Chapter 46

Individuals vary considerably in their response to environmental cold. Factors that increase the possibility of injury due to cold include poor general physical condition, nonacclimatization, childhood or advanced age, systemic illness, and the use of alcohol and other sedative drugs. High wind velocity (wind-chill factor) and moisture may markedly increase the propensity for cold injury at low temperatures.

### Systemic Hypothermia

#### Essentials of Diagnosis

• Signs and symptoms depend on degree of hypothermia
• Rewarming methods include passive external, active external, and active internal rewarming

#### General Considerations

##### Healthy Persons

Accidental hypothermia occurs when an external cold challenge overwhelms an individual's capacity to produce or conserve heat. 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.

##### 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.

#### Clinical Findings

Because lowered body temperature is the sole finding in some patients brought to the emergency department, the diagnosis often depends on awareness of the possibility of hypothermia.

##### Temperature

In the hypothermic patient, oral and axillary temperatures are not accurate. Instead, rectal probes should be used. The temperature varies widely in hypothermia, and accurate monitoring is essential.

##### Symptoms and Signs

Hypothermia is classified as mild when core body temperature is between 34°C (93.2°F) and 36°C (96.8°F). Patients will exhibit tachycardia, tachypnea, and shivering. Hypothermia is moderate between 30°C (86°F) and 34°C. Loss of the shivering reflex and mild alterations in level of consciousness occur. Bradycardia and atrial fibrillation may start to appear. Hypothermia becomes severe below temperatures of 30°C. Patients may appear dead at this stage with fixed, dilated pupils, loss of other reflexes, and coma.

Ventricular fibrillation and asystole may occur spontaneously at core temperatures below 28°C (82.4°F). Note: For this reason, a hypothermic patient should not be considered dead until all reasonable resuscitative measures have failed. No one is dead until he or she is “warm and dead.”

##### Laboratory Findings

Several laboratory findings are unique to hypothermia. Hypoglycemia, hypomagnesemia, and hypophosphatemia are common, particularly in alcoholics. Hyperglycemia may be seen as a result of hemorrhagic pancreatitis in patients with prolonged exposure to the cold. Sodium and potassium levels may be elevated or depressed. Arterial blood gas samples drawn at cold temperatures are generally analyzed ...

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