• Clinical science

Hypothermia and frostbite

Abstract

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.

Etiology

References:[1][2]

Pathophysiology

  • 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:
    • Conserving heat; (peripheral vasoconstriction – direct and sympathetic)
    • Increasing heat production; (shivering; , increased sympathetic tone)
  • 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

References:[2][3]

Hypothermia

  • Definition: core body temperature under 35°C (95°F)
  • Clinical features
    • 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)

Excitement

  • Confusion, amnesia, dysarthria, and impaired judgement
  • Ataxia, apathy
  • Tachycardia, tachypnea
  • Cold diuresis

Moderate, 28–32°C (82–90°F)

Exhaustion

Severe, < 28°C (82°F)

Paralysis

  • Diagnostic tests (mainly to assess comorbidities and complications)
  • Treatment
    • Resuscitation (ABCDE approach); 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
        • IV administration of warmed crystalloid
        • Warmed irrigation of peritoneum, thorax as needed
        • Extracorporeal blood rewarming as needed
    • 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)!

References:[4][1][5][6][2][3]

Frostbite

  • Definition: severe localized tissue injury; due to freezing of interstitial and cellular spaces after prolonged exposure to very cold temperatures
  • Clinical features
    • Acute frostbite can occur in isolation or as a complication of hypothermia
      • Areas most frequently affected: face (nose, cheeks, chin), ears, fingers, and toes
      • Cold and paresthesia of affected region
      • Pale (white or grayish-yellow), blue-red, or blistered hard or waxy skin
        • First degree: superficial, central pallor and anesthesia, bordering edema
        • Second degree: large clear or hemorrhagic blisters, no underlying tissue loss
        • Third degree: deeper injury, smaller blisters, skin blackens in weeks
        • Fourth degree: complete tissue necrosis extending to bone, likely requiring amputation
    • Chronic forms of frostbite
      • Pernio or chilblains: acute or repetitive exposure to damp cold above the freezing point; localized inflammatory lesions, which may be painful or pruritic
      • Immersion foot (trench foot): damage to sympathetic nerves and vasculature of the foot due to dampness and cold.
        • Hemorrhagic bullae may be red, numb, or painful.
        • The condition became especially prominent during WWI.
  • Diagnostics
    • Clinical diagnosis
    • CT, MRI/MRA, bone scan to determine extent of nonviable tissue
  • Treatment
    • Remove wet clothing; avoid walking on frostbitten feet
    • Evaluate for concurrent hypothermia and treat that first!
    • Rewarming
      • 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 tetanus prophylaxis
    • Manage suspected infections aggressively with antibiotics and sterile dressings
    • If frostbite is severe, consider using thrombolytics.
    • Therapeutic amputation is reserved only for deep infection.

Patients are often affected with both hypothermia and frostbite. Treatment of hypothermia should take priority because it can be acutely life-threatening!

References:[4][7]

last updated 11/19/2018
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