Hypothermia during Avalanche Burial

Core body temperature cooling during avalanche burial results in hypothermia, and further core temperature cooling during extrication and evacuation of an avalanche burial victim may result in more severe hypothermia. We performed two studies measuring the rate of core body temperature cooling during snow burial and after extrication from snow burial. Subjects were completely buried in a large mound of age hardened snow (mean density 47%) while core body temperature was monitored with a rectal probe (Tre). All subjects dressed in a lightweight clothing insulation system consisting of a one piece gore-tex suit worn over medium weight capilene underwear with a hood, face mask, goggles, mittens, and boots. Inspired and expired carbon dioxide (CO2) levels and arterial oxygen saturation (SaO2) were also monitored. In our first study avalanche burial was simulated by having 12 subjects breathe with a device (AvaLung 2TM, Black Diamond Equipment Ltd.) that resulted in hypercapnia (high CO2) over 30 to 60 minutes. Mean snow temperature was – 2.6 +2.1 ° C. Burial time was 49 +14 minutes. Rate of decrease in Tre was 1.3 +0.5 ° C / hr. The fraction of inspired carbon dioxide (FICO2) increased from 1.4 +1.0 % to 7.0 +1.4 % and SaO2 decreased from 97 +1 % to 90 +6 % (P<0.01). In a second separate study 11 subjects were buried for 60 minutes breathing an inspired gas mixture containing 5% CO2 and 21% oxygen (O2). Tre cooling rate was 1.3 ±0.4 o C/hr. SaO2 remained > 90% for all subjects. In this study we also measured core body temperature for 30 minutes after extrication from the snow during passive rewarming. Maximum Tre cooling rate during passive rewarming increased to 2.2 ±1.3 o C/hr at 20 +8 minutes after extrication. Tre cooling rate during snow burial was 1.3 o C/hr. This suggests that survivors of prolonged avalanche burial may not become as rapidly hypothermic as previously thought. The greatest Tre cooling rate occurred just after extrication from snow burial. This suggests that core body temperature cooling during extrication and evacuation significantly contributes to hypothermia in avalanche burial victims. Medical care of avalanche burial victims should include measures to insulate and rewarm as soon as possible after extrication.