Item: Hypothermia during snow burial
Title: Hypothermia during snow burial
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: Mary Beth Scholand, MD, Colin K. Grissom, MD, Martin I Radwin, MD, and Chris H. Harmston, MSE, Pulmonary Division, LDS Hospital, Salt Lake City, Utah, 84143, University of Utah, Salt Lake City, Utah 84132, Black Diamond Equipment Ltd., Salt Lake City
Abstract: The development of hypothermia during avalanche burial has never been prospectively studied. Previous retrospective reports of core body temperature in avalanche burial victims after extrication estimate an average decrease in core body temperature of - 3 0 C per hour. The objective of this study was to measure decrease in core body temperature during snow burial under conditions of normal blood carbon dioxide (C02), or normocapnic conditions, as compared to conditions of elevated blood carbon dioxide, hypercapnic conditions. An elevated blood carbon dioxide is expected to occur during avalanche burial as persons rebreathed expired C02. Eight subjects were buried breathing with a device that diverts expired air to the snow surface and maintains normocapnia. Three of the 8 subjects were also buried breathing with a device that diverts expired air around to the back of the subject (Avalung TM, Black Diamond Equipment, Ltd., Salt Lake City, Utah), which results in the gradual development of hypercapnia. Physiologic measurements made at baseline and followed throughout the study burials included core body temperature, arterial oxygen saturation % (Sp02), partial pressure of end-tidal C02 (ETC02) in mmHg and partial pressure of inspired C02 (PiC02) in mmHg. The study set up consisted ofa large mound of compacted snow of similar density to avalanche debris (mean density 35%, range 28% - 39%). Subjects sat in a trench dug into one end of the mound. While breathing on either the modified device tbat maintained normocapnia, or the AvaLung device that resulted in hypercapnia, subjects were completely buried in densely compacted snow with the head 50 cm under the surface. Study burial endpoints were after a time period of 90 minutes, when Sp02 % <84, core body temperature < 35 0 C or at the subjects request. Subjects were in constant communication with the surface crew via intercom. During normocapnic burials breathing with the modified device where expired air was diverted to the snow surface, core body temperature decreased at a mean rate of - 0.7 0 C per hour (range - 0.33 to - 1.73 0 C per hour). End study respiratory parameters remained unchanged from mean baseline values of Sp02 96%, ETC02 40 mm Hg and PiC02 5 mm Hg. During the hypercapnic burials breathing with the AvaLung, core body temperature decreased at a rate of -1.2 0 C per hour in all three subjects. Respiratory parameters changed from baseline with the ETC02 increasing to an end study mean of 59 mm Hg, PiC02 increasing to 43 mm Hg and Sp02 decreasing to 90%. Core body temperature decreased at a rate of 1.5 to 3 times faster in the hypercapnic group as compared to the normocapnic group. These preliminary data suggest the rate of decrease in core body temperature during snow burial is less than the previously reported 3 0 C per hour. As a result of rebreathing C02 during snow burial, hypercapnia develops and appears to accelerate the rate of decrease in core body temperature. These findings may have important implications for triage and resuscitation of avalanche burial victims.
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Keywords: avalanche accidents, avalanche rescue, hypothermia, hypercapnia
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