Wilderness Medical Society snowmass 2005 Page 111
Colin Grissom, M.D. "New Hope For Surviving the Avalanche"
Page
5
breathing into an air pocket in snow during avalanche burial. Hypoxemia and
hypercapnia occur as expired air is rebreathed. A smaller air pocket or more dense snow
causes a more rapid development of hypoxia and hypercapnia. Larger air pockets and less
dense snow allow more mixing of expired air with ambient air in the snowpack and result
in longer survival before hypoxia and hypercapnia become severe enough to cause death
from asphyxiation. Brugger and colleagues suggest that an equilibrium may occur where
the FIO2 and FICO2 in an air pocket reach a plateau within a physiologically tolerable
range and the avalanche victim may survive prolonged burial. It should be emphasized
that this may occur even with small air pockets, as has been observed in the extrication of
survivors of avalanche burials of up to two hours in duration
7
.
Radwin and colleagues
19
demonstrated that there is sufficient ambient air in
densely packed snow to permit normal oxygenation and ventilation as long as all expired
air is diverted out of the snowpack. They studied subjects totally buried in dense snow
while inhaling air directly from the snowpack (density 300 to 680 kg/m3 or 30 to 68 %
water) through a two-way non-rebreathing valve attached to respiratory tubing that
diverted all expired air to the snow surface. Subjects maintained normal oxygenation and
ventilation for up to 90 minutes. This study demonstrated that there is sufficient air for
breathing 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) (Figure 4). This breathing device allows inspiration of air from the snowpack via a
one-way inspiratory valve and then diverts expired air around to the back via a one-way
expiratory valve. The device also has the advantage of preventing 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 inspired air. Grissom and colleagues
10
compared breathing with this device while buried in dense snow to breathing without the
device, but with a 500 cc air pocket in the snow (Figure 3). Mean burial time was 58
minutes breathing with the device and 10 minutes breathing with a 500 cc air pocket in
the snow. Development of hypoxia and hypercapnia were significantly delayed while
breathing with the device. This device has resulted in survival from actual avalanche
burials
18
.
