Efficacy of Head and Torso Rewarming Using a Human Model for Severe Hypothermia

To evaluate the rewarming effectiveness of a similar amount of heat (from a charcoal heater) applied to either the head or torso in a human model for severe hypothermia in which shivering is pharmacologically inhibited in mildly hypothermic subjects.

Six male subjects were cooled on 3 different occasions, each in 8°C water for 60 min, or to a lowest core temperature of 35°C. Shivering was inhibited by intravenous meperidine (1.5 mg·kg^-1), administered during the last 10 min of the cold-water immersion. Subjects then exited from the cold water, were dried, and were placed in a 3-season sleeping bag for 120 min in one of the following conditions: spontaneous rewarming only, charcoal heater on the head, or charcoal heater on the torso. Supplemental meperidine (to a maximum cumulative dose of 3.3 mg·kg^-1) was administered as required during rewarming to suppress shivering.

No significant differences were found in the postcooling afterdrop amount or core rewarming rates among the 3 conditions (0.8°C·h^-1). 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 with the spontaneous condition (56.9±12 W) (P<0.05).

In our study, head and torso warming had the same core rewarming rates when shivering was pharmacologically inhibited in mildly hypothermic subjects. Therefore, in nonshivering cold subjects, head warming is a viable alternative if torso warming is contraindicated (eg, when performing cardiopulmonary resuscitation or working on open chest wounds).