This document summarizes clinical studies and cost analyses that demonstrate the importance of maintaining perioperative normothermia. Several studies show that hypothermia can lead to increased surgical site infections, longer hospital stays, more blood loss and transfusions, prolonged drug effects, and increased mortality. Additionally, meta-analyses found that maintaining normothermia results in cost savings of $2495 to $7073 per patient in the US due to reductions in complications. Prewarming patients for 30 minutes before surgery can help prevent inadvertent perioperative hypothermia.

1. 3M Infection Prevention Solutions
The importance of maintaining
perioperative normothermia:
clinical studies and cost analyses

2. Consequences of mild perioperative hypothermia
Surgical site infection and hospital length of stay
Kurz A, Sessler DI, Lenhardt R. Perioperative Infection Rate Length of Hospital Stay
normothermia to reduce the incidence of surgical- 20% 16
wound infection and shorten hospitalization. Study 15%
14
12
of Wound Infection and Temperature Group. N. Engl. J. 10
Days
Med. 1996;334(19):1209-1215. 10% 8
6
5% 4
This study of 200 patients undergoing elective colorectal 2
surgery randomly assigned to two temperature management 0% 0
Hypothermic Normothermic Hypothermic Normothermic
groups - standard intraoperative care without active
warming or active warming - indicates that maintenance P = 0.009 P = 0.01
of normothermia decreased the incidence of surgical site
infection and shortened hospital length of stay.
Melling AC, Ali B, Scott EM, Leaper DJ. Effects of Infection Rate
16%
preoperative warming on the incidence of wound 14%
infection after clean surgery: a randomised 12%
controlled trial. Lancet. 2001;358(9285):876-880. 10%
8%
6%
4%
This study of 421 breast, varicose vein, or hernia surgery
2%
patients randomly assigned to either a standard (unwarmed) 0%
group or a group receiving at least 30 minutes of applied Unwarmed Warmed
local or systemic warming before surgery indicates that P = 0.001
warming patients before surgery appears to assist in the
prevention of surgical wound infection.
Morbid myocardial outcomes
Frank SM, Fleisher LA, Breslow MJ, et al. Perioperative Morbid Cardiac Events Ventricular Tachycardia
7% 10%
maintenance of normothermia reduces the incidence
6%
of morbid cardiac events: a randomized clinical trial. 5%
8%
JAMA. Apr 9 1997; 277(14):1127-1134. 4% 6%
3% 4%
2%
This study involved 300 patients over the age of 60 2%
1%
undergoing peripheral vascular, abdominal, or thoracic 0% 0%
surgery who either had a history of, or were at high risk for, Hypothermic Normothermic Hypothermic Normothermic
coronary artery disease. Patients were randomly assigned to
either standard care (no active warming) or active warming. P = 0.02 P = 0.04
Results indicate that hypothermia was an independent
predictor of morbid cardiac events and ventricular
tachycardia.

3. Blood loss and transfusion requirement
Surgical Blood Loss
Schmied H, Kurz A, Sessler DI, Kozek S, Reiter A. Mild 1000
hypothermia increases blood loss and transfusion 800
requirements during total hip arthroplasty. Lancet. Feb
600-
3 1996;347(8997):289-292.
mL
400
This study of 60 patients undergoing hip arthroplasties
200
randomly assigned to normothermic or mildly hypothermic
0
groups indicates that a decline in core temperature on a Hypothermic Normothermic
level ordinarily experienced during surgery contributed to
significantly greater blood loss among the hypothermic group P = 0.008
versus the normothermic group.
Rajagopalan S, Mascha E, Na J, Sessler DI. The Increases in blood loss and transfusion risk
effects of mild perioperative hypothermia on blood 25%
loss and tranfusion requirement. Anesthesiology. 20%
Jan 2008;108(1):71-77. 15%
This meta-analysis of randomized studies comparing blood 10%
loss and/or transfusion requirements of normothermic 5%
patients to that of surgical patients with mild intraoperative 0%
Blood loss Transfusion risk
hypothermia indicates that maintenance of normothermia
is associated with lower blood loss and a reduced risk of P = 0.009 P = 0.027
transfusion requirement.
Prolonged and altered drug effect
Heier T, Caldwell JE, Sessler DI, Miller RD. Mild Duration of Action of Vecuronium
Intraoperative hypothermia increases duration of 70
action and spontaneous recovery of vecuronium 60
50
blockade during nitrous oxide-isoflurane anesthesia
Minutes
40
inhumans. Anesthesiology. 1991;74(5):815-819. 30
This study of 20 elective surgery patients assigned to 20
10
normothermic or mildly hypothermic (>34.5°C) groups 0
indicates that mild hypothermia increased vecuronium’s Hypothermic Normothermic
duration of action and therefore the patient’s time for recovery
P = <0.05
from vecuronium-induced neuromuscular blocking action.
Prolonged recovery Time to recovery
100 160
Lenhardt R, Marker E, Goll V, et al. Mild intraoperative
80 140
hypothermia prolongs postanesthetic recovery. 120
Minutes
Anesthesiology. 1997;87(6):1318-1323. 60 100
80
40
This study of 150 patients undergoing elective abdominal 60
20 40
surgery assigned to standard care (no active warming) or 20
0 0
active warming groups indicates that hypothermia prolonged Hypothermic Normothermic Hypothermic Normothermic
post-operative recovery and time to discharge from the
>36°C not in discharge criteria >36°C in discharge criteria
recovery unit, particularly when discharge critieria included a
core temperature >36°C. P = < 0.001 P = < 0.001

