Respiration during snow burial using an artificial air pocket

Context Asphyxia is the most common cause of death after avalanche burial. A device that allows a person to breathe air contained in snow by diverting expired carbon dioxide (CO2) away from a 500-cm(3) artificial inspiratory air pocket may improve chances of survival in avalanche burial. Objective To determine the duration of adequate oxygenation and ventilation during burial in dense snow while breathing with vs without the artificial air pocket device. Design Field study of physiologic respiratory measures during snow burial w ith and without the device from December 1998 to March 1999. Study burials were terminated at the subject's request, when oxygen saturation as measure d by pulse oximetry (SpO(2)) dropped to less than 84%, or after 60 minutes elapsed. Setting Mountainous outdoor site at 2385 m elevation, with an average barom etric pressure of 573 mm Hg. Participants Six male and 2 female volunteers (mean age, 34.6 years; range, 28-39 years). Main Outcome Measures Burial time, SpO(2), partial pressure of end-tidal CO 2 (ETCO2), partial pressure of inspiratory CO2 (PICO2), respiratory rate, a nd heart rate at baseline (in open atmosphere) and during snow burial while breathing with the device and without the device but with a 500-cm(3) air pocket in the snow. Results Mean burial time was 58 minutes (range, 45-60 minutes) with the dev ice and 10 minutes (range, 5-14 minutes) without it (P=.001). A mean baseli ne SpO(2) of 96% (range, 90%-99%) decreased to 90% (range, 77%-96%) in thos e buried with the device (P=.01) and to 84% (range, 79%-92%) in the control burials (P=.02). Only 1 subject buried with the device, but 6 central subj ects buried without the device, decreased SpO(2) to less than 88% (P=.005). A mean baseline ETCO2 of 32 mm Hg (range, 27-38 mm Hg) increased to 45 mm Hg (range, 32-53 mm Hg) in the burials with the device (P=.02) and to 54 mm Hg (range, 44-63 mm Hg) in the control burials (P=.02). A mean baseline Pi co, of 2 mm Hg (range, 0-3 mm Hg) increased to 32 mm Hg (range, 20-44 mm Hg ) in the burials with the device (P=.01) and to 44 mm Hg (range, 37-50 mm H g) in the control burials (P=.02). Respiratory and heart rates did not chan ge in burials with the device but significantly increased in control burial s. Conclusions In our study, although hypercapnia developed, breathing with th e device during snow burial considerably extended duration of adequate oxyg enation compared with breathing with an air pocket in the snow. Further stu dy will be needed to determine whether the device improves survival during avalanche burial.