Discussion

Current scientific knowledge suggests that localized cold injury represents a continuous spectrum ranging from minimal to severe tissue destruction and loss. Frostbite has been categorized into four degrees of severity. First-degree frostbite is characterized by an anesthetic central white plaque with peripheral erythema. Second-degree injury reveals blisters filled with clear or milky fluid surrounded by erythema and edema, which appear in the first 24 hours. Third-degree injury is associated with hemorrhagic blisters that result in a hard black eschar, seen over the course of 2 weeks. Fourth-degree injury produces complete necrosis and tissue loss.

In general, treatment for the four categories of frostbite is the same until demarcation occurs within 3 to 4 weeks after injury.

Hypothermia is classified as being either mild (as previously described) or moderate—with temperatures between 28° C and 32° C, loss of shivering, and diminished level of consciousness—or severe, with core temperatures below 28° C and loss of reflexes, coma, and, eventually, ventricular fibrillation and death. Moderate to severe hypothermia is a medical emergency necessitating maintenance of airway, breathing, and circulation.

Most victims of hypothermia and localized cold injuries are in one of three categories: the urban poor, wilderness enthusiasts, and winter sports participants.

Frostbite is more common in persons exposed to cold at high altitudes. The areas of the body most likely to suffer are those farthest from the trunk or large muscles: ear lobes, nose, cheeks, fingers, hands, toes, and feet. Touching cold metal with bare hands can cause immediate frostbite, as can the spilling of gasoline or other volatile liquids on the skin when the temperature is very low. Factors contributing to hypothermia as well as localized cold injuries include alcohol intoxication, homelessness, and major psychiatric disorders. For those who participate in winter outdoor recreational and sports activities, direct exposure of skin and wearing constricting clothing, such as tight-fitting footwear, will predispose them to frostbite.

Frostnip is a superficial freezing of the skin, a precursor to frostbite, and produces reversible skin changes, including blanching and numbness that resolve with warming. It is important to treat frostnip early to avoid progression to frostbite. With gentle rewarming, the frostnip-affected area becomes hyperemic, and the sensation of pain returns rapidly.

Frostbite occurs when tissue freezes and crystals form in the extracellular space between cells. This occurs at ambient temperatures below 32° F (0° C). With dehydration, vasoconstriction, and low epidermal temperature, circulation is limited as blood viscosity increases, and water, hydrostatically pulled out of cells, begins to freeze. Close to 60% of frostbite injuries involve the lower extremities, in particular the great toe and feet. Predisposing diseases can include Raynaud disease, peripheral vascular disease, and diabetes mellitus. Tobacco smoking is another factor that can increase the likelihood of developing frostbite.

Planning for the threat of hypothermia can prevent cold injury. Individuals in cold and isolated areas should never be alone, or they should carry communication devices, such as cell phones or walkie-talkies. They should limit heat loss by insulating and dressing appropriately. Many layers are better than one thick layer. Waterproofed outer clothing is essential. Clothing materials should be wool, wool blends, or polypropylene. Cotton is not recommended. All extremities and the head should be covered. The face should be covered, especially with high wind chill. The feet should be protected with two layers of socks. The first layer should be made of polypropylene and the second layer made of wool.