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Chapter 209: Hypothermia

Doug Brown

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 remain unknown.4

TABLE 209-1Causes of Secondary Hypothermia
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TABLE 209-1 Causes of Secondary Hypothermia

Predominantly Increased Heat Loss

  • Burns

  • Iatrogenic (i.e., blood transfusions and other cold infusions, cooling blankets, inadequate insulation)

  • Recent birth

Predominantly Impaired Thermogenesis

  • Impaired shivering (i.e., advanced or very young age, malnutrition, physical exhaustion, neuromuscular disease)

Multifactorial

  • Medications and toxins (i.e., alcohol, anesthetic agents, narcotics, sedatives, vasodilators)

  • Metabolic and endocrine disorders (i.e., alcoholic or diabetic ketoacidosis, hypoadrenalism, hypoglycemia, hypopituitarism, hypothyroid, lactic acidosis, Wernicke's encephalopathy)

  • Neurologic (i.e., space-occupying lesion, stroke, spinal cord injury)

  • Sepsis (small subset of sepsis cases, more common in the elderly or cachectic patient)

  • Shock

  • Trauma

HYPOTHERMIA CLASSIFICATION

Historically, hypothermia has been classified as mild, moderate, severe, and profound, based on core temperature, shivering, level of consciousness, and vital signs.5,6,7 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, hypothermia stage IV) 5,6,7 described in Table 209-2 is a hybrid of the Swiss7 and classical systems5 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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TABLE 209-2 Staging and Treatment of Accidental Hypothermia
Stage Clinical Symptoms Typical Core Temperature Treatment
Mild (HT I) Conscious, shivering 35–32°C

Warm environment and clothing, warm sweet drinks, and active movement (if possible)

HT I patients with significant trauma or comorbidities or those suspected of secondary hypothermia should receive HT II treatment
Moderate (HT II) Impaired consciousness* (may or may not be shivering) <32–28°C

Active external and minimally invasive rewarming techniques (warm environment; chemical, electrical, or forced air heating packs or blankets; warm parenteral fluids)

Cardiac and core temperature monitoring

Minimal and cautious movements to avoid arrhythmias

Full-body insulation, horizontal position, and immobilization
Severe (HT III) Unconscious*, vital signs present <28°C

HT II management plus:

Airway management as required

Preference ...

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