Perioperative warming

Inadvertent hypothermia is when the body temperature falls below 36° C. This state is common in patients undergoing surgery. Hypothermia can lead to various complications. Many methods exist to keep the patient warm during surgery to avoid such complications. Warming methods can be divided into passive, which aim to isolate the patient to prevent heat loss, and active, which actively supply heat to the patient. What methods are preferred varies between different hospitals and different types of surgery.


Are there any systematic reviews which point to a specific method of warming being preferable during surgery?

We searched three electronic databases. We only included systematic reviews published in English. We identified 125 articles out of which 13 were considered potentially relevant. One person read these in full text. Five articles were included in the answer.

Identified literature

Table 1. Systematic reviews comparing different warming methods for the prevention of hypothermia during surgery.
Included studies Population/Intervention Outcome
Madrid et al (2016) Cochrane Database Syst Rev [1]
67 RCTs comparing different active body surface warming systems (ABWS) with each other, or with passive warming methods, or different techniques of administering the same ABWS method. Population:
Adult patients (<18 years) undergoing elective surgery with varying forms of anesthesia.
Comparison of the effectiveness of different active body surface warming systems (ABSW) which transfer heat through the skin. These included:
Electric blankets
Electric heated mattresses and pads
Warm-water circulation systems
Other conductive warming systems
Forced air warming systems
Core temperature in combination with one or more of the following:
Surgical site infection
Major cardiovascular complications
All-cause mortality
Blood loss
Intraoperative intravenous fluids infused
Other cardiovascular complications
Participant-reported outcomes
Pressure sores/ulcers
Adverse effects
Authors' conclusion:
“Forced-air warming (FAW), applied in the surgical pre- or intraoperative phases or both, seems to have a beneficial effect in terms of a lower rate of surgical site infection and complications, at least in people undergoing abdominal surgery with risk of infection, compared to not applying any active warming system. Intraoperative FAW also seems to have a beneficial effect in terms of lower rates of major cardiovascular complications when applied to people with documented substantial cardiovascular risk. It also improves patient comfort, as it maintains the core temperature within the normal range.”
Alderson et al (2014) Cochrane Database Syst Rev [2]
22 RCTs of which 16 contained data for analysis. Population:
Adult patients (<18 years) undergoing elective and emergency surgery with general or regional anesthesia or both.

Comparison of the effectiveness of thermal insulation (reflective blankets or clothing) to:
1. Other methods of thermal insulation.
2. Warming of intravenous- and irrigation fluids.
3. Warming of inspired and insufflated gases.
4. Active warming systems.
Core temperature before, during and after surgery.
Major cardiovascular complications
Infection and complications in the surgical wound
Bleeding complications
Other cardiovascular complications
Patient reported outcomes
All-cause mortality
Length of stay
Unplanned high dependency, or intensive care admission
Adverse effects
Authors' conclusion:
“There is no clear benefit of extra thermal insulation compared with standard care. Forced air warming does seem to maintain core temperature better than extra thermal insulation, by between 0.5 ºC and 1 ºC, but the clinical importance of this difference is unclear.”
Moola and Lockwood (2011) Int J Evid Based Healthc [3]
18 RCTs Population:
Adult patients (<18 years) undergoing different types of surgery.

The effectiveness of all passive and active warming systems and combined strategies.
Core temperature
Authors' conclusion:
“There are significant benefits associated with forced-air warming in terms of better outcomes such as higher core temperatures, reduced incidence of shivering and morbid cardiac events, increased thermal comfort, reduced blood loss, and reduced surgical site infections and shorter length of hospital stay. /…/ Single strategies such as forced-air warming were more effective than passive warming; however, combined strategies, including preoperative commencement, use of warmed fluids plus forced-air warming as other active strategies were more effective in vulnerable groups (age or durations of surgeries)”.
Galvão, Liang and Clark (2010) J Adv Nurs [4]
23 RCTs Population:
Adult patients (<18 years) undergoing elective surgery with general, regional, epidural or spinal anesthesia.

The effectiveness of different types of cutaneous warming systems.
Forced air warming
Cotton blankets
Reflective blankets
Radiant warming
Circulating water systems
Carbon fiber resistive heating
Energy transfer pads
Steri-drape cardiovascular sheet
Warm water and pulsating negative preassure
Warm air system
Core temperature before, during and after surgery
Authors' conclusion:
“Current evidence suggests that circulating water garments offer better temperature control than forced-air warming systems, and both are more effective than passive warming devices.”

“There is potential for the effectiveness of forced-air systems to be improved via the use of surgical access blankets, but currently there is insufficient evidence to determine whether this will elevate effectiveness to that of circulating water garments.”
Mahoney and Odom (1999) AANA journal [5]
20 RCTs Population:
Patients of various ages (14-73 years) undergoing different types of elective surgery

Forced air warming
Passive warming
Circulating water blanket
No treatment
Humidified air
Space blanket
Unspecified methods
Core temperature
Adverse effects related to excessive bleeding and resultant blood therapy
Myocardial infarction
Mechanical ventilation
Authors' conclusion:
”Patients in whom normothermia has been maintained during the intraoperative period experience fewer adverse outcomes /…. / Intraoperative normothermia is more effectively maintained by using forced air warming.”


  1. Madrid E, Urrutia G, Roque i Figuls M, Pardo-Hernandez H, Campos JM, Paniagua P, et al. Active body surface warming systems for preventing complications caused by inadvertent perioperative hypothermia in adults. Cochrane Database Syst Rev 2016;4:Cd009016.
  2. Alderson P, Campbell G, Smith AF, Warttig S, Nicholson A, Lewis SR. Thermal insulation for preventing inadvertent perioperative hypothermia. Cochrane Database Syst Rev 2014:Cd009908.
  3. Moola S, Lockwood C. Effectiveness of strategies for the management and/or prevention of hypothermia within the adult perioperative environment. Int J Evid Based Healthc 2011;9:337-45.
  4. Galvao CM, Liang Y, Clark AM. Effectiveness of cutaneous warming systems on temperature control: meta-analysis. J Adv Nurs 2010;66:1196-206.
  5. Mahoney CB, Odom J. Maintaining intraoperative normothermia: a meta-analysis of outcomes with costs. Aana j 1999;67:155-63.

SBU Enquiry Service consists of systematic literature searches to highlight studies that can address questions received by the SBU Enquiry Service from Swedish healthcare or social service providers. Relevant references are compiled by an SBU staff member, in consultation with an external expert when needed. The quality of the studies identified is not systematically reviewed.

Published: 9/25/2018
Contact SBU:
Report no: ut201830
Registration no: SBU 2018/289

Literature search

Project group

Rebecka Björnfors and Christel Hellberg at SBU.

Page published