Lessons learned from avalanche survival patterns.

E366 CMAJ, April 19, 2011, 183(7) © 2011 Canadian Medical Association or its licensors The study by Haegeli and coauthors in CMAJ provides new insight into survival patterns after complete avalanche burial. The authors report survival curves from data for 301 complete avalanche burials in Canada from 1980 to 2005 and compare them with the standard survival curve derived from Swiss data for 946 complete burials during the same period. The Swiss data, which have re mained remarkably consistent since first reported in 1994, show survival of more than 90% of people in the first 15 to 20 minutes of burial, followed by a steep decline in survival to 35% from 20 to 35 minutes of burial because of asphyxiation in most situations. The curve then plateaus until 90 minutes owing to survival of those with an air pocket, but then drops off because of hypothermia complicated by hypercapnia and hypoxia. Haegeli and coauthors report that the overall proportion of people who survived was 47%, with no significant differences between the Can adian and Swiss data sets. However, the probability of survival by duration of burial did differ significantly between the two samples. The proportion of survivors was significantly lower in Canada than in Switzerland among people buried for 11–20 minutes and among those buried for more than 35 minutes. Compared with the Swiss survival curve, the Canadian survival curve showed an earlier and quicker drop in survival in the early stages of burial (< 35 minutes) and poorer survival associated with prolonged burial. That the overall proportion of survivors did not differ between the two countries is a consequence of the shorter extrication times in Canada (median 18 minutes v. 35 minutes in Switzerland). The Swiss survival curve is based on robust data and has been thought to apply throughout the world. The Canadian data, however, show that different geographic regions may have different survival curves. This has implications for avalanche rescue. In Canada, quick extrication, preferably within 10 minutes after burial, is important to survival. This means that companions of a buried individual need to be prepared with avalanche transceivers, probes and shovels to find and dig out the person quickly. Organized rescue takes longer, with less chance of survival. This may explain the poorer survival after 35 minutes in the Canadian data set: more remote locations, where it takes an organized rescue team longer to reach an avalanche accident site, decrease chances of survival. The emphasis on companion rescue is clear from the Canadian data. However, with less than 50% of people surviving a complete avalanche burial, even when transceivers are used, prevention is the key. Haegeli and coauthors analyzed the Canadian data extensively, focusing on whether specific outdoor activities, snow climate and trauma influenced survival. Although the proportion of snowmobilers who died was greater than that among skiers in Canada, the comparison of survival curves between snowmobilers and skiers was not different. This is informative be cause there were no snowmobilers in the Swiss data set. Use of snowmobiles for backcountry travel has increased in North America; however, such use did not significantly affect the survival curve in the Canadian sample and did not explain the difference between the Canadian and Swiss overall survival curves. A novel insight from the Canadian data set is the difference in survival curves by snow climate. The drop in survival occurred earliest in the maritime snow climate. This climate is found at lower elevations and has wetter and denser snow that is known to accelerate asphyxiation. The continenLessons learned from avalanche survival patterns