Hypothermia

Hypothermia is a decrease in body temperature to 94° F or lower. At low temperatures, the body's organs become sluggish and less effective.

When the body temperature is low, messages travel more slowly through the brain and the rest of the nervous system. Abnormal heart rhythms (arrhythmias) may occur. The heart also slows down, and blood pressure falls. The kidneys make less urine, and digestion slows because muscles in the digestive tract contract less. If body temperature falls below about 86° F, organs are likely to stop working altogether, and death is likely.

Causes

An older person's body temperature may begin to fall whenever the body is exposed to temperatures cooler than it. The fall in body temperature is not likely to make a difference when the surrounding temperature is above 80° F, but it can become a problem when the surrounding temperature starts dipping below 70° F. Heat loss is also increased by wind, by sitting or lying on a cold surface, and by being immersed in cold water.

For additional detail on this topic, see The Body's Response to Cold Temperatures.

Symptoms

Initial symptoms of hypothermia come on slowly and without fanfare; thus hypothermia may sneak up on a person. When body temperature falls to between 95° and 97° F, the person may report feeling cold and, more than likely, will begin to shiver. However, by the time body temperature has fallen to 94° F or lower, reports of feeling cold and shivering usually stop. Instead, the skin may feel cold to the touch, even in such areas as the back and abdomen, which tend to be better insulated from the cold.

Movements become slow and clumsy, and the person becomes stiff or even rigid. Speech is thick and slow, and balance worsens. The person may stumble or fall. Some people appear to be intoxicated or to be experiencing a stroke. Thinking becomes less clear, and judgment is usually impaired. Rather than seeking a source of heat, some people actually remove their clothing.

Other changes may become apparent. The heartbeat slows down and may become irregular. Breathing also slows down.

If the body temperature falls below about 86° F, an older person usually becomes sleepier and sleepier, slips into a coma, and, in all likelihood, dies a short time later.

Diagnosis

The diagnosis of hypothermia is made when the body temperature is measured at or below 94° F. Most ordinary thermometers do not record temperatures below 96° F. A doctor may use a special thermometer that reads very low temperatures.

Once a doctor has determined that a person has hypothermia, an electrocardiogram may be performed to determine how much the cold temperature has affected the heart, and routine blood tests indicate whether other organs have been affected.

Prevention

Hypothermia is almost always preventable. Older people are advised to take the following precautions to prevent hypothermia:

• Maintain a warm environment. Older people sometimes keep their homes at a lower-than-desirable temperature as a means of saving money, but the thermostat should be set at 68° F or higher. It is especially important that the bedroom be kept warm. Fuel assistance programs and home winterization programs may help defray costs.
• Wear several layers of clothing. Clothing made of wool or synthetic materials such as polypropylene are especially useful, because these materials insulate even when they become wet. Because the body loses a large amount of heat from the head, wearing a hat is important. Fingers and toes must also be protected.
• Eat warm foods and drink warm fluids. Food provides the body with fuel to be burned, and warm fluids provide heat and prevent dehydration.
• Avoid alcoholic beverages. Alcohol dilates blood vessels in the skin, which makes the body temporarily feel warm but actually causes greater heat loss.
• Exercise regularly. Exercise can increase the body's production of heat

Outlook and Treatment

Hypothermia requires emergency medical treatment. Chances of recovery depend on how long the person has been cold, how low the body temperature has fallen, and the person's general health before hypothermia developed. The longer the amount of time, the lower the temperature, and the worse the person's general health, the lower the chances are of recovery.

The first goal when hypothermia is suspected or diagnosed is to keep the person warm and dry so that body temperature does not fall further. The person must be handled gently, because sudden movements may cause a dangerous abnormal heart rhythm. The person is also kept still, because exertion pumps very cold blood from the extremities back to the heart.

If the person appears to be in a coma or even to have died, the heart may still be beating, although very slowly and weakly. Cardiopulmonary resuscitation (CPR) should not be started unless it is certain that there is no pulse, because chest compressions could stop the heart.

Emergency treatment focuses on warming the person, but problems already caused by the cold body temperature, such as abnormal heart rhythms and dehydration, must also be corrected. The person is placed in a warm room and covered with special blankets or insulating materials to retain whatever heat the body is still producing. These measures may be all that is needed to warm the body in cases of mild hypothermia. Doctors want the warming to be slow and steady, increasing the body temperature by about 1 to 2° F per hour. It might seem as though warming should be done as fast as possible. However, rapid warming can sometimes increase the risk of very low blood pressure (shock) or life-threatening abnormal heart rhythms. Therefore, rapid warming is done only if the person is extremely ill and the body temperature is below 90° F.

Rapid warming is carried out by having the person breathe heated oxygen through a face mask or by passing heated fluids into the blood through a vein (intravenously) or into the abdominal or chest cavity through a plastic tube. Special heating blankets may also be used. In addition, the blood may be warmed by pumping it out of the body, warming it, and returning it to the body.

Some people with hypothermia who have arrived at the hospital with no signs of life recover. Efforts to restart the heart while a person is hypothermic often fail. Therefore, a decision to discontinue these efforts is not made until after the person's body temperature has been raised above 94° F.