Hypothermia is a drop in internal body temperature to a below-normal level. When the body’s core temperature drops too low, the heart rate and metabolism slow dramatically, oxygen consumption decreases, loss of consciousness may ensue, and eventually, cardiac arrest may occur.
Body temperatures between 90°F and 96°F indicate mild hypothermia; temperature below 90°F indicates moderate to severe hypothermia. The lower the temperature, the more severe the symptoms. (Incidentally, most household thermometers do not register temperatures below 94°F and thus are not reliable indicators of severe hypothermia.)
Hypothermia may develop even at moderate external temperatures of 30°F to 50°F, especially in windy or wet weather. (Water conducts heat away from the body about 25 times faster than air.) The elderly are particularly vulnerable, because the ability to regulate body temperature diminishes with age. Hypothermia is a common killer of outdoor recreationists and constitutes a medical emergency.
What Causes Hypothermia?
- Exposure to cold weather, especially in wind and rain. Hypothermia may also occur in moderate cold or even indoors, especially among infants or the elderly.
- Immersion in cold water rapidly leads to hypothermia, but even water as warm as 70°F may lead to hypothermia if exposure is prolonged.
- Risk factors include alcohol use; diabetes mellitus; disorders of the pituitary, thyroid, or adrenal glands; fatigue; and use of beta-blocking drugs (often prescribed to treat high blood pressure).
Symptoms of Hypothermia
- Numbness, starting in the extremities
- Pallor, or a bluish or grayish tinge to the skin (cyanosis)
- Slurred speech or stuttering
- Memory loss
- Emergency symptoms: drowsiness, dramatically decreased pulse and breathing rate, dilated pupils, loss of consciousness
- Wear several layers of warm, nonrestrictive clothing in cold or wet weather. Keep your head warm (since heat evaporates easily through the scalp). Don’t stay out too long in the cold. Be aware that fatigue, poor nutrition, and illness may increase your risk.
- Alcohol, drug use, and lack of oxygen at high altitudes may impair judgment and lead to increased cold exposure. Alcohol also increases heat loss.
- Check often on elderly relatives or friends during cold weather.
- Suspect hypothermia when severe, uncontrollable shivering is present, or when cold exposure leads to confusion, stuttering, or drowsiness.
- A doctor may use a special low-reading thermometer to measure body temperature.
- Call an ambulance or proceed to the nearest emergency room immediately.
- Someone suffering from hypothermia outdoors should go, or be brought, inside as soon as possible. Wet clothing should be removed and replaced with dry clothing, blankets, or a warm sleeping bag. Make sure the top of the head is covered.
- Skin-to-skin contact or careful use of an electric blanket are effective for rewarming. Concentrate on rewarming the torso, since rewarming the limbs may in fact draw blood away from the vital organs.
- Warm, nonalcoholic drinks may be given if the patient is conscious.
- Warm intravenous fluids and heated oxygen may be given in the emergency room. In severe cases, directly warming the patient’s blood may be employed.
When to Call a Doctor
EMERGENCY Call an ambulance or rescue squad if hypothermia develops. Administer the measures described above until emergency help arrives.
Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference
Simeon Margolis, M.D., Ph.D., Medical Editor
Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50
Updated by Remedy Health Media