The Medical Minute: Cold weather injuries

December 20, 2006

By John Messmer
Penn State Family and Community Medicine
Penn State Milton S. Hershey Medical Center
Penn State College of Medicine

Humans are essentially a tropical species. Although they've learned to protect themselves against the cold, too often they fail to take necessary precautions against the elements and risk cold-related injuries, such as frostbite and hypothermia. Hypothermia is an excessively low body temperature that occurs when people lose more body heat than they make. Frostbite is frozen tissue -- the water in the tissue freezes into ice.

Bodies generate heat through muscle activity. Small children, particularly babies, need more protection than their parents because they do not generate as much body heat and lose heat more easily. The elderly are more susceptible because they have less heat generating muscle mass than younger people.

The skin participates in temperature management. That's why keeping bodies covered up against the cold is so important. People lose heat through blood vessel dilatation and evaporation of sweat. In cold temperatures, the blood vessels constrict to shunt heat back to the organs. Unfortunately, this takes heat away from the skin making it more susceptible to freezing. Extremities -- fingers, toes, nose and ears -- are most susceptible. Smoking, diabetes, heart failure, alcoholism, cancer chemotherapy, narcotics, tranquilizers and some antidepressants, and some blood pressure medications affect skin circulation increasing the risk of cold injury.

Multiple thin layers of dry clothing trap more heat than one thick layer. Hats reduce heat loss from the scalp which can shed up to 10 percent of the body's heat. Gloves, scarves and ear muffs also are important accessories. Shoes and socks are usually enough protection for dry winters, but snow and slush can lead to wet feet and increase the risk of something called immersion foot or trench foot, a cold-induced injury that results from prolonged exposure of wet feet to cold but not necessarily freezing temperature. Hunters and others who will be walking through snow should have insulated, waterproof boots. If socks get sweaty, changing into dry socks is recommended, although wool socks will continue to insulate when wet. For prolonged outdoors activities, an inner layer of polypropylene or similar fiber helps trap heat and wick away perspiration.

Moisture on wet clothing also draws heat out of the body quickly and increases the risk of cold injury. Wet gloves or socks provide little protection. When skin is wet it doesn't take freezing temperatures to cause cold-related injuries.

As it chills, exposed skin first becomes painful due to reduced blood flow. The earliest sign of frostbite developing is numbness in the affected part. The colder the temperature, the faster this occurs. If the sense of touch is reduced but still present no significant damage has occurred. When nothing can be felt in the affected area, frostbite has occurred in the skin. Fingers and toes get a "clumsy" feeling and do not move or bend. If medical attention and re-warming do not occur, frostbite damage can occur to the deeper muscle and bone.

If the fingers, nose, ears or toes burn or hurt, first try to protect them better. Put on gloves; use ear muffs or a scarf or get indoors. Frostbitten skin is pale. Thawing is painful and strong pain medication may be needed. It would be better to allow the part to remain frozen and seek medical attention rather than trying to thaw it alone. If medical attention is not readily available thawing can be started in a warm place where it will not refreeze.

The best way to thaw a frostbitten part is in warm water at about 100 degrees. Proper water temperature is important since further damage can occur if the frostbitten part is thawed too slowly or burned after being frozen. Rubbing the frozen part damages it further. Once thawed, protect the part from freezing again or the damage will be much worse. In severe freezes, the extent of damage may not be apparent for days or weeks. Medical attention should be obtained as soon as possible.

While frostbite results from freezing of the skin, hypothermia occurs when the body's inner temperature drops below 95 degrees. Heat flows out from the skin once the temperature drops below about 70 degrees so hypothermia can occur well above freezing.

Hypothermia also is treated by re-warming. If the person is conscious, put him or her in a warm room with layers of covering, such as, sweaters, blankets and so on. Provide warm beverages to increase internal temperature. If the person does not feel better in an hour, seek medical attention. If the person is confused or unconscious, cover him or her with blankets except for the nose and mouth and call 911. Low body temperature can cause potentially fatal heart rhythm problems so treatment in a hospital is best.

Smoking and alcohol make cold injury worse. Dehydration and smoking reduce blood flow to the skin, further cooling it and making it susceptible to freezing. Smokers may need extra protection for frostbite susceptible parts. Don't buy into the old image of a St. Bernard carrying spirits to a snowy rescue. Alcohol increases blood flow to the skin which may cause a feeling of warmth, but it actually speeds heat loss.

For people who can't move to Florida for the winter, remember these precautions and enjoy a safe and happy winter.

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Last Updated March 19, 2009