25th July 2023

Hypothermia

Overview

Hypothermia is defined as a core body temperature <5 degrees Celsius. Low-reading thermometers, preferably oesophageal, are required as tympanic thermometers are unreliable in very low temperature states. It can be classified as primary or secondary.

Primary hypothermia is due to environmental exposure with no underlying medical condition that can cause thermodysregulation. Examples include trauma patients, whereby hypothermia is part of the lethal triad, coagulopathy, acidosis, and perioperative hypothermia, which may be deliberate or accidental.

Secondary hypothermia can arise from decreased heat production (hypopituitarism, hypothyroidism, severe malnutrition, hypoglycemia, hypoadrenalism), increased heat loss (burns, erythroderma, vasodilation due to toxic substances), impaired thermoregulation (Parkinson’s disease, multiple sclerosis, pancreatitis, cerebrovascular accident, prolonged cardiac arrest), drugs (beta blockers, neuroleptics, general anaesthetic agents) and other substances (ethanol, sedatives, hypnotics).

Risk factors include elderly patients, cognitive impairment, malnourished and multiple comorbidities.

Severity

• Mild: 32-35 degrees Celsius (lethargy, confusion, shivering, loss of fine motor coordination).
• Moderate: 28-32 degrees Celsius (delirium, slowed reflexes).
• Severe: <28 degrees Celsius (very cold skin, unresponsive, coma, difficulty breathing, arrhythmia).

Investigations

• Coagulation profile: disseminated intravascular coagulation may occur.
• ECG changes include bradycardia, ‘J’ wave (Osborn wave: small hump at the end of QRS complex), first degree heart block, long QT interval, atrial and ventricular arrhythmias.
• CXR: aspiration pneumonia, pulmonary oedema.

Management

The main principles are stabilising airway breathing and circulation, rewarming (warmed and humidified oxygen, heated IV saline, warm blankets, heat lamps), careful monitoring (ideally in an acute care setting) and treatment of complications such as cardiac arrhythmias. Assess and treat any underlying associated disorders, such as drug ingestion. Complications include multiorgan failure, metabolic acidosis, electrolyte imbalances and lethal arrhythmias. Overall mortality increases with the severity of hypothermia.