Frozen Mythbusters: Myth #6 of 13.
There are a variety of myths regarding human response to cold exposure.  These myths are explained and debunked by Dr. Murray Hamlet, DMV, Dr. Gordon Giesbrecht, PHD, and Frank Hubbell, DO.  After posting the thirteen myths, a complete article from the Wilderness Medicine Newsletter will be loaded for anyone interested in all the chilly little details.
Myth #6
             You should never actively rewarm a hypothermia victim in the field because you could cause massive peripheral vasodilation, cardiovascular instability, and ventricular fibrillation.
              If a patient is really hypothermic, there will be a substantial central drive for peripheral vasoconstriction, and muscle blood flow will be very low because of low tissue temperature and metabolism. Gordon has tried to heat the arm of a hypothermic subject with a warm water blanket. After quite a while with no effect on core rewarming, he removed the water blanket. The pattern of the water blanket was etched into the subject’s arm in 1st degree burns (this resolved in a day so no damage was done). The reason for the minor burn was that a considerable amount of heat was being delivered to the arm, but there was no vasodilation to enable blood flow to take the heat away from the skin. Thus the skin sustained a minor burn.
                Likewise in the field, none of the heat sources that would be available would be able to cause significant vasodilation until core rewarming had occurred. The only exception is if you go to someone’s cabin and put your patient into a tub of warm/hot water. Then you COULD cause a massive increase in peripheral blood flow and ultimately death.
             Other heat sources like warm water bottles, warm bodies, electric heating blankets, or forced air warmers (these could operate in an ambulance or aircraft) would not pose a threat to the patient and would be advised as any help to warm the heart is beneficial. The most efficient portable heat source that Gordon has studied is the Norwegian Charcoal Heatpac. It produces 250 watts which would be very helpful to warm an insulated patient. (A Google search will lead you to several articles about this amazing little device.)
             Busted – Other than a tub of warm/hot water (which you should never put a patient in), there are no sources of heat that will cause rapid, massive vasodilation and its disastrous complications. A hypothermic patient has intense central demand to remain vasoconstricted, and this will only be reversed in a gradual way, and only as the core temperature increases. In hypothermia, the heart stops as a result of low temperature and the time it spends at that low temperature. It only makes sense that gradually warming the heart has to be more healthy than keeping it low.

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