Spontaneous endogenous core temperature rewarming after cooling due to snow burial.

OBJECTIVE: To measure afterdrop and rewarming in subjects placed in a hypothermia wrap immediately after extrication from 60 minutes of snow burial. METHODS: We 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. RESULTS: Tes 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). CONCLUSION: Afterdrop 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.

Hypercapnia effect on core cooling and shivering threshold during snow burial.

INTRODUCTION: Hypercapnia during avalanche burial may increase core temperature cooling rate by decreasing the temperature threshold for shivering or by increasing respiratory heat loss. METHODS: We studied the effect of hypercapnia on rectal core temperature (T(re)) cooling rate, respiratory heat loss, heat production, and the T(re) shivering threshold during snow burial (mean snow temperature -3.2 + 2.7 degrees C) in 11 subjects. In a 60-min hypercapnic burial subjects breathed a 5% carbon dioxide and 21% oxygen inhaled gas mixture and in a separate 60-min normocapnic burial subjects breathed ambient air. After extrication from snow burial subjects were passively rewarmed in a 15 degrees C shelter and T(re) afterdrop was measured. RESULTS: The deltaT(re) over 1 h of burial in the hypercapnic study was 1.28 +/- 0.4 degrees C and in the normocapnic study was 0.97 +/- 0.4 degrees C (P = 0.045). Minute ventilation, respiratory heat loss, total metabolic rate, and metabolic rate of the respiratory muscles were greater during the hypercapnic burial. There was no difference in shivering threshold between the hypercapnic and normocapnic conditions. Afterdrop in the hypercapnic study (0.69 +/- 0.4 degrees C at 21 +/- 8.1 min after extrication) was not different than in the normocapnic study (0.86 +/- 0.3 degrees C at 23.1 +/- 5.3 min after extrication). In both the hypercapnic and normocapnic studies afterdrop cooling rate was significantly greater during extrication than during snow burial. DISCUSSION: Hypercapnia significantly increased T(re) cooling rate by increasing respiratory heat loss but did not suppress shivering. Afterdrop may significantly contribute to hypothermia during rescue of avalanche burial victims.