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.