Hypothermia

Key Features

Essentials of Diagnosis

• Systemic hypothermia is a core body temperature (CBT) below 35°C

• Accurate CBT measurement must be obtained using a low-reading core temperature probe than measures as low as 25°C

• The CBT 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

• Risk factors

  • Diabetes mellitus and other endocrine dysfunctions (hypothyroidism, adrenal insufficiency, hypopituitarism)

  • Kidney or liver dysfunction

  • Psychiatric conditions

  • Poor nutrition

  • Sedentary lifestyle

  • Homelessness, inadequately heated housing, inadequate or wet clothing

  • Occupational or recreational exposure

  • Prior cold weather injury

  • Pharmacologic effects

  • Sepsis, infection

  • Hypoglycemia

• Heat loss occurs more rapidly with

  • High wind velocity ("windchill factor")

  • Water immersion or wet clothing

  • Direct contact with a cold surface

• Accidental hypothermia may occur in the hospital setting due to

  • Prolonged postoperative hypothermia or administration of large amounts of refrigerated stored blood products (without rewarming)

  • Rapid infusion of intravenous fluids

  • Prolonged exposure of an undressed patient during resuscitation or surgical procedures

• Systemic hypothermia

  • Depresses physiologic function, resulting in decreased respiratory drive, oxygen consumption, central or peripheral nerve conduction, gastrointestinal motility, myocardial repolarization, metabolism of drugs

  • May decrease activity of coagulation cascade and the immune response

Clinical Findings

Symptoms and Signs

Systemic hypothermia

• In mild cases with core temperature between 35°C and 32°C (stage I):

  • Shivering

  • Impaired coordination

  • Poor judgment

  • Hemodynamic stability

  • Normal level of consciousness

• With core temperature between 32°C and 28°C (stage II):

  • Shivering stops

  • Bradycardia, dilated pupils, slowed reflexes, cold diuresis, and confusion and lethargy ensue

• With core temperature between 28°C and 24°C (stage III)

  • Loss of consciousness

  • Vital signs present

• Below 24°C (stage IV):

  • Vital signs lost

  • Coma, loss of reflexes, asystole or ventricular fibrillation, which may lead the clinician to assume that patient is dead despite reversible hypothermia

Hypothermia of the extremities

• Exposure of the extremities to cold produces immediate localized vasoconstriction followed by generalized vasoconstriction

• When the skin temperature falls to 25°C, the area becomes cyanotic

• At 15°C, there is a deceptively pink, well-oxygenated appearance to the skin. Tissue damage occurs at this temperature

Differential Diagnosis

• Infection

• Other cause of altered mental status (eg, hypoglycemia, drugs, stroke)

• Hypothyroidism

• Anorexia or malnutrition (poor fat stores)

• Adrenal insufficiency

• Burns

• Spinal cord injury

Diagnosis

Laboratory Tests

• Must assess acid-base status; electrolytes (particularly potassium); glucose; kidney, liver, and pancreas function; and coagulation; and must exclude rhabdomyolysis

Diagnostic Procedures

• ECG may reveal J wave or Osborn wave (positive deflection in the terminal ...