly for purposes of

testifying.” Daubert v. Merrell Dow Pharms., Inc., 43

F.3d 1311, 1317 (9th Cir. 1995).

Additionally, while Daubert instructed that the

focus of the reliability inquiry “must be solely on

principles and methodology, not on the conclusions

that they generate,” 509 U.S. at 595, the Supreme

Court later clarified that “conclusions and

methodology are not entirely distinct from one

another,” Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146

App-12

(1997). Thus, “a district court’s focus on principles and

methodology need not completely pretermit judicial

consideration of an expert’s conclusions,” Kuhn, 686

F.3d at 625 (internal quotation marks omitted), and a

district court may exclude expert testimony if it finds

“that there is simply too great an analytical gap

between the data and the opinion proffered,” Joiner,

522 U.S. at 146. Or, to put it in the language we have

frequently used both before and after Daubert and

Joiner, a district court may exclude an expert’s opinion

if it is “so fundamentally unsupported” by its factual

basis “that it can offer no assistance to the jury.” E.g.,

Loudermill v. Dow Chem. Co., 863 F.2d 566, 570 (8th

Cir. 1988); United States v. Finch, 630 F.3d 1057, 1062

(8th Cir. 2011).

When a district court excludes an expert’s opinion

for being fundamentally unsupported, yet another

“intriguing juxtaposition” is evident in our case law.

See Johnson, 754 F.3d at 562. On the one hand, we

have recognized that we owe “significant deference” to

the district court’s “determination that expert

testimony is excessively speculative,” and we “can

reverse only if we are convinced that the District Court

made a clear error of judgment on the basis of the

record before it.” Grp. Health Plan, Inc. v. Philip

Morris USA, Inc., 344 F.3d 753, 760 (8th Cir. 2003)

(internal quotation marks omitted). On the other

hand, we have stated numerous times that, “[a]s a

general rule, the factual basis of an expert opinion

goes to the credibility of the testimony, not the

admissibility.” E.g., United States v. Coutentos, 651

F.3d 809, 820 (8th Cir. 2011); see also Klingenberg v.

Vulcan Ladder USA, LLC, 936 F.3d 824, 829-30 (8th

Cir. 2019) (distinguishing cases where we affirmed the

App-13

exclusion of experts’ opinions as too speculative

because, in those cases, the experts’ opinions were

“wholly speculative,” “connected to the facts by only

the expert’s ipse dixit,” “patent speculation,” “pure

conjecture,” and “vague theorizing based upon general

principles”).

Thus, excluding an expert’s opinion for being

fundamentally unsupported is an exception to the

general

rule

that

“[g]aps

in

an

expert

witness’s . . . knowledge”

go

to

weight,

not

admissibility. See Robinson v. GEICO Gen. Ins., 447

F.3d 1096, 1100 (8th Cir. 2006); cf. Finch, 630 F.3d at

1062 (“Doubts regarding whether an expert’s

testimony will be useful should generally be resolved

in favor of admissibility.” (brackets omitted)).

“Vigorous cross-examination, presentation of contrary

evidence, and careful instruction on the burden of

proof are the traditional and appropriate means” of

addressing “shaky but admissible evidence.” Daubert,

509 U.S. at 596.

With these principles in mind, we analyze the

reasons provided by the MDL court for excluding

Plaintiffs’ general-causation medical experts and Dr.

Elghobashi (whose CFD model and testimony formed

part of the factual basis for the general-causation

medical experts’ opinions).

B.

We first consider the MDL court’s determination

that “too great an analytical gap” existed between “the

literature” and Plaintiffs’ medical experts’ generalcausation opinions. This literature falls generally into

two categories: (1) an epidemiological study reporting

an association between forced-air warming and PJIs;

App-14

and (2) studies and reports ostensibly supporting both

of Plaintiffs’ mechanistic theories of causation. We

consider this evidence to assess whether the MDL

court “made a clear error of judgment on the basis of

the record before it” in finding the experts’ opinions

too speculative to be admitted. See Grp. Health Plan,

344 F.3d at 760 (internal quotation marks omitted).

1.

All three medical experts relied on a 2011

observational epidemiological study as support for

their conclusion that the Bair Hugger is capable of

causing PJIs. See P.D. McGovern et al., Forced-Air

Warming and Ultra-Clean Ventilation Do Not Mix, 93B J. Bone & Joint Surgery 1537 (2011) (“McGovern

2011”). As an observational epidemiological study,

McGovern 2011 explored whether forced-air warming

was associated with an increased rate of PJIs by

comparing a group of individuals warmed convectively

to a group of individuals warmed conductively. See id.

at 1537. See generally Reference Manual, supra, at

552, 555-56.

Specifically, McGovern 2011 reviewed infection

data from 1,437 hip- or knee-replacement surgeries

performed at a particular hospital for a 2.5-year

period. Id. at 1537, 1540. From July 2008 to March

2010, the patients were warmed with Bair Huggers;

from March 2010 to June 2010, the hospital gradually

transitioned to using conductive patient-warming

devices; and from June 2010 to the end of the study,

the patients were warmed solely with conductive

patient-warming devices. Id. at 1540, 1543. The

investigators found that patients warmed convectively

were nearly four times more likely to contract a PJI

App-15

than patients warmed conductively. Id. at 1541. The

authors of McGovern 2011 acknowledged that the

study did “not establish a causal basis” for this

association. Id. at 1543. And they acknowledged that

their findings may have been “confounded” 4 by “other

infection control measures instituted by the hospital”

during the study period (specifically identifying two

such potentially confounding measures) and that they

were “unable to consider all [patient-medical-history]

factors” associated with PJIs, including a number of

“important predictors for deep infection,” due to

limited data in the records they reviewed. Id.

The MDL court found that McGovern 2011 itself

was sufficiently reliable to be admitted. But the MDL

court faulted the experts’ reliance on it in ways that

contributed to the analytical gap it found. For

instance, the MDL court deemed it unreliable for the

experts to draw an inference of causation from this

study when the study disclaimed having proved

causation. The MDL court also faulted how the

experts handled the study’s limitations.

As for the first point, we disagree that it is per se

unreliable for an expert to draw an inference of

causation from an epidemiological study that

disclaimed proving causation. “[E]pidemiology cannot

prove causation.” Reference Manual, supra, at 598.

“Confounding occurs when another causal factor (the

confounder) confuses the relationship between the agent of

interest and outcome of interest.” Reference Manual, supra, at

591. For instance, if those who drink alcohol are more likely to

smoke than those who do not, then smoking may be a confounder

in a study finding an association between drinking alcohol and

emphysema. See id. at 592.

4

App-16

Instead, epidemiology enables experts to find

associations, which by themselves do not entail

causation. See id. at 552-53, 598. But an observational

study such as McGovern 2011 “can be brought to bear”

on the question of causation, id. at 217, and “can be

very useful” to answering that question, id. at 221.

Ultimately

“causation

is

a

judgment

for

epidemiologists and others interpreting the

epidemiologic data.” Id. at 598; see also id. at 222 (“In

the end, deciding whether associations are causal

typically . . . rests on scientific judgment.”). Thus, it

was not necessarily unreliable for the experts to rely

on McGovern 2011 to draw an inference of causation

just because the study itself recognized, consistent

with these principles, that the association did not

establish causation. So long as an expert does the work

“to bridge the gap between association and causation,”

a study disclaiming having proven causation may

nevertheless support such a conclusion. See id. at 218.

We recognize that there is language from Joiner

that, when taken out of context, might appear to

suggest otherwise. See 522 U.S. at 145 (“Given that

[the authors of the study in question] were unwilling

to say that PCB exposure had caused cancer among

the workers they examined, their study did not

support the experts’ conclusion that Joiner’s exposure

to PCB’s caused his cancer.”). But the context

indicates that the problem with the experts’ opinions

in that case was that they failed to bridge the gap left

by the study in question. See id. at 145-46 (recounting

numerous issues with the experts’ factual basis).

As for the second issue, the MDL court rightly

faulted the experts for how they handled McGovern

App-17

2011’s limitations. “Assessing whether an association

is causal requires an understanding of the strengths

and weaknesses of the study’s design and

implementation,” and “the key questions” in

evaluating epidemiological evidence “are the extent to

which a study’s limitations compromise its findings

and permit inferences about causation.” Reference

Manual, supra, at 553. The experts did not adequately

address McGovern 2011’s limitations. Neither Dr.

Jarvis nor Dr. Stonnington mentioned the identified

potential confounders or limitations in McGovern

2011 in their reports. Dr. Samet, on the other hand,

did address in his report the two potential confounders

identified by the authors in the study itself, and he

meaningfully explained why in his view these

variables did not confound the study’s findings. But

Dr. Samet did not meaningfully address the other

limitations identified by the McGovern 2011 authors

except to say that confounding by other factors “seems

unlikely” for ostensibly logical reasons. 5

In the context of discussing this point, the MDL court also

faulted Dr. Samet for departing “from his own description of

reliable methodology.” Specifically, it noted that, with respect to

the criterion of consistency that experts use in making judgments

about causation, see Reference Manual, supra, at 600, Dr. Samet

noted that that criterion “is generally applied as a consideration

related to interpretation of findings of multiple observational

studies and hence is not applicable to the single study by

McGovern.” Because there was only one epidemiological study

here, Dr. Samet instead “point[ed] to the consistency of the

findings of studies addressing the effect of the Bair Hugger device

on particle counts at the surgical site.” In context, we do not read

this as Dr. Samet misapplying his own methodology but rather

acknowledging that the consistency factor was not relevant in its

conventional sense but nevertheless the consistency of the

5

App-18

However, McGovern 2011 was not the only basis

on which the experts relied in forming their opinions.

In addition to the epidemiological data from

McGovern 2011, the experts also relied on studies and

reports ostensibly showing plausible mechanisms by

which forced-air warming can cause PJIs. See id. at

599-600, 604 (identifying the “biological plausibility”

of a general-causation theory as one factor guiding

epidemiologists in “making judgments about

causation” and noting that “[w]hen biological

plausibility exists, it lends credence to an inference of

causality”). Thus, the experts’ failure to handle

McGovern 2011’s limitations properly is not fatal to

the admissibility of their opinions. See id. at 599-600

(listing “factors that guide epidemiologists in making

judgments about causation”; noting that “there is no

threshold number that must exist”; and including

among these factors “[b]iological plausibility” along

with “[c]onsideration of alternative explanations”).

“[A]n inference of causation based on the totality of the

evidence” may be reliable even if “no one line of

evidence support[s] a reliable inference of causation”

by itself. Milward v. Acuity Specialty Prods. Grp., Inc.,

639 F.3d 11, 23 (1st Cir. 2011); see also United States

v. W.R. Grace, 504 F.3d 745, 765 (9th Cir. 2007)

mechanistic studies supported an inference of causation from

McGovern 2011’s finding of an association. As he explained in the

next paragraph of his report following the language the MDL

court quoted, the mechanistic evidence is consistent with

McGovern 2011’s findings. The Reference Manual directs

epidemiologists to consider whether the finding of an association

is “consistent with other relevant knowledge,” supra, at 606, and

we fail to see how mechanistic evidence would not count as “other

relevant knowledge.”

App-19

(noting that whether an expert’s opinion testimony

satisfies Rule 702 “requires consideration of the

overall sufficiency of the underlying facts and data”).

Accordingly, we turn to the other evidence these

experts considered.

2.

The studies and reports ostensibly showing the

“biological plausibility” of the medical experts’

general-causation opinions broadly fall into two

categories. One set ostensibly supports Plaintiffs’

airflow-disruption theory, and the other ostensibly

supports Plaintiffs’ dirty-machine theory.

a.

All three medical experts relied on Plaintiffs’

airflow-disruption theory as a plausible causal

mechanism to support their general-causation

opinions. Again, according to this theory, waste heat

generated by the Bair Hugger creates convection

currents that disrupt laminar airflow in operating

rooms and transmit nonsterile air to the surgical site,

causing PJIs. The experts relied on two general

categories of evidence for this theory: (i) Dr.

Elghobashi’s CFD model and (ii) published studies

examining airflow patterns in operating rooms as well

as the correlation between particles and bacteria. We

consider each category in turn.

i.

To investigate whether forced-air warming

“play[s] a role” in transporting squames (skin flakes

capable of carrying bacteria that are present in

operating rooms) to the surgical site, Dr. Elghobashi

prepared a CFD model using large eddy simulation (a

App-20

way to model fluid turbulence) to simulate the Bair

Hugger’s effect on airflow and dispersion of squames

in an ultra-clean-ventilation operating room. Dr.

Samet and Dr. Jarvis relied on Dr. Elghobashi’s

model. The parties agree, and the MDL court found,

that the physics underlying Dr. Elghobashi’s model is

reliable. Dr. Elghobashi eventually published his

model with several coauthors in a peer-reviewed

journal. See X. He et al., Effect of Heated-Air Blanket

on the Dispersion of Squames in an Operating Room,

34 Int’l J. Numerical Methods Biomedical Eng’g, May

2018, at 1 (“He 2018”).

Dr. Elghobashi’s model replicated an orthopedic

operating room, including details such as laminar

airflow, an operating table, surgical drapes, a patient

underneath the drapes prepared for knee surgery, four

surgeons (two with hands extended over the patient,

two with hands down), two side tables, two surgical

lamps, the Bair Hugger blanket applied to the

patient’s torso under the drapes, and the Bair Hugger

central unit sitting on the floor near the head of the

operating table. Dr. Elghobashi accounted for the heat

generated by the Bair Hugger as well as heat

emanating from other sources, including the surgeons,

patient, surgical lamps, and even the exposed surface

of the patient’s knee. He then included approximately

three million 10-μm-sized squames on the floor of the

operating room near the operating table (a person

sheds on average about ten million squames a day).

After inputting a number of airflow-related details,

Dr. Elghobashi simulated whether the Bair Hugger

could lift these 10-μm-sized squames—particles

undisputedly large enough to carry bacteria and thus

be “dangerous”—up to four “regions of interest” in the

App-21

operating room, such as where the surgical tools are

kept and the surgical site itself.

Dr. Elghobashi’s model showed that, with the

Bair Hugger off, the laminar airflow in the operating

room was able to disperse the squames away from the

regions of interest and to airflow outlets. From this, he

concluded that “without the hot air discharged from

the blower, the ventilation air circulation alone cannot

disperse the squames to the surgical site.” But with

the Bair Hugger on, within less than a minute the

operating-room airflow was sufficiently disrupted by

Bair-Hugger-generated heat that convection currents

generated by the Bair Hugger lifted a statistically

significant number of squames to the regions of

interest.

Dr. Elghobashi’s conclusion was that “the hot air

from the blower and resultant thermal plumes are

capable of lifting [squames] and transporting them to

the side tables, above the operating table, and the

surgical site.” And he added that if other variables

were introduced into the model, such as movement of

medical staff, “then the probability of dispersing the

squames to the surgical site will be increased even

further.” In the published version of the study, Dr.

Elghobashi noted that “several . . . complexities

involving other medical equipment in an [operating

room], motion of the medical staff, opening and closing

of the [operating-room] door, among others are not

accounted for,” but he asserted that “these

complexities may not impact the main conclusions of

the present study.” He 2018, supra, at 18.

The MDL court excluded Dr. Elghobashi’s opinion

and his model for three reasons. First, it found that

App-22

his conclusion “relies on an unproven and untested

premise.” Second, it found that there was “too great an

analytical gap between the CFD results and Dr.

Elghobashi’s conclusion that the surgical team’s

movement would only increase the Bair Hugger’s

effect in the real world.” Third, Dr. Elghobashi’s CFD

model was developed for litigation, raising “concerns

about its reliability and objectivity.” We conclude that

entirely excluding Dr. Elghobashi and his model for

these reasons was an abuse of discretion. See, e.g.,

United Fire & Cas. Co. v. Whirlpool Corp., 704 F.3d

1338, 1341-42 (11th Cir. 2013) (per curiam) (reversing

in part the district court’s “sweeping exclusion” of an

expert’s testimony (citing, inter alia, Weisgram v.

Marley Co., 169 F.3d 514, 518 (8th Cir. 1999))).

