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 |Favorite Table|Download (.pdf) TABLE 209-1 Causes of Secondary Hypothermia
Predominantly Increased Heat Loss
Iatrogenic (i.e., blood transfusions and other cold infusions, cooling blankets, inadequate insulation)
Predominantly Impaired Thermogenesis
Impaired shivering (i.e., advanced or very young age, malnutrition, physical exhaustion, neuromuscular disease)
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)
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 |Favorite Table|Download (.pdf) 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 to treat in an ECMO/CPB center, if available, due to ...
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