- Clinical science
Hypothermia is defined as a core body temperature below 35°C (95°F). It is classified as mild, moderate, or severe based on core temperature. Clinical features range from shivering to progressive bradycardia, coagulopathy, and circulatory collapse. Assessment should begin with determination of the core temperature, followed by ECG. Further tests are mainly used to determine comorbidities or complications (e.g., frostbite). Treatment entails rewarming and supportive care. Mild frostbite is reversible, while severe cases may require amputation. Cardiac arrhythmias are the most common cause of death.
- Primary (environmental exposure to cold) or secondary (underlying condition with inadequate temperature regulation) etiologies which result in:
- Increased heat loss: drugs (induced vasodilation), erythroderma (burns, psoriasis), surgery, sepsis, multiple trauma
- Decreased heat production: endocrine disorders (hypopituitarism, hypoadrenalism, and hypothyroidism), severe malnutrition, hypoglycemia, damage to posterior hypothalamic nucleus, and neuromuscular inefficiencies
- Impaired thermoregulation: damage to the preoptic nucleus of the hypothalamus due to CNS trauma, strokes, toxicologic and metabolic derangements, intracranial bleeding, Parkinson disease, CNS tumors, Wernicke disease, or multiple sclerosis
- Substance use
- Increasing age
- Psychiatric disease
- The body loses heat through radiation; (most significant means of heat loss), conduction; , convection; , and direct contact with cold surfaces.
- The hypothalamus attempts to maintain a temperature of approximately 36.5°C (97.7°F) to 37.5°C (99.5°F) by:
Hypothermia affects all organ systems
- General tissue oxygen demand decreases by ∼ 6% per degree Celsius below 35°C.
- Weakened cellular immune response
- Cardiovascular effects: ↓ depolarization of cardiac cells → ↓ cardiac output and ↓ mean arterial pressure
- CNS effects: ↓ CNS metabolism
- Definition: core body temperature under 35°C (95°F)
- Mental status changes should be proportional to other clinical signs
- Determine central core temperature reading with a low-reading temperature probe in the bladder or rectum or an esophageal probe.
|Stages of hypothermia||Signs and Symptoms|
Mild, 32–35°C (90–95°F)
Moderate, 28–32°C (82–90°F)
Severe, < 28°C (82°F)
Diagnostic tests (mainly to assess comorbidities and complications)
- ECG (best initial test): prolongation of all ECG intervals; elevated J point (characteristic J or Osborn wave)
- Imaging: chest x-ray to exclude pulmonary edema or aspiration pneumonia; CT if head trauma suspected
- Laboratory tests: complete metabolic panel, complete blood count, or arterial blood gas to exclude bleeding diathesis and early organ dysfunction
- Resuscitation (); place two large (14 or 16 gauge) peripheral IVs.
- Prevent further heat loss and begin rewarming
- Mild hypothermia: : passive external rewarming (remove wet clothing, cover with blankets, warm room )
- Moderate hypothermia, refractory mild hypothermia, and as an adjunct treatment for severe hypothermia: : active external rewarming (warm blankets, radiant head, forced warm air)
- Severe hypothermia, refractory moderate hypothermia, or unstable patients: active internal/core rewarming
- Manage cold-induced injuries (e.g., frostbite) with supportive care or surgery (e.g., amputation) as needed
Avoid rough handling of patients and always warm the trunk BEFORE the extremities; both can lead to peripheral vasodilation in extremity musculature and recirculation of cold, acidemic blood. This afterdrop results in a drop in temperature and arrhythmias! Even positioning for chest x-ray can be dangerous!
Patients with moderate to severe hypothermia may have arrhythmias that are unresponsive to defibrillation; cardiopulmonary resuscitation should be performed until the patient's core body temperature reaches 30–32°C (86–90°F)!
- Definition: severe localized tissue injury; due to freezing of interstitial and cellular spaces after prolonged exposure to very cold temperatures
- Clinical features
- Clinical diagnosis
- CT, MRI/MRA, bone scan to determine extent of nonviable tissue
- Remove wet clothing; avoid walking on frostbitten feet
- Evaluate for concurrent hypothermia and treat that first!
- Passive: remove wet clothing, cover with blankets, warm room (preferably 28°C (82°F))
- Active: immerse affected extremity in a warm (preferably 37–39°C) circulating water bath
- Analgesia and
- Manage suspected infections aggressively with antibiotics and sterile dressings