The MDL court mainly faulted Dr. Elghobashi for

opining that if additional real-world conditions (such

as personnel movement) that have a significant

impact on airflow disruption were introduced into his

model, then the Bair Hugger’s effect on the dispersion

of squames would be exaggerated in a real-world

operating room. We affirm this aspect of the MDL

court’s exclusion. In neither his expert report nor his

published study did Dr. Elghobashi provide support

for this assertion, and at the Gareis trial he explained

that he knew this “based on [his] knowledge” and said

to “trust [him] about this.” “[N]othing in either

Daubert or the Federal Rules of Evidence requires a

district court to admit opinion evidence that is

connected to existing data only by the ipse dixit of the

expert.” Joiner, 522 U.S. at 146.

But we do not affirm the MDL court’s categorical

exclusion of Dr. Elghobashi and his model. Dr.

App-23

Elghobashi set out to determine whether forced-air

warming “play[s] a role in transporting squame

particles to the surgical site”; his CFD model tested

this hypothesis; and he found that forced-air warming

does play a role, at least in certain operating-room

conditions with limited airflow disruptions from other

sources. So limited, his conclusion was tested and

supported by the CFD model, and the problematic

analytical gap found by the MDL court is gone.

Granted, the MDL court also decided to exclude

Dr. Elghobashi’s testimony and model because they

were “developed for litigation.” See generally Lauzon,

270 F.3d at 687. But, with Dr. Elghobashi’s testimony

properly limited so as to eliminate the other reasons

for its exclusion, this factor alone does not warrant

exclusion. The scientific reliability of a “hired gun”

expert’s testimony can “be shown ‘by proof that the

research and analysis supporting the proffered

conclusions have been subjected to normal scientific

scrutiny through peer review and publication.’”

Lauzon, 270 F.3d at 693 (quoting Daubert, 43 F.3d at

1318). That happened here—Dr. Elghobashi’s report

in this case appears in a peer-reviewed journal. See He

2018, supra. In these circumstances—where a “hired

gun” expert’s work has been peer reviewed and

published, and the developed-for-litigation concern is

the only remaining reason for excluding the

testimony—we conclude that lingering questions of

reliability and objectivity go to weight rather than

admissibility. See DiCarlo v. Keller Ladders, Inc., 211

F.3d 465, 468 (8th Cir. 2000) (“An expert witness’s

bias goes to the weight, not the admissibility of the

testimony, and should be brought out on crossexamination.” (internal quotation marks omitted)).

App-24

Accordingly, the MDL court abused its discretion

insofar as it excluded all of Dr. Elghobashi’s

testimony. His testimony, properly limited as we have

specified here, is admissible. Therefore, his limited

testimony and CFD model may be considered as part

of the factual basis for Plaintiffs’ medical experts’

airflow-disruption-theory-based

general-causation

6

opinions.

As for the support that the CFD model and such

limited testimony would provide (if admissible) for the

medical experts’ general-causation opinions to the

extent that they are based on the airflow-disruption

theory, the MDL court noted that there was “too great

an analytical gap between the CFD results and the

medical experts’ conclusions that the Bair Hugger

causes infection.” The MDL court explained that this

was because the CFD model did not account for many

sources of turbulence often present in a real-world

operating room, thus leaving questions unanswered

about the real-world effects of the Bair-Huggercreated turbulence. We agree that there are gaps

between Dr. Elghobashi’s model simulating a “pure

operating room” and the opinion that the airflow6 In a footnote, the MDL court noted that if Dr. Elghobashi’s

testimony were so limited, it “would not assist the trier of fact in

resolving the factual dispute” in the cases in this MDL because

every such case will require Plaintiffs to prove specific causation.

But Dr. Elghobashi’s model and limited testimony are relevant

and admissible insofar as they provide part of the factual basis

for Plaintiffs’ medical experts’ general-causation opinions. See

Archer Daniels Midland Co. v. Aon Risk Servs., Inc. of Minn., 356

F.3d 850, 858 (8th Cir. 2004) (“An expert need not have an

opinion on an ultimate issue of fact in order for the testimony to

be admissible.”).

App-25

disruption theory is a plausible mechanism for how

the Bair Hugger causes PJIs in real-world operating

rooms. But Dr. Elghobashi’s CFD model is not the lone

support for the airflow-disruption theory, and whether

too great an analytical gap exists here requires

consideration of the totality of the evidence on this

point. See W.R. Grace, 504 F.3d at 765.

ii.

In addition to Dr. Elghobashi’s model, the medical

experts relied on a number of published studies to find

the airflow-disruption theory a plausible mechanism

of how the Bair Hugger causes PJIs, thereby

supporting their general-causation opinions. The

MDL court found that the studies themselves were

sufficiently reliable to be admitted. But it concluded

that there remained “too great an analytical gap

between these studies and the experts’ conclusion that

the Bair Hugger causes infection” by way of this

mechanism. First, the MDL court found that the

proposition that the Bair Hugger increases particleladen airflow over the surgical site was inadequately

supported because the studies that the experts cited

for this proposition did not simulate “real world”

operating-room conditions. Second, the MDL court

found that, even assuming this first proposition was

correct, the proposition that the particles in this

airflow carried bacteria was inadequately supported

because Dr. Jarvis “admitted” at the Gareis trial that

no study showed that the Bair Hugger has any impact

on particles that are large enough to carry bacteria

(other than “perhaps” the CFD model).

As for whether the Bair Hugger increases

particle-laden airflow over the surgical site, the MDL

App-26

court was correct that many of these studies, like Dr.

Elghobashi’s model, did not test the Bair Hugger’s

effects on airflow disruption and particle counts with

all potentially relevant variables included in the

analysis. See, e.g., McGovern 2011, supra, at 1537-38

(testing the airflow-disruption hypothesis by using a

mannequin warmed underneath surgical draping with

the Bair Hugger while having a surgeon stand

motionless next to the surgical site and an anesthetist

stand at the head of the operating-room table); K.B.

Dasari, M. Albrecht & M. Harper, Effect of Forced-Air

Warming on the Performance of Operating Theatre

Laminar Flow Ventilation, 67 Anaesthesia 244, 245,

248 (2012) (“Dasari 2012”) (finding that forced-air

warming created significant levels of excess heat

above and around the surgical site under laminarairflow conditions compared to conductive warming

technologies after applying forced-air warming to a

mannequin underneath surgical drapes and having

two people walk around in the laminar airflow but

acknowledging that “in a working operating [room]

there are more people and many other ways by which

the system might be disrupted”); A.J. Legg, T. Cannon

& A.J. Hamer, Do Forced Air Patient-Warming

Devices Disrupt Unidirectional Downward Airflow?,

94-B J. Bone & Joint Surgery 254, 255 (2012) (“Legg

2012”) (testing the airflow-disruption theory by

placing a volunteer draped for surgery with the

warmer applied under the drapes on an operating

table within an enclosure meant to facilitate laminar

airflow and having a surgeon stand within the

enclosure, but not including any assistants or

instrument trays in the enclosure); A.J. Legg & A.J.

Hamer, Forced-Air Patient Warming Blankets Disrupt

App-27

Unidirectional Airflow, 95-B Bone & Joint J. 407, 407

(2013) (“Legg 2013”) (using similar conditions as in

Legg 2012); Kumar G. Belani et al., Patient Warming

Excess Heat: The Effects on Orthopedic Operating

Room Ventilation Performance, 117 Anesthesia &

Analgesia 406, 406-07, 410 (2013) (“Belani 2013”)

(testing the airflow-disruption theory by draping a

mannequin, applying warming devices underneath

the drapes to the mannequin’s torso, and having an

anesthetist stand motionless at the head of the

mannequin, but cautioning that their findings were

“dependent on [the] exact setup” of the experiment,

which omitted “instrument trays and a working

surgical team”).

These limitations notwithstanding, a few of these

studies make findings and observations that

ameliorate the problematic gap the MDL court found

between the simulated operating-room conditions in

these studies and real-world operating rooms. For

instance, in McGovern 2011, the authors noted how

the surgical lighting, drapes, and personnel in their

study created “fragile [airflow] conditions” that

facilitated the Bair Hugger’s ability to disrupt airflow

significantly enough to transmit air from nonsterile

areas of the operating room to the surgical site.

McGovern 2011, supra, at 1542. Similarly, in Belani

2013, the authors found that surgical lighting and

drapes magnified the Bair Hugger’s effects. Belani

2013, supra, at 410. In other words, findings in these

studies provide empirical support bridging the

analytical gap from simulated operating-room

conditions to real-world operating-room conditions.

This analytical gap, then, was at least partially

illusory.

App-28

As for whether particles in the increased airflow

over the surgical site include bacteria-laden particles,

the MDL court made too much of Dr. Jarvis’s

“admission.” As Dr. Jarvis explained at the Gareis

trial, the key study on which the medical experts

relied to correlate particles with bacteria found a

statistically significant association between the

presence of bacteria and the presence of particles

measuring both 5.0-10.0 μm in diameter and ≥10.0 μm

in diameter. See Gregory W. Stocks et al., Predicting

Bacterial Populations Based on Airborne Particulates:

A Study Performed in Nonlaminar Flow Operating

Rooms During Joint Arthroplasty Surgery, 38 Am. J.

Infection Control 199, 199-202 (2010) (“Stocks 2010”). 7

The Legg 2012 authors found a statistically significant

increase in particles measuring 5.0 μm in size over the

surgical site when forced-air warming was used. Legg

2012, supra, at 255-56. And, as discussed above, Dr.

Elghobashi’s (admissible) CFD model showed

particles measuring 10.0 μm in size reaching “regions

of interest” (including the region simulating the

surgical site) with the machine on for a short period of

time. In other words, the proposition that the increase

in particles caused by the Bair Hugger includes

bacteria-laden particles finds support in the record.

The question for the MDL court was whether

there was sufficient support in the factual basis for the

experts’ opinions that the Bair Hugger is capable of

causing airflow disruption in a real-world operating

room that transmits bacteria to the surgical site. The

MDL court held that there was not. But, as we have

7 This study also noted that “[a]irborne bacteria-carrying

particles measure 4 μm to 20 μm.” Id. at 203.

App-29

just seen, there is significant support for the

proposition that the Bair Hugger independently is

capable of disrupting airflow so as to transmit bacteria

to the surgical site when other airflow-disruptive

variables are controlled for, and there also is empirical

support for the proposition that those other variables

can facilitate the Bair Hugger’s airflow-disruptive

effect in a real-world operating room. Thus,

notwithstanding the significant deference owed here,

we conclude that the MDL court committed a clear

error of judgment on the basis of the record before it,

see Grp. Health Plan, 344 F.3d at 760, in holding that

the experts’ general-causation opinions premised on

the airflow-disruption theory were “so fundamentally

unsupported” that they had to be excluded, see

Loudermill, 863 F.2d at 570. In light of the evidence

the experts relied on to find the airflow-disruption

theory a plausible mechanism to explain the

association found in McGovern 2011, this was an

instance in which our “general rule” that deficiencies

in an expert’s factual basis go to weight and not

admissibility should have been followed. See, e.g.,

Klingenberg, 936 F.3d at 830.

b.

All three medical experts also relied on the dirtymachine theory as a plausible causation mechanism to

support their general-causation opinions. Again,

according to this theory, the Bair Hugger is capable of

emitting bacteria harbored within the machine

through the blanket and ultimately to the surgical

site, causing PJIs. The experts relied on published

studies and reports ostensibly supporting this

App-30

mechanistic theory. 8 The MDL court found “too great

an analytical gap between the experts’ conclusions”

and these studies, faulting them for ignoring the

limitations in these studies, none of which examined

whether contaminated air emitted from the device

“could reach the surgical site and cause infection.”

For the dirty-machine theory to be plausible and

for the experts’ opinions to be reliably based on this

theory, four premises need to be sufficiently supported

in the evidence relied on by the experts. Cf. Hirchak,

980 F.3d at 609 (noting that, under Rule 702, “the

expert opinion itself—not just one of its several

premises—must be ‘based on sufficient facts’”). First,

the Bair Hugger internally must harbor bacteria in

either the central unit or the hose. Second, the Bair

Hugger must be capable of blowing that internal

According to his deposition testimony, Dr. Jarvis also

considered the experiment done by Plaintiffs’ engineering expert

Michael Buck, in which Buck found that the Bair Hugger emitted

out of the blanket 5-10 μm sized particles and >10 μm sized

particles. Seemingly because neither Dr. Jarvis nor the other two

medical experts cited Buck’s experiment in their reports,

however, 3M argues that none of these experts relied on Buck’s

work and so this work cannot be considered part of the factual

basis for their opinions. See Hirchak v. W.W. Grainger, Inc., 980

F.3d 605, 609 (8th Cir. 2020) (noting that evidence an expert did

not consider cannot rescue the expert’s opinion from

inadmissibility “by filling its analytical gaps”); Turner v. Iowa

Fire Equip. Co., 229 F.3d 1202, 1209 (8th Cir. 2000) (rejecting

plaintiffs’ attempt to bolster their expert’s causation opinion with

materials corroborating it because the expert “simply did not rely

upon those items in formulating his opinion”). We decline to

resolve this point because we find that the studies and reports

that the experts undisputedly relied on provide enough of a

factual basis to render a clear error of judgment the MDL court’s

finding of “too great” an analytical gap here.

8

App-31

contamination into the blanket. Third, that internal

contamination must be capable of escaping the

blanket. And fourth, that internal contamination

must be able to reach the surgical site.

The first premise is well supported by the studies

that the experts cite, many of which found that Bair

Huggers were internally contaminated with bacteria.

See, e.g., M.S. Avidanet al., Convection Warmers—Not

Just Hot Air, 52 Anaesthesia 1073, 1074-75 (1997)

(“Avidan 1997”); A.T. Bernards et al., Persistent

Acinetobacter Baumannii? Look Inside Your Medical

Equipment, 25 Infection Control & Hosp.

Epidemiology 1002, 1002, 1004 (2004) (“Bernards

2004”); Mark Albrecht, Robert Gauthier & David

Leaper, Forced-Air Warming: A Source of Airborne

Contamination in the Operating Room?, 1 Orthopedic

Reviews 85, 85-87 (2009) (“Albrecht 2009”); Mark

Albrecht et al., Forced-Air Warming Blowers: An

Evaluation of Filtration Adequacy and Airborne

Contamination Emissions in the Operating Room, 39

Am. J. Infection Control 321, 322, 324-25 (2011)

(“Albrecht 2011”).

The second premise also finds support in these

studies. See, e.g., Avidan 1997, supra, at 1074 (finding

that air blown out of Bair Hugger hoses contained

microbes); Albrecht 2009, supra, at 85, 87 (finding that

Bair Hugger hoses were emitting particles in the size

range of airborne microbes).

The third and fourth premises find less support

but are not unsupported. On the one hand, one of the

studies expressly recognized that, for a “direct risk”

from the internal contamination to be present, the

airflow from the machines would have to reach the

App-32

surgical site, and it observed that it was “presently

unknown whether this happens” because the blanket

“may act as a low-efficiency microbial filter” and

“surgical drapes may act as a barrier.” See Mike Reed

et al., Forced-Air Warming Design: Evaluation of

Intake Filtration, Internal Microbial Buildup, and

Airborne-Contamination Emissions, 81 Am. Ass’n

Nurse Anesthetists J. 275, 279 (2013) (“Reed 2013”).

On the other hand, a subsequent report described an

incident in which a short-circuit inside a Bair Hugger

generated smoke that was emitted through the

blanket and deposited as soot on the patient’s body in

the pattern of the holes in the Bair Hugger blanket,

undermining

the

blanket-as-secondary-filter

hypothesis and supporting the third premise. See T.

Moon et al., Forced Air Warming Device Failure

Resulting in Smoke and Soot on a Surgical Patient, 4

Open Access J. Surgery, May 2017, at 1 (“Moon

2017”). 9 And the fourth premise finds support in

several sources. For one, in a 2004 report on a

bacterial-outbreak investigation, the investigators

reported that they traced the outbreak strain to the

interior of a ventilator and a Bair Hugger, explained

that the outbreak subsided once they cleaned the

ventilator and replaced the Bair Hugger’s filter, and

offered their view that “the outbreak strain was

9 Moon 2017 does not provide unimpeachable support for the

third premise, to be sure, because it was unknown whether the

particles blown out of the blanket and onto the patient were of

the size capable of carrying bacteria. We note, however, that one

of 3M’s own experts effectively conceded the validity of the third

premise, testifying when asked at deposition that “some

particles” blown into the blanket will leave it and that some of

those particles “[m]ost likely” will carry bacteria.

App-33

transmitted by being carried on contaminated dust

from within the machines to the exterior during

operation.” Bernards 2004, supra, at 1003.

