This review of cutaneous warming systems for temperature control in patients undergoing elective surgery found circulating water garments were more effective than forced-air warming systems and both were more effective than passive warming devices. Forced-air warming systems were similar to carbon fibre systems. The authors’ conclusions should be treated with caution since meta-analyses were not significant and evidence was limited.

To evaluate the effectiveness of cutaneous warming systems for temperature control in patients undergoing elective surgery.

MEDLINE, CINAHL, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL) were searched from 2000 to April 2009 for publications in English, Spanish and Portuguese; search terms were reported. The bibliography of each retrieved article was handsearched. Experts in the field were contacted. Only studies published as full papers in journals were included.

Randomised controlled trials (RCTs) of cutaneous warming systems for temperature control in patients aged 18 years or older who underwent elective surgery were eligible for inclusion. Studies were excluded if prewarming interventions were used during the preoperative period or induced hypothermia was used. The primary outcome was core body temperature. Data collection had to take place during the intraoperative period.

All of the identified studies compared forced-air warming systems with other interventions. These included passive insulation, circulating water garments, radiant warming systems, carbon fibre resistive heating systems, circulating water mattresses, energy transfer pads, circulating water mattress plus passive warming, warm water plus pulsating negative pressure, and convective warming and other forced-air warming systems. One study compared a circulating water mattress plus passive warming with and without forced-air warming systems. One study compared forced-air warming systems at the surgical site to forced-air warming systems at the upper body. Anaesthesia was general in two thirds of the studies and spinal, general or regional, epidural or not reported in one third of the studies. Core temperature was measured in a number of sites, most commonly oesophageal or tympanic. Types of surgery varied widely: five studies included abdominal surgery patients, four studies were of off pump coronary bypass and two studies each were of caesarean section and laparoscopic cholecystectomy.

Two independent reviewers performed the selection.

Methodological quality was assessed by two reviewers independently using the five-point Jadad scale of randomisation, blinding, withdrawals and drop-outs. Discrepancies were resolved by discussion. Allocation concealment was assessed.

Temperature of patients at baseline, intraoperatively and at the end of the intraoperative period were extracted with standard deviations. Where a number of intraoperative temperatures were recorded (such as in a graph), mean intraoperative temperature was calculated. Mean final and baseline temperatures were used to calculate mean differences in temperature, with 95% confidence intervals (CI).

Two independent reviewers performed data extraction using a validated extraction form and crosschecked data.

Mean differences were pooled using a random-effects model to give weighted mean differences (WMDs) with 95% CIs. Separate comparisons were made between forced-air warming systems and other warming systems. Publication bias was not assessed as there were too few studies with sufficient outcome measurement. Between-study heterogeneity was determined using I². Possible sources of heterogeneity were discussed.

Twenty-three RCTs were identified (n=1,749 participants, mean 76, range 16 to 324). Overall methodological quality was reported as moderate: 19 trials with a Jadad score of 3 and four trials with a moderate to low score of 2.

There was a non-significant trend for forced-air warming systems to have superior temperature control over passive insulation with cotton blankets (WMD 0.29°C, 95% CI -0.02 to 0.59, p=0.06, I²=80%; three studies) and radiant warming systems (WMD 0.16°C, 95% CI -0.01 to 0.33, p=0.06, I²=19%; three studies).

Circulating water garments showed a non-significant trend for better temperature control than forced-air warming systems (WMD -0.73°C, 95% CI -1.51 to 0.05, p=0.07, I²=97%; four studies). Two studies compared baseline and interim (during surgery) temperatures and found no significant differences between circulating water garments and forced-air warming systems (I²=0%). Comparison of interim and final temperatures revealed no significant differences between the two warming systems (I²=18%).

Individual study results: Forced-air warming systems had significantly better temperature control than a cotton blanket (three out of five studies), a reflective blanket (one study), radiant warming (two out of three studies) and forced-air warming systems plus a surgical access blanket (one study). Forced-air warming systems plus carbon fibre resistive heating (two studies) and forced-air warming systems with or without a surgical access blanket (one study) were significantly better than a circulating water mattress. Two studies compared different forced-air warming systems finding no significant differences.

There was no significant difference in temperature control between forced-air warming systems and carbon fibre resistive heating (two out of three studies), a resistive carbon fibre underblanket (one study) and use of a WarmAir system (one study).

Circulating water garments were significantly better than forced-air warming systems (four studies). Energy transfer pads were significantly better than forced-air warming systems (one study). Warm water and pulsating negative pressure were significantly better than forced-air warming systems (one study).

Circulating water garments had significantly better temperature control than forced-air warming systems plus carbon fibre resistive heating (one study). One study used circulating water garments plus Steri-Drape cardiovascular sheets and found no significant difference with and without a full access underbody forced-air warming systems.

Evidence suggested that circulating water garments offered better temperature control than forced-air warming systems and both were more effective than passive warming, radiant warming and circulating water mattresses.

The review addressed a well-defined question in terms of interventions, study design and relevant outcomes. The included participants were specified for age and elective surgery. Types of surgery varied enormously and might have been narrowed. Relevant databases were searched in three languages. Only full papers were included and there was a limited search for unpublished studies, so some relevant studies may have been missed. It was not possible to assess publication bias. Study quality was assessed using suitable criteria and results reported in full. Efforts were made to reduce error and bias during most review processes. Relevant study details were reported, but no details of the age or gender of participants were reported. Statistical heterogeneity was assessed and there was evidence for heterogeneity with some outcomes. The statistical method used for the meta-analysis of the RCTs seemed appropriate.

The authors’ conclusions should be treated with caution as there were many relevant interventions and limited data were available to enable definitive conclusions to be made for individual interventions. Conclusions were based on trends that were not statistically significant.

Practice: The authors stated that the 0.73°C difference in temperature noted for circulating water garments over forced-air warming systems was important given that a 1°C change from normothermic status indicates hypothermia. Benefits of different warming systems should be considered in the light of initial and ongoing maintenance costs. Some funding agencies do not support certain warming systems. The suitability of different methods for particular patient groups should be considered.

Research: The authors suggested that research would be best focused on optimising the effectiveness of circulating water garments rather than forced-air warming systems. Further research was needed to establish the cost-benefit ratio of the various warming techniques and their initial costs and maintenance costs. Comparisons of circulating water garments and forced-air warming systems were needed.

Brazilian Council for Scientific and Technological Development; Alberta Heritage Foundation for Medical Research; Canadian Institutes for Health Research; University of Sao Paulo.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.