Grissom CK, McAlpine JC, Harmston CH, Radwin MI, Giesbrecht GG, Scholand MB, Morgan JS. Hypercapnia effect on core cooling and shivering threshold during snow burial. Aviat Space Environ Med 2008; 79:735–42.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°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°C shelter and T_re afterdrop was measured. Results: The T_re over 1 h of burial in the hypercapnic study was 1.28 ± 0.4°C and in the normocapnic study was 0.97 ± 0.4°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°C at 21 ± 8.1 min after extrication) was not different than in the normocapnic study (0.86 ± 0.3°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.