Additionally, some of the airflow-disruption studies

the experts relied on reported that air from where the

blanket exhausted waste heat reached the surgical

site and that certain draping arrangements would

facilitate that. See, e.g., McGovern 2011, supra, at

1537, 1539-40; Belani 2013, supra, at 407.

Accordingly, we conclude that it was a clear error

of judgment for the MDL court to find that the experts’

opinions insofar as they were based on the dirtymachine theory were so fundamentally unsupported

that they should be excluded. See Grp. Health Plan,

344 F.3d at 760; Loudermill, 863 F.2d at 570.

Certainly, there are weaknesses in the dirty-machine

theory. Again, however, redress for such weaknesses

lies in cross-examination and contrary evidence rather

than exclusion. See Bonner, 259 F.3d at 929; but cf.

Polski v. Quigley Corp., 538 F.3d 836, 839-41 & n.4

(8th Cir. 2008) (affirming the exclusion of an expert’s

causation opinion based on an untested mechanistic

theory that the expert himself previously had

effectively stated was implausible).

*

*

*

In sum, we do not dispute the MDL court’s

determination that there are weaknesses in the

factual basis for Plaintiffs’ medical experts’ generalcausation opinions. On the one hand, they have

epidemiological evidence reporting an association

between Bair Hugger use and PJIs, but on the other

hand they failed to grapple adequately with the

shortcomings of that evidence. On the one hand, they

App-34

have identified two plausible mechanisms explaining

this association, but on the other hand there are

weaknesses in the supports for both mechanisms.

This said, the question the MDL court ultimately

had to answer was whether these shortcomings left

“too great an analytical gap” between the factual bases

for the experts’ opinions and the general-causation

opinions themselves, see Joiner, 522 U.S. at 146; or, in

other words, whether the opinions were “so

fundamentally unsupported” that they should be

excluded rather than admitted and left to be

impeached through cross-examination at trial (as

evidently happened effectively at the Gareis trial), see

Loudermill, 863 F.2d at 570. While giving due

deference to the MDL court’s determination, we

nevertheless conclude that the MDL court committed

a clear error of judgment on the basis of the record

before it in finding that the experts’ general-causation

opinions were so fundamentally unsupported that

they had to be excluded. 10

10 In arguing to the contrary, 3M relies heavily on our decision

in Glastetter v. Novartis Pharmaceuticals Corp., where we

affirmed the exclusion of medical experts who “lacked a proper

basis” for their general-causation opinions that a certain

medication could cause intracerebral hemorrhages. 252 F.3d 986,

988-89 (8th Cir. 2001) (per curiam). We find Glastetter

distinguishable, most saliently because the experts in that case

had no epidemiological evidence on which to rely to link the

medication to its purported effect, see id. at 992, unlike Plaintiffs’

general-causation experts here, cf. id. (noting that

“epidemiological studies and reports are much desired by

litigants in cases involving medical causation”); Norris v. Baxter

Healthcare Corp., 397 F.3d 878, 882 (10th Cir. 2005)

(“[E]pidemiology is the best evidence of general causation in a

toxic tort case.”).

App-35

We emphasize that this conclusion is a narrow

one—again, the standard for admissibility is “lower

than the merits standard of correctness,” Kuhn, 686

F.3d at 625—that turns greatly on the fact that the

opinions at issue here address general causation

(whether the Bair Hugger can cause a PJI) rather

than specific causation (whether the Bair Hugger did

cause a particular plaintiff’s PJI). See Junk, 628 F.3d

at 450. In several places in its order excluding the

medical experts, the MDL court suggested that the

weaknesses in the experts’ general-causation

evidence, particularly in the evidence regarding the

mechanisms of causation, would present significant

hurdles for the specific-causation showing these

Plaintiffs must make to prevail—that is, that they

would not have contracted a PJI but for use of the Bair

Hugger during their surgeries. Whether this is so is

not at issue in this appeal, and we express no view on

it here. We hold only that the MDL court abused its

discretion in excluding these experts’ generalcausation opinions on the basis of excessive analytical

gaps.

C.

The MDL court’s analytical-gap determination

constituted the primary justification for its decision to

exclude Plaintiffs’ general-causation medical experts.

But it did briefly find as well that lack of general

acceptance of the causal inferences made by the

experts also supported excluding their testimony. In

Daubert, the Court rejected “a rigid ‘general

acceptance’ requirement” that could alone be

dispositive, but it did acknowledge that general

acceptance (or lack thereof) “can yet have a bearing on

App-36

the inquiry.” 509 U.S. at 588, 594. However, this factor

must be applied while bearing in mind “that a rigid

general acceptance requirement would be at odds with

the liberal thrust of the Federal Rules and their

general approach of relaxing traditional barriers to

opinion testimony.” Lauzon, 270 F.3d at 691 (internal

quotation marks omitted).

The MDL court considered three data points in its

general-acceptance analysis. First, it noted how, in a

statement put out by the 2013 International

Consensus Meeting on Periprosthetic Joint Infection,

there was a strong consensus that, although forced-air

warming devices posed a “theoretical risk,” no studies

had “shown” an increase in surgical-site infections

related to the use of these devices, and although

“[f]urther study” was warranted there was no need to

stop using forced-air warming devices based on the

evidence at that time. Second, it considered a letter

issued by the Food and Drug Administration in 2017

reporting the agency’s determination that it had been

“unable to identify a consistently reported association”

between forced-air warming and surgical-site

infection and continuing to recommend using such

devices “when clinically warranted.” Third, it noted

that, in a statement put out by the 2018 International

Consensus Meeting on Musculoskeletal Infection,

there was a strong consensus that there was “no

evidence to definitively link” forced-air warming to an

increased risk of PJIs.

Notably, however, in that 2018 statement, the

authors of the rationale for the bottom-line consensus

recognized that “the literature is conflicting,” and they

called for further study to examine the issue. And

App-37

Plaintiffs’ experts’ general-causation inferences are

not without support in the medical community. See,

e.g., A.M. Wood et al., Infection Control Hazards

Associated with the Use of Forced-Air Warming in

Operating Theatres, 88 J. Hospital Infection 132, 132

(2014) (concluding, after a review of the literature on

the issue, that forced-air warming “does contaminate

ultra-clean air ventilation,” though acknowledging

that “current research” had not shown a “definite link”

between forced-air warming and surgical-site

infections such as PJIs); cf. Primiano v. Cook, 598 F.3d

558, 565 (9th Cir. 2010) (recognizing that “medical

knowledge is often uncertain” and that “[l]ack of

certainty is not, for a qualified expert, the same thing

as guesswork”). Even some of the other authorities 3M

calls to our attention as showing a lack of general

acceptance acknowledge that “concerns exist” about a

link between forced-air warming and surgical-site

infections, see Melissa D. Kellam, Loraine S.

Dieckmann & Paul N. Austin, Forced-Air Warming

Devices and the Risk of Surgical Site Infections, 98

AORN J. 353, 365 (2013), and suggest modifications to

forced-air-warming devices to “reduce the risk” they

may pose, see ECRI Update: You’re Getting Warm:

Uncovering Forced-Air Warming Units, ECRI

Institute (May 1, 2017).

To exclude the experts’ opinions here because

their conclusions lacked general acceptance would be

to take a side on an issue that is “currently the focus

of extensive scientific research and debate.” See

Milward, 639 F.3d at 22; cf. Bonner, 259 F.3d at 929

(“[N]either Rule 702 nor Daubert requires that an

expert opinion resolve an ultimate issue of fact to a

scientific absolute in order to be admissible.”).

App-38

Accordingly, in light of our rejection of the MDL

court’s analytical-gap rationale for exclusion, we

conclude that the lack of general acceptance does not

independently justify exclusion of Plaintiffs’ generalcausation medical experts. Cf. Milward, 639 F.3d at

22, 26 (criticizing the district court in that case for

placing “undue weight on the lack of general

acceptance” of an expert’s conclusions about causation

and ultimately reversing its exclusion of that expert).

III.

The MDL court’s grant of summary judgment to

3M was derivative of its order excluding Plaintiffs’

general-causation

medical

experts

and

Dr.

Elghobashi. Because we reverse in relevant part the

exclusion of those experts, we reverse the grant of

summary judgment. See, e.g., Kuhn, 686 F.3d at 633. 11

IV.

We next consider Plaintiffs’ challenge to the MDL

court’s discovery ruling prohibiting them on relevancy

grounds from obtaining discovery concerning

conductive patient-warming devices. Plaintiffs argue

that this ruling was an abuse of discretion because the

discovery is relevant to their design-defect claims. We

find no basis to reverse.

“Appellate review of a trial court’s determination

concerning discovery matters is very narrow.”

McGowan v. Gen. Dynamics Corp., 794 F.2d 361, 363

(8th Cir. 1986). “[W]e will only reverse upon a showing

11 We thus do not reach Plaintiffs’ argument in the alternative

that summary judgment was erroneously granted even if the

general-causation medical experts and Dr. Elghobashi were

properly excluded.

App-39

of a ‘gross abuse of discretion resulting in fundamental

unfairness in the trial of the case.’” Ahlberg v. Chrysler

Corp., 481 F.3d 630, 637-38 (8th Cir. 2007) (quoting

Firefighters’ Inst. for Racial Equality ex rel. Anderson

v. City of St. Louis, 220 F.3d 898, 902 (8th Cir. 2000)).

We assume without deciding that, as Plaintiffs

argue, the MDL court erroneously concluded that this

discovery was irrelevant across the entire MDL

because some states would (or might allow a jury to)

recognize conductive patient-warming devices as

reasonable alternative designs to convective patientwarming devices. Even so, Plaintiffs have not even

argued on appeal, let alone shown, that the MDL

court’s discovery ruling resulted in fundamental

unfairness to them in trying their cases. See

Moses.com Secs., Inc. v. Comprehensive Software Sys.,

Inc., 406 F.3d 1052, 1060 (8th Cir. 2005) (declining to

reverse a discovery ruling where the party seeking

reversal of the discovery rulings at issue did not

specify how the rulings “resulted in fundamental

unfairness” and the record did not support a finding

that the party “suffered prejudice as a result of the

rulings”); Ahlberg, 481 F.3d at 634 (“[P]oints not

meaningfully argued in an opening brief are waived.”).

Even if we considered the point, we would not find

fundamental unfairness on this record. Plaintiffs

apparently had other reasonable-alternative-design

evidence available to them, as is demonstrated by

their recitation of studies suggesting that filterrelated modifications to the Bair Hugger would make

it safer. See, e.g., Restatement (Third) of Torts: Prod.

Liab. § 2 cmt. f (Am. Law Inst. 1998) (providing an

example of a modified existing product as a reasonable

App-40

alternative design). In addition, Plaintiffs were

permitted discovery regarding other convective

warming devices for reasonable-alternative-design

purposes. See id. (“[O]ther products already available

on the market may serve the same or very similar

function at lower risk and at comparable cost. Such

products may serve as reasonable alternatives to the

product in question.”).

V.

We now turn to Plaintiffs’ challenge to the MDL

court’s decision to seal certain filings on its own

docket. We review the district court’s decision to seal

records for an abuse of discretion. IDT Corp. v. eBay,

709 F.3d 1220, 1223 (8th Cir. 2013).

Plaintiffs take issue with the sealing of seven

filings: (1) MDL Docket Entry No. 221-19 (also located

at MDL Docket Entry Nos. 347, 887, 938, and 1801);

(2) MDL Docket Entry No. 221-20 (also located at

MDL Docket Entry Nos. 895 and 1806); (3) MDL

Docket Entry No. 340 (also located at MDL Docket

Entry No. 944); (4) MDL Docket Entry No. 377 (also

located at MDL Docket Entry No. 945); (5) MDL

Docket Entry No. 901 (also located at MDL Docket

Entry No. 1808); (6) MDL Docket Entry No. 937; and

(7) Docket Entry No. 1805 (which is another version of

the document at MDL Docket Entry No. 937). 12 As the

12 Plaintiffs assert in passing that “[t]he MDL court erroneously

sealed dozens of court records,” but in both their opening brief

and appellate motion they argue specifically only that these

seven records should be unsealed. Accordingly, we decline to

consider their challenge to the sealing of any other documents

besides these seven. See McKay v. City of St. Louis, 960 F.3d

1094, 1099 n.2 (8th Cir. 2020).

App-41

MDL court found, these documents contain sensitive

business and strategic planning information. For

each, 3M asserted that it would suffer competitive

harm if the document was unsealed. The MDL court

agreed and ordered these files kept under seal.

Plaintiffs argue this was an abuse of discretion. We

find no abuse of discretion.

“[T]here is ‘a common-law right of access to

judicial records.’” Webster Groves Sch. Dist. v. Pulitzer

Pub. Co., 898 F.2d 1371, 1376 (8th Cir. 1990) (quoting

Nixon v. Warner Commc’ns, Inc., 435 U.S. 589, 597

(1978)). “This right of access is not absolute,” however,

“but requires a weighing of competing interests.” Id.

When this common-law right is implicated, “we give

deference to the trial court rather than taking the

approach of some circuits and recognizing a ‘strong

presumption’ favoring access.” Id. (quoting United

States v. Webbe, 791 F.2d 103, 106 (8th Cir. 1986)).

Whether sealing is warranted, the common-law

right of access notwithstanding, turns on “the relevant

facts and circumstances of the particular case.”

Warner Commc’ns, 435 U.S. at 599. The district court

“must consider the degree to which sealing a judicial

record would interfere with the interests served by the

common-law right of access and balance that

interference against the salutary interests served by

maintaining confidentiality of the information sought

to be sealed.” IDT Corp., 709 F.3d at 1223. Interests

served by the common-law right include bolstering

public confidence in the judicial system by allowing

citizens to evaluate the reasonableness and fairness of

judicial proceedings, allowing the public to keep a

watchful eye on the workings of public agencies, and

App-42

providing a measure of accountability to the public at

large (which pays for the courts). Id. at 1222. But these

interests have “bowed before the power of a court to

insure that its records are not used to gratify private

spite,” to “promote public scandal,” to serve “as

reservoirs of libelous statements for press

consumption,” or to serve “as sources of business

information that might harm a litigant’s competitive

standing.” Warner Commc’ns, 435 U.S. at 598

(internal

quotation

marks

omitted).

The

“consideration of competing values” that must be done

here is “heavily reliant on the observations and

insights of the presiding judge.” Webbe, 791 F.2d at

106.

Here, the MDL court concluded that keeping the

contested records under seal was warranted because

they contained sensitive, commercially competitive

material “to which [3M’s] need to maintain

confidentiality . . . outweighs the public’s right of

access.” The record shows that Dr. Augustine—who,

as we noted above, created a competitor device to the

Bair Hugger and has helped foment this litigation

against 3M—has attempted to exploit and

misrepresent information learned in this MDL to 3M’s

detriment and to his commercial benefit. In other

words, the MDL court’s sealing decision was based on

“salutary interests,” see IDT Corp., 709 F.3d at 1223,

before which the common-law right of access “has

bowed,” see Warner Commc’ns, 435 U.S. at 598. See

also United States v. McDougal, 103 F.3d 651, 658 (8th

Cir. 1996) (agreeing that, “as a matter of public

policy,” courts “should avoid becoming the

instrumentalities of commercial or other private

App-43

pursuits”). Accordingly, we find no abuse of discretion

in this decision.

In arguing that we should hold otherwise,

Plaintiffs point out a “[m]odern” trend that “‘the

weight to be given the presumption of access’” is

“‘governed by the role of the material at issue in the

exercise of Article III judicial power and resultant

value of such information to those monitoring the

federal courts.’” IDT Corp., 709 F.3d at 1224 (quoting

United States v. Amodeo, 71 F.3d 1044, 1049 (2d Cir.

1995)). In these cases, “the strong weight to be

accorded the public right of access” in some instances

derives from the central role the documents in

question play “in determining litigants’ substantive

rights” and “from the need for public monitoring of

that conduct.” Amodeo, 71 F.3d at 1049. “Where

testimony or documents play only a negligible role in

the performance of Article III duties,” however, “the

weight of the presumption is low.” Id. at 1050.

