Objective To evaluate the rewarming effectiveness of the same amount of heat, using a charcoal heater, donated to the head or torso while using a human model for severe hypothermia where shivering is pharmacologically inhibited in mildly hypothermic subjects.

Methods Six male subjects were cooled on three different occasions each, in 8°C water, for 60 min or to a core temperature of 35°C. Shivering was inhibited by intravenous meperidine (1.5 mg/kg), administered during the last ten minutes of the cold-water immersion. Subjects then exited from the cold-water immersion and then were rewarmed for 120 min by one of the following: spontaneous rewarming only; charcoal heater on the head; or charcoal heater on the torso. Supplemental meperidine (maximum cumulative dose of 3.3 mg/kg) was administered as required during rewarming to suppress shivering.

Results No significant differences were found in the afterdrop amount or core rewarming rates among the three conditions. During the last 30 min of rewarming the net heat gain was significantly higher in the Head (85.8±25.3 W) and Torso (81.5±6.3 W) conditions compared to Spontaneous condition (56.9±12 W) (p<0.05).

Conclusions In our study, Head and torso warming had the same core rewarming rates in a human model for severe hypothermia where shivering was pharmacologically inhibited in mildly hypothermic subjects. In non-shivering cold subjects, head warming is a viable alternative if torso warming is contraindicated.

Funding NSERC, Canada.