Forced Air Warming Devices in Orthopaedics: A Focused Review of the Literature

Abstract

The current focus on maintaining normal body temperature in the operating room makes the use of patient warming devices routine—or even mandatory—in many hospitals. Forced air warming devices such as the Bair Hugger (3M Healthcare, St. Paul, Minnesota) maintain or increase core temperature in patients during the perioperative period, with benefits that include reduced surgical wound infections, maintenance of normal coagulation, and faster discharge from the post-anesthesia care unit (PACU)1-5. However, some recent literature has raised concerns regarding a possible increased risk of deep surgical site infections specifically associated with the use of the forced air warming systems in the orthopaedic operating room5-12. One concern is that a convective device could disrupt unidirectional downward laminar airflow, which may be especially critical in joint arthroplasty operating rooms. This concern is based on theoretical mechanisms, laboratory simulations, retrospective case series, and studies showing potentially pathogenic organisms growing in the hoses and filters of forced air warming devices6-12. However, multiple other studies13-15 and a Continuing Education statement by the Association of periOperative Registered Nurses (AORN)16 suggest that proper use of the forced air warming devices mitigates or eliminates this risk while maximizing the benefits of patient warming. The purpose of the present manuscript is to review the current literature on the use of patient warming devices in orthopaedic surgery, specifically in joint arthroplasty.

Hypothermia (core body temperature, <36°C) is a constant risk during general anesthesia because of factors such as impaired thermoregulation, heat loss secondary to a cold operating room, redistribution of body heat from the core to the vasodilated periphery, and infusion of cool intravenous fluids. Major adverse consequences of perioperative hypothermia can include adrenergic activation, myocardial ischemia, thermal discomfort, decreased drug metabolism, coagulopathy and increased …

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the
Orthopaedic
forum
Forced Air Warming Devices in Orthopaedics:
A Focused Review of the Literature
Robby S. Sikka, MD, and Richard C. Prielipp, MD, MBA, FCCM
The current focus on maintaining normal body temperature in
the operating room makes the use of patient warming devices
routine—or even mandatory—in many hospitals. Forced air
warming devices such as the Bair Hugger (3M Healthcare, St.
Paul, Minnesota) maintain or increase core temperature in
patients during the perioperative period, with benefits that in-
clude reduced surgical wound infections, maintenance of nor-
mal coagulation, and faster discharge from the post-anesthesia
care unit (PACU)
1-5
. However, some recent literature has raised
concerns regarding a possible increased risk of deep surgical
site infections specifically associated with the use of the forced
air warming systems in the orthopaedic operating room
5-12
.
One concern is that a convective device could disrupt unidi-
rectional downward laminar airflow, which may be especially
critical in joint arthroplasty operating rooms. This concern is
based on theoretical mechanisms, laboratory simulations, ret-
rospective case series, and studies showing potentially patho-
genic organisms growing in the hoses and filters of forced air
warming devices
6-12
. However, multiple other studies
13-15
and a
Continuing Education statement by the Association of periOp-
erative Registered Nurses (AORN)
16
suggest that proper use of
the forced air warming devices mitigates or eliminates this risk
while maximizing the benefits of patient warming. The pur-
pose of the present manuscript is to review the current litera-
ture on the use of patient warming devices in orthopaedic
surgery, specifically in joint arthroplasty.
Importance of Normothermia
Hypothermia (core body temperature, <36°C) is a constant
risk during general anesthesia because of factors such as im-
paired thermoregulation, heat loss secondary to a cold operat-
ing room, redistribution of body heat from the core to the
vasodilated periphery, and infusion of cool intravenous fluids.
Major adverse consequences of perioperative hypothermia can
include adrenergic activation, myocardial ischemia, thermal
discomfort, decreased drug metabolism, coagulopathy and in-
creased blood loss, wound infections, prolonged recovery room
stay, and increased staff and hospital costs
1,2,4,14,15
. Moreover, it is
now accepted that maintaining normothermia in surgical pa-
tients substantially lowers the risk of postoperative surgical site
infections
12,14,16,17
. Indeed, Kurz et al. showed that an intraoper-
ative core body temperature decrease of only 2°C can triple the
rate of soft-tissue wound infection
17
. Therefore, maintaining
normothermia is a vital part of the SCIP (Surgical Care Im-
provement Project) measure developed by The Joint Commis-
sion and the PQRS (Physician Quality Reporting System)
measure developed by the CMS (Centers for Medicare & Med-
icaid Services) in the U.S., and documented use of patient
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any
aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work,
with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has
had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in
this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
Peer Review: This article was reviewed by the Editor-in-Chief and one Deputy Editor, and it underwent blinded review by two or more outside experts. The Deputy Editor
reviewed each revision of the article, and it underwent a final review by the Editor-in-Chief prior to publication. Final corrections and clarifications occurre d during one or
more exchanges between the author(s) and copyeditors.
