Hypoxia and hypercapnia during respiration into an artificial air pocket in snow: implications for avalanche survival
Introduction
Falk et al. [1] proposed in 1994 that the precipitous drop in calculated survival probability for persons completely buried in an avalanche (i.e. snow coverage of at least head and chest, n=422) from 92% at 15 min to 30% at 35 min was due to acute asphyxiation of victims without an air pocket and free airways; the further drop from 27% at 90 min to 3% at 130 min represented deaths from gradual hypoxia and hypothermia in victims with a closed air pocket. Based on that report, avalanche survival is considered impossible beyond 35 min without an air pocket and free air passages. Establishment of the presence or absence of an air pocket on extrication of victims has been recognised by the International Commission for Mountain Emergency Medicine since 1996 as a major criterion in determining on-site triage of avalanche victims with asystole by the emergency physician [2] and also field management strategy [3].
This study was prompted by the observation that some rescue protocols of avalanche accidents in Switzerland [4] and Austria [5], [6] document the survival of skiers, without an indication of permanent hypoxic damage, after prolonged complete snow burial despite there being only a small closed air pocket on extrication. Our aim was to investigate the pathophysiological respiratory changes in subjects breathing into an artificial air pocket in snow in a specifically devised experimental setting and to relate the findings to avalanche survival in a fortuitous or self-created air pocket.
Section snippets
Materials and methods
The experimental study, approved by the Ethics Committee of the University of Innsbruck, Tyrol, Austria, was undertaken on a ski-slope in Fulpmes, Tyrol, at 1640 m above sea level. An avalanche was simulated by throwing down snow of varied density from an overlying slope against a temporary wall 8–10 m below. This procedure was repeated for each test. After the wall supports had been removed, cylindrical air spaces, each 1- or 2-l in volume, were punched out of the snow horizontally by machine
Results
Fig. 1 shows the significant decrease in peripheral oxygen saturation (SpO2) in all tests from 99% (median baseline value, range 93–100%) to 88% (range 71–94%; P<0.001) in the first 4 min, whilst the end-tidal CO2 partial pressure (ETCO2) rose from 5.07 kPa (median baseline value, range 3.47–6.93 kPa) to 6.8 kPa (range 5.87–8.27 kPa; P<0.001). Simultaneously, the air pocket O2 concentration sank from 21 to 11.5% (median value, range 8.9–13.1%; P=0.01), whilst the CO2 concentration rose from 0
Discussion
The significant positive correlation of the decrease in SpO2 within 4 min to snow density (Fig. 3) is in agreement with the generally expected influence of snow conditions on survival in an avalanche, namely air diffusion and oxygen permeability around the air pocket are considered to be higher with dry, than with wet, snow [11]. In this context, it is surprising that the increase in ETCO2 within 4 min, in contrast to the concurrent decrease in SpO2, was neither influenced by air pocket volume
Limitations and perspectives
Although the degree of hypoxia in the volunteers in our experimental study was dependent on air pocket volume, as well as snow density, it was not possible to establish limits for air pocket volume or snow density enabling long-term survival in an avalanche. Comprehensive air pocket documentation in all avalanche victims and determination of the prevailing snow density are prerequisites for further clarification. Assessment of SpO2, ETCO2, and core temperature in all avalanche victims
Acknowledgements
We thank the members of the Mountain Rescue Organisation, Bruneck, Italy, who kindly volunteered to participate in this study, as well as members of the Mountain Rescue Organisation, Fulpmes/Tyrol, Austria, for logistic help in simulating an avalanche, Karin Hillebrand for technical assistance, the Alutech AluSuisse company (in particular, Wilhelm Prax, Production Manager), Schwarzach/Tyrol, Austria, for manufacturing, and donating the technical components required for the air pocket model. We
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2021, ResuscitationCitation Excerpt :About two-thirds of completely buried avalanche victims die within 30 min from cardiac arrest associated with hypoxia and hypercapnia. Breathing into an air pocket allows longer survival, as the higher oxygen availability slows oxygen desaturation.5 Increased porosity of the snow surrounding the air pocket seems to favour oxygen (O2) diffusion into and carbon dioxide (CO2) out of the air pocket, decelerating the development of hypoxia and hypercapnia.3