Clinical paperThe impact of avalanche rescue devices on survival☆
Introduction
In the 17 member countries of the International Commission for Alpine Rescue (ICAR) in Europe and North America, the median annual mortality from snow avalanches registered between 1994 and 2003 was 141 (range 111–199).1 Most avalanche accidents are sports-related and involve skiers, snowboarders and, especially in the USA, snowmobilers, in open, i.e. non-controlled, areas away from ski resorts.2 If caught in an avalanche, the chance of survival depends on: (a) the grade of burial; (b) the duration of burial; (c) the presence of an air pocket and a clear airway and (d) the severity of mechanical injuries.3
A Swiss analysis of avalanche accidents between 1981 and 1998 showed an overall mortality rate of 23.0%. This rose to 52.4% for those victims who were completely buried but in only 4.2% of persons who were partially or not buried.2 A “complete burial” is defined as where snow covers the victim's head and chest; otherwise the term “partial burial” applies.4
For completely buried victims, survival is related to the duration of burial.5 The calculated survival function for avalanche burials in open areas, presented by Brugger et al. in 2001, shows a precipitous drop in survival probability from 91% at 18 min after burial to 34% at 35 min (acute asphyxiation of victims without an air pocket), a flattening of the curve between 35 and 90 min (“latent phase” for victims with an air pocket), followed by a second drop to only 7% at 130 min (death of victims with a “closed” air pocket from slow asphyxia and hypothermia).2 Victims completely buried under an avalanche cannot survive beyond 35 min without an air pocket.6 An air pocket is defined as any air space surrounding the mouth or nose, no matter how small, with a patent airway.7
The significance of major trauma in causing death in avalanche accidents is controversial, as the incidence of fatal injury in the published studies has varied between 48 and 50%.9, 10 A recent study on 105 avalanche victims in Austria (1996–2005) reports 5.6% died from injury.11
From these studies, it is inferred that death from an avalanche is attributable primarily to asphyxiation, whereas hypothermia and fatal injuries are of lesser importance. All rescue devices for skiers and snowboarders currently on the market aim to avoid acute asphyxiation by (a) reducing the depth of burial, (b) reducing the duration of burial or (c) by prolonging survival after complete burial.
There are two commonly used rescue devices: the avalanche transceiver, which is intended to speed up locating a completely buried person, and the avalanche airbag, which aims to prevent the person from being completely buried.
- 1.
The avalanche transceiver, developed in 1968 in the USA, is capable of transmitting and receiving an electromagnetic signal at 457 kHz. The device is intended for the search for completely buried persons, who have no visible or audible sign at the surface; both the buried person and the searching companion have to be equipped with a transceiver. In a retrospective analysis of 328 complete burials in Switzerland between 1981 and 1994, Brugger et al. showed that using an avalanche transceiver to locate a buried victim reduced the median extrication time significantly from 120 to 35 min, but the decrease in the mortality rate was not significant (76–66%; P = 0.054).12 A subsequent study by Hohlrieder et al. on 278 complete burials in the Austrian Alps between 1994 and 2003 showed a significant reduction in median burial time from 102 to 20 min, as well as a significant reduction in mortality from 68.0 to 53.8% (P = 0.011).13 In the last decade, transceivers have been developed further, using multiple antennae and optical displays, so that in ideal conditions they will give an accurate indication of the search direction and distance to the buried person. This appears to have improved location efficiency.14, 15 It has also been recognized that the rescuer must have an avalanche probe and a shovel to dig out the victim(s) from the snow as quickly as possible if the reduced location time achieved with a transceiver is to be translated into a significant reduction in mortality.16, 17
- 2.
The avalanche airbag came to the market in 1991. It consists of two balloons integrated into a backpack.18 By pulling a string, the balloons fill with 120–150 l of a mixture of nitrogen from a cartridge and environmental air. In an avalanche, the skier avoids being completely buried by using the physical effect of “inverse segregation”19; the skier remains on the surface of the snow or is only partially buried.
To date, no study has been made to compare the efficiency of these avalanche rescue devices. It is the aim of this study to evaluate the influence of both avalanche rescue devices on mortality during avalanche accidents.
Section snippets
Data collection
A retrospective data analysis was performed of all recorded avalanche accidents involving persons buried in open areas, excluding persons buried in buildings and vehicles, from Switzerland winter 1990/1991 to 2003/2004 (without 2001/2002)20, 21 and Austria from 1998/1999 to 2004/2005 (n = 2337). In Switzerland, data is collected by the Swiss Institute for Snow and Avalanche Research, Davos, Switzerland; data from 2001/2002 have been omitted as the records for this winter were incomplete. In
Results
Of the 2337 persons, we excluded 833 (35.6%) because of missing data on the width and length of the avalanche; the remaining 1504 persons who were involved in 752 avalanches were included in this study (Figure 1). 1296 (86.2%) persons were involved in an avalanche in Switzerland, and 208 (13.8%) in Austria. The mortality of persons excluded (150 out of 833, 18%) was not significantly different from those included (279 out of 1504, 18.6%; P = 0.75 Chi-square test) hence missing data did not
Discussion
The higher mortality rate in Austria compared with Switzerland is partially due to the higher rate of complete burial and the higher burial depth in the Austrian Alps. However, even after compensation of the grade and depth of burial mortality still remained significantly higher in Austria. This might be caused by topographic and logistic differences.
In this study, persons equipped with an avalanche airbag who were caught by an avalanche had a greatly reduced mortality rate; the relative risk
Limitations
This study is a retrospective analysis of rescue data aimed at determining the influence of rescue devices on mortality rate. Such observational studies are frequently subject to systematic errors that may adulterate any statistical calculation. A major problem is that the records of avalanches are not designed to evaluate rescue devices, and hence the records continue to be incomplete. While being equipped with an avalanche airbag is well documented in all persons involved in avalanches, the
Conclusions
In conclusion, this study showed a favourable assessment of both the avalanche airbag and avalanche transceiver in reducing the mortality rate of ski tourers and off-piste skiers. We suggest that further technical development and the use of rescue devices with a buoyant effect should be encouraged. Due to statistical limitations, it was not possible to make a direct comparison between the devices. For a reliable statistical evaluation of rescue devices, it is essential, in future, to document
Conflict of interest
This study was not supported financially or materially by any producer of avalanche rescue devices. The authors are not involved in any financial interest and did not receive any grants or patents concerning the devices.
Acknowledgment
The authors thank Stephanie Thaler, Innsbruck Medical University, for the data preparation and review of the Austrian rescue data.
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2022, Wilderness and Environmental MedicineCitation Excerpt :Beacons (transceivers), shovels, and probes are considered standard avalanche safety equipment that should be carried by all members of a group.6 In victims who were completely buried, beacons were seen to reduce burial time and mortality significantly.7 Group size is also an important aspect of avalanche rescue.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at 10.1016/j.resuscitation.2007.06.002.
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