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J Bone Joint Surg Am. 2014;96:e200(1-7) dhttp://dx.doi.org/10.2106/JBJS.N.00054

warming devices is a part of the requirements for receiving full
reimbursement from the CMS. Any warming device may be
used for the purpose of active warming intraoperatively. The
goal is to maintain normothermia, or at least a body temper-
ature of ‡36°C(‡96.8°F) recorded within the thirty minutes
immediately before, or the fifteen minutes immediately after,
anesthesia end time. Moreover, these normothermic goals ap-
ply to all patients, regardless of age, who are undergoing sur-
gical procedures under general or neuraxial anesthesia lasting
sixty minutes or more, although SCIP normothermia require-
ments are limited to colorectal procedures
18,19
.
Forced air warming devices such as the Bair Hugger sys-
tem rely on convective warming and definitively improve the
ability of anesthesia professionals to maintain normothermia in
patients undergoing abdominal and orthopaedic procedures
20-22
.
Other devices (e.g., HotDog; Augustine Temperature Manage-
ment, Eden Prairie, Minnesota) use conductive heating as the
primary energy mechanism and may theoretically result in
higher thermal efficiency compared with forced air warming
12
.
The issue of rewarming patients who are already hypothermic
is another challenge, as rewarming generally requires greater en-
ergy and more time compared with maintaining normothermia.
Plattner et al. investigated rewarming by means of a resistive
warming device (HotDog) and a forced air warming device (Bair
Hugger), and they showed that core temperature increased twice
as rapidly in the Bair Hugger group. The hypothermic patients
randomized to forced air warming achieved a higher mean core
body temperature during surgery at two, three, and four-hour
time points
23
.
However, Leijtens et al. showed the prevalence of hypo-
thermia in patients undergoing major joint arthroplasty to be
26% to 28% despite the use of forced air warming, and those
patients who developed hypothermia during total hip arthro-
plasty were 3.7 times more likely than normothermic patients
to develop a periprosthetic infection
24
. Thus, maintaining
normothermia during total hip arthroplasty surgery is a
straightforward strategy to reduce the risk of surgical site
infection—and at far less cost than the highly specialized
orthopaedic laminar-air-flow operating room
25-27
.
Warming Devices and Laminar Airflow
The rate of infection following joint arthroplasty involving the
lower limbs is currently <1%
28
. In a multicenter study involving
8052 joint replacements, Lidwell et al. concluded that the risk
of deep and superficial wound infections was substantially re-
duced in surgical procedures performed in operating rooms
with ultraclean air ventilation compared with conventional
ventilation
20
. Current ultraclean ventilation systems protect the
surgical site from airborne contamination through a constant
delivery of filtered air with a uniform downward velocity (0.3 to
0.5 m/s)
11,24
. This system is dependent on proper airflow vol-
umes and temperature gradients. Unidirectional vertical air-
flow ventilation is more effective than horizontal ventilation,
especially in combination with walls around the operating area.
Body exhaust suits also reduce the number of airborne bacte-
ria
4
. However, local sources of excess thermal energy can result
in temperature gradients that interrupt the downward airflow
of ultraclean air
4
. These interruptions in the velocity of down-
ward airflow likely increase the entry of contaminants into the
surgical site. Heat rising against the downward laminar airflow
may also draw nonsterile contaminants up and into the surgical
site.
TABLE I Proper Maintenance and Use of Forced Air Warmers
Recommendations
1. The filter should be changed every 6 months or 500 hours. A counter is available on some devices (e.g., Bair Hugger 700 series) to indicate the
total hours of use.