Even assuming this is the correct framework to

govern the sealing issue here, but cf. Webster Groves

Sch. Dist., 898 F.2d at 1376 (noting that we give

deference to the district court’s sealing decisions

“rather than taking the approach of some circuits and

recognizing a ‘strong presumption’ favoring access”),

we nonetheless would find no abuse of discretion. The

only place where Plaintiffs indicate that the MDL

court “discussed and analyzed” these documents is in

a footnote in its Daubert reconsideration order where

it mentioned in passing that it was “unable to

determine” from these documents whether they

undermined its general-acceptance analysis. As noted

above, the general-acceptance factor played a

App-44

negligible role in the MDL court’s Daubert decision.

And these documents played a negligible role in the

MDL

court’s

general-acceptance

analysis.

Accordingly, any “presumption of access” to these

documents is “low,” and the “countervailing reason[s]”

justifying sealing here trump the right of access. See

Amodeo, 71 F.3d at 1050.

Plaintiffs also ask us to join several other circuits

and hold that there is a First Amendment

presumption of public access to summary-judgment

materials (which they contend the contested records

are). See, e.g., Rushford v. New Yorker Magazine, Inc.,

846 F.2d 249, 253 (4th Cir. 1988). We have yet to

decide “whether there is a First Amendment right of

public access to the court file in civil proceedings.” IDT

Corp., 709 F.3d at 1224 n.*. We have said, however,

that for such a right to be recognized at least two

prerequisites must be satisfied: (1) there is a historical

tradition of accessibility to the records in question,

and (2) there is a significant positive role for public

access in the functioning of the judicial process in

question. Id. Plaintiffs do not even mention, let alone

meaningfully argue, the first prerequisite, so we

decline to consider this argument. See McKay, 960

F.3d at 1099 n.2.

VI.

Plaintiffs also have filed a motion on appeal

asking us to unseal the same documents they want us

to order the MDL court to unseal. See Warner

Commc’ns, 435 U.S. at 598 (“Every court has

supervisory power over its own records and

files . . . .”). The rationale discussed in Section V for

affirming the MDL court’s sealing decisions regarding

App-45

the seven documents at issue applies with equal force

here, so we deny Plaintiffs’ request for us to unseal

these documents. 13

VII.

For the foregoing reasons, we affirm in part and

reverse in part the exclusion of Dr. Elghobashi’s CFD

model and opinion, we reverse the exclusion of

Plaintiffs’

general-causation

medical

experts’

opinions, we reverse the grant of summary judgment

to 3M, we affirm the discovery ruling challenged by

Plaintiffs on appeal, and we affirm the decision to seal

those filings whose sealing Plaintiffs challenge on

appeal. Finally, we deny Plaintiffs’ motion on appeal

to unseal those same filings.

13 In their opening brief, Plaintiffs also ask us to unseal “all

appellate briefs and appendices provisionally filed under seal.”

Plaintiffs filed unopposed motions to file redacted versions of

their briefs that were provisionally filed under seal and to allow

the unsealing of most of the contents in the appellate appendices

that also were provisionally filed under seal, and we already

granted these motions. To the extent they seek further unsealing,

their request appears redundant of the request they make in

their appellate motion to unseal, which we deny.

App-46

Appendix B

UNITED STATES COURT OF APPEALS

FOR THE EIGHTH CIRCUIT

________________

No. 19-2899

________________

IN RE: BAIR HUGGER FORCED AIR WARMING DEVICES

PRODUCTS LIABILITY LITIGATION

________________

GEORGE AMADOR,

v.

Plaintiff-Appellant,

3M COMPANY; ARIZANT HEALTHCARE, INC.,

Defendants-Appellees.

________________

Filed: November 9, 2021

________________

ORDER

________________

The petition for rehearing en banc is denied. The

petition for rehearing by the panel is also denied.

Judge Loken would grant the petition for

rehearing en banc.

Judge Benton and Judge Stras did not participate

in the decision or consideration of this matter.

November 09, 2021

Order Entered at the Direction of the Court:

Clerk, U.S. Court of Appeals, Eighth Circuit.

App-47

Appendix C

UNITED STATES DISTRICT COURT

FOR THE DISTRICT OF MINNESOTA

________________

MDL No. 15-2666

________________

IN RE: BAIR HUGGER FORCED AIR WARMING DEVICES

PRODUCTS LIABILITY LITIGATION

________________

Filed: July 31, 2019

________________

MEMORANDUM

________________

This multidistrict litigation (“MDL”) is before the

Court on Defendants’ motions to exclude the expert

testimony of Drs. William Jarvis, Jonathan Samet,

Michael Stonnington, and Said Elghobashi, under

Federal Rule of Evidence 702. For the reasons set forth

below, the Court grants the motions and grants

summary judgment for Defendants.

BACKGROUND

Plaintiffs allege that Defendants’ Bair Hugger

Forced Air Warming Device (“the Bair Hugger”)

caused their periprosthetic joint infection (“PJI”) as a

sequela to orthopedic-implant surgery. The Bair

Hugger, a device for keeping surgical patients warm,

consists of a portable heater or blower connected by a

flexible hose to a disposable blanket that is placed over

(or in some cases under) surgical patients. The Bair

Hugger intakes air from the surrounding area and

App-48

passes it through the intake filter and internal air

pathways of the machine and into an outlet hose. The

warm air travels through the distal end hose, which

does not have an air filter, and into the blanket,

providing warmth to the patient during surgery.

Because the patient’s torso (in hip and knee surgeries)

and the Bair Hugger blanket are covered with surgical

draping, the warm air does not blow directly onto the

surgical site.

Plaintiffs allege two theories about how the Bair

Hugger can cause PJI. First, Plaintiffs allege that the

Bair Hugger’s warm air flow escapes the bottom edge

of the surgical drape, creating turbulence in the

operating room (“OR”), which lifts squames (shed skin

flakes that can carry bacteria) into the air and into the

surgical site, and increases the risk of infection. The

Court has termed this theory the “airflow disruption”

theory. Dr. Elghobashi, a recognized expert in

computational fluid dynamics (“CFD”), built a CFD

simulation to model this theory. The simulation

purports to show that the Bair Hugger generates

extreme turbulence in the OR causing squames to

reach the surgical site. Second, Plaintiffs claim that

the device, which lacks an adequate filtration system,

emits contaminants into the OR, and thus, increases

the bacterial load reaching the surgical site. The Court

has labeled this second theory the “dirty machine”

theory.

Plaintiffs’ three medical experts—Drs. Jarvis,

Samet, and Stonnington—have opined that the Bair

Hugger causes PJI. For purposes of general causation,

the issue in this litigation is whether use of the Bair

Hugger device increases the risk of PJI compared to

App-49

the risk of infection when the device is not used. The

medical experts reviewed many studies that support

both theories of causation, including Dr. Elghobashi’s

CFD simulation, and one epidemiological study that

found a statistically significant association between

the Bair Hugger and PJI. Defendants argue, however,

that the scientific literature expressly disclaims

causation and asks the Court to exclude these opinions

for this reason.

In its December 13th, 2017 Daubert order, this

Court found the testimony of Plaintiffs’ engineering

expert—Dr. Elghobashi—and Plaintiffs’ medical

experts—Drs. Jarvis, Samet, and Stonnington—to be

admissible. The Court found that Dr. Elghobashi ran

a simulation, using accepted physics principles, to

show how the Bair Hugger’s warm air flow could cause

squames to float upward toward the surgical wound.

The Court also found that Drs. Jarvis, Samet, and

Stonnington relied on Dr. Elghobashi’s testimony as

well as the epidemiological study for reliable

mechanistic and statistical evidence that the Bair

Hugger causes PJI.

Defendants had also argued that if the Court

excluded Plaintiffs’ three general causation experts,

then summary judgment would be appropriate.

Because the Court denied Defendants’ Daubert

motion, the Court subsequently denied Defendants’

summary judgment motion.

In April 2018, the Court heard argument on the

parties’ case-specific dispositive motions in Gareis, the

App-50

first bellwether trial in the MDL. 1 The Court denied

Defendants’ motion to exclude expert testimony by Dr.

Elghobashi. The Court also denied Defendants’ motion

to exclude expert testimony by Drs. Jarvis and

Stonnington. Id.

In May 2018, the Court heard pretrial motions in

Gareis. The Court granted Defendants’ motion to

exclude evidence pertaining to Plaintiffs’ “dirty

machine” theory. The Court determined that

“Plaintiffs have no evidence that however many

Staphylococcus epidermidis might be in the Bair

Hugger, that that number would have a meaningful

impact on the bacterial load of that pathogen in the

operating room.” Gareis 16-cv-4187, ECF No. 306

(Order re Mot. in Lim.) at 2. Thus, the Court held that

Plaintiffs failed to introduce sufficient proof to support

this theory of causation. Id.

The trial commenced on May 14, 2018 and ended

May 30, 2018. Drs. Elghobashi, Jarvis, and

Stonnington all testified. On May 30th, a jury

returned a verdict in favor of Defendants. The jury

concluded that Plaintiffs did not prove by a

preponderance of the evidence that the Bair Hugger

1 This was not the first scheduled bellwether trial. On May 30,

2017, pursuant to Pretrial Order No. 19, the Court selected eight

bellwether cases from the parties’ proposed cases and then each

party exercised one strike to finalize the six cases in the “Final

Bellwether Trial Pool.” On June 16, 2017, the Court determined

the order of these six bellwether trials, listing Gareis as last.

Because the first five cases never made it to trial, Gareis became

the first bellwether to go to trial. On March 13, 2018, the Court

repopulated the bellwether pool and the parties selected an

additional twelve potential bellwethers (“the Bellwethers

Second”) per Pretrial Order No. 24.

App-51

caused the plaintiff’s infection. The jury further

concluded that Plaintiffs did not prove by a

preponderance that the Bair Hugger system was

unreasonably dangerous and a safer alternative

design existed.

In August 2018, 3M requested leave to move for

reconsideration of the Court’s Daubert rulings. In

their letter request, Defendants argued that new

evidence undermines the scientific support proffered

by Plaintiffs’ medical experts in their general

causation opinions. Under Local Rule 7.1(j), a party

must show “compelling circumstances” to obtain

permission from the court to move for reconsideration.

Motions for reconsideration serve “the limited

function of correcting manifest errors of law or fact

or . . . present[ing] newly discovered evidence.”

Bradley Timberland Res. v. Bradley Lumber Co., 712

F.3d 401, 407 (8th Cir. 2013). On November 20, 2018,

the Court concluded that Defendants demonstrated

compelling circumstances and granted the request. 2

On January 24, 2019, Defendants filed their

motion to reconsider and asked the Court to exclude

the testimony of Plaintiffs’ medical experts and Dr.

Elghobashi pursuant to Federal Rule of Evidence 702

and grant summary judgment in favor of Defendants.

On February 21, 2019, Plaintiffs filed their

Prior to granting Defendants’ request to file a motion for

reconsideration, the Court had directed the two joint nominees in

the Bellwethers Second—Hives and Axline—to prepare for trial.

Axline was set to be tried on December 3, 2018. But by November

15, 2018, Hives had been dismissed and Plaintiffs’ counsel had

indicated that they intended to dismiss the remaining claims in

Axline. ECF No. 1597 (Pretrial Order No. 27).

2

App-52

Memorandum in Opposition. Defendants replied on

March 14, 2019. On May 6, 2019, the Court posed

three additional questions to clarify issues relating to

both general and specific causation. The parties

responded on May 16, 2019. Both parties also

presented their arguments at a hearing on June 12,

2019.

LEGAL STANDARD

Rule 702 of the Federal Rules of Evidence governs

the admissibility of expert testimony. It states that a

qualified expert witness may testify to “scientific,

technical, or other specialized knowledge” if it “will

assist the trier of fact to understand the evidence or to

determine a fact in issue” and if “(1) the testimony is

based upon sufficient facts or data, (2) the testimony

is the product of reliable principles and methods, and

(3) the witness has applied the principles and methods

reliably to the facts of the case.” Fed. R. Evid. 702.

The key inquiry is whether the experts’

methodology is reliable enough to assist the trier of

fact. To aid in this inquiry, the Supreme Court in

Daubert identified four nonexclusive factors a court

can apply: “(1) whether the theory or technique ‘can be

(and has been) tested’; (2) ‘whether the theory or

technique has been subjected to peer review and

publication’; (3) ‘the known or potential rate of error’;

and (4) whether the theory has been generally

accepted.” Lauzon v. Senco Prod., Inc., 270 F.3d 681,

686-87 (8th Cir. 2001) (citing Daubert v. Merrell Dow

Pharm., 509 U.S. 570, 593-94 (1993)). “Daubert’s

progeny provides additional factors such as: whether

the expertise was developed for litigation or naturally

flowed from the expert’s research; whether the

App-53

proposed expert ruled out other alternative

explanations; and whether the proposed expert

sufficiently connected the proposed testimony with the

facts of the case.” Id. “[T]he trial court is left with great

flexibility in adapting its analysis to fit the facts of

each case.” Jaurequi v. Carter Mfg. Co., 173 F.3d 1076,

1082 (8th Cir. 1999).

DISCUSSION

In their motion for reconsideration, Defendants

challenge the testimony of Dr. Elghobashi, an

engineering expert, and all three medical experts. The

Court will address each argument in turn. If the Court

grants Defendants’ Daubert motions, Defendants

argue that summary judgment should follow. See, e.g.,

In re Viagra Prod. Liab. Litig., 658 F. Supp. 2d 950,

968 (D. Minn. 2009) (granting summary judgment

following the exclusion of plaintiffs’ general causation

expert). In the alternative, Defendants request that

the Court certify the general causation issue under 28

U.S.C. § 1292(b).

The Court has reviewed the arguments made

during Defendants’ initial Daubert motion to exclude

Plaintiffs’ medical and engineering experts, the

experts’ testimony during the Gareis trial in May

2017, and the new evidence proffered by Defendants

in their motion to reconsider. For the following

reasons, the Court grants Defendants’ Daubert

motions, and consequently, grants summary judgment

in favor of Defendants.

I.

DR. ELGHOBASHI’S TESTIMONY

Dr. Elghobashi’s testimony relies on a CFD model,

which simulated the impact of the Bair Hugger on the

dispersion of squames in an OR. The model compared

App-54

the blower off and on and concluded that operating the

Bair Hugger increases the number of squames

reaching the surgical site.

Defendants do not dispute Dr. Elghobashi’s

qualifications. Dr. Elghobashi is a professor at the

University of California Irvine Department of

Mechanical and Aerospace Engineering and a

recognized expert in the field of computational fluid

dynamics. Relying on the CFD simulation, Dr.

Elghobashi opines that the Bair Hugger disrupts

airflow in the OR and causes squames to reach the

surgical site.

Plaintiffs’ attorneys hired Dr. Elghobashi to

create a CFD model to study the interaction between

the OR heating ventilation and air conditioning

(“HVAC”) system and forced-air warming devices to

understand the effect of blowing hot air on the

dispersion of squames in an OR. A “large-eddy

simulation” (“LES”) is one of the methods used in

computational fluid dynamics simulations. This

modeling relies on engineering principles and several

governing equations related to fluid dynamics and

heat transfer that are solved by super computers. The

parties agree, and the Court found in its December

13th, 2017 order, that the physics underlying Dr.

Elghobashi’s simulation is reliable.

Dr. Elghobashi retained another CFD expert, Dr.

Sourabh Apte, to build the computer simulation using

certain inputs provided by Dr. Elghobashi. The LES

replicated an OR with an operating table, side tables,

surgical lamps, medical staff, and a patient. At trial,

Dr. Elghobashi listed a number of key parameters—or

“boundary conditions”—that were required to

App-55

calculate how the squames would move within the OR.

Those parameters included the size, number and

location of inlet and outlet vents for the HVAC, the

volumetric airflow through those vents, the

temperature of the air blown into and exiting from the

Bair Hugger warming blanket, and the volumetric

airflow exiting from the Bair Hugger blower.

He then evaluated the effect of the Bair Hugger

on particles—ten microns in size or greater—that are

large enough to carry bacteria. His simulation placed

three million squames on or within one centimeter of

the OR floor near the operating table. He also created

four imaginary “boxes” in the simulated airspace at

locations representing key areas such as the area

where surgical tools are stored and the area of the

surgical procedure. The goal of the simulation was to

determine if squames lifted into the air by the Bair

Hugger reached those areas.

