Spontaneous Endogenous Core Temperature Rewarming After Cooling Due to Snow Burial

ObjectiveTo measure afterdrop and rewarming in subjects placed in a hypothermia wrap immediately after extrication from 60 minutes of snow burial.MethodsWe measured esophageal core body temperature (Tes) in 6 subjects buried in compacted snow (mean density 39%) for up to 60 minutes at an altitude of 2450 m while breathing with an AvaLung (Black Diamond Equipment, Salt Lake City, UT). Mean snow temperature was –3.5 ± 1.0°C and mean air temperature was 0 ± 2°C. Subjects wore a 1-piece Gore-Tex suit over medium weight Capilene underwear with a hood, face mask, goggles, mittens, and boots. After extrication from snow burial subjects were immediately placed in a hypothermia wrap. Tes was measured for an additional 60 minutes as subjects rewarmed by shivering.ResultsTes cooling rate during snow burial was 0.84 ± 0.3°C/h during a mean burial time of 58 ± 4 minutes. Tes afterdrop (0.77 ± 0.4°C) occurred 12 ± 8 minutes after extrication from snow burial at a cooling rate of 4.0 ± 0.8°C/h (P <.001 Tes snow burial vs afterdrop cooling rate). Rewarming rate was 1.1 ± 0.3°C/h over the subsequent 48 ± 8 minutes (P = 0.045 snow burial cooling vs rewarming rate).ConclusionAfterdrop rate increased about 4-fold as compared to snow burial cooling rate for a transient time period in subjects who were placed immediately into an insulating hypothermia wrap. Spontaneous endogenous rewarming increased core body temperature at a slightly higher rate than it decreased during snow burial. These findings suggest that field rewarming of mildly hypothermic and shivering avalanche burial victims is possible, but they should be insulated quickly to limit significant afterdrop.