2. Calibration testing should occur every six months by biomedical engineering staff at the user’s institution. The manufacturer should check or
replace devices that fail calibration testing.
3. Do not warm patients with the warming unit’s hose alone, as severe thermal injury may occur. Always connect the hose to a new, manufacturer-
approved warming gown for each patient.
4. Do not continue warming if the red overtemperature indicator light illuminates or an audible alarm sounds, as thermal injury may result. Turn the
warming unit off immediately and check the patient’s skin.
5. Do not use a forced air warming device over transdermal medications; increased drug delivery and patient death or injury may result.
6. Do not allow the patient to lie on the warming unit hose or allow the hose to contact the patient’s skin during patient warming.
7. Equipment is not suitable for use in the presence of a flammable anesthetic mixture (e.g., containing air, oxygen, or nitrous oxide).
8. Do not place the nonperforated side of the blanket on the patient. Thermal injury may result.Always place the perforated side (the side with small
holes) toward the patient.
9. The warming device should be disconnected from the power source before cleaning. Between patients, the outside of the hose should be
cleaned with a damp, soft cloth and a mild detergent or antimicrobial spray and then dried with a separate cloth.
10. If a fault occurs in the unit, unplug the temperature management unit and wait for five minutes. Reconnect the temperature management unit to
a grounded power source. The unit will perform the normal power-on-reset sequence and then enter the standby mode. If the unit does not return to
normal operation, contact a service technician.
11. Temperature and calibration testing should be performed every 6 months or 500 hours of use.
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According to several recent studies, forced air warming
devices may be a source of rising thermal currents that affect
the normal downward airflow of laminar airflow systems
6-12
.
This may raise the number of bacterial particles—as well as the
temperature—over the surgical site. McGovern et al. reported
an infection rate of 3.1% with use of forced air warming com-
pared with 0.8% with a conductive warming device
12
.The
authors suggested that discontinuing the forced air warming
would decrease the infection rate by 74%
10,11
. Legg et al. showed
that forced air warming devices increased the mean tempera-
ture and the number of particles over the surgical site, thereby
increasing the number of pathogens over the surgical site
10,11
.
However, several of those studies were funded by the manu-
facturers of competing devices
6-10,12
. Most studies on the use of
forced air warming devices and other warming technologies in
combination with laminar airflow are clearly underpowered
and poorly controlled, and conclusions regarding the indepen-
dent effect of the warming devices on surgical site contamina-
tion and infection are uncertain
15,29
.
Other studies (again, usually industry-funded) have indi-
cated that forced air warming does not increase the risk of par-
ticulate dispersion near surgical sites
13,22,30-34
. These studies have
shown that perioperative temperature management with forced
air warming actually decreases the risk of surgical site infection.
Sessler et al.
32
conducted a simulation study similar to that of
McGovern et al.
12
and showed that forced air warming did not
reduce air quality in an operating room with laminar flow ven-
tilation. No difference in infection rate was evident in a series of
patients undergoing vascular, breast, and hernia surgery who
were warmed with either a conductive heating or forced air
warming (Bair Hugger) device. However, patients who did not
have any warming device did have a higher rate of infection
27
.
The authors of several systematic reviews have recommended
the use of forced air warming because of its improved ability to
maintain normothermia and suggested that it has little role in
disrupting laminar airflow
5,31,35
. Thus, the literature appears to
indicate that forced air warming can impact laminar flow under
certain very specific conditions, but any actual clinical impact on
surgical site infections must be considered unproven at this time.
On the basis of the current evidence, it is likely that both forced
air warming and conduction-based warming decrease the risk of
hypothermia in orthopaedic patients undergoing arthroplasty,
and maintenance of normothermia is critical to a strategy for
minimizing surgical site infections. Neither type of device can
completely eliminate the risk of hypothermia, and both share
risks of adverse side effects such as burns and pressure sores
36
.
Indeed, all medical devices require training, education, and
maintenance for proper use.
