Elsevier

Resuscitation

Volume 58, Issue 1, July 2003, Pages 81-88
Resuscitation

Hypoxia and hypercapnia during respiration into an artificial air pocket in snow: implications for avalanche survival

https://doi.org/10.1016/S0300-9572(03)00113-8Get rights and content

Abstract

Snow avalanche case reports have documented the survival of skiers apparently without permanent hypoxic sequelae, after prolonged complete burial despite there being only a small air pocket on extrication. We investigated the underlying pathophysiological changes in a prospective, randomised 2×2 crossover study in 12 volunteers (28 tests) breathing into an artificial air pocket (1- or 2-l volume) in snow. Peripheral SpO2, ETCO2, arterialised capillary blood variables, air pocket O2 and CO2, snow density, and snow conditions at the inner surface of the air pocket were determined. SpO2 decreased from a median of 99% (93–100%) to 88% (71–94%; P<0.001) within 4 min of breathing into the air pocket; the reduction was greater at 1 l, than 2 l, volume air pocket (P=0.013, intention to treat P=0.003) and correlated to snow density (r=0.50, P=0.021, partial correlation coefficient). ETCO2 rose simultaneously from median 5.07 kPa (3.47–6.93 kPa) to 6.8 kPa (5.87–8.27 kPa; P<0.001), with consequent respiratory acidosis. Despite premature interruption due to hypoxia (SpO2≤75%) in 17 of 28 tests (61%), a respiratory steady state prevailed in five tests until protocol completion (30 min). We conclude that the degree of hypoxia following avalanche burial is dependent on air pocket volume, snow density and unknown individual personal characteristics, yet long-term survival is possible with only a small air pocket. Hence, the definition of an air pocket, “any space surrounding mouth and nose with the proviso of free air passages” is validated as the main criterion for triage and management of avalanche victims. Our experimental model will facilitate evaluating the interrelation between volume and inner surface area of an air pocket for survival of avalanche victims, whilst the present findings have laid the basis for future investigation of possible interactions between hypoxia, hypercapnia, and hypothermia (triple H syndrome) in snow burial.

Sumàrio

Os casos referidos de avalanches de neve documentaram a sobrevivência dos esquiadores sem sequelas hipóxicas permanentes, após ficarem completamente soterrados com apenas uma pequena máscara de ar. Investigámos as alterações patofisiológicas subjacentes de uma forma prospectiva, num estudo cruzado 2×2 randomizado em 12 voluntários (28 testes) a respirarem para uma máscara de ar artificial (1 ou 2 l de volume) na neve. Foram determinadas a SpO2 periférica, ET CO2, parâmetros do sangue capilar arterializado, O2 e CO2 na máscara de ar, densidade da neve e condições da neve na superfı&#x0301;cie interna da máscara de ar. A SpO2 diminuiu de uma mediana de 99% (93–100%) para 88% (71–94%; P<0.01) durante 4 minutos a respirar para a máscara de ar; a redução foi superior com máscaras de ar com volume de 1l relativamente às de 2l (P=0.013, Intenção de tratar P=0.003) e correlaciona-se com a densidade da neve (r=0.50, P=0.021, coeficiente de correlação parcial). O CO2 ET subiu simultaneamente de uma mediana 5.07 Kpa (3.47–6.93 Kpa) para 6.8 Kpa (5.87–8.27 Kpa; P<0.001), com a consequente acidose respiratória. Apesar da interrupção prematura devida à hipóxia (SpO2<75%) em 17 dos 28 testes, em cinco testes prevaleceu um estado respiratório de equilı&#x0301;brio até serem completados os protocolos (30 min). Concluı&#x0301;mos que o grau de hipóxia, por soterramento numa avalanche de neve, está dependente do volume da máscara de ar, da densidade da neve e de caracterı&#x0301;sticas pessoais individuais desconhecidas; ainda assim, a sobrevivência a longo termo é possı&#x0301;vel apenas com uma pequena máscara de ar. Daqui a definição de máscara de ar como “qualquer espaço à volta da boca e nariz que permita a livre passagem de ar “, é validada como o principal critério para triagem e abordagem das vı&#x0301;timas de avalanche. O nosso modelo experimental facilitará a avaliação da interrelação entre o volume e a área de superfı&#x0301;cie interna de uma máscara de ar necessários para a sobrevivência das vı&#x0301;timas de avalanche; enquanto que os achados presentes criaram a base para futuras investigações de possı&#x0301;veis interacções entre hipóxia, hipercarbia e hipotermia (Sı&#x0301;ndrome do triplo H) no soterramento por neve.

Resumen

Reportes de casos de avalancha de nieve han documentado la sobrevida de esquiadores después de quedar completamente sepultados, aparentemente sin secuelas permanentes de hipoxia, a pesar de quedarles solo un pequeño bolsillo de aire durante la extricación. Investigamos los cambios fisiopatológicos subyacentes en un estudio randomizado, cruzado 2×2 en 12 voluntarios (28 pruebas) respirando en un bolsillo artificial de aire (1- ó 2-litros de volumen) en la nieve. Se midieron SpO2, ETCO2, parámetros en sangre capilar arterial, O2 y CO2 en el bolsillo de aire, densidad de la nieve y condiciones de la nieve en la superficie interna del bolsillo. La SpO2 disminuyó desde una mediana de 99% (93–100%) a 88% (71–94%; P<0.001) en 4 minutos de respirar en el bolsillo de aire; la reducción fue mayor en el bolsillo de volumen de 1 litro, que en el de 2 litros (P=0.013, intención de tratar P=0.003) y se correlacionó con la densidad de la nieve (r=0.50, P=0.021, coeficiente de correlación parcial). El ETCO2, se elevó simultáneamente de una mediana de 5.07 kPa (3.47–6.93 kPa) a 6.8 kPa (5.87–8.27 kPa; P<0.001), con consecuente acidosis respiratoria. A pesar de la interrupción prematura por la hipoxia (SpO2<75%) en 17 de los 28 pruebas (61%), prevaleció un estado respiratorio estable en 5 pruebas hasta completar el protocolo (30 min). Concluimos que el grado de hipoxia después de ser sepultado por una avalancha es dependiente del volumen del bolsillo de aire resultante, densidad de la nieve y caracterı&#x0301;sticas personales desconocidas, siendo posible la sobrevida a largo plazo con un pequeño bolsillo de aire. Por esto,la definición de bolsillo de aire, “cualquier espacio que rodee la nariz y boca que permita libre paso de aire”, es validado como principal criterio de triage y manejo de vı&#x0301;ctimas de avalanchas. Nuestro modelo experimental facilitará la evaluación de la interrelación entre volumen y superficie interna de un bolsillo de aire para la sobrevida de vı&#x0301;ctimas de avalanchas, mientras que los hallazgos han puesto una base para futura investigación de posibles interacciones entre hipoxia, hipercapnia e hipotermia (sı&#x0301;ndrome triple H) en victimas sepultadas por nieve.

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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    Citation 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

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