Cold injuries are usually due to prolonged exposure to cold temperatures, although they can occur with brief exposure to extremely cold conditions. They occur because our body's ability to generate heat and to limit heat loss is quite limited. For heat regulation, our body uses its core (internal organs such as the brain and heart) and its shell (skin, muscles, and limbs). Cold injury to our body's core is called hypothermia, and cold injury to our body's shell is called frostbite. Hypothermia and frostbite commonly occur together, but they can occur separately.

What is hypothermia?
Hypothermia is a decrease in core body temperature from exposure to a cold environment. Surprisingly, hypothermia can even occur at mild temperatures if exposure is prolonged. Our body's natural defenses against the cold are quite limited. Initially, the blood vessels in our skin constrict to reduce heat loss and to keep blood flowing to the vital organs. Shivering (involuntary muscle contraction) and the increased release of hormones result in increased heat production. However, blood vessel constriction and hormone release are usually inadequate to maintain our body's temperature in cold environments. Individuals who drink alcohol, as well as those who suffer from fatigue, spinal cord injuries, or poor nutrition, are at greater risk for hypothermia.

Treatment of hypothermia
To help someone with hypothermia, contact the emergency medical system immediately. Remove all cold, wet clothing and replace it with warm, dry clothing to prevent further heat loss. If the person is not breathing or has no pulse, begin cardiopulmonary resuscitation (CPR), and do not stop until emergency medical personnel arrive. If the patient is not alert or is unconscious, take care to immobilize the neck when moving the patient: moving a patient with a fractured neck can result in permanent nerve damage or paralysis.

Avoid rapid rewarming with hot water or massaging cold extremities. If done improperly, it could lead to serious tissue damage. Therefore, a trained person should handle the rewarming process. In addition, do not give alcohol or nicotine products to someone suffering from hypothermia.

What is frostbite?
Frostbite is a localized cold injury to a body part that may occur with or without hypothermia. Frostbite commonly affects specific body parts, such as the feet and toes or the hands and fingers. In some instances, tissue damage is so extensive it may require amputation.

When human tissue is exposed to near-freezing temperatures, the tissue temperature decreases. As the tissue temperature decreases, it goes through four phases of frostbite. In the first phase, the blood vessels constrict, causing inadequate blood flow and oxygen delivery to the tissues. In the second phase, the tissue temperature drops below 24.8°F, and ice crystals form in the tissues. Unless the body part is rewarmed, frostbite will progress to the third and fourth phases. In the third phase, fluid leaks from the blood vessels into the damaged tissue. In the fourth phase, the blood vessels clot, resulting in irreversible loss of blood flow to the damaged tissue.

Frostbite symptoms typically start with a sensation of extreme coldness, followed by numbness, and then clumsiness. Superficial frostbite results in numbness and the development of clear, fluid-filled blisters. Deeper frostbite causes deeper blisters filled with purplish fluid. In all types of frostbite, the damaged tissue may swell and darken in color after rewarming.

Treatment of frostbite
If someone is suffering from hypothermia and frostbite, the hypothermia should be treated first; if the body shell is rewarmed before the body core, blood can pool in the extremities, possibly causing cardiac arrest.

If the frostbite victim is close to an emergency facility, do not attempt rewarming. You can prevent further heat loss by replacing any wet clothing with dry clothing.

If medical help is more than 2 hours away, rewarm the body part in warm water (104-108°F). Great effort must be taken to prevent refreezing after rewarming, because refreezing results in almost certain tissue death. Do not massage the affected area and do not expose the tissue to excessive heat either can result in increased tissue damage.

How do I prevent cold injuries?
To prevent hypothermia and frostbite in cold conditions, wear layered clothing to create insulation. This should include mittens or gloves, a cap or hood, thermal underwear, and multiple layers of socks. Be sure to change wet garments promptly and drink plenty of fluids to avoid dehydration.

Tim W. Allari, M.D.
Columbus, Georgia