HYPOTHERMIA

DEFINITION

Hypothermia (pronounced hi-po-ther-mee-ah) occurs when the body temperature falls below 95°F (35°C). The condition is often fatal.

DESCRIPTION

People who live in cold climates are obviously at risk for hypothermia. They may be stranded out of doors overnight without protection from the cold. Their body temperatures may drop so low that they develop hypothermia. Eventually, they may freeze to death.

Hypothermia also occurs in more moderate climates during cold weather. The problem is more likely to occur among elderly and homeless people. Elderly people may not remember to keep their homes heated properly. Or they may be too poor to pay their heating bills. Their homes may remain at a constant temperature of 50° to 65°F (10° to 17°C). A continuous exposure to this temperature can cause hypothermia.

Homeless people may have to spend most of their lives out of doors. In cold weather, their body temperatures may drop to dangerously low levels. Official records indicate that nearly twelve thousand homeless people died of hypothermia between 1979 and 1994. However, these numbers are probably not accurate. Many deaths of homeless people from hypothermia probably go unreported.

Males, non-whites, and alcoholics are at high risk for hypothermia. These groups make up a large fraction of the homeless population.

CAUSES

The human body functions normally over a very narrow range of temperatures. If body temperature goes higher than about 100°F (38°C) or lower than about 97°F (36°C), problems develop. The chemical changes that take place in cells begin to occur either too rapidly or too slowly. At low temperatures, those chemical changes may slow down so much that the body ceases to function entirely. That condition is known as hypothermia.

Hypothermia is divided into two types: primary and secondary. Primary hypothermia occurs when the body's heat-balancing mechanisms are working properly but the body is subjected to extremely cold conditions. For example, a person might fall into an icy lake. The conditions are so cold that hypothermia develops in spite of the otherwise healthy body.

In secondary hypothermia, the body's heat-balancing mechanisms are not working properly. Hypothermia may develop even if a person is exposed to even mildly cold conditions. Some conditions that can cause secondary hypothermia are stroke (see stroke entry), diabetes (see diabetes mellitus entry), malnutrition, bacterial infection, thyroid condition, spinal cord injury (see spinal cord injury entry), and the use of certain medications and other substances. Alcohol is one such substance. It can interfere with portions of the heat-balancing system. A person may not recognize when he or she is becoming dangerously cooled.

Secondary hypothermia is often a threat to the elderly. They are likely to be on medications or suffering from some medical condition that can cause secondary hypothermia. Elderly people sometimes keep their homes cool to save money on heating costs. They may develop hypothermia even if the temperature is no colder than 60°F (15.5°C).

SYMPTOMS

The signs and symptoms of hypothermia follow a typical course. Though the body temperature at which they occur vary from person to person depending on age, health, and other factors.

Some of the first signs of hypothermia may be lack of coordination, cold and pale skin, and intense shivering. As body temperature begins to fall, speech becomes slurred, muscles go rigid, vision problems develop, and the patient becomes disoriented.

At body temperatures below 90°F (32°C), heart rate, respiratory (breathing) rate, and blood pressure fall. Eventually the patient loses consciousness and may appear to be dead. At even very low temperatures, however, a person may survive for several hours. They can sometimes be successfully revived.

DIAGNOSIS

The situation in which a person is found is often an important clue to diagnosis. Someone pulled from a lake in the middle of winter, for example, is likely to be suffering from hypothermia. Pulse, blood pressure, temperature, and respiration should be checked immediately and monitored. Oral (mouth) temperatures are often not accurate at cold temperatures. Instead, the temperature is taken at some other part of the body, such as in the ear or rectum.

A doctor might use an electrocardiogram (ECG; pronounced ih-LEK-trocar-DEE-uh-gram; it measure electrical activity of the heart to make sure it is functioning normally) to get information on the functioning of the patient's heart. Blood and urine tests may also be ordered to see how well body functions are operating.

TREATMENT

A person with hypothermia requires immediate medical attention. First aid for such patients is not as obvious as it may seem, however. For example, rubbing the patient's skin or giving him or her a drink of alcohol can be dangerous. Also, the patient should be checked for signs of frostbite (see frostbite entry). Attempting to warm a frostbitten area can be very dangerous.

The first step is to move the patient to a warm, dry location. Gentle handling is necessary to void disturbing the heart. Giving the patient a warm drink can be helpful if he or she can swallow.

Once a patient has reached the hospital, the warming procedure depends on the seriousness of the patient's condition. The stage of hypothermia is defined by the patient's body temperature. The three stages of hypothermia and the temperatures at which they occur are as follows:

• Mild hypothermia: 90° to 95°F (32° to 35°C)
• Moderate hypothermia: 86° to 90°F (30° to 32°C)
• Severe hypothermia: less than 86°F (30°C)

Mild hypothermia is treated with passive rewarming. That is, the patient's body is allowed to come back to its normal temperature on its own. Wet clothing is removed and the patient is covered with blankets and placed in a warm room.

Moderate hypothermia is first treated with active rewarming. That is, the patient is wrapped in an electric heating blanket or placed in a warm bath. As his or her temperature begins to rise, these aids are removed. The body is allowed to return to its normal temperature on its own.

Severe hypothermia usually requires internal rewarming. Some method is needed to start warming the patient's internal organs and tissues. For example, patients may be provided with warm oxygen to breathe. Or they may be given warm fluids to drink. In extreme cases, a procedure known as a cardiopulmonary bypass may be used. In this procedure, a tube is inserted into the patient's blood vessels. Blood is directed out of the body and through an external machine. The external machine warms up the blood. The blood is then returned to the body. This treatment is not available in all hospitals.

PROGNOSIS

People who experience mild or moderate hypothermia usually enjoy a complete recovery. The prognosis for people who experience severe hypothermia is less certain. Recovery depends on a number of factors, such as the person's own body chemistry and how soon treatment was provided.

PREVENTION

Hypothermia can be prevented by following some simple rules. First, people who have to spend time outdoors in cold weather should wear adequate clothing. Head covering is especially important since 30 to 50 percent of body heat is lost through the head. Clothing should also be kept as dry as possible. Water absorbs heat faster than air, so wet clothes cause body temperature to drop quickly. Alcoholic beverages should be avoided also. Alcohol causes blood vessels to expand, causing the body to lose heat faster.

The best method for preventing hypothermia is to wear appropriate clothing in cold temperatures. (©

Jeff Greenberg

. Reproduced by permission of

Photo Researchers, Inc.

)

For a number of reasons, hypothermia is a special problem among elderly people. They may be subject to a variety of medical problems that make them more sensitive to cold temperatures. The medications they take may also make them more subject to hypothermia. Elderly people sometimes forget to take necessary precautions against chills, such as keeping the house warm enough and getting adequate meals.

Friends and neighbors can play an important role in preventing the elderly from developing hypothermia. They can check up on older relatives and friends to make sure that they continue to take necessary precautions against hypothermia.

FOR MORE INFORMATION

Forgey, William W. The Basic Essentials of Hypothermia. Guilford, CT: Globe, Pequot Press, 1999.

Hall, Christine B. Cold Can Kill: Hypothermia. University of Alaska Sea Grant, 1994.