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ESSENTIALS OF DIAGNOSIS

  • Systemic hypothermia is a core body temperature below 35°C.

  • Accurate core body temperature measurement must be obtained using a low-reading core temperature probe that measures as low as 25°C.

  • Core body temperature must be over 32°C before terminating resuscitation efforts.

  • Extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass may be considered in hypothermic patients with hemodynamic instability or cardiac arrest.

GENERAL CONSIDERATIONS

Systemic hypothermia is defined as core body temperature below 35°C. This may be primary, from exposure to prolonged ambient, extremely low temperature, or secondary, due to thermoregulatory dysfunction. Both may be present at the same time. Heat loss occurs more rapidly with high wind velocity or “windchill factor,” water or wet clothing exposure, or with direct contact with a cold surface.

The human body generates internal heat through muscle activity via shivering or increased physical exertion and preserves heat via peripheral vasoconstriction. Hypothermia must be considered in any patient with prolonged exposure to an ambient cold environment, especially in any patients with prior cold weather injury as well as the risk factors listed in the Cold & Heat section. In prolonged or repetitive cold exposure, hypothermia ensues if the body’s thermoregulatory responses become impaired.

Systemic hypothermia depresses physiologic function, resulting in decreases in respiratory drive, oxygen consumption, central and peripheral nerve conduction, gastrointestinal motility, myocardial repolarization, metabolism of drugs and perhaps the coagulation cascade and the immune response.

Iatrogenic accidental hypothermia may occur in the hospital setting due to rapid infusion of intravenous fluids, prolonged exposure of an undressed patient during resuscitation or surgical procedures, or administration of large amounts of refrigerated stored blood products without rewarming. This section does not cover induced hypothermia post-resuscitation.

CLINICAL FINDINGS

Symptoms and signs of hypothermia are typically nonspecific and markedly variable based on the patient’s underlying health and circumstances of cold exposure. Laboratory studies must assess acid-base status; electrolytes, particularly potassium and glucose; kidney, liver, and pancreas function; coagulation; and rhabdomyolysis. Inaccurate laboratory values will occur if the blood sample is warmed to 37°C for testing. All patients must be evaluated for associated conditions including hypoglycemia, trauma, infection, overdose, and peripheral cold injury. Prolonged hypothermia may also lead to dysrhythmias, conduction abnormalities, pulmonary edema, or pneumonia. Death from systemic hypothermia is often due to arrhythmia.

Accurate core body temperature measurements must be obtained using a low-reading core temperature probe that measures as low as 25°C. Standard thermometers cannot differentiate between temperatures in significant hypothermia, making oral, axillary, and otic temperatures inaccurate and unreliable. Hypothermia and the corresponding management strategies are classified based on clinical signs and symptoms according to the Swiss staging system. Stage I hypothermia is typically seen when the core body temperature is between 32°C and 35°C and is defined by shivering and possibly poor judgment or coordination but with hemodynamic stability and a normal level of consciousness. ...

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