Chapter 69 Cold Injuries
The involvement of children and youth in snowmobiling, mountain climbing, winter hiking, and skiing places them at risk for cold injury. Cold injury may produce either local tissue damage, with the injury pattern depending on exposure to damp cold (frostnip, immersion foot, or trench foot), dry cold (which leads to local frostbite), or generalized systemic effects (hypothermia).
Pathophysiology
Ice crystals may form between or within cells, interfering with the sodium pump, and may lead to rupture of cell membranes. Further damage may result from clumping of red blood cells or platelets, causing microembolism or thrombosis. Blood may be shunted away from an affected area by secondary neurovascular responses to the cold injury; this shunting often further damages an injured part while improving perfusion of other tissues. The spectrum of injury ranges from mild to severe and reflects the result of structural and functional disturbance in small blood vessels, nerves, and skin.
Etiology
Body heat may be lost by conduction (wet clothing, contact with metal or other solid conducting objects), convection (wind chill), evaporation, or radiation. Susceptibility to cold injury may be increased by dehydration, alcohol or drug use, substance abuse, impaired consciousness, exhaustion, hunger, anemia, impaired circulation due to cardiovascular disease, and sepsis; it is also greater in very young or aged persons.
Hypothermia occurs when the body can no longer sustain normal core temperature by physiologic mechanisms, such as vasoconstriction, shivering, muscle contraction, and nonshivering thermogenesis. When shivering ceases, the body is unable to maintain its core temperature; when the body core temperature falls to <35°C, the syndrome of hypothermia occurs. Wind chill, wet or inadequate clothing, and other factors increase local injury and may cause dangerous hypothermia, even in the presence of an ambient temperature that is not <17-20°C (50-60°F).
Clinical Manifestations
Frostnip
Frostnip results in the presence of firm, cold, white areas on the face, ears, or extremities. Blistering and peeling may occur over the next 24-72 hr, occasionally leaving mildly increased hypersensitivity to cold for some days or weeks. Treatment consists of warming the area with an unaffected hand or a warm object before the lesion reaches a stage of stinging or aching and before numbness supervenes.
Immersion Foot (Trench Foot)
Immersion foot occurs in cold weather when the feet remain in damp or wet, poorly ventilated boots. The feet become cold, numb, pale, edematous, and clammy. Tissue maceration and infection are likely, and prolonged autonomic disturbance is common. This autonomic disturbance leads to increased sweating, pain, and hypersensitivity to temperature changes, which may persist for years. The treatment is largely prophylactic and consists of using well-fitting, insulated, waterproof, nonconstricting footwear. Once damage has occurred, patients must choose clothing and footwear that are more appropriate, dry, and well-fitting. The disturbance in skin integrity is managed by keeping the affected area dry and well-ventilated and by preventing or treating infection. Only supportive measures are possible for control of autonomic symptoms.
Frostbite
With frostbite, initial stinging or aching of the skin progresses to cold, hard, white anesthetic and numb areas. On rewarming, the area becomes blotchy, itchy, and often red, swollen, and painful. The injury spectrum ranges from complete normality to extensive tissue damage, even gangrene, if early relief is not obtained.
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