Hypothermia, a potentially fatal condition, occurs when body temperature falls below 95°F (35°C). Although it is an obvious danger for people living in cold climates, many cases have occurred when the air temperature is well above freezing. Elderly people, for instance, have succumbed to hypothermiaafter prolonged exposure to indoor air temperatures of 50-65°F (10-18.3°C).

Measured orally, a healthy person's body temperature can fluctuate between 97°F (36.1°C) and 100°F (37.8°C). Survival depends on maintaining temperature stability within this range by balancing the heat produced bymetabolism with the heat lost to the environment through (for the mostpart) the skin and lungs. When environmental or other changes cause heat loss to outpace heat production, the brain triggers physiological and behavioralresponses to restore the balance. Shivering, for example, aids heat production by accelerating metabolism. But if the cold stress is too great and the body's defenses are overwhelmed, body temperature begins to fall. Hypothermia is considered to begin once body temperature reaches 95°F (35°C), though even smaller drops in temperature can have an adverse effect.

Hypothermia is divided into two types: primary and secondary. Primary hypothermia occurs when the body's heat-balancing mechanisms are working properly but are subjected to extreme cold, such as exposure to cold air or cold water.Hypothermia due to cold air usually takes at least several hours to develop,but immersion hypothermia will occur within about an hour of entering the water because water draws heat away from the body much faster than air does. Secondary hypothermia affects people whose heat-balancing mechanisms are impaired in some way and cannot respond adequately to moderate or perhaps even mildcold. Among the reasons for the failure of the body's heat-balancing are diabetes, malnutrition, bacterial infection, thyroid disease, and the use of medications and other substances that affect the brain or spinal cord, such as alcohol.

Secondary hypothermia is often a threat to the elderly, who may be on medications or suffering from illnesses that affect their ability to conserve heat.Malnutrition and immobility can also put the elderly at risk. Some medical research also suggests that shivering and blood vessel narrowing (two of the body's defenses against cold) may not be triggered as quickly in older people.For these and other reasons, the elderly can, over a period of days or even weeks, fall victim to hypothermia in poorly insulated homes or other surroundings. In addition, hypothermia can easily be misdiagnosed as a stroke or some other common illness of old age.

The signs and symptoms of hypothermia follow a typical course. The impact ofhypothermia on the nervous system becomes apparent quite early. Coordination,for instance, may begin to suffer as soon as body temperature reaches 95°F (35°C). Other early signs include cold and pale skin and intense shivering; the latter stops between 90°F (32.2°C) and 86°F (30°C).As body temperature continues to fall, speech becomes slurred, the muscles go rigid, and the victim becomes disoriented and has trouble seeing. Other harmful consequences include dehydration as well as liver and kidney failure. Heart rate, respiratory rate, and blood pressure rise during the first stages of hypothermia, but fall once the 90°F (32.2°C) mark is passed.Below 86°F (30°C), most victims are comatose, and below 82°F (27.8°C) the heart's rhythm becomes dangerously disordered. Yet even at verylow body temperatures, people can survive for several hours and be successfully revived, though they may appear to be dead.

Emergency medical help should be summoned whenever a person appears hypothermic, exhibiting the danger signs described above. Until emergency help arrives, a victim of outdoor hypothermia should be brought to shelter and warmed byremoving wet clothing and footwear, drying the skin, and wrapping him or herin warm blankets or a sleeping bag. Gentle handling is necessary when movingthe victim to avoid disturbing the heart. Rubbing the skin or giving the victim alcohol can be harmful, though warm drinks such as clear soup and tea arerecommended for those who can swallow.

Rewarming is the essence of hospital treatment for hypothermia. Mild hypothermia (in which the patient's body temperature is 90-95°F [32.2-35°C])is reversed with passive rewarming, using the patient's own metabolism to rewarm the body. Moderate hypothermia (86-90°F [30-32.2°C]) is often treated first with active external rewarming and then with passive rewarming. Active external rewarming involves applying heat to the skin, for instance by placing the patient in a warm bath or wrapping the patient in electric blankets.

Severe hypothermia (a body temperature of less than 86°F [30°C]) requires active internal rewarming, such as cardiopulmonary bypass, in which thepatient's blood is circulated through a rewarming device and then returned tothe body. The alternative is to introduce warm oxygen or fluids into the body.

People who spend time outdoors in cold weather can reduce heat loss by wearing their clothing loosely and in layers and by keeping their hands, feet, andhead well covered (30-50% of body heat is lost through the head). Because water draws heat away from the body so easily, staying dry is important, and wetclothing and footwear should be replaced as quickly as possible. Wind- and water-resistant outer garments are also crucial. Alcohol should be avoided because it promotes heat loss by expanding the blood vessels that carry body heat to the skin.

Preventing hypothermia among the elderly requires vigilance on the part of family, friends, and caregivers. An elderly person's home should be properly insulated and heated, with living areas kept at a temperature of 70°F (21.1°C). Warm clothing and bedding are essential, as are adequate food, rest,and exercise. Older people who live alone should be visited regularly--at least once a day during very cold weather--to ensure that their health remainssound and that they are taking good care of themselves. For help and advice,family members and others can turn to government and social service agencies.Meals on Wheels and visiting nurse programs, for instance, may be available,and it may be possible to obtain financial aid to winterize and heat homes.

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