Frostbite occurs when ice crystals form within or between living cells in tissue. As freezing extends, cell death occurs.
Frostbite usually occurs in extreme cold; extremities and exposed skin (fingers, toes, nose, cheeks or ears) are most often affected. Altitude and hypothermia aggravate frostbite, due to preferential constriction of peripheral blood vessels and shunting of blood to the core.
Tissues that are adjacent to frozen areas are also at risk, as local vasoconstriction and thrombosis (clotting) of small vessels deprive cells of blood flow and oxygen. Furthermore, when injured areas are re-warmed and blood flow returns, inflammatory chemicals (thromboxanes and prostaglandins) are released that may further damage adjacent tissues.
Therefore, damage to frostbitten areas may appear deceptively slight at first glance. The true extent of injury may not be apparent for days or even weeks.
Risk Factors for Frostbite
Factors that predispose individuals to frostbite may stem from underlying physical characteristics or from decreased awareness to the degree of cold exposure:
- Insufficient clothing
- Malnutrition
- Generally poor state of health
- Advanced age
- Lack of acclimatization
- Racial disposition (e.g., blacks)
- Interference with blood flow (i.e., constrictive clothing)
- Prior cold injury
- Vascular disease (atherosclerosis, Buerger’s disease, etc.)
- Raynaud’s syndrome or cryoglobulinemia
- Tobacco use
- Alcohol or drug use
- Peripheral neuropathy (diabetes, chemotherapy, etc.)
- Hypoxemia (COPD, high altitude, etc.)
- Unconsciousness
Signs and Symptoms of Frostbite
Acute
- Affected area is cold, waxy, numb, and white
- With warming, skin becomes blotchy and red, swollen, and extremely painful. Blisters—filled with either clear fluid or blood—form within 4 to 6 hours
Subacute to Chronic
- Dry gangrene (hard, black covering over healthy tissue)
- Wet gangrene (gray, edematous, soft; may become infected)
- Auto-amputation (severely damaged tissues slough away, leaving healthy tissue beneath)
- Chronic neuropathy (hypersensitivity to cold, numbness, excessive sweating, pain, poor nail growth)
Treatment of Frostbite
In the Field
- The longer a body part remains frozen, the greater the ultimate damage. Frostbitten areas should be re-warmed rapidly by total immersion in warm water (≤104.9ºF). Patients can seldom tolerate more than 15 to 30 minutes of warming; the use of progressively warmer baths isn't particularly helpful.
- If warm water is unavailable, the affected extremity should be gently cleaned, dried, and wrapped in clean cloth or dressings.
- Rubbing the affected body part may cause further damage and should be avoided. Since the affected part is numb, using a dry, uncontrolled heat source (e.g., fire, heating pad) may lead to unrecognized burns.
- The victim should be kept warm (e.g., wrapped in a sleeping bag) during transport.
- If the victim's feet are frostbitten and a walk is required, it is inadvisable to warm the feet in the field. Thawed tissues are sensitive to the trauma of walking, and tissues that are thawed and refrozen will suffer more severe damage than those that are left frozen.
At the Hospital
- Warming is continued (or initiated) in circulating water baths.
- Analgesics are administered to control pain, which can be excruciating.
- Intact blisters are left alone. Those that have ruptured are trimmed away.
- Anti-inflammatories—both topical and systemic—are administered. Affected areas are elevated to prevent swelling. Tetanus toxoid is usually given.
Long-term Management of Frostbite
- If wet gangrene occurs, antibiotics are administered to prevent infection.
- Warm whirlpool baths several times daily, followed by drying and rest, are the best management until demarcation between viable and necrotic tissue occurs.
- Amputation, if necessary, is delayed as long as possible to allow shedding of dry gangrene and to allow recovery of the maximum amount of healthy tissue. Many weeks of observation and conservative management may be necessary for victims of severe frostbite.
(Sources: Merck Manual, 18th Edition 2006:2610-11; Backer H. Medical limitations to wilderness travel. Emergency Medicine Clinics of North America 1997; 15: 17-41; Dellon AL. Frostbite and diabetic neuropathy. Wounds 2003; 15(12): 399-404)
