COLD INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 399

Ventricular Fibrillation
Ventricular fibrillation is a life-threatening condition in which the thousands of muscle
fibers that make up the heart contract independently. Since all the muscle fibers must con-
tract together for the cardiac chambers to squeeze out blood, no blood is pumped when the
fibers are not synchronized. The effect would be the same if the heart were not beating at
all.
Thehypothermicheartisextremely pronetoventricular fibrillation. Ithasappropriately
beencomparedtoamousetrap,readytosnapwiththeslightestbumporjolt—oftenwithout
a recognizable precipitating event. Hypothermic individuals have begun fibrillating in hos-
pital emergency rooms even though the possibility of that event was well recognized and
every effort to avoid it was being made.
Severely hypothermic individuals cannot be placed in a basket stretcher and carried out
of the wilderness. The unavoidable jarring and bouncing associated with evacuation over
rough terrain almost inevitably provokes fibrillation. Although profound hypothermia pro-
longs the time an individual can survive the absence of effective blood circulation without
sustainingsignificantneurologicdamage,thattimeislimitedtoonehourorslightlylonger.
Rescuers must realize that a severely hypothermic individual in ventricular fibrillation
who cannot be evacuated by helicopter, or in less than an hour by stretcher, may be in
a hopeless situation. The individual must receive CPR to avoid neurologic damage, but
CPR can only be administered intermittently while the person is being carried on a stretch-
er. Cardioversion (defibrillation with electrical shocks) is almost never effective until the
hearthasbeenwarmedto90°F(32°C).Inasituationthreatenedbyhazardousweather,ava-
lanche, or other danger, rescue leaders may be achieving the greatest benefit by extracting
their team and—although difficult—abandoning the unfortunate hypothermic person.
Individuals with severe hypothermia in the wilderness usually must either be evacuated
byhelicopterorrewarmedonthespot.Leadersofmajorrescueorganizationshaverealized
that almost none of the severely hypothermic individuals carried out of the wilderness by
hand without rewarming have survived. They now try to rewarm such individuals where
they are found.
Rewarming
Severelyhypothermicpersonsrequireexternalheatsourcesforrewarmingbecausetheir
metabolism is so slow they cannot generate enough heat to rewarm themselves, even if
completely protected from the environment.
Theoretically, the most effective rewarming methods would rewarm the core of the
body first (central rewarming). Since the heart would be among the first tissues rewarmed,
it would be protected from fibrillation. In hospitals, central rewarming can be achieved
with heated peritoneal dialysis fluids and similar techniques. Heart-lung machines or other