Effect of preoperative warming on intraoperative hypothermia: a randomized-controlled trial

Purpose The purpose of this study was to evaluate the effects of preoperative forced-air warming on intraoperative hypothermia. Methods In this randomized-controlled trial, adult patients scheduled for elective, non-cardiac surgery under general anesthesia were stratified by scheduled surgical duration (< 2.5 hr or ≥ 2.5 hr) and then randomized to a pre-warming group using a BairPaws™ forced-air warming system for at least 30 min preoperatively or to a control group with warmed blankets on request. All patients were warmed intraoperatively via convective forced-air warming blankets. Perioperative temperature was measured using the SpotOn™ temperature system consisting of a single-use disposable sensor applied to the participant’s forehead. The primary outcome was the magnitude of intraoperative hypothermia calculated as the area under the time-temperature curve for core temperatures < 36°C between induction of general anesthesia and leaving the operating room. Secondary outcomes included surgical site infections, packed red blood cell requirements, and 24 hr postoperative opioid consumption. Results Two hundred participants were analyzed (101 control; 99 pre-warmed). Pre-warmed participants had a lower median [interquartile range] magnitude of hypothermia than controls (0.00 [0.00-0.12] °C·hr −1 vs 0.05 [0.00-0.36] °C·hr −1 , respectively; median difference, −0.01°C·hr −1 ; 95% confidence interval, −0.04 to 0.00°C·hr −1 ; P = 0.005). There were no between-group differences in the secondary outcomes. Conclusion A minimum of 30 min of preoperative forced-air convective warming decreased the overall intraoperative hypothermic exposure. While redistribution hypothermia still occurs despite pre- and intraoperative forced-air warming, their combined application results in greater preservation of intraoperative normothermia compared with intraoperative forced-air warming alone. Trial registration www.clinicaltrials.gov (NCT02177903). Registered 25 June 2014.