Accidental hypothermia can develop in healthy individuals in extreme climatic conditions where cold defense mechanisms are overwhelmed or in patients with altered thermoregulatory mechanisms. The first situation is mainly encountered in young well-developed individuals while playing sports or working outdoors, and includes events such as snow avalanche accidents, immersion in cold water, or prolonged exposure to cold after falling into a crevasse or being trapped in a cave.
Hypothermia can be precipitated by alteration of thermoregulatory mechanisms; for example, alcoholic intoxication induces peripheral vasodilatation, decreases shivering capacity, depresses central thermoregulatory mechanisms, and impairs judgment. Alcoholics may stay outside for many hours wearing few clothes, either asleep or unconscious, in parks, on river banks, or in snow. Many drugs, such as tricyclic antidepressants, phenothiazines, or barbiturates, can lead to hypothermia either when used at toxic levels for self-poisoning or when administered in normal dose range for therapeutic purpose. Endocrine dysfunction, such as hypothyroidism, hypopituitarism, hypoglycemia, or diabetic ketoacidosis, may also result in hypothermia. Additional risk factors include central nervous system lesions (stroke, hemorrhage, trauma, tumor), spinal cord injuries, Parkinson's disease, Wernicke's encephalopathy, Alzheimer's disease, schizophrenia, anorexia nervosa, agenesis of the corpus callosum, or spontaneous periodic hypothermia.
The ability to conserve heat is lost when large areas of skin are injured, as in extensive burns. Newborn babies have a relatively large surface to body mass ratio, and premature infants have decreased subcutaneous tissue fat, leading to heat loss.
Decreased cold sensation, decreased muscle mass and shivering capacity, low physical activity, malnutrition, and impaired sympathetic nervous system activity and cardiac function make the elderly susceptible to hypothermia. Debilitating conditions, such as hepatic, renal, or cardiac failure, septic states, or malnutrition, may also contribute to hypothermia.
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