Dr. Elghobashi ran simulations with the Bair

Hugger blower off and on. From those simulations, he

performed mathematical calculations to project the

movement of the squames. The CFD model showed

that the warm air from the Bair Hugger disrupts the

HVAC airflow and lifts squames into the “imaginary

boxes of interest” above the operating table. ECF

No. 1813-14, PX19 (Elghobashi Rpt.) at 59. In

contrast, when the Bair Hugger is off—and “only the

ventilation air from the inlet grilles and thermal

plumes created by the warm surfaces including

surgical lights, surgeons’ heads, patient’s head, and

patient’s knee are responsible for the dispersion of

squames”—the model demonstrated that the squames

are quickly dispersed to the outlet grilles and no

App-56

squames enter the imaginary boxes of interest. Id. at

57. From these results, Dr. Elghobashi “concluded

that without the hot air discharged from the blower,

the ventilation air circulation alone cannot disperse

the squames to the surgical site.” Id. Additionally, he

observed that “[t]he thermal plumes from various

warm surfaces only slightly affect the air coming from

the inlet grilles and do not affect the motion of the

squames.” Id.

Defendants argue that Dr. Elghobashi’s trial

testimony establishes that his CFD model does not

support general causation. At trial, Dr. Elghobashi

admitted that his simulation does not account for

many other sources of turbulence that would be found

in any real-world OR, such as the movement of

medical personnel. Consequently, Defendants argue

that Dr. Elghobashi cannot rely on the CFD results to

conclude that the Bair Hugger system would have a

similarly meaningful impact in a real OR.

Plaintiffs respond that Dr. Elghobashi explained

at trial that these additional variables, if measured,

would only exacerbate the Bair Hugger’s effect. They

contend Dr. Elghobashi, in isolating the Bair Hugger’s

effect, applied reliable scientific methodology.

Further, Plaintiffs assert that any disagreement with

“the factual basis of an expert opinion goes to the

credibility of the testimony, not the admissibility.”

Bonner v. ISP Techs., Inc., 259 F.3d 924, 929 (8th Cir.

2001) (quoting Hose v. Chicago Northwestern Transp.

Co., 70 F.3d 968, 974 (8th Cir. 1996)).

The Court excludes Dr. Elghobashi’s testimony for

the following reasons. First, Dr. Elghobashi’s

conclusion relies on an unproven and untested

App-57

premise. Second, there is too great an analytical gap

between the CFD results and Dr. Elghobashi’s

conclusion that the surgical team’s movement would

only increase the Bair Hugger’s effect in the real

world. Third, the CFD simulation was developed for

litigation, which raises concerns about its reliability

and objectivity.

A. There is Too Great an Analytical Gap

Between the CFD Results and Dr.

Elghobashi’s Conclusion About RealWorld Effects

Defendants do not challenge the reliability of CFD

generally. Rather, Defendants challenge the

reliability of the causal inferences that Dr. Elghobashi

draws from the CFD model.

The Supreme Court in Daubert emphasized that

a key consideration in assessing whether scientific

knowledge will assist the trier of fact is “whether it

can be (and has been) tested.” 509 U.S. at 593. Indeed,

the Court recognized that “[s]cientific methodology

today is based on generating hypotheses and testing

them to see if they can be falsified.” Id.

Applying Daubert, the Eighth Circuit affirmed the

exclusion of expert testimony where that expert’s

causation theory relied on “an unproven and indeed

untested premise.” Polski v. Quigley Corp., 538 F.3d

836, 840 (8th Cir. 2008). In Polski, plaintiffs alleged

that the use of Cold-Eeze, a nasal spray made for the

treatment of cold symptoms, permanently impaired

their senses of taste and smell. Id. at 837. Plaintiffs’

expert opined that the spray emitted from the ColdEeze bottle traveled into the nasal cavity, and caused

zinc ions in the spray to come into direct contact with

App-58

the olfactory epithelium. Id. at 839. But the expert

never tested this theory, which the district court

observed “could have easily and ethically been tested.”

Id. at 840. According to the Eighth Circuit, the district

court did not abuse its discretion by concluding that

this untested theory was “not sufficiently reliable to be

admitted under Rule 702.” Id. at 839-41 (quoting

Polski v. Quigley Corp., No. 04-4199, 2007 WL

2580550, at *5 (D. Minn. Sept. 5, 2007)). The Eighth

Circuit explained that plaintiffs had the burden of

establishing the testimony’s admissibility, which

“required sufficient proof that [the expert’s] testimony

was ‘the product of reliable principles and methods,’

and that [the expert] ‘applied the principles and

methods reliably to the facts of the case.’” Id. at 841

(quoting Fed. R. Evid. 702).

This case similarly involves an unproven and

untested theory. Although Dr. Elghobashi did conduct

the CFD modeling, which in broad terms might be

considered a “test,” he never tested his ultimate

conclusion. The CFD model showed that—in a

simulated OR—the Bair Hugger increases the number

of squames that reach the surgical site. The model also

showed that, when the Bair Hugger is off, the squames

are quickly dispersed to the outlet grilles and do not

reach the surgical site. Relying on the CFD model, Dr.

Elghobashi concluded that squames would not reach

the surgical site “without the hot air discharged from”

the Bair Hugger. ECF No. 1813-14, PX19 (Elghobashi

Rpt.) at 55.

Both Dr. Elghobashi and plaintiffs’ counsel

repeatedly emphasize that the simulation is intended

to represent what happens in a real-world OR where

App-59

a knee surgery is being performed. At trial, Dr.

Elghobashi testified that the CFD simulation reflects

conditions “identical to what happens in reality”

because he only omitted “insignificant machines,

computers and things which are not really important.”

Gareis 16-cv-4187, ECF No. 474 (May 21, 2018 Trial

Tr.) at 893:4-8. Plaintiffs’ counsel similarly

emphasized that the simulation was “not an

animation” but “a real world model of what happens

based on generally accepted mathematical principles.”

ECF No. 1000 (Oct. 25, 2017 Daubert Hearing Tr.) at

411:8-10. 3

To the extent Plaintiffs imply that the CFD model

reconstructs the particle movement in a surgery where infection

occurs, the model is inadmissible for this purpose. Simulations

“offered as evidence of what actually happened” are more like

“experimental evidence and require a showing of substantial

similarity.” 5 Christopher B. Mueller & Laird C. Kirkpatrick,

Federal Evidence § 9:26 (4th ed. 2019). In the Eighth Circuit, “[a]

court may properly admit experimental evidence if the tests were

conducted under conditions substantially similar to the actual

conditions.” Dunn v. Nexgrill Industries, Inc., 636 F.3d 1049,

1055 (8th Cir. 2011) (emphasis in original) (quoting McKnight v.

Johnson Controls, Inc., 36 F.3d 1396, 1401 (8th Cir. 1994)). The

simulated OR in the CFD model falls short of being “substantially

similar” to a real-life OR. Moreover, the Court emphasizes that

in other accident reconstruction cases where federal courts

recognized the reliability of CFD, the experts compared their

models to photographs of the accident to support or refute their

theory. See, e.g., Turner v. Liberty Mut. Fire Ins. Co., No. 4:07CV-00163, 2007 WL 2713062, at *3 (N.D. Ohio Sept. 14, 2007)

(the expert “compared the results of the simulation to ‘physical

and eyewitness evidence [photographs] to support or refute the

hypothesis’”); Dejana v. Marine Tech., Inc., No, 4:11-cv-1690,

2013 WL 4768407 at *9-12 (E.D. Mo. Dec. 20, 2013) (the expert

compared the results to photographs of the accident).

Consequently, the Court’s subsequent analysis focuses on the

3

App-60

However, at trial, Dr, Elghobashi testified that

the simulated OR omitted other sources of heat and

air movement. 4 Most notably, the simulated OR does

not account for the movement of personnel, which has

a significant impact on airflow disruption. Gareis 16cv-4187, ECF No. 474 (May 21, 2018 Trial Tr.) at

961:7-962:1. For example, in his expert report, Dr.

Elghobashi discussed the Chow & Wang (2012) study,

which—using Reynolds-averaged Navier Stokes

(“RANS”) modeling 5—found that the periodic bending

movement of one surgeon increased the concentration

of particles to a larger-than-recommended value near

the surgical site. ECF No. 1813-14, PX19 (Elghobashi

Rpt.) at 4-5. Further, at trial, Dr. Elghobashi

cautioned that turbulent flow cannot be measured by

admissibility of the CFD model for the purpose of predicting the

movement of airflow in a theoretical surgery based on

mathematical equations. In this context, “[i]t is essential that the

model be based on assumptions and data that are consistent with

the evidence in the case rather than on speculation.” Mueller &

Kirkpatrick, Federal Evidence § 9:26.

4 Dr. Elghobashi’s published study similarly acknowledged that

there are “several other complexities involving other medical

equipment in an OR, motion of the medical staff, opening and

closing of the OR door, among others are not accounted for.” ECF

No. 1813-30, PX36 (He 2018) at 19. While the study suggests that

“these complexities may not impact the main conclusions of the

present study,” the study provides no support for this statement.

Id. Here, the Court cites to Dr. Elghobashi’s submission for

publication, which Plaintiffs attached to their briefing. At trial,

Dr. Elghobashi confirmed that this study was published in

January 2018. Gareis 16-cv-4187, ECF No. 474 (May 21, 2018

Trial Tr.) at 863:22-865:7; 929:2-6.

5 Dr. Elghobashi accepts the validity of RANS modeling but

considers LES simulations to be superior.

App-61

hand because even reaching a hand in “would be

invasive to the flow” and “interrupt the results.”

Gareis 16-cv-4187, ECF No. 474 (May 21, 2018 Trial

Tr.) at 895:14-21. For this reason, Dr. Elghobashi

explained that scientists measure turbulent flows

with “noninvasive means” such as laser beams. Id.

Despite meaningful differences between the CFD

simulation and the real world, Dr. Elghobashi made

no attempt to limit his testimony about the Bair

Hugger’s effect to ORs without these other sources of

turbulence. 6 Instead, he concluded that the Bair

Hugger’s effect on the dispersion of squames would be

exaggerated in a real-world OR. Yet, this hypothesis

was never tested. Because Dr. Elghobashi never

factored in other sources of heat and air movement,

the CFD model did not test whether squames would

be able to reach the surgical site without the hot air

discharged from the blower in a real OR. The model

also did not test whether squames would be

significantly more likely to reach the surgical site

when the Bair Hugger is turned on in a real OR. Thus,

applying Polski, the Court finds that Dr. Elghobashi’s

conclusion relies on an unproven and untested

6 Dr. Elghobashi’s testimony might be admissible, if relevant,

had he limited his conclusion to basic principles of

thermodynamics—such as the conclusion that the Bair Hugger

may cause particles to rise by blowing hot air. McKnight, 36 F.3d

1396 at 1401 (citing Champeau v. Fruehauf Corp., 814 F.2d 1271,

1278 (8th Cir. 1987)) (“[W]here the experimental tests do not

purport to recreate the accident, but instead the experiments are

used to demonstrate only general scientific principles, the

requirement of substantially similar circumstances no longer

applies.”).

App-62

premise. 7 Dr. Elghobashi’s failure to test his theory

“undermines the reliability of [his] opinion and

renders it too speculative to admit.” See Werth v. HillRom, Inc., 856 F. Supp. 2d 1051, 1061-63 (D. Minn.

2012) (excluding expert opinions where the experts

“never attempted to validate their theory . . . they

simply theorized that this might have happened”).

The Court also finds In re Mirena IUD Prod. Liab.

Litig., 169 F. Supp. 3d 396 (S.D.N.Y. 2016) instructive.

In In re Mirena, the plaintiffs argued that the Mirena,

an intrauterine device, perforated the plaintiffs’

uteruses. Id. at 407. Dr. Jarrell, a biomedical engineer,

opined that although the Mirena generally has flexible

arms, these arms become stiff and rigid when loaded

in “constrained conditions” sometimes causing

perforation. Id. at 438. To test his theory, Dr. Jarrell

applied double-sided tape to the device’s arms to apply

pressure in order to mimic a constrained condition. Id.

at 441. He then measured the force that the device

transferred to uterine tissue. Id. However, Dr. Jarrell

admitted at his deposition that “he did not have any

basis to suggest that the way the Mirena became rigid

in his experiment [with double-sided tape] occurs in

vivo (inside a human being).” Id. For this reason, the

court found that these testing conditions did not

7 Plaintiffs argue that Daubert does not require testing, only

testability. For support, Plaintiffs cite Holverson v.

ThyssenKrupp Elevator Corp, Civ. No. 12-2765, 2014 WL

3573630 at *9 (D. Minn. July 18, 2014) in which the court allowed

expert evidence despite the expert’s failure to test his theory of

liability. However, the court justified its decision by emphasizing

that although the expert did not test his theory, it was

corroborated by several real-world facts. Id. That is not the case

here.

App-63

“reliably replicate the conditions inside a woman’s

uterus, and therefore render[ed] his methodology and

the conclusions he draws from it unreliable.” Id.

Accordingly, the court concluded that the differences

between the testing conditions and the real world

creates “too great an analytical gap between the data

and the opinion proffered.” Id. at 442 (quoting Gen.

Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997)).

Here, too, there is an analytical gap between the

CFD results and Dr. Elghobashi’s conclusion that the

surgical team’s movement would only increase the

Bair Hugger’s effect. Dr. Elghobashi contends that he

did not include other sources of turbulence in order to

“isolate the effect of the Bair Hugger” because “that’s

how we do science.” Gareis 16-cv-4187, ECF No. 474

(May 21, 2018 Trial Tr.) at 963:1-5. But in trying to

isolate the Bair Hugger, Dr. Elghobashi’s simulation

misleadingly implies that the Bair Hugger system is

the only variable in the OR, and that squames could

not reach the surgical site without the Bair Hugger

operating. Such an extrapolation contradicts Dr.

Elghobashi’s acknowledgement that the movement of

personnel meaningfully impacts turbulent airflow. 8

Based on the CFD model alone, Dr. Elghobashi does

“not have any basis” to suggest that squames would

only reach the surgical site when the Bair Hugger is

8 As discussed below, other researchers have emphasized that

“[t]he primary source of these airborne microorganisms is the

people in the operating room, such that the number of people,

door openings, and room traffic all increase the quantity of

airborne colony-forming units (CFU).” ECF No. 1813-32, PX38

(Darouiche 2017) at 2.

App-64

blowing in a real OR. Cf. In re Mirena, 169 F. Supp. 3d

at 441.

Dr. Elghobashi also speculates about the Bair

Hugger’s effect in a real OR. Dr. Elghobashi, without

support, 9 emphasizes that his model was the “best

case scenario for 3M” because introducing other

sources of turbulence, such as the surgical team’s

movement, would only have enhanced the dispersion

of squames and increased the Bair Hugger’s effect.

Gareis16-cv-4187, ECF No. 474 (May21, 2018 Trial

Tr.) at 917:13-15. But “nothing in either Daubertor the

Federal Rules of Evidence requires a district court to

admit opinion evidence that is connected to existing

data only by the ipse dixit of the expert.” Joiner, 522

U.S. at 146. Dr. Elghobashi has not cited any study

that factors in other sources of turbulence and reaches

a similar conclusion. Nor has he tested this theory

even though such tests are feasible. 10 Thus, his

9 At trial, Dr. Elghobashi

stated: “I know that based on my

knowledge . . . [w]e gave you the best case scenario, trust me

about this, trust me.” Gareis 16-cv-4187, ECF No. 474 (May 21,

2018 Trial Tr.) at 917:13-15.

10 Although Dr. Elghobashi’s CFD code had been validated, he

made no attempt to validate his CFD simulation with

experimental evidence. Dr. Elghobashi admitted in his published

study there are “a lack of detailed experimental

measurements . . . in an OR during a clinical trial” that would

“help validate the numerical predictions.” ECF No. 1813-30,

PX36 (He 2018) at 19. He acknowledged that “such detailed data

during a clinical trial are potentially feasible but may cost up to

$ 2 M.” Id. For support for this cost estimate, Dr. Elghobashi cites

a “private communication.” Id. at 21. Dr. Elghobashi also testified

that he could have simulated personnel movement, but he was

not asked to. Gareis 16-cv-4187, ECF No. 474 (May 21, 2018 Trial

Tr.) at 918:1-8. While Dr. Elghobashi only ran two simulations

App-65

conclusion that the Bair Hugger significantly impacts

the trajectories of squames in a real-world OR, ECF

No. 1813-14, PX19 (Elghobashi Rpt.) at 63-64, is

nothing more than his say-so.

