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Individuals vary considerably in their response to cold environments. Hypothermia can occur in a wide variety of environmental settings. Factors that increase the risk of injury from cold include poor general physical condition, nonacclimatization, childhood or advanced age, systemic illness, malnutrition, rapid temperature changes, and the use of alcohol and other sedative drugs. High wind velocity (wind-chill factor) and moisture markedly increase the propensity for cold injury at low temperatures.



  • Signs and symptoms depend on degree of hypothermia.

  • Rewarming methods include passive external, active external, and active internal rewarming.

General Considerations

A. Healthy Persons

Accidental hypothermia occurs when an external cold challenge overwhelms an individual’s capacity to produce or conserve heat. Common mechanisms involved in heat loss include convection (direct transfer of heat from skin to environment), conduction (transfer of heat by direct contact), radiation (heat loss via infrared electromagnetic energy), and evaporation (vaporization of water from sweat). Radiation accounts for the majority of normal heat loss.

Hypothermia may occur in otherwise healthy individuals during occupational or recreational exposure to cold or as a result of accidents or other misfortunes. Alcohol and drug abuse is a common predisposing cause.

B. Persons with Predisposing Factors

Systemic hypothermia may follow exposure to even slightly lowered temperatures when preexisting altered homeostasis exists as a result of debility or disease. Accidental hypothermia is more likely to occur in elderly or inactive people and those with cardiovascular, dermatologic, or cerebrovascular disease; mental retardation; myxedema; hypopituitarism; or alcoholism. The use of sedative–hypnotic or antidepressant drugs may be a contributing factor. Medical comorbidities and pharmacologic agents can alter thermoregulation, impair heat production, and increase heat loss in this susceptible population.

Clinical Findings

Because lowered body temperature is the sole finding in some patients brought to the emergency department (ED), the diagnosis often depends on awareness of the possibility of hypothermia. The clinical picture often does not correlate with the degree of hypothermia.

A. Temperature

In the hypothermic patient, oral and axillary temperatures are not accurate. Instead, rectal probes and esophageal monitors should be used to accurately measure the core body temperature. The temperature varies widely in hypothermia, and accurate monitoring is essential in guiding therapy.

B. Symptoms and Signs

The degree of hypothermia can be classified based on the Swiss staging system. Stage 1 (HT1) has a typical core temperature of 32–35°C. Patients will be conscious with tachycardia, tachypnea, and shivering. In stage 2 (HT2) the typical core temperature ranges between 28 and less than 32°C. Symptoms include loss of the shivering reflex and mild alterations in level of consciousness. Bradycardia ...

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