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Hypothermia

Key points

• Hypothermia is defined as a core body temperature below 35ºC (95ºF)
• Suspect toxic, metabolic, or endocrine etiology in patients who present with hypothermia without a history of environmental exposure
• Initial management includes rewarming, cardiopulmonary and hemodynamic stabilization, trauma assessment, finger stick for blood glucose determination, blood tests to assess patient's general biochemical and physiologic status, and an electrocardiogram (ECG) and cardiac monitoring to identify arrhythmias
• Rewarm at rates of 0.5ºC to 2ºC per hour (0.9ºF-3.6ºF/h) using one or more rewarming techniques, including passive external rewarming with removal of wet clothing and wrapping in warm blankets; active external rewarming with hot water bottles and other devices; active core rewarming via airway and heated body cavity irrigation; and extracorporeal blood rewarming via cardiopulmonary bypass
• Patients with severe hypothermia (<30°C or 86°F) are at risk of ventricular arrhythmias and require more rapid rewarming with active internal rewarming techniques
• Monitor patient during active core warming for dysrhythmias or vascular collapse
• Cardiac drugs and defibrillation are generally less effective or ineffective in the presence of acidosis, hypoxia, and hypothermia
• Patient movement should be kept to a minimum as it can lead to dysrhythmias
• Patients with severe hypothermia may appear to be dead, but should be rewarmed before terminating resuscitative efforts. Due to vasoconstriction and profound bradycardia that can be seen in severe hypothermia, palpating pulses can be difficult
• Hypothermia induces a neuroprotective state, and there are many case reports of patients surviving prolonged resuscitation attempts

Background

Description

• Hypothermia is defined as a core body temperature below 35ºC (95ºF)
  • Mild: 35ºC to 32ºC (95ºF-90ºF)
  • Moderate: 32ºC to 30ºC (90ºF-86ºF)
  • Severe: below 30ºC (<86ºF)
• Classification by temperature is not universal and actual temperature cut-offs vary by source
• The body has a limited capacity to increase heat production, and hypothermia occurs when heat loss is greater than heat production
• Hypothermia can be considered:
  • Primary due to straightforward exposure to cold environments
  • Secondary due to disease or an environmental exposure coupled with another reason, such as intoxication
  • Intentional as in cardiac bypass or post-resuscitation therapeutic hypothermia
• Hypothermia affects all organs of the body; minor deviations from normal temperature can lead to clinically significant dysfunction
• Absence of respiratory and cardiac function may return as patients are rewarmed

Epidemiology

• Varies widely depending on location and season
• Estimates are difficult to quantify as hypothermia is often listed as a secondary diagnosis
• 0.3/100,000 deaths from primary hypothermia
• Extremes of age (young children and the elderly) are the most vulnerable to hypothermic injury
• Adults have highest probability of being exposed to hypothermic conditions
• Males more affected than females
• In urban populations of the U.S., most cases of hypothermia are due to homelessness, mental illness, or illicit drug and/or alcohol use
• Outdoor workers are at increased risk
• Poverty may be associated with inadequate indoor heating and poor clothing and predispose to climate-related hypothermia

Causes and risk factors

Causes:

• Decreased heat production:
  • Nutritional depletion: malnutrition, hypoglycemia, extremes of age (the very young and the very old)
  • Endocrine disorders: hypopituitarism, hypoadrenalism, hypothyroidism
  • Neuromuscular dysfunction: impaired shivering, immobility
• Increased heat loss:
  • Environmental exposure: trauma, mental illness, disorientation, suicide, myocardial infarction, recreational exposure such as skiing or mountain climbing
  • Drug intoxication: alcohol, toxins, sedative/hypnotics, narcotics, barbiturates
  • Skin disorders: burns
  • Iatrogenic: prolonged cardiopulmonary resuscitation (CPR), postsurgical, therapeutic, cold intravenous fluids, overcooling of patients with heat stroke
• Impaired thermoregulation:
  • Central: spinal cord injury, cerebrovascular accident
  • Peripheral: neuropathy, diabetes
  • Metabolic/toxic: drugs (benzodiazepines, phenothiazines, tricyclic antidepressants, barbiturates, lithium, clonidine), anorexia, diabetic ketoacidosis, hepatic failure, uremia, lactic acidosis, hypoglycemia
• Miscellaneous:
  • Sepsis: Gram-negative sepsis, meningitis
  • Pancreatitis
  • Uremia
  • Vascular insufficiency
  • Carcinomatosis
  • Seizure disorder
  • Peritonitis

Risk factors:

• Age: Mild hypothermia is more common in the elderly because of comorbidities, medications, reduced metabolic rate, and immobility. Elderly patients may have poor nutrition or be challenged by poverty resulting in inadequate heating
• Arterial disease
• Diabetes mellitus (type 1 or type 2)
• Altered mental status
• Homelessness
• Drug use (licit and illicit)

Screening

Summary approach

Not applicable.

Primary prevention

Summary approach

• Limit exposure to cold environmental temperature
  • If hypothermia is due to inadequate housing, clothing, or heat source, refer patient to social services
  • Extremes of age and those patients with medical, nutritional, or another propensity for hypothermia should be extra vigilant in minimizing cold exposure
• Avoid alcohol and illicit drugs during periods of cold exposure. Abstinence from alcohol and illicit drugs will minimize cases of hypothermia
• Satisfy fluid and nutritional requirements; correct dietary deficiencies