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INTRODUCTION AND EPIDEMIOLOGY

Accidental hypothermia is an involuntary drop in core temperature below 35°C (<95°F) and can often be associated with significant morbidity and mortality.1 Therapeutic hypothermia, also called targeted temperature management, is a purposeful drop in core temperature usually performed with the hope of ameliorating tissue damage associated with an ischemic event.2,3

Accidental hypothermia can be subclassified as primary, due to simple environmental exposure, or secondary, due to impaired thermoregulation (Table 209-1). Primary accidental hypothermia is commonly seen in cold climates, whereas secondary accidental hypothermia can be seen worldwide. The true incidence of accidental hypothermia and its related morbidity and mortality remains unknown,4 but estimates suggest it is 0.1 to 5 cases per 100,000 inhabitants in nontropical climates.5

TABLE 209-1Causes of Secondary Hypothermia

HYPOTHERMIA CLASSIFICATION

Historically, hypothermia has been classified as mild, moderate, severe, and profound, based on core temperature, shivering, level of consciousness, and vital signs.6-8 Unfortunately, there is considerable variation in clinical features at any given temperature, and a reliable core temperature is sometimes unavailable during initial assessment. Shivering is particularly unreliable because it may be present or absent across a wide temperature range. The modified staging system (mild, moderate, severe, and hypothermic cardiac arrest)6-8 described in Table 209-2 is a hybrid of the Swiss8 and classical systems6 that is based primarily on level of consciousness, the presence or absence of vital signs, and core temperature (when available).

TABLE 209-2Staging and Treatment of Accidental Hypothermia

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