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Asphyxiation occurs during avalanche burial because the person either inhales snow that
occludes the upper airway or because expired air is rebreathed. Acute upper airway ob-
structionresultinginasphyxiationisoneofthecausesofearlyasphyxiationduringthefirst
fifteen to thirty minutes of avalanche burial. Asphyxiation due to rebreathing expired air
mayalsooccurduringthefirstfifteen tothirtyminutes ofavalanche burialifthereisnoair
pocket for breathing, or it may be delayed if an air pocket is present. Inspired air contains
21 percent oxygen (O
2
) and less than 0.03 percent carbon dioxide (CO
2
), whereas expired
aircontainsabout16percentO
2
and5percentCO
2
.Rebreathing expiredairinanenclosed
space results in progressive hypoxia (decreased blood oxygen concentrations) and hyper-
capnia (increased blood carbon dioxide concentrations) that eventually cause death from
asphyxiation. The larger the air pocket, the greater the surface area for diffusion of expired
air into the snowpack and diffusion of air from the snowpack into the air pocket, and the
longer the survival time before death occurs from asphyxiation.
Ice mask formation around the buried person's face or air pocket surface accelerates as-
phyxiation bypreventing diffusion ofexpired air away from the air pocket. Ice mask form-
ation occurs when water in heated and humidified expired air condenses, freezes on the
snow surface in front of the face, and forms a barrier that is impermeable to diffusion of
air.
Utah investigators demonstrated that sufficient air is present in densely packed snow to
permit normal oxygenation and ventilation as long as all expired air is diverted out of the
snowpack. They studied individuals totally buried in densely compacted snow while inhal-
ing air directly from the snowpack (density 300 to 680 kg/m3 or 30 to 68 percent water)
through a two-way nonrebreathing valve attached to respiratory tubing that diverted all ex-
pired air to the snow surface. Individuals maintained normal oxygenation and ventilation
for up to the protocol target of ninety minutes. This study demonstrated that sufficient air
for breathing is present in snow of similar density to avalanche debris, as long as expired
air is not rebreathed.
This is the principle behind a breathing device designed to prolong survival during
avalanche burial, the AvaLung® (Black Diamond Equipment, Ltd., Salt Lake City, Utah,
www/bdel.com/gear/avalung_ii.php
)
(
Fig. 30-1
)
. This breathing device allows inspiration
of air from the snowpack through a one-way inspiratory valve and diverts expired air
around to the buried person's back through a one-way expiratory valve. The device also
prevents ice mask formation. The limitation of the device is that expired air permeates
around the buried person's body and through the snow and eventually contaminates in-
spired air.
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