Hypothermia is the physical state in which the core temperature of the body is significantly below its healthy norm of 98.6°F (37°C). Hypothermia is a condition that is the opposite of hyperthermia, the excessively elevated temperature present in an overheated body. Hypothermia most typically occurs in cold weather circumstances, where the body is inadequately protected from the elements, or where external sources of heat are not available. The ability of the human body to dissipate heat through perspiration and the functions of the cardiovascular system is far better than its ability to retain heat in response to environmental conditions.

Hypothermia is not itself an illness or an injury, but it represents the triggering mechanism for a number of cold-related outcomes, including organ damage and failure of the cardiovascular system. Hypothermia is a separate and unrelated condition to the injury known as frostbite, which is a freezing of the tissue and skin; given the cause of frostbite, hypothermia and frostbite often occur in the same circumstances.

Hypothermia is popularly associated with cold, snowy, and intemperate weather. While such conditions are a background to hypothermic events, this condition can occur where the air temperature is 40°F (4°C) or lower; it is also a common result for sailors, paddlers, or rowers that become soaked in cold water temperatures, either through the spray created by moving boats, or if the athlete is actually immersed in cold water. Athletes that are either waiting to join a competition, such as cross-country runners prior to race start, or football players standing on a sideline, are also vulnerable to hypothermia in some conditions.

The generally recognized risk factors associated with the potential for hypothermia include:

  • Low air temperatures, often combined with inadequate clothing or protection; the reflex
    Fire department personnel wearing dry suits which allow them it be in 38°F (3°C) water for up to four hours before hypothermia sets in.
    action of the body to cold exposure is to shiver, an involuntary effort to generate heat.
  • Wind chill, the combined effect of temperature and wind on the human body; wind chill is a deceptive phenomenon, as it may occur in all types of cold weather environments, including sunshine. As a general proposition, at temperatures below 40°F (4°C), winds at speeds as low as 5 mph (8 km/h) can significantly induce increased sensations of cold; the greater the wind speed, the more pronounced the effect of cold will be.
  • Moisture; skin that is wet, though either excess perspiration or environmental effects, will freeze more readily than dry skin. Moisture will also magnify the effect of wind chill.
  • Consumption of alcohol, which tends to stimulate blood flow in the peripheral parts of the body, an action that contributes to heat loss.
  • Amount of skin exposed to the elements by the athlete; exposed skin permits heat to be lost by both convection and radiation to the immediate environment.
  • Consumption of caffeine or any other diuretic, which acts to reduce fluid volumes in the cardiovascular system.

In its mildest manifestation, hypothermia causes pronounced shivering, numbness, and a cold feeling through out the body. As the body temperature remains low, the symptoms become more pronounced, as the person will experience an inability to move quickly or decisively, accompanied by dizziness and confused thinking. At its most extreme, the affected person will experience a rigidity of the muscles, followed by a lapse into coma. At a body temperature of less than 95°F (35°C), the person must receive immediate attention or, as a result of a progressive decline in the function of the organs and the internal systems, death will result.

Once detected, the management of hypothermia is a straightforward process. The first and most important consideration is the removal of the injured person from the cold environment. It is important that while the person is made warmer, that he or she not be so heated as to induce perspiration, which will result in a reduction of body fluid available to circulate and slowly warm the person. The second treatment step is the removal of any wet clothing and dressing the person with dry clothes, or wrapping the person in a blanket, as wet clothing has very poor thermal qualities. The temptation to rub or otherwise seek to stimulate circulation in the extremities of the hypothermic person should be resisted; such efforts may direct cold blood from the limbs to the heart, causing a sudden shock to that organ. The warming of the hypothermic person is best done gradually.

In outdoor cold weather endurance events, such as cross-country skiing, it is possible for a case of hypothermia to occur at the same time the athlete is experiencing dehydration. The return to normal fluid levels will determine how quickly the thermoregulatory system can resume normal function.

SEE ALSO Acclimatization; Cold-related illnesses and emergencies; Hydration; Hypothermia; Thermoregulatory system.