TABLE II Alternative or Adjunctive Warming Options for Patients*
Device Example Benefits, Potential Risks, Contraindications
Patient warming blanket QUINEN Warming Blanket (Shreeyash) Covers large part of patient, making observation of
skin difficult; not practical for extremity surgery
Circulating water garment Allon ThermoWrap (MTRE) Potential for leaking and burns as well as pressure
sores; not practical for extremity surgery. Typically
uses microprocessor in device
Thermal pad Patient Warming System (Pintler) Potential risk for cutaneous burns
Warming mattress PerfecTemp (Medline) Potential risk for cutaneous burns
Fluid warmer HOTLINE (Smiths), Fluid Ranger (3M),
Level 1 (Smiths)
Air emboli
40
Reflective blanket GRI-Alleset Healthcare or Thermoreflect
patient warming products
Risk of cutaneous burns is low but may increase if
combined with FAW; pressure sores may develop.
Passive warming with reflective heating blankets
or elastic bandages wrapped tightly around the legs
were found to be ineffective in reducing the
prevalence or magnitude of hypothermia
35
Passive covering Blanket Increased risk of burns if used with FAW and areas
of high heat develop
Conductive warming HotDog (Augustine) Risk of pressure sores and cutaneous burns
Forced air warming Bair Hugger (3M) Risk of cutaneous burns and of colonization of filter
and tubing. Proper maintenance minimizes risk, and
proper draping and use may decrease risk of
disruption of laminar airflow
*For forced air warming (FAW) devices, the maximum contact surface temperature should not exceed 48°C, and the mean contact surface
temperature should not exceed 46°C under normal conditions. For circulating liquid devices, the contact surface temperature should not exceed
43°C, and the mean contact surface temperature should not exceed 42°C under normal conditions. The fluid warming standard requires that the
device does not heat the fluid above 44°C under normal conditions
41,42
.
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Proper Use of Equipment and Drapes
The primary heating unit in forced air warming devices re-
quires cleaning and routine maintenance (Table I). Delayed
or deficient maintenance may result in adverse events. Gjolaj
et al.
26
described the results of bacterial testing of Bair Hugger
units. After six months or more than 500 hours of usage (the
time at which the manufacturer recommends installation of
new filters), the distal end of the outflow hose was positive for
TABLE III Articles Evaluating Forced Air Warming Devices* ä
Albrecht
2009
7
Albrecht
2011
6
Belani 2013
8
McGovern
2011
12
Legg 2012
10
Dasari 2012
9
Legg 2013
11
Reed 2013
38
Study design Lab. expt. Lab. expt. Lab. expt. Retrospective
case series
Lab. expt. Lab. expt. Lab. expt. Lab. expt.
Simulated or
actual
patients
Simulated Simulated Simulated Patients
undergoing
THA and TKA
Simulated Simulated Simulated Simulated
No. of
patients or
subjects
Hospitals,
n = 5. Particle
counts, n =
25. Swabbing,
n = 17.
Rinsing, n = 9
11 2 per group 1437 with
371 treated
with conductive
warmer and
1066 with FAW
5 5 locations at
5 heights
5 1 hospital with
23 FAW units
End points Particle
counts
Intake filter
retention
efficiency/
performance,
airborne
particles, FAW
colonization
Bubble count
over the
simulated
surgical site
Infection Particle
counts and
temp. over
surgical site
Temp. at
simulated
surgical site
Airflow
visualization,
drape temp.,
and particle
entrainment
Intake filter
efficiency/
performance and
air path microbial
colonization
Statistical
significance
No No Yes Yes Yes Yes Yes No
Summary of
findings
FAW
equipment
design is
questionable
with respect
to its ability
to prevent
airborne
contamination
58% of FAW
units were
found to
generate
airborne
contamina-
tion. No direct
link between
infection and
FAW. New
filters may
improve
efficiency
FAW disrupted
laminar airflow;
disruption was
dependent
on the exact
setup of the
room
High risk of
developing
deep infections
with FAW use
(odds ratio =
3.8, p = 0.024)
Temp. over
surgical site
and the no. of
particles were
greater with
FAW. Unable
to definitively
conclude that
these are
causes of
infection
Greater temp.
over the
surgical site
with FAW vs.
conductive
warming and
resistive
blanket
Disruption
of laminar
airflow and
increased no.
of particles
over the
surgical site
with FAW.
Drape temp.
also increased.
Authors
suggested
certain OR
setups may
impact
laminar flow
Filter efficiency
was 64% in
lab. experiments
but filters
performed within
specifications in
the OR. 70% of
FAW units had
higher particle
counts at the
hose end
compared with
the intake
Study
limitations
Testing was
done without
the blanket,
which is
required for
proper airflow.
