Heat conservation vs convective warming in adults undergoing elective surgery

Abstract

Purpose: To determine the relative efficacy of heat conservation and convective warming in maintaining perioperative normothermia, (central temperature ≤36°C). Methods: Thirty-seven patients undergoing elective gynaecological, orthopaedic, or general surgery scheduled to last two hours were prospectively studied. Patients were randomized to one of two groups. Group 1 patients received heat conservation with reflective blankets (Thermadrape(TM), Vital Signs, Inc., Totowa, NJ) applied preoperatively and warmed iv fluids (Hotine(TM) SIMS Level 1 Technologies Inc, Rockland, MA). Group 2 patients received convective warming (BairHugger, Augustine Medical, Inc., Eden Prairie, MN) after induction of anaesthesia and iv fluids at room temperature. All patients received general anaesthesia, with isoflurane. Tympanic membrane and forearm-fingertip skin temperature gradients were measured perioperatively at 15 min intervals. Results: Central temperature decreased after induction to a minimum level of 35.9 ± 0.1°C in group 1 and 36.0 ± 0.1°C in group 2 and then increased towards pre-induction values in group 2, and were higher (P < 0.05) than in group 1: 95% group 2 patients had central temperature ≤36.0°C at the end of surgery (vs 69% of group 1, P < 0.05). During the first 30 min in PACU central temperatures were higher in group 1 than in group 2 (36.8 ± 0.1°C vs 36.2 ± 0.2°C, P < 0.05). After 60 min, central temperatures were similar (36.8°C). The incidence of shivering and degree of peripheral cutaneous vasoconstriction were also similar. Conclusion: Patients receiving convective warming were more likely to leave the operating room normothermic, and had higher central temperatures during the first 30 min in the recovery room. The intergroup temperature differences were small and by 60 min, had disappeared.