To be sure, expert testimony inherently involves

some amount of educated guesswork: “A certain

amount of speculation is necessary, an even greater

amount is permissible (and goes to the weight of the

testimony), but too much is fatal to admission.” Grp.

Health Plan, Inc. v. Philip Morris USA, Inc., 344 F.3d

753, 760 (8th Cir. 2003). Dr. Elghobashi’s attempted

gap-filling is more like a leap of faith than an

inferential leap. Dr. Elghobashi’s model implies that

the Bair Hugger is the but-for cause of squames

reaching the surgical site in the simulated OR. And he

assumes that a real OR would amplify the Bair

Hugger’s effect. At the same time, he conceded at trial

that other factors exist in a real OR that significantly

impact airflow and the trajectories of squames.

Because his simulation never factors in these other

sources of turbulence, it cannot answer important

questions, such as: (1) in a real OR, can these other

with the constraints discussed above, the Court emphasizes that

in other cases where federal courts recognized the reliability of

CFD in litigation, the experts based their conclusions on

comparisons between several simulations. See, e.g., Quiet

Technology DC-8 v. Hurel-Dubois UK Ltd., 326 F.3d 1333, 1338

(11th Cir. 2003) (the expert relied on 16 simulations); Liquid

Dynamics Corp. v. Vaughan Co., Inc., 449 F.3d 1209, 1217-21

(Fed. Cir. 2006) (the expert relied on 40 to 50 iterations of the

simulation); Dejana, 2013 WL 4768407 at *9-12 (the expert

performed more than 100 CFD simulations of a boat operating at

different speeds to determine at what speed the predicted

damage matched the actual photos of damage).

App-66

sources of turbulence carry squames to the surgical

site without the Bair Hugger?; (2) if they can, does the

number of squames reaching the surgical site increase

when the Bair Hugger is turned on?; and (3) how

would the non-Bair Hugger created turbulence

interact with or affect the Bair Hugger-generated

eddies? Dr. Elghobashi never attempts to answer

these questions and bridge the gap in his analysis.

Instead, he simply assumes that the Bair Hugger

significantly increases the number of squames

reaching the surgical site in a real OR. Such

speculation renders his methodology and the

conclusions he draws from it unreliable.

Plaintiffs argue that, as a general rule, any

disagreement with “the factual basis of an expert

opinion goes to the credibility of the testimony, not the

admissibility.” Bonner, 259 F.3d at 929 (quoting Hose,

70 F.3d at 974). Plaintiffs are correct that a dispute

solely over inputs, such as the Bair Hugger’s air

temperature, might not render Dr. Elghobashi’s

testimony inadmissible. 11 See, e.g., In re Zurn Pex

11 The CFD model was limited to specific boundary conditions,

such as number and placement of vents and the temperature of

the air exiting the Bair Hugger. At trial, Dr. Elghobashi admitted

that adjusting any inputs would alter the results, which is why

“prescribing correct boundary conditions is crucial to predicting

a given flow.” Gareis 16-cv-4187, ECF No. 474 (May 21, 2018

Trial Tr.) at 862:14-18. Consequently, if any inputs differ in the

real world or from OR to OR, then the simulation results may not

useful to the fact finder in those cases. Cf. Lauzon, 270 F.3d at

687 (analyzing, under Daubert’s relevance factor, “whether the

proposed expert sufficiently connected the proposed testimony

with the facts of the case”). For instance, Defendants argue that

their expert, “who took actual measurements of the temperature

of the air exiting a Bair Hugger blanket, could not replicate Dr.

App-67

Plumbing Prod. Liab. Litig., 644 F.3d 604, 614 (8th

Cir. 2011) (“A district court necessarily has

‘considerable discretion’ in deciding whether to admit

expert testimony where the factual basis is

disputed.”); Quiet Tech, 326 F.3d at 1343-44

(admitting CFD model of jet engine over challenge to

expert’s inputs and equations).

But, here, Plaintiffs have held out the CFD

simulation as representing a real-world OR even

though there are meaningful differences. This is not a

mere quibble over whether there are three doctors

versus four, whether the OR doors were opened once

or several times, or whether the OR dimensions vary

slightly. Dr. Elghobashi’s conclusions have drifted

from the factual realities of his test. Bonner, 259 F.3d

at 929-30 (quoting Hose, 70 F.3d at 974) (recognizing

that courts must exclude expert testimony where it is

“so fundamentally unsupported that it can offer no

assistance to the jury”). “[C]ourts retain broad

discretion under Rule 403 to exclude computer

animations or simulations, particularly where they

are based on questionable assumptions or project such

a slanted or distorted view of the evidence as to be

unfairly prejudicial or misleading.” Mueller &

Kirkpatrick,

Federal

Evidence

§ 9:26.

Dr.

Elghobashi’s testimony is not saved from exclusion

Elghobashi’s assumption of 106°F (41.11°C)—after measuring

several areas of the blanket, the highest average temperature []

recorded was 36°C.” ECF No. 805 (Mem. in Supp. of Defs.’ 2017

Mot. to Exclude Engineering Experts) at 43. In its December

13th, 2017 order, however, the Court found that the simulation’s

inputs were not so fundamentally unsupported that they could

offer no assistance to the jury.

App-68

simply because he initially applied reliable physics

principles. 12

This decision “does not mean that [Dr.

Elghobashi’s] theory is necessarily wrong; it simply

means that the theory meets none of the indicia of

reliability identified in Daubert and therefore must be

excluded.” Polski, 538 F.3d at 841 (emphasis in

original) (quoting Polski, 2007 WL 2580550, at *5). For

these reasons, Dr. Elghobashi’s testimony is not

sufficiently reliable and too speculative to be

presented to the jury.

B. Dr. Elghobashi Developed the CFD

Model During Litigation

Additionally, Dr. Elghobashi’s testimony and

CFD model were “developed for litigation.” Lauzon,

270 F.3d at 687. At trial, Dr. Elghobashi testified that

Plaintiffs’ counsel hired him in April 2016 to conduct

a CFD simulation relating to issues in this litigation.

Gareis 16-cv-4187, ECF No. 474 (May 21, 2018 Trial

Tr.) at 923:8-12. Prior to his involvement in this

litigation, he had never conducted a CFD model

involving a medical device or an OR. Id. at 933:7-20.

Because Dr. Elghobashi had never observed a Bair

12 Even if the Court limited Dr. Elghobashi’s testimony to the

effect of the Bair Hugger in a quiet OR where no surgery is being

performed, this limited testimony would not assist the trier of

fact in resolving the factual dispute. In every case in this MDL,

Plaintiffs will ultimately have to prove that their infection would

not have occurred but for the use of the Bair Hugger system, or

that the Bair Hugger system was a substantial contributing

cause. Elghobashi’s CFD simulation does not allow for any realworld comparison between an OR with a Bair Hugger and an OR

without a Bair Hugger.

App-69

Hugger in an OR, the plaintiffs’ lawyers joined Dr.

Elghobashi on a visit to an OR room, where one lawyer

pretended to be the patient on the operating table as

no actual surgery was taking place. Id. at 954:24955:17.

“[I]n determining whether proposed expert

testimony amounts to good science, we may not ignore

the fact that a scientist’s normal workplace is the lab

or the field, not the courtroom or the lawyer’s office.”

Daubert v. Merrell Dow Pharm., Inc., 43 F.3d 1311,

1317 (9th Cir. 1995). When an experts’ findings are

developed in the course of litigation, courts have

raised concerns about the objectivity and reliability of

the findings as well as the possibility that the parties

have “shop[ped] for experts who will come to the

desired conclusion.” Id. These same concerns exist

here. For instance, plaintiffs’ lawyers accompanied Dr.

Elghobashi on his one and only visit to an OR. Dr.

Elghobashi also took minimal measurements for the

model’s inputs. Instead, he relied on materials

provided by the plaintiffs’ attorneys. Gareis 16-cv4187, ECF No. 474 (May 21, 2018 Trial Tr.) at 947:1825.

Plaintiffs defend Dr. Elghobashi’s study because

it is peer-reviewed and published. But the published

study discloses significant conflicts of interest. 13 While

13 In the published study, the authors originally declared no

conflicts of interest. ECF No. 1813-30, PX36 (He 2018) at 19. But

at trial, Dr. Elghobashi admitted that the editors subsequently

added the following disclosure: “Dr. Elghobashi is a testifying

witness in a court case against 3M, in which the plaintiffs urge

that the Bair Hugger patient warming system causes

periprosthetic joint infections by disrupting the airflow in ORs.

App-70

the study’s publication indicates that other scientists

think it has scientific value, this does not guarantee

that the conclusions reached are reliable.

For these reasons, the Court excludes Dr.

Elghobashi’s testimony.

II. MEDICAL EXPERTS

The medical experts rely on a number of nonepidemiological studies and Dr. Elghobashi’s CFD

model, which together describe the mechanism by

which the Bair Hugger transmits contaminated

airborne particles into the sterile surgical site. They

also cite the McGovern Observational Study

(“Observational Study”), an epidemiological study,

which found a statistically significant association

between the Bair Hugger and infection.

Defendants do not dispute the experts’

qualifications. Dr. Jarvis is a medical doctor with

experience in infectious disease, healthcare

epidemiology, and infection control. He formerly

worked at the Center for Disease Control with a focus

on infectious diseases associated with healthcare. Dr.

Samet is a medical doctor with a master’s degree in

epidemiology from the Harvard School of Public

Health. His research focuses on the health

consequences of inhaled agents, including tobacco and

radon, and is known for his work as the plaintiffs’

expert in the tobacco litigation. Dr. Stonnington, an

orthopedic surgeon in Mississippi, relies on his

seventeen years of clinical experience.

Dr. Apte is a paid consultant for the plaintiffs.” Gareis 16-cv4187, ECF No. 474 (May 21, 2018 Trial Tr.) at 929:3-931:4.

App-71

Defendants argue that: (1) the Court’s order in

Gareis that excluded Plaintiffs’ “dirty machine” theory

should apply to the entire MDL; (2) the Jeans (2018)

study demonstrates that the Observational Study is

unreliable; and (3) the consensus at the 2018

International Consensus Meeting (“ICM”) on

Musculoskeletal Infection reinforces that Plaintiffs’

medical experts have made an improper inference

regarding causation.

Plaintiffs respond that the Observational Study is

relevant and reliable evidence of general causation—

notwithstanding the Jeans (2018) study—and that the

2018 ICM does not preclude expert opinions on

causation. Additionally, Plaintiffs contend that the

Court’s ruling in Gareis about the “dirty machine”

theory should not apply to the entire MDL.

The Court finds that Plaintiffs’ medical expert

opinions are unreliable and should be excluded under

Daubert because: (1) there is too great an analytical

gap between the literature and the experts’ general

causation opinions; (2) the experts failed to consider

obvious alternative explanations; and (3) the causal

inferences made by the experts have not been

generally accepted by the scientific community.

A. There is Too Great an Analytical Gap

Between the Scientific Literature and

the General Causation Opinions of

Plaintiffs’ Medical Experts

The state of the scientific literature presents a

challenge for the general causation experts. No

medical organization, regulator, or peer-reviewed

study has found that the Bair Hugger causes PJI.

Moreover, the only epidemiological study on which the

App-72

experts rely has expressly disclaimed causation and

acknowledged potential confounders. Still, each of

plaintiffs’ three medical experts reach this conclusion

in their reports. None has done so through an

experiment, laboratory work, or a new epidemiological

study of his own. Drs. Jarvis and Samet arrive at this

conclusion by drawing upon the existing literature as

well as Dr. Elghobashi’s CFD model. Dr. Stonnington

relies on his medical training, education, and

knowledge, as well as his clinical experience, 14 and to

a lesser extent, the scientific literature. Plaintiffs

emphasize that the experts have relied on the totality

of the evidence to draw this conclusion.

The Supreme Court established that a court may

exclude expert testimony where there is “too great an

analytical gap between” the underlying evidence and

the expert’s opinion. Joiner, 522 U.S. at 146. In Joiner,

14 Dr. Stonnington’s anecdotes from his own practice, on their

own, are insufficient to establish causation. In Glastetter v.

Novartis Pharm. Corp., 252 F.3d 986, 990 (8th Cir. 2001), the

Eighth Circuit warned that “[c]ausal attribution based on case

studies must be regarded with caution.” The Court acknowledged

that “[c]ase reports make little attempt to screen out alternative

causes . . . [a]nd they often omit relevant facts about the patient’s

condition.” Id. at 989-90 (quoting Federal Judicial Center,

Reference Manual on Scientific Evidence 475 (3d ed. 2011)). As an

initial matter, the Court finds that Dr. Stonnington’s anecdotal

evidence may even be less reliable than the case reports at issue

in Glastetter. That is because Dr. Stonnington admitted during

the Gareis trial that, apart from his opinion in the Gareis case,

he never recorded in a patient’s medical record or told a patient

that the Bair Hugger caused his or her infection. Gareis 16-cv4187, ECF No. 471 (May 16, 2018 Trial Tr.) at 425:18-25.

Moreover, Dr. Stonnington’s anecdotal reports do not include

basic numerical data or years when infections occurred.

App-73

the plaintiff alleged that his exposure to

polychlorinated biphenyls (“PCB”) as an electrician

“promoted” his cancer. Id. at 139-40. According to the

Supreme Court, the district court did not abuse its

discretion when it excluded expert testimony because

the experts had relied on four epidemiological studies

that were “not a sufficient basis” for their conclusion

that exposure to PCB caused cancer. Id. at 145. To

support its holding, the district court analyzed the

limits of each study. For example, the district court

noted that one study observed a statistically

significant association but involved a number of

confounding variables. Id. at 146.

The Eighth Circuit similarly affirmed the district

court’s exclusion of expert testimony where the

medical texts underlying an expert’s report failed to

present persuasive scientific evidence of causation. In

Glastetter v. Novartis Pharm. Corp., 252 F.3d 986,

988-90 (8th Cir. 2001), the Eighth Circuit considered

whether plaintiff’s experts had articulated a theory to

explain how Parlodel, a medication, caused an

intracerebral hemorrhage (ICH) in the plaintiff’s

brain. The experts had theorized that Parlodel causes

arteries to constrict—known as vasoconstriction—

resulting in elevated blood pressure, which in turn is

a risk factor for ICHs. Id. at 989. However, the Eighth

Circuit agreed with the district court that the evidence

underlying the expert’s theory “does not demonstrate

to an acceptable degree of medical certainty that

Parlodel can cause an ICH.” Id. The court analyzed

several medical texts that the experts relied on, noting

that “[a]t least one text ventured a hesitant conclusion

that Parlodel causes vasoconstriction, but the

explanation made clear that more research was

App-74

needed before causation could be firmly established.”

Id. at 990. The court concluded that “these texts do not

present persuasive scientific evidence that Parlodel

causes vasoconstriction.” Id.

Plaintiffs contend that proponents of expert

testimony need not prove that the conclusions are

correct, and courts must not determine which of

several theories has the best provenance. Kuhn v.

Wyeth, 686 F.3d 618, 625 (8th Cir. 2012); see also

Johnson v. Mead Johnson & Co., 754 F.3d 557, 562

(8th Cir. 2014) (“[D]istrict courts are admonished not

to weigh or assess the correctness of competing expert

opinions.”). This does not mean, however, that an

expert’s conclusions are off limits. In Joiner, the

Supreme Court clarified that “conclusions and

methodology are not entirely distinct from one

another” and “nothing in either Daubert or the Federal

Rules of Evidence requires a district court to admit

opinion evidence that is connected to existing data

only by the ipse dixit of the expert.” 522 U.S. at 146.

The Court concluded that it was “within the District

Court’s discretion to conclude that the studies upon

which the experts relied were not sufficient, whether

individually or in combination, to support their

conclusions.” Id. at 146-47. Consequently, it is within

the Court’s discretion to review the studies underlying

an expert’s report and to find that the expert’s

conclusion is not supported by the totality of the

evidence. The Court does so below.

1.

The “Dirty Machine” Theory

Plaintiffs’ first theory of causation is that the Bair

Hugger, lacking an adequate filtration system, emits

contaminants into the OR, and thus increases the

App-75

bacterial load reaching the surgical site. In May 2018,

in response to a motion in limine, the Court excluded

evidence supporting this theory from the Gareis trial,

finding that Plaintiffs lacked any scientific evidence to

support it. Gareis 16-cv-4187, ECF No. 306 (Order re

Mot. in Lim.) at 2 (“Plaintiffs have no evidence that

anyone has caught colony-forming units of bacteria

floating out of the blanket’s perforations.”). 15

Defendants argue that because this ruling did not

depend on any case-specific facts in Gareis, this ruling

should apply to the entire MDL.

