Medical care in hypothermia

Before a severely hypothermic patient reaches hospital, the treatment priority is optimal cardiopulmonary resuscitation (CPR); neither drugs nor defibrillation are likely to be effective in advanced life support protocols until the patient’s core body temperature reaches 30°C.

Note: Optimal CPR is the most useful treatment for a severely hypothermic patient before rewarming has occurred.

Specific considerations for advanced life support in hypothermic patients includeDow, 2019:

  • taking 1 minute to assess for a carotid pulse and signs of breathing before starting chest compressions; compressions can cause rhythm deterioration and loss of perfusion if performed on a hypothermic person who has even minimal cardiac output
  • restricting defibrillation of shockable rhythms to one attempt if the person’s core body temperature is below 30°C; standard algorithms for defibrillation apply once their core body temperature is above 30°C
  • restricting the use of adrenaline (epinephrine) if the patient’s core body temperature is below 30°C, because of reduced drug metabolism and increased protein binding
  • ensuring normocapnia (if it is feasible to monitor) by controlling the rate of ventilation, to minimise cerebral vasoconstriction
  • reducing the dosage and increasing the intervals between doses of anaesthetics and paralysing agents, if used
  • considering transport to a facility with extracorporeal support capability (may be required if core body temperature is below 28°C or the patient has haemodynamic instability).

Most cardiac arrhythmias associated with hypothermia resolve spontaneously with gradual rewarming at a rate of 1 to 2ºC per hour. Avoid rapid rewarming of peripheries because it can cause further core cooling (afterdrop), increasing the risk of arrhythmias, hypotension and electrolyte disturbances; see Rewarming of a person with hypothermia. Electrolyte concentrations can change rapidly and unpredictably with rewarming, and should be monitored closely. Any electrolyte disturbances should be corrected.

If resuscitation and rewarming does not result in an increase in core body temperature, seek specialist advice before stopping resuscitation. There are well-documented cases of complete recovery from very prolonged hypothermic cardiac arrest (lasting hours), and prolonged resuscitation attempts are warranted. The saying ‘No one is dead until they are warm and dead’ acknowledges this. An automated compression device (a ‘thumper’) may be used.

Note: ‘No-one is dead until they are warm and dead.’

If an unconscious person with hypothermia is breathing, or has a pulse but breathing is difficult to assess:

  • deliver supplemental oxygen if available, especially above 2500 metres elevation, because altitude-related hypoxaemia may also be presentDow, 2019
  • ventilate (eg with bag and mask) if mask oxygen alone does not improve hypoxaemia; chest inflation may be difficult due to chest wall stiffness resulting from cold.

A hypothermic patient may require intubation. Intubation is considered safe if it is performed gently, and if the benefits outweigh concerns about precipitating ventricular fibrillation.

If a hypothermic patient is hypoglycaemic, administer glucose according to local protocols.

If vascular access is difficult, intraosseous administration can be considered to deliver drugs.

Hypothermic patients typically have intravascular volume depletion, and fluid resuscitation is required. Sodium chloride 0.9% solution warmed to approximately 40 to 42ºC is the preferred fluid, and should be administered slowly as the patient rewarms and their intravascular space expands. A relative level of hypotension can be normal in hypothermia—it is important to be aware of this and to regularly reassess fluid requirements as the patient rewarms, to avoid intravascular fluid overload.