Emergency War Surgery NATO Handbook: Part I: Types of Wounds and Injuries: Chapter IV: Cold Injury

Hypothermia

United States Department of Defense

Hypothermia victims, depending on their core temperatures and the durations of their exposure, present with different degrees of physiologic depression. Cold suppresses metabolic function and decreases oxygen demand, thereby enhancing survival. Recognition of this survival potential is critical to successful resuscitation. Everyone involved in the treatment and evacuation of these casualties must be cognizant of the phrase "No one is cold and dead, only warm and dead." Failure to respond to rewarming is the only criterion for death in hypothermia.

Two major defenses against hypothermia are peripheral vasoconstriction and shivering. Peripheral vasoconstriction reduces cutaneous blood flow, which conserves core heat by decreasing both radiant and convective heat losses to the environment. Shivering is an involuntary muscle activity that increased heat production. The end result of peripheral vasoconstriction, which decreases circulating volume, is cold diuresis. Shivering produces significant metabolite production, including lactic acid. The longer one is exposed to cold, the greater will be one's metabolic derangement. Dry land hypothermics shiver violently and diurese for long periods of time. This experience diuresis results in more severe metabolic abnormalities. On the other hand, water immersion hypothermics who cool rapidly do not shiver quite as long and often present with a normal electrolyte and pH profile. As cells drop below 30°C in an acid medium the sodium pump fails and potassium leaks out of cells into the general circulation. As the core temperature drops in the presence of acidosis and hyperkalemia, severe cardiac arrhythmias occur. Hemorrhage from wounds in a cold environment leads to rapid hypothermia.

Hypothermics have decreased cerebral metabolic activity. They show a stumbling gait, incoordination, slurred speech, and a psychologically inward retreat. Their senses are dull; they are apathetic, drowsy, and more exhausted than their activity would warrant. This state progresses to unconsciousness. The disorientation, confusion, irrational judgment, and poor decision making ability pose a significant threat in leadership roles since the small unit leader is usually exposed to the same physical and cold stresses as his troops. The leader may, in fact, not be able to recognize the signs and symptoms of hypothermia in those he leads if he is experiencing the same symptoms himself. This scenario can result in disaster.

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Operational Medicine 2001

Health Care in Military Settings

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