Accidental Hypothermia

Accidental hypothermia is an unintentional fall in core temperature below 35 degrees Celsius.

Clinical staging by presentation guides care

• Stage I (32 to 35 degrees Celsius): conscious and shivering

• Stage II (28 to 32 degrees Celsius): impaired consciousness, shivering lost

• Stage III (24 to 28 degrees Celsius): unconscious but with vital signs

• Stage IV (under 24 degrees Celsius): apparent death, with absent vital signs

Causes

Environmental exposure (mountain, sea, urban winter), immersion, alcohol and drug intoxication, homelessness, malnutrition, old age, infection, hypothyroidism, adrenal insufficiency, hypoglycemia, trauma, burns and spinal cord injury.

Physiology

Shivering stops under 32 degrees Celsius. Heart rate and cardiac output fall, atrial fibrillation appears, and ventricular fibrillation risk rises sharply under 28 degrees Celsius. Cold diuresis causes hypovolemia. Enzyme and platelet function fall, so coagulopathy appears.

Drug metabolism slows, and consciousness declines. Rough handling can precipitate ventricular fibrillation. Metabolic demand is low, which protects the brain, so survivors of prolonged cardiac arrest with full neurological recovery are reported at core temperatures as low as 13.7 degrees Celsius.

• Stage I: shivering, tachycardia, tachypnea, hypertension, cold diuresis, ataxia and apathy
• Stage II: drowsiness, confusion, bradycardia, hypotension, muscle rigidity, loss of shivering and paradoxical undressing
• Stage III: coma, slow shallow breathing, fixed dilated pupils, absent reflexes, and weak or hard-to-find pulses
• Stage IV: no detectable signs of life
• ECG: sinus bradycardia, atrial fibrillation with slow response, long PR, QRS and QT intervals, and Osborn (J) waves
• Red flags: temperature under 28 degrees Celsius, cardiac arrhythmia, coma, trauma and a patient who is hypothermic after immersion or burial

• Core temperature with a low-reading thermometer (esophageal probe preferred, bladder or rectal acceptable, tympanic readings unreliable in the cold).

• ECG and continuous monitoring.

• Blood tests: glucose, electrolytes (potassium is the prognostic marker in arrest), creatinine, creatine kinase, lactate, amylase, full blood count, coagulation (results are artifactually normal because they are run at 37 degrees Celsius), blood gas (interpret without temperature correction), cultures, thyroid function, cortisol, blood alcohol and toxicology.

• Chest radiograph, and CT for trauma or when the cause is unclear.

• Confirmation of cardiac arrest: palpate for a central pulse for up to 1 minute and use ECG, echocardiography or Doppler, since a very slow circulation may be missed.

Differentials: sepsis, myxedema coma, adrenal crisis, hypoglycemia, intoxication, intracranial hemorrhage and trauma.

1. Gentle handling: keep the patient horizontal, avoid rough movement and rubbing of limbs, remove wet clothing, insulate against wind and ground, and protect the head.
2. Stage I: passive rewarming (dry insulation, warm sweet drinks) plus active external rewarming with forced warm air (40 to 43 degrees Celsius).
3. Stage II and III:
   • Forced warm air and heated blankets, with warm humidified oxygen at 40 to 46 degrees Celsius.
   • Warmed IV crystalloid (38 to 42 degrees Celsius), 20 mL/kg boluses (children 10 to 20 mL/kg), titrated to circulation.
   • Intubate gently if needed, and avoid central lines that reach the right atrium.
   • Transfer to a centre with extracorporeal rewarming for any patient with instability or temperature under 28 degrees Celsius.
   • Active internal rewarming with pleural, peritoneal or bladder lavage using fluid at 40 to 42 degrees Celsius when extracorporeal methods are not available.
   • Aim for a rewarming rate of 0.5 to 2 degrees Celsius an hour with non-invasive methods.
4. Cardiac arrest:
   • Start CPR with continuous compressions and ventilation, and use a mechanical device during transport.
   • Ventricular fibrillation or tachycardia: up to 3 shocks. If there is no response, delay further shocks until core temperature is over 30 degrees Celsius.
   • Withhold epinephrine and other drugs while core temperature is under 30 degrees Celsius. Between 30 and 35 degrees Celsius give epinephrine 1 mg IV at intervals of 6 to 10 minutes (double the normal interval).
   • Extracorporeal membrane oxygenation or cardiopulmonary bypass is the preferred rewarming method for arrest.
   • Continue resuscitation until core temperature is at least 32 degrees Celsius. Admission potassium over 12 mmol/L indicates futility.
5. Metabolic care: glucose 50% 25 to 50 mL IV for hypoglycemia, thiamine 200 mg IV for suspected alcohol use, hydrocortisone 100 mg IV when adrenal insufficiency is possible, and levothyroxine 200 micrograms IV for suspected myxedema coma.
6. Infection: piperacillin-tazobactam 4.5 g IV every 6 hours when sepsis is suspected.
7. Rewarming complications: monitor potassium (it falls on rewarming), treat hypotension with warmed fluids, monitor for compartment syndrome and pancreatitis, and keep the patient in intensive care.
8. Frostbite: rapid rewarming of affected parts in water at 37 to 39 degrees Celsius for 15 to 30 minutes, ibuprofen 400 mg orally every 8 hours with food, and specialist review for iloprost.

Prevention: layered clothing, avoiding alcohol in the cold, heating for vulnerable older people, and early rescue after immersion. Follow-up for neurological and frostbite sequelae.