Effect of head and face insulation on cooling rate during snow burial.

OBJECTIVES: Avalanche victims are subjected to a number of physiological stressors during burial. We simulated avalanche burial to monitor physiological data and determine whether wearing head and face insulation slows cooling rate during snow burial. In addition, we sought to compare 3 different types of temperature measurement methods. METHODS: Nine subjects underwent 2 burials each, 1 with head and face insulation and 1 without. Burials consisted of a 60-minute burial phase followed by a 60-minute rewarming phase. Temperature was measured via 3 methods: esophageal probe, ingestible capsule, and rectal probe. RESULTS: Cooling and rewarming rates were not statistically different between the 2 testing conditions when measured by the 3 measurement methods. All temperature measurement methods correlated significantly. CONCLUSIONS: Head and face insulation did not protect the simulated avalanche victim from faster cooling or rewarming. Because the 3 temperature measurement methods correlated, the ingestible capsule may provide an advantageous noninvasive method for snow burial and future hypothermia studies if interruptions in data transmission can be minimized.

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.

Hypercapnia increases core temperature cooling rate during snow burial.

Previous retrospective studies report a core body temperature cooling rate of 3 degrees C/h during avalanche burial. Hypercapnia occurs during avalanche burial secondary to rebreathing expired air, and the effect of hypercapnia on hypothermia during avalanche burial is unknown. The objective of this study was to determine the core temperature cooling rate during snow burial under normocapnic and hypercapnic conditions. We measured rectal core body temperature (T(re)) in 12 subjects buried in compacted snow dressed in a lightweight clothing insulation system during two different study burials. In one burial, subjects breathed with a device (AvaLung 2, Black Diamond Equipment) that resulted in hypercapnia over 30-60 min. In a control burial, subjects were buried under identical conditions with a modified breathing device that maintained normocapnia. Mean snow temperature was -2.5 +/- 2.0 degrees C. Burial time was 49 +/- 14 min in the hypercapnic study and 60 min in the normocapnic study (P = 0.02). Rate of decrease in T(re) was greater with hypercapnia (1.2 degrees C/h by multiple regression analysis, 95% confidence limits of 1.1-1.3 degrees C/h) than with normocapnia (0.7 degrees C/h, 95% confidence limit of 0.6-0.8 degrees C/h). In the hypercapnic study, the fraction of inspired carbon dioxide increased from 1.4 +/- 1.0 to 7.0 +/- 1.4%, minute ventilation increased from 15 +/- 7 to 40 +/- 12 l/min, and oxygen saturation decreased from 97 +/- 1 to 90 +/- 6% (P < 0.01). During the normocapnic study, these parameters remained unchanged. In this study, T(re) cooling rate during snow burial was less than previously reported and was increased by hypercapnia. This may have important implications for prehospital treatment of avalanche burial victims.