Plaintiffs respond that the Court’s decision

depended on the lack of evidentiary support in Dr.

Jarvis’s specific causation opinion but contend that

the medical experts’ general causation reports

nevertheless support this theory. For example, Drs.

Jarvis and Stonnington cite several studies like

Avidan (1997), Albrecht (2009) and (2011), and Reed

(2013), which found that the Bair Hugger internally

generates and then emits contaminated particles out

of the distal hose. Drs. Jarvis and Stonnington then

conclude that because the devices emit contaminated

air, these devices increase the risk of infection. ECF

No. 1813-1, PX1 (Jarvis Rpt.) at 10-11; ECF No. 18133, PX3 (Stonnington Rpt.) at 6-7. Dr. Samet, citing

evidence summarized by Dr. Jarvis, similarly

concludes that the Bair Hugger “could increase the

dose of organisms delivered to the surgical site.” ECF

No. 1813-2, PX2 (Samet Rpt.) at 17.

15 The parties’ experts disagree about whether the Bair Hugger

blanket may act as a filter.

App-76

The Court finds that there is too great an

analytical gap between the experts’ conclusions and

the scientific literature summarized in their reports.

In reaching these conclusions, the experts ignore the

underlying studies’ limitations. For example, these

studies support a conclusion that the Bair Hugger

emits contaminated air out of the distal hose. But no

study even considered whether contaminated air

emitted from the hose could reach the surgical site and

cause infection. 16 Both Albrecht studies clarify that

the researchers did not evaluate or establish a direct

link between forced-air warming and increased

surgical site infection rates. ECF No. 750 (Mem. in

Supp. of Defs.’ 2017 Mot. to Exclude General

Causation Medical Experts) at 25. Additionally, Reed

(2013)—the most recent study cited by the experts in

support for this theory—explicitly rejected finding a

direct link between the Bair Hugger’s contaminated

air and infection because it is “presently unknown”

whether the contaminated air would reach the

surgical site. ECF No. 950-20, PX30 (Reed 2013) at 6.

Because Plaintiffs’ medical experts do not cite any

studies after Reed (2013), the Court finds no support

for their conclusion that the contaminated emissions

reach the surgical site.

Perhaps the experts assume that this

contaminated air reaches the surgical site via the

“airflow disruption” theory. But as discussed below,

16 Because the patient’s torso and the Bair Hugger blanket are

covered with surgical draping, the warm air does not blow

directly onto the lower body surgical site. (In upper body

surgeries, like shoulder surgeries, the blanket is placed over the

lower half of the patient’s body.)

App-77

the studies underlying this theory also do not

establish that the Bair Hugger causes infection.

2.

The “Airflow Disruption” Theory

At the Gareis trial, Plaintiffs and their medical

experts articulated their second theory of causation—

the “airflow disruption” theory—as follows: HVAC

systems in ORs create a “forcefield” around the

surgical site by pushing particles down to the floor

where vents take those particles, including any

bacteria, out of the room. However, when the Bair

Hugger is turned on, hot air escapes from the Bair

Hugger blanket and the bottom edge of the surgical

draping, rises, and then disrupts the protective

“forcefield.” This in turn causes squames (sometimes

referred to as colony forming units (“CFUs”)) to float

into the surgical site.

The experts rely on two bodies of supporting

evidence: empirical studies that examine air flow

patterns in ORs and Dr. Elghobashi’s testimony and

CFD simulation. Defendants challenge both lines of

evidence. Defendants contend that the empirical

studies do not reflect real-world conditions and thus,

standing alone without Dr. Elghobashi’s CFD model,

do not provide sufficient support to infer general

causation.

Reliance on Empirical Studies

Plaintiffs assert that several empirical studies

have found that the convection currents produced by

the Bair Hugger significantly increase the number of

particles in the sterile field. 17 Plaintiffs concede that

17 See, e.g., ECF No. 1813-16, PX21 (Legg 2012); ECF No. 181317, PX22 (Legg 2013); ECF No. 1813-18, PX23 (Belani 2012);

App-78

these studies do not involve real ORs, but argue that

it would be an abuse of discretion for the Court to

require the experts to rely only on studies that

perfectly reflect the real world. Plaintiffs contend that

as long as the methods employed by the expert are

scientifically valid, “mere disagreement with the

assumptions and methodology used does not warrant

exclusion of expert testimony.” Hill v. Sw. Energy Co.,

858 F.3d 481, 486 (8th Cir. 2017) (quoting SEC v. Das,

723 F.3d 943, 950 (8th Cir. 2013)). The Court agrees

that these peer-reviewed studies are not so unreliable

that they should be excluded from the evidence.

Rather, for the following reasons, the Court finds that

there is too great an analytical gap between these

studies and the experts’ conclusion that the Bair

Hugger causes infection.

Plaintiffs’ experts piece together an array of

studies to ultimately conclude that the Bair Hugger

causes PJI. First, the experts contend that the Bair

Hugger increases the number of particles over the

surgical site. While these studies demonstrate that

forced-air warming devices can increase particle

counts over the surgical site under certain conditions,

they do not conclude that this same increase exists in

the real world. For example, all three experts rely on

the Legg studies, which found increased particle

counts over the surgical site associated with the use of

the Bair Hugger. Yet, these studies explicitly limit

their findings to their exact operating theater set up.

ECF No. 1813-16, PX21 (Legg 2012) at 4; ECF

No. 1813-17, PX22 (Legg 2013) at 5. Moreover, in the

ECF No. 1813-19, PX24 (Dasari 2012); ECF No. 1813-20, PX25

(McGovern 2011).

App-79

2013 study, the authors acknowledge that “[t]his

study does not show that forced-air warming increases

the risk of infection.” ECF No. 1813-17, PX22 (Legg

2013) at 5. Additionally, Drs. Jarvis and Samet cite

the Dasari (2012) study, which measured

temperatures in an OR around a draped mannequin

and found that the Bair Hugger significantly elevated

mean temperatures over the surgical site. The authors

limited their conclusions, however, to the study set up

and cautioned that “the definitive effects of this excess

heat on clinical outcomes are presently unknown.”

ECF No. 1813-19, PX24 (Dasari 2012) at 6. Lastly, all

three experts cite the Belani (2013) study, which used

bubbles to investigate the effect of forced-air warming

on OR airflow and found that the forced-air warming

significantly disrupted airflow and increased bubble

counts over the surgical site. 18 These researchers also

cautioned that their conclusions were based on the

study’s “exact setup” and that the researchers were

“unsure of the exact degree of ventilation disruption

that might occur in a working OR during orthopedic

surgery.” ECF No. 1813-18, PX23 (Belani 2013) at 6.

Furthermore, these studies only consider particle

counts, and not whether forced-air devices increase

infection. Attempting to close the analytical gap

between increased particle counts and infection, the

experts cite several studies linking higher particle

counts at the surgical site with increased risk of

infection. For example, all three experts cite the

18 The McGovern (2011) study includes both an observational

study, discussed in detail below, and a “bubble” experiment with

similar findings to the Belani study. ECF No. 1813-20, PX25

(McGovern 2011) at 6.

App-80

Stocks (2010) study, which found a correlation

between the number of airborne particles equal or

greater than ten microns in size and the number of

CFUs. ECF No. 1813-33, PX39 (Stocks 2010) at 6.

Dr. Jarvis’s trial testimony, however, exposed

that the Stocks study cannot bridge this gap. At trial,

Dr. Jarvis testified that particle size matters because

no study has found that smaller particles can carry

bacteria. Gareis 16-cv-4187, ECF No. 473 (May 18,

2018 Trial Tr.) at 759:17-760:19. Dr. Jarvis also

admitted that there is no study that shows that the

Bair Hugger has any impact on particles that are large

enough to carry bacteria other than the “CFD models

perhaps.” Id. at 761:5-8. Consequently, Dr. Jarvis

conceded that no study has found that the Bair

Hugger increases the number of bacteria arriving at

the surgical site. Id. at 768:23-769:1.

The experts also cite a randomized controlled

study, Darouiche (2017), which found a correlation

between reducing CFUs at the surgical site and lower

rates of infection. But this study also fails to close this

gap. First, the researchers did not even study forcedair warming devices. The study involved the Air

Barrier System, which passes ambient air through a

filter at the surgical site. Second, this study recognized

that “[t]he primary source of these airborne

microorganisms is the people in the OR, such that the

number of people, door openings, and room traffic all

increase the quantity of airborne colony-forming units

(CFU).” ECF No. 1813-32, PX38 (Darouiche 2017) at

2. Thus, this study lends support for the theory that

personnel movement in the OR is a major risk factor

App-81

of infection 19—a factor not reflected in Dr.

Elghobashi’s simulation or the studies described

above. 20 Therefore, as a whole, these studies are too

far removed from the conditions of real ORs to support

Plaintiffs’ experts’ conclusion that the Bair Hugger

system causes infection in real-world operations.

Reliance on Dr. Elghobashi’s CFD Model

Given the gap in the scientific literature discussed

above, Dr. Elghobashi’s CFD model plays an essential

role in understanding the impact of the Bair Hugger

on larger particles that carry bacteria. See Gareis 16cv-4187, ECF No. 473 (May 18, 2018 Trial Tr.) at

763:18-23 (Dr. Jarvis testifying that “that’s where Dr.

Elghobashi in his model can help fill in that gap,

where the studies haven’t been done”). As Dr. Jarvis

acknowledged at trial, the CFD simulation is the only

study that even considered the impact of the Bair

Hugger on particles ten microns in size. Id. at 761:5-8;

807:5-12. Dr. Jarvis also testified that “we have a

variety of studies that answer each one of these

questions, and when you put [the studies] all together,

you get a picture similar to what Dr. Elghobashi has

shown with his CFD model that illustrates why the

19 Dr. Jarvis also testified at trial that personnel movement has

the greatest impact on ten-micron particles. Gareis 16-cv-4187,

ECF No. 473 (May 18, 2018 Trial Tr.) at 752:18-753:5.

20 ECF No. 1813-16, PX21 (Legg 2012) at 3 (single surgeon with

no nurse or assistants); ECF No. 1813-17, PX22 (Legg 2013) at 2

(single surgeon); ECF No. 1813-18, PX23 (Belani 2013) at 3

(single anesthetist stood motionless at the head of the table); ECF

No. 1813-19, PX24 (Dasari 2012) at 6 (two people walked

around); ECF No. 1813-20, PX25 (McGovern 2011) at 3 (surgeon

and anesthetist stood motionless).

App-82

Bair Hugger will increase the risk of prosthetic joint

infections.” Gareis 16-cv-4187, ECF No. 472 (May 17,

2018 Trial Tr.) at 631:6-10.

But even if the CFD model were admissible, there

is too great an analytical gap between the CFD results

and the medical experts’ conclusion that the Bair

Hugger causes infection. See, e.g., In re Mirena IUD,

169 F. Supp. 3d at 441 (excluding a general causation

expert’s opinion as unreliable because it was based on

a lab test using “equipment apparently intended to

mimic the uterus” but that admittedly “[did] not

reliably replicate the conditions inside a woman’s

uterus”). Drs. Jarvis and Samet rely on the simulated

off-and-on comparison as evidence that the Bair

Hugger disrupts the airflow, brings contaminants

from the floor area into the sterile surgical field, and

increases the risk of infection in a real-world OR. But,

as discussed above, Dr. Elghobashi’s simulation does

not reflect many sources of turbulence and particles

that one would expect in a real OR.

Remarkably, the experts fail to acknowledge

these differences, let alone explain how these

differences might impact their analysis. Neither

expert, for instance, acknowledges the surgical team’s

movements—one key difference between the CFD

model and a real OR. As discussed above, personnel

movement in the OR is a major risk factor of infection.

As a result, the CFD model—which does not simulate

the surgical team’s movement—cannot be relied on to

establish that the Bair Hugger significantly increases

the number of contaminated particles at the surgical

site in the real world. Consequently, the experts make

too great an inferential leap in their conclusions.

App-83

Furthermore, even if Drs. Samet and Jarvis had

addressed these differences, they would not have been

qualified to fill this analytical gap. It is outside their

expertise to opine on how atmospheric eddies are

impacted by the Bair Hugger in a real OR as opposed

to in a simulated OR. Perhaps Drs. Samet and Jarvis

rely on Dr. Elghobashi’s caveat at the end of his report

that the inclusion of personnel movement and

additional squames in the simulation would only

further increase the probability that squames would

travel to the surgical site. But as discussed above, Dr.

Elghobashi’s assumption is problematic as it has not

been tested. “[N]othing in either Daubert or the

Federal Rules of Evidence requires a district court to

admit opinion evidence that is connected to existing

data only by the ipse dixit of the expert.” Joiner, 522

U.S. at 146.

3.

The Observational Study

In addition to the mechanistic evidence describe

above, the medical experts also rely on epidemiological

evidence. Specifically, Plaintiffs’ medical experts cite

one epidemiological study, the McGovern (2011)

Observational Study (“Observational Study”), to show

a real-world association between the Bair Hugger and

PJI.

Epidemiology is the “statistical study of disease or

injury in human populations.” Federal Judicial

Center, Reference Manual on Scientific Evidence 286

(3d ed. 2011). According to the Reference Manual on

Scientific Evidence, “[e]pidemiology focuses on the

question of general causation” by identifying agents

that are “associated with an increased risk of disease

in groups of individuals.” Id. at 552. However, “[a]n

App-84

association identified in an epidemiologic study may

or may not be causal.” Id. at 552-53. Because all

studies have flaws, “[i]n evaluating epidemiologic

evidence, the key questions, then, are the extent to

which a study’s limitations compromise its findings

and permit inferences about causation.” Id. at 553.

The Observational Study found a statistically

significant association between the Bair Hugger and

infection. 21 The Observational Study was an

epidemiological study that compared infection rates at

Wansbeck Hospital in Northumbria, England, during

a period when the Bair Hugger and a period when a

conductive warming device were in use. The

researchers reviewed infection data to determine

whether joint infection rates were associated with the

type of patient warming device that was used. It was

an observational study, meaning that it was not

blinded and controlled like a clinical study.

The study authors warned against conflating

correlation with causation: “[t]his study does not

establish a causal basis . . . the data are observational

and may be confounded by other infection control

measures instituted at the hospital.” ECF No. 181320, PX25 (McGovern 2011) at 8. Further, the authors

expressly acknowledged that there was a period when

different anti-thrombotic and different prophylactic

antibiotic drugs were being used with the two groups

of patients. Id. Finally, the authors noted that they

were “unable to consider all factors that have been

associated with SSI, as the details of blood

21 The parties dispute, however, if tabulation errors exist in the

Observational Study that would impact the statistical

significance of the association.

App-85

transfusion, obesity, incontinence and fitness for

surgery, which have been identified elsewhere as

important predictors for deep infection, were not

sufficiently detailed in the medical record.” Id.

Defendants first argue that the Observational

Study is so unreliable that it should be excluded. The

Court disagrees. The study is reliable as it is published

and peer reviewed. And, even if the study has certain

limitations, those limitations could be presented to a

jury. Kuhn, 686 F.3d at 632 (holding that the expert’s

“reliance on the studies may be tested through the

traditional means of cross examination and

presentation of contrary evidence”).

Nevertheless, as outlined above, it is unreliable

for an expert to rely on studies to support conclusions

that the study authors were themselves unwilling to

reach. See Joiner, 522 U.S. at 145-46; see also Huss v.

Gayden, 571 F.3d 442, 459 (5th Cir. 2009) (“It is

axiomatic that causation testimony is inadmissible if

an expert relies upon studies or publications, the

authors of which were themselves unwilling to

conclude that causation had been proven.”). Joiner

and Glastetter focused on whether the underlying

studies provide a sufficient basis for an experts’

causation opinions, but district courts have also

analyzed whether an expert addresses a study’s

limitations as a way of determining if the study

reliably supports a causation opinion. For example, in

In re Mirena Ius Levonorgestrel-Related Prod. Liab.

Litig. (No. II), 341 F. Supp. 3d 213, 277 (S.D.N.Y.

