Prevention of hypothermia during hip surgery: effect of passive compared with active skin surface warming

We have measured aural canal (core) and skin temperatures, and body heat content in 45 patients undergoing elective hip arthroplasty. They received general anaesthesia which included thiopentone, vecuronium and enflurane and nitrous oxide in oxygen. Patients were allocated randomly to three groups: group 1, control (n = 15), received no intraoperative warming device; group 2 had passive skin surface warming (metallized plastic sheet, Thermolite (n = 15); and group 3 had active skin surface warming (forced heated air, Bair-Hugger) (n = 15). Duration of surgery, fluid administration and the temperature and relative humidity of the operating theatre were similar for the three groups. Core temperature and mean body heat content decreased significantly during surgery in groups 1 and 2 (aural canal temperature 1.5 and 1.0 degrees C, and mean body heat content 287 and 189 kJ, respectively), while in group 3 these variables remained near preoperative values (P = 0.001). Mean skin and hand temperatures decreased in the control group, increased in the active warming group and were unchanged in the passive warming group (P < 0.005), indicating that the forced heated air system was very efficient in providing thermal homeostasis during surgery, while the metallized plastic sheet was able to insulate the skin only from radiant and convective heat losses, without attenuating the reduction in core temperature.