We wanted to find out the effects of extra insulation on preventing hypothermia and its complications for adults having an operation.
People can get cold during operations, particularly because of the drugs used as anaesthetics. This can sometimes cause potentially dangerous heart problems. The cold can also make people shiver and feel uncomfortable after an operation. Ways have therefore been developed to try to keep people warm during an operation. One way is to use reflective blankets or clothing as extra insulation.
We looked at the evidence up to February 2014 and found 22 studies involving several hundred patients. The studies involved people aged over 18 years having routine or emergency surgery. We disregarded studies where people were deliberately kept cold during the operation, where they were having head surgery or skin grafts, or where the person was having a procedure under local anaesthetic.
We looked at studies comparing what happened when using reflective blankets or clothing against what happened when someone had normal care, using non-reflective blankets or clothing.
We also looked at studies comparing what happened when using a machine to force warm air through the person’s blankets (forced air warming) against what happened when using reflective blankets or clothing.
There is no clear evidence that using reflective blankets or clothing increases a person’s temperature compared with what happens when someone has usual care.
There is some evidence that using forced air warming increases a person’s temperature compared with what happens when using reflective blankets or clothing. The temperature increase was between 0.5 ºC and 1 ºC. It is unclear how this temperature difference would reduce the consequences of coldness, with uncertain effects on blood loss, shivering and time spent in recovery. We were unable to find sufficient information to look at adverse effects of insulation or warming, or major events affecting the heart or circulatory system.
Quality of the evidence
Most of the evidence was low quality. We were particularly concerned about the potential for skewed results from operating theatre staff changing their behaviour when they knew ways of keeping the patient warm had changed.
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.
Inadvertent perioperative hypothermia occurs because of interference with normal temperature regulation by anaesthetic drugs and exposure of skin for prolonged periods. A number of different interventions have been proposed to maintain body temperature by reducing heat loss. Thermal insulation, such as extra layers of insulating material or reflective blankets, should reduce heat loss through convection and radiation and potentially help avoid hypothermia.
To assess the effects of pre- or intraoperative thermal insulation, or both, in preventing perioperative hypothermia and its complications during surgery in adults.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 2), MEDLINE, OvidSP (1956 to 4 February 2014), EMBASE, OvidSP (1982 to 4 February 2014), ISI Web of Science (1950 to 4 February 2014), and CINAHL, EBSCOhost (1980 to 4 February 2014), and reference lists of articles. We also searched Current Controlled Trials and ClinicalTrials.gov.
Randomized controlled trials of thermal insulation compared to standard care or other interventions aiming to maintain normothermia.
Two authors extracted data and assessed risk of bias for each included study, with a third author checking details. We contacted some authors to ask for additional details. We only collected adverse events if reported in the trials.
We included 22 trials, with 16 trials providing data for some analyses. The trials varied widely in the type of patients and operations, the timing and measurement of temperature, and particularly in the types of co-interventions used. The risk of bias was largely unclear, but with a high risk of performance bias in most studies and a low risk of attrition bias. The largest comparison of extra insulation versus standard care had five trials with 353 patients at the end of surgery and showed a weighted mean difference (WMD) of 0.12 ºC (95% CI -0.07 to 0.31; low quality evidence). Comparing extra insulation with forced air warming at the end of surgery gave a WMD of -0.67 ºC (95% CI -0.95 to -0.39; very low quality evidence) indicating a higher temperature with forced air warming. Major cardiovascular outcomes were not reported and so were not analysed. There were no clear effects on bleeding, shivering or length of stay in post-anaesthetic care for either comparison. No other adverse effects were reported.