4. Mortality
Bush HL, Jr., Hydo LJ, Fischer E, Fantini GA, Silane Mortality Rate
14%
MF, Barie PS. Hypothermia during elective abdominal 12%
aortic aneurysm repair: the high price of avoidable 10%
morbidity. J. Vasc. Surg. Mar 1995,21(3):392-400; 8%
discussion 400-402. 6%
4%
This retrospective study of 262 elective abdominal aortic 2%
aneurysm repairs indicates that hypothermia (<34.5°C) 0%
increased risk of mortality, as well as increased risk of Hypothermic Normothermic
transfusion, organ dysfunction, ICU length of stay and
hospital length of stay. P = < 0.01
Patient discomfort
Kurz A, Sessler DI, Narzt E, et al. Postoperative hemodynamic and thermoregulatory consequences of intraoperative core
hypothermia. J. Clin. Anesth. 1995;7(5):359-366.
This study of 74 patients undergoing elective colon surgery randomly assigned to standard care (hypothermic) or additional warming (normothermic)
groups indicates that intra-operative hypothermia caused significant thermal discomfort postoperatively and increased time to recovery, with shivering
common within the hypothermic group and uncommon among normothermic patients.
Prewarming to avoid perioperative hypothermia
Sessler DI, Schroeder M, Merrifield, B, Matsukawa
T, Cheng C. Optimal duration and temperature of Changes in heat content
80
prewarming. Anesthesiology. 1995;82(3): 674-681. 60
40 Heat gain from
This study of 7 healthy male volunteers indicates that 30 20 prewarming
kcal
0
minutes of forced-air warming before induction of anesthesia
-20 Heat loss from
(i.e. prewarming) can increase peripheral tissue heat content -40 redistribution
by more than the amount redistributed from the core during -60
the first hour after induction of anesthesia, and thus prevents
the core temperature drop that ordinarily follows anesthetic-
induced vasodilation.

5. Perioperative hypothermia: causes and patterns
Key Findings
Matsukawa T, Sessler DI, Sessler AM, et al. Heat flow and distribution during induction of general anesthesia. Anesthesiology.
1995;82:662-73.
This study of 6 healthy male volunteers showed a mean core temperature decrease of 1.6± 0.3°C in the first hour after induction of anesthesia, with
81% of the decrease attributed to redistribution of heat from the core to the periphery due to anesthetic-induced vasodilation.
Sessler, DI. Perioperative heat balance. Anesthesiology. Feb 2000;92(2):578-596.
This review of clinical data seperates perioperative temperature drop into three phases:
• Phase I: rapid decrease in core temperature mainly due to redistribution of heat from the core to the periphery due to anesthetic
induced vasodilation.
• Phase II: slow, linear path decline in temperature within 2-3 hours following anesthesia induction.
• Phase III: three to five hours after anesthesia induction core temperature plateaus as the body begins to resist temperature drop
through vasoconstriction.
Phases of Inadvertent Hypothermia
0
Phase I: Rapid decrease in core temperature
-1
Δ Core Temp (°C)
-2
Phase II: Slow, linear decline in temperature
Phase III: Temperature plateau
-3
0 2 4 6
Elapsed Time (h)

6. Perioperative hypothermia: costs
Cost-effectiveness of maintaining normothermia: U.S. meta-analysis
U.S. Outcome Cost savings per Cost savings per
Mahoney CB, Odom J. Maintaining intraoperative normothermia: patient (high end patient (low end
A meta-analysis of outcomes with costs. AANA J. cost assumptions) cost assumptions)
1999;67(2):155-163.
Red blood cells $229.43 $117.60
This meta-analysis of 18 studies covering 1575 patients indicates that
Plasma $76.90 $71.50
cost savings associated with maintaining normothermia ranged from
$2495 to $7073 per patient. Platelets $38.07 $38.07
Length of stay $4602.00 $1534
ICU time $314.25 $104.75
Infection $1696.80 $545.40
Myocardial infarction $90.23 $67.67
Transfusion $0.20 $0.07
Ventilation $25.68 $16.05
Total cost savings $7073.56 $2495.11
U.K.
National Institute for Health and Clinical Excellence. CG65 Perioperative hypothermia (inadvertent): full guideline, April 2008.
An economic analysis conducted by the U.K. National Institute for Health and Clinical Excellence on the cost-effectiveness of interventions to prevent inadvertent
perioperative hypothermia indicates that the cost saving per inadvertent perioperative hypothermia case avoided ranged from £101 to £686, depending upon age of
patient and magnitude of surgery.
Estimated savings per IPH case avoided: U.K. NICE Costs of IPH complications: U.K. NICE
Consequence Scenario (age or Cost Consequence Unit cost
surgery magnitude)* savings £
Surgical wound infection (minor surgery) £950
Morbid cardiac events 50 years 59
70 years 111 Surgical wound infection (major surgery) £3858
Minor surgery 13 Transfusion £244
Hospital length of stay
Intermediate surgery 51
Major surgery 204 Morbid cardiac event (ischemia) £2024
Surgical wound infection Minor surgery 86 Morbid cardiac event (cardiac arrest) £2021
Intermediate / major surgery 347
Morbid cardiac event (myocardial infarction) £1674
Pressure ulcer Intermediate / major surgery 17
Minor surgery - Mechanical ventilation £1144
Blood transfusion Intermediate / major surgery 5 Pressure ulcer £1064
Minor surgery -
PACU length of stay per hour £44
Post-operative All ages and magnitudes 2
mechanical ventilations of surgery Hospital length of stay per day £275
Summary of cost of each adverse consequence of IPH, NICE Inadvertent peroperative hypothermia: full guideline (April 2008), page 511
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