Did not
demonstrate
that detected
particles were
bacteria.
Author conflict
of interest
Testing was
done without
the blanket,
which is
required
for proper
airflow. No
demonstration
of proper
maintenance
of filters and
FAW units.
Author conflict
of interest
Did not control
for room
setup. Author
conflict of
interest
Coauthor was
employee of
conductive
warming
company. Did
not account
for age or
medical
comorbidities.
Assumed
causation. Did
not account for
other infection
control
measures
implemented
during study
period
Did not
simulate OR
traffic and
personnel
Assumed
higher temp.
at surgical
site increases
risk of
infection. Did
not simulate
normal OR
traffic. Author
conflict of
interest
No direct
relationship
shown
between
laminar airflow
being affected
and increased
bacteria over
surgical site
Relied on
particle counts
rather than
sampling of
microorganisms
from hose-end
airflow. High
percentage of
control swab
contamination
(50%). Testing
was done
without blanket
*THA =total hip arthroplasty, TKA =total knee arthroplasty, FAW =forced air warming, OR =operating room, ICU =intensive care unit, and CFU =colony-forming unit.
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bacterial growth in twelve of twenty-nine units, and the filter
was positive in three units. Routine care that included changing
of the filter and cleaning of the unit was then performed, and
the testing was repeated after three months. The repeat cultures
of the units with a previous positive culture showed no growth
in the tubing or filter. This suggests that proper maintenance of
the Bair Hugger is essential to reduce the risk of infection.
Other studies have also revealed measurable growth of bacteria
in ventilation filters, and the authors attributed the cause
of infection outbreaks to colonized filters
6,7
. Frequent mainte-
nance of the forced air warming units and cleaning of the
outside and tubing of the warming unit are required to reduce
TABLE III (continued)
Baker 2002
39
Bernards
2004
37
Huang 2003
13
Sharp 2002
33
Tumia 2002
22
Sessler
2011
32
Zink 1993
34
Moretti
2009
31
Avidan
1997
30
Lab. expt. Lab. expt. Retrospective
case series
Lab. expt. Clinical study Lab. expt. Clinical study Retrospective
case series
Lab. expt.
Neither Neither Patients
undergoing
aortic surgery
with prosthetic
graft
Simulated Actual patients
and lab.
simulation
Simulated Actual
patients but
simulated
surgery
Actual Neither
1 FAW system 1 FAW system 16 patients 12 different
conditions
ranging from
empty ORs
to various
volunteers
with FAW
6 2 8 30 patients,
20 who
received FAW
and 10 who
did not
10 FAW
systems from
ORs
Cultures of
FAW hose and
filter
Cultures of
FAW hose and
filter
Culture sites
on patient
and in FAW
system
Assessment
of laminar
flow using
smoke visual
tracer
Increase in
number of
CFUs
Assessment
of laminar
flow using
smoke visual
tracer
Culture sites
of abdomen
Infections and
culture sites
on patient
and in FAW
system
Cultures of
filter and hose
No No No No No No Yes No No
Heavy growth
of bacteria
from all sites
Same strain of
Acinetobacter
as that
responsible for
an outbreak.
After device
was cleaned,
the bacteria
were not found
Decrease in
bacterial
counts at all 6
sites, including
the axilla and
the FAW
system
No significant
effect of FAW
use on laminar
airflow
Nonsignificant
increase in
CFUs when
FAW was on
compared
with when it
was off (p =
0.48)
No impairment
of laminar
flow and no
unwanted
airflow
disturbances
using FAW
More
coagulase-
negative
colonies when
FAW system
was off (p <
0.05), but
overall no
difference in
total no. of
colonies
between when
it was on and
off
No postopera-
tive infections
40% of FAW
system hoses
had potentially
pathogenic
organisms.
100% showed
no growth
from the air
when the FAW
system blanket
was worn
Only a single
device was
tested
Only a single
device was
tested. The
study was a
part of an
investigation
into an
Acinetobacter
outbreak in
the ICU
Small number
of patients.
No mention of
air handling
method in the
OR
Did not
simulate
normal OR
traffic
Unknown
patient
characteristics.