2018), a district court found that an expert “fail[ed] to

consider the alternative, and benign, explanations

that that study identified for the correlation it found

App-86

between Mirena and IIH.” The court determined that

the report “pays only lip service” to the study’s “caveat

about confounders” as “[i]t nowhere reveals that the

[epidemiological] study had not controlled for obesity

or recent weight gain.” Id. at 277-78. Consequently,

the court found that the report inappropriately treated

the correlation as “affirmative evidence of causation”

and excluded the expert’s testimony because it did not

meet the standards for reliability articulated in

Daubert. Id. at 278.

Here, too, the experts fail to address the

McGovern researchers’ caveats about confounders and

alternative

explanations,

and

thus,

they

inappropriately treat the association as affirmative

evidence of causation. Both Drs. Jarvis and

Stonnington cite the Observational Study without

discussing the study’s limitations and possible

confounders. And although Dr. Samet mentions

potential confounders acknowledged by the study

authors, his description of them is misleading. Dr.

Samet states that the Observational Study “has been

criticized as potentially reflecting confounding by the

non-comparability of prophylactic antibiotic use and

thromboprophylaxis in the two periods.” ECF

No. 1813-2, PX2 (Samet Rpt.) at 12. He likens these

criticisms “to the strategies employed for decades by

the tobacco industry.” Id. But by framing these

criticisms as disingenuous, he aims to dismiss

potential confounders without seriously considering

them.

Additionally, Dr. Samet departs from his own

description of reliable methodology when opining

about causation. Junk v. Terminix Int’l Co., 628 F.3d

App-87

439, 448 (8th Cir. 2010) (affirming the district court’s

holding that the expert’s “failure to follow his own

general practice . . . created ‘too great an analytical

gap’ between his opinion and the data on which it

relied”). Dr. Samet applies several criteria to

determine if causation exists. With regard to “strength

of association,” Dr. Samet reports that the

Observational Study establishes “a statistically

significant association unlikely to be explained by

confounding or other bias.” ECF No. 1813-2, PX2

(Samet Rpt.) at 16. Next, Dr. Samet applies the

criteria of consistency. Dr. Samet acknowledges,

however, that this factor is not applicable to the

Observational Study since this factor is generally

related to the “findings of multiple observational

studies.” Id. Instead, Dr. Samet points to the series of

empirical studies, which as discussed above, found

that the Bair Hugger’s convection currents increase

the number of particles in the sterile field. But these

studies do not establish—let alone consider—whether

there was an association between the Bair Hugger and

infection.

Without further explanation of Dr. Samet’s

thought process and how he weighed these criteria,

the Court is left to guess why Dr. Samet finds that the

consistency factor is met despite conceding that “[t]he

McGovern paper supplies the only estimate of the

risk” and absent that estimate he “would not be able

to judge the quantitative magnitude of the

association.” ECF No. 1720-1, DX25 (Aug. 8, 2017

Samet Dep.) at 282:16-283:20. Dr. Samet’s application

of the factors does not reassure the Court that he has

bridged the gap between the scientific literature and

App-88

his causation opinion. 22 See In re Mirena (No. II), 341

F. Supp. 3d at 247 (collecting cases) (“As courts have

recognized, it is imperative that experts who apply

multi-criteria methodologies such as Bradford Hill or

the ‘weight of the evidence’ rigorously explain how

they have weighted the criteria. Otherwise, such

methodologies are virtually standardless and their

applications to a particular problem can prove

unacceptably manipulable. Rather than advancing the

search for truth, these flexible methodologies may

serve as vehicles to support a desired conclusion.”).

B. Plaintiffs’ Medical Experts Failed to

Consider Alternative Explanations

Courts also weigh the ability of an expert to rule

out alternative explanations. Lauzon, 270 F.3d at 693

(collecting cases). The Eighth Circuit noted that this

factor is often cited when discussing a causation

opinion arrived at by differential diagnosis. Id. at 693

n.7. This factor is also relevant here, though, given the

background risk—that is, the risk of infection in the

general population when the Bair Hugger has not

been used. See McClain v. Metabolife Int’l, Inc., 401

F.3d 1233, 1243 (11th Cir. 2005) (noting that “[a]

Defendants also argue that Dr. Samet does not seem to

employ “the ‘same level of intellectual rigor’ that he employs in

his academic work.” Milward v. Acuity Specialty Prods. Grp.,

Inc., 639 F.3d 11, 26 (1st Cir. 2011) (quoting Kumho Tire Co. v.

Carmichael, 526 U.S. 137, 152 (1999)). Here, Dr. Samet relies on

one epidemiological study with potential confounders. In

contrast, Dr. Samet’s report to the Surgeon General, which

concluded that smoking causes lung cancer, was based upon the

consistently strong associations observed in at least seven

observational studies. ECF No. 956-1, DX25 (Aug. 8, 2017 Samet

Dep.) at 80:3-24.

22

App-89

reliable methodology should take into account the

background risk”).

Although an “expert’s causation conclusion should

not be excluded because he or she has failed to rule out

every possible alternative cause,” experts should

discount “obvious alternatives” and “explain why

other conceivable causes are excludable.” Lauzon, 270

F.3d at 693; see also Fed. R. Evid. 702 advisory

committee’s note to 2000 amendment (experts should

“adequately account[] for obvious alternative

explanations”). The Court interprets this guidance to

require experts at the very least to examine other

conceivable causes flagged by researchers in key

studies cited in their reports. 23 For instance, Dr. Reed,

a senior author on the Observational Study—the only

study establishing an association between the Bair

Hugger and infection—testified that many efforts

were being undertaken at the hospital at the time of

the study to decrease its infection rates and

specifically called out one plausible confounder: the

introduction of screening for methicillin-sensitive

Staphylococcus Aureus (“MSSA”) at the end of the Bair

Hugger only period. ECF No. 751-1, DX8 (Dec. 4, 2016

Dr. Samet asserts that the deposition testimony of the

Observational Study authors resolves the possibility of

confounding. Dr. Samet considered two potential confounders

mentioned in McGovern: the prophylactic antibiotic regimen and

the thromboprophylaxis protocol, ECF No. 956-1, DX25 (July 11,

2017 Samet Dep.) at 48:20-49:22, which the McGovern authors

later confirmed were not confounding factors. See, e.g., ECF

No. 1813-39, PX48 (Nov. 29, 2016 Nachtsheim Dep.) at 349:1425. Dr. Samet, however, never addressed other plausible

confounders discussed by the Observational Study researchers in

their depositions.

23

App-90

Reed Dep.) at 78:21-25; 114:7-115:10. In a subsequent

study involving Dr. Reed, the researchers recently

reiterated that “there were significant confounding

factors in [the Observational Study].” ECF No. 18501, DX16 (Kumin 2018) at 7.

Dr. Samet, however, never mentioned—let alone

investigated—this alternative explanation. ECF

No. 1813-2, PX2 (Samet Rpt.) at 12 (summarily

concluding that “confounding by other, unidentified

factors seems unlikely” because the “change in the

warming method was temporally abrupt”). Nor did he

examine the raw data underlying the Observational

Study to try to confirm whether or not this potential

confounder identified by the researchers could be an

alternative explanation for the decrease in PJI. ECF

No. 956-1, DX25 (July 11, 2017 Samet Dep.) at 41:513. 24

Plaintiffs argue that such failures go to weight

and not admissibility. This would be true had Dr.

Samet opined, for example, on why MSSA screening is

not an alternative explanation. But here, Dr. Samet’s

report offers no explanations about MSSA screening

for Defendants to attack on cross examination. 25 Cf.

24 In In re Mirena (No. II), the district court noted—as evidence

that the expert paid only “lip service” to the epidemiological

study’s confounders—that the expert did “not attempt

independently to examine the data underlying that study” or

“perform a corrected analysis of [the study] to try to account for

[confounding factors].” 341 F. Supp. 3d. at 278.

25 At the motion for reconsideration hearing, Plaintiffs’ counsel

reiterated that they do not have supplemental expert reports that

address the Jeans study because the Court denied Plaintiffs’

motion to conduct additional discovery and to supplement expert

opinions. ECF No. 1980 (June 12, 2019 Mot. for Reconsideration

App-91

Lauzon, 270 F.3d at 694 (“[Defendant] may attack [the

expert’s] explanations of causation on cross

examination, thereby requiring [the expert] to offer

valid explanations as to why his conclusion remains

reliable.”).

Plaintiffs argue that such analysis was

unnecessary because the researchers only listed

potential confounders as opposed to actual

confounders, and all observational studies include

these sorts of “pointless” caveats. ECF No. 1980 (June

12, 2019 Mot. for Reconsideration Hearing Tr.) at 9394. Setting aside whether this is an accurate

characterization of observational studies generally,

the Court notes that a study now confirms that at least

one of these conceivable confounders—MSSA

screening—has a statistically significant impact on

reducing surgical site infections. In July 2018, Dr.

Reed and his colleagues published a study specifically

addressing the impact of MSSA screening on PJI,

which included deep and superficial infection. The

Jeans (2018) study found a significant decrease in the

MSSA infection rate after the introduction of the

screening program as well as a significant reduction

in the overall infection rate. ECF No. 1813-43, PX52

(Jeans 2018) at 4. While noting that “improvement in

infection rates could have been down [sic] to other

factors . . .,” the authors concluded that the “dramatic

reduction

in

MSSA

SSI

[surgical

site

Hearing Tr.) at 139:22-140:13. However, Dr. Samet relied on Dr.

Reed’s deposition in his original expert report, which identified

MSSA screening as a plausible confounder, and so this does not

explain why Dr. Samet failed to examine MSSA screening in his

initial expert report.

App-92

infections] . . . suggests

that

screening

decolonization was responsible.” Id.

and

The parties dispute whether the Jeans study

confirms that the introduction of MSSA screening

confounded the Observational Study. Dr. Jarvis stated

in an affidavit that “the Jeans Study does not ‘suggest’

that MSSA screening confounded the McGovern

study.” ECF No. 1916-2, PX75 (Jarvis Aff.) at 2.

Further, Dr. Samet stated in an affidavit that the

Jeans study does not change his opinion that the Bair

Hugger is a substantial contributing cause of PJI. ECF

No. 1916-1, PX74 (Samet Aff.) at 3. 26

The Court need not determine whether or not

Jeans actually establishes that MSSA screening

confounded the Observational Study. Mead Johnson,

754 F.3d at 562 (“district courts are admonished not to

weigh or assess the correctness of competing expert

opinions”). The Court merely finds that Jeans

confirms that Plaintiffs’ medical experts failed to

examine

conceivable

alternative

explanations

In response to Defendants’ motion for reconsideration,

Plaintiffs’ counsel had argued that Jeans does not confound

McGovern. On May 16, 2019, Plaintiffs’ counsel filed an affidavit

by Dr. Samet, which for the first time considered whether “MSSA

screening might have affected the findings on the type of

warming device in the study by McGovern.” ECF No. 1916-1,

PX74 (May 14, 2019 Samet Aff.) ¶ 2. Dr. Samet’s last-minute

analysis was raised solely to support Plaintiffs’ argument that

Jeans does not confound McGovern. His analysis does not change

the Court’s conclusion that the medical experts’ methodology was

unreliable. The timing of this affidavit only underscores the fact

that the experts did not initially examine these issues when

becoming the first researchers (of which the Court is aware) to

conclude that the Bair Hugger causes PJI.

26

App-93

acknowledged by the Observational Study authors in

their depositions.

It is true that Plaintiffs’ medical experts “need not

rule out every alternative explanation for the observed

hospital’s dropoff in infections.” ECF No. 1024 (Dec.

13, 2017 Daubert Order) at 9; see also Mead Johnson,

754 F.3d at 563 (recognizing that the Eighth Circuit

has “consistently ruled that experts are not required

to rule out all possible causes”). But it is important for

Plaintiffs’ general causation experts to seriously

consider

whether

an

observational

study’s

“alternative explanations in terms of confounding

[are] less plausible than the proposed causal link.”

Federal Judicial Center, Reference Manual on

Scientific Evidence 221 (3d ed. 2011) (noting the

circumstances under which observational studies

provide “good evidence”). This is especially true where

both the experts and the studies on which they rely

have acknowledged multiple mechanisms for CFU to

enter a wound site and acknowledged that infections

occur even when the Bair Hugger is not used. See, e.g,

ECF No. 1813-20, PX25 (McGovern 2011) at 7 (noting

that infections in knee and hip surgeries occurred

when the conductive warming device was used); ECF

No. 1813-32, PX38 (Darouiche 2017) at 2 (“[t]he

primary source of these airborne microorganisms is

the people in the operating room such that the number

of people, door openings, and room traffic all increase

the quantity of airborne colony-forming units (CFU)”);

ECF No. 1920-1, DX22 (Jan. 12, 2018 Jarvis Dep.) at

74:6-11 (agreeing that infections occur in “lots and

lots” of surgeries where the Bair Hugger is not used).

App-94

C. The Causal Inferences Made by

Plaintiffs’ Medical Experts Have Not

Been Generally Accepted by the

Scientific Community

Additionally, the Supreme Court in Daubert

directed courts consider whether the theory has

attracted “widespread acceptance within a relevant

scientific community. 509 U.S. at 594. For instance, “a

known technique which has been able to attract only

minimal support within the community’ may properly

be viewed with skepticism.” Id. at 594 (citations

omitted). The Eighth Circuit cautioned, however, that

this factor “must be weighed with the Supreme Court’s

admonition that ‘a rigid general acceptance

requirement would be at odds with the liberal thrust

of the Federal Rules and their general approach of

relaxing the traditional barriers to opinion

testimony.’” Lauzon, 270 F.3d at 691 (quoting

Daubert, 509 U.S. at 588).

Here, the medical and scientific community has

repeatedly rejected the causal inferences made by

Plaintiffs’ experts. 27 In 2013, the International

Consensus Meeting (“ICM”) on Periprosthetic Joint

Infection, which involved more than 400 experts in

musculoskeletal infection from 52 countries, reached

27 At the motion for reconsideration hearing, Plaintiffs argued

that other scientists agree with their experts’ causation

conclusions. ECF No. 1980 (June 12, 2019 Mot. for

Reconsideration Hearing Tr.) at 122:17-123:24. For support,

Plaintiffs’ counsel referred to statements reflected in 3M’s

internal documents but did not attach as evidence the actual

statements from the scientists. Thus, from this evidence, the

Court is unable to determine the extent that these scientists

support the experts’ conclusions.

App-95

a “strong consensus” (89% agree, 5% disagree, 6%

abstain) as follows: “We recognize the theoretical risk

posed by FAW [forced-air warming] blankets and that

no studies have shown an increase in SSI [surgical site

infections] related to the use of these devices. We

recommend further study but no change to current

practice.” ECF No. 751-2, DX18 (ICM 2013) at 31. In

2017, the FDA reviewed available data and literature,

was “unable to identify a consistently reported

association between the use of forced air thermal

regulating systems and surgical site infection,” and

continued to recommend use of forced-air warming

systems. ECF No. 751-1, DX1 (Aug. 30, 2017 FDA

letter) at 2. In 2018, the ICM on Musculoskeletal

Infection reached a strong consensus (93% agree, 2%

disagree, 5% abstain) that “[t]here is no evidence to

definitively link [forced-air warming] to an increased

risk of SSIs/PJIs.” ECF No. 1720-1, DX2 (ICM 2018)

at 12.

The Court recognizes that Plaintiffs do not need

definitive proof of causation. But “the courtroom is not

the place for scientific guesswork, even of the inspired

sort. Law lags science; it does not lead it.” Rosen v.

Ciba-Geigy Corp., 78 F.3d 316, 319 (7th Cir. 1996); In

re Mirena, 169 F. Supp. 3d at 450 (quoting Anderson

v. Bristol Myers Squibb Co., No. 95-CV-03, 1998 WL

35178199, at *12 (S.D. Tex. Apr. 20, 1998)) (“[I]t is not

that experts are ‘insincere in their opinions or that

their opinions may not some day be validated through

scientific research and experiment; it is simply that

the law cannot wait for such a confirmation.’”). The

fact that the medical and scientific community has

rejected these causal inferences further supports the

Court’s conclusion that there is too great an analytical

App-96

gap between

conclusions.

the

evidence

and

the

expert’s

D. Conclusion

For these reasons, the Court finds that that the

medical experts have repeatedly used the scientific

literature to reach conclusions rejected by researchers,

and therefore, there is too great an analytical gap

between the experts’ opinions and the literature. 28

Thus, the Court excludes the experts’ general

causation opinions and unsupported extrapolations

that the Bair Hugger cau

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