Unknown
manufacturer
of FAW
system
Did not
simulate
normal OR
traffic
Skin was not
prepped. No
surgical team
was present
and no surgery
was performed
on patients.
Only skin flora
was assessed
Unknown
follow-up
period.
Unknown
location of
FAW cover.
Small no. of
patients
Positive
cultures from
tubing may
not be
associated
with infection
in the patient
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colonization and the associated risk to the patient. Some au-
thors even propose the addition of an HEPA (high-efficiency
particulate air) antimicrobial filter to forced air warming sys-
tems, but relevant studies are lacking
30,37-39
.
Legg and Hamer simulated the impact of surgical drapes
and equipment on forced air warming devices and laminar flow
in an operating room environment
11
. For instance, the authors
noted that, depending on the arrangement of medical equip-
ment in the operating room, forced air warming devices may be
more likely than conductive warmers to disrupt laminar airflow
around the surgical field. They also noted that even the use of a
vertical drape between the surgical field and the anesthesia
team at the head of the table affects the laminar flow. Surgical
drapes placed vertically as part of the sterile surgical field may
themselves be warmed by forced air warming devices, leading
to accessory convection currents traveling upward and disrupt-
ing downward laminar flow. Indeed, the authors suggest that if
the artificial enclosure created by the vertical drape is elimi-
nated, the production of additional heat is less likely to be
important because warm air can leave more easily. They rec-
ommend using a well-insulated surface that is not in contact
with the patient to distribute the additional heat that may oth-
erwise be transferred to the drape. The authors further recom-
mend putting the vertical drape up before the Bair Hugger is
turned on, ensuring that the Bair Hugger is properly connected
to the gown with no leaks, and following all manufacturer in-
structions regarding the placement of the gown. Clearly, proper
use of forced air warming devices and associated warming
gowns is required to maximize heat transfer to the patient while
minimizing heat transfer to the drapes and surrounding lam-
inar airflow.
The risks of burns and pressure sores, even involving the
nonoperatively treated extremity, increase when warming de-
vices are not used properly. Burns can result from improper
placement of the warming device or from placement of the
tubing on the patient. Mayo stands, trays, and surgical equip-
ment placed on or near a patient can limit expansion of the
warming blanket or gown. This can force air into a small area
and increase the risk of burns. These burns are often first or
second-degree and may heal with scarring. Appropriate con-
sultation with plastic surgeons or wound nurses may allow
for prompt treatment and skin coverage as needed. There are
also several alternatives or adjunctive warming devices that
may be used to increase patient temperature. Some of these
devices and their risks and benefits are described in Table II.
Several studies have indicated that the use of these devices in
addition to forced air warming increases the ability to main-
tain normothermia
35,40-42
.
Clinical Importance
It is important to consider both the risks and benefits of warm-
ing devices when deciding how to utilize them for patients
undergoing joint arthroplasty. There are medical, safety, and
economic implications to the choice
43,44
.Furtherstudyis
warranted to prove or disprove a causal relationship between
use of forced air warming and periprosthetic joint infections
(Table III). In the meantime, appropriate strategies include
proper maintenance of equipment and filters to reduce bacte-
rial colonization, appropriate placement of forced air warming
blankets in accordance with manufacturer recommendations,
and recognition of the potential effects of these devices on
laminar airflow. Future studies will need to limit bias, include
large study populations, have a consistent definition of hypo-
thermia, carefully control associated and relevant variables
(e.g., operating room traffic and antibiotic protocols), and en-
sure equivalent efficacy of warming in all study groups. Such
studies will aid clinicians in choosing appropriate future strat-
egies for warming. n
NOTE: The authors acknowledge Drs. Marc Swiontkowski and Thomas Vangsness for their editorial
assistance.
Robby S. Sikka, MD
TRIA Orthopaedic Center,
University of Minnesota,
8100 Northland Drive,
Minneapolis, MN 55431.
E-mail address: robbysikka@gmail.com
Richard C. Prielipp, MD, MBA, FCCM
Department of Anesthesiology,
University of Minnesota,
420 Delaware Street S.E.,
Minneapolis, MN 55455.
E-mail address: prielipp@umn.edu
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FORCED AIR WARMING DEVICES IN ORTHOPAEDI CS:
AFOCUSED REVIEW OF THE LITERATURE