Cardiac arrest is when normal blood circulation suddenly stops because the heart fails to contract effectively. The underlying abnormal cardiac rhythms most commonly associated with cardiac arrest are:
ventricular fibrillation (VF)
asystole
pulseless electrical activity
pulseless ventricular tachycardia (VT).
Cardiac arrest leads to loss of consciousness, respiratory failure and, ultimately, death.
Treatment for cardiac arrest includes immediate cardiopulmonary resuscitation to restore the circulation and prevent subsequent brain injury. Defibrillation may be used to treat VF and pulseless VT rhythms. Standard care may also include mechanical ventilation and drugs such as adrenaline and amiodarone. Resuscitation Council UK's 2021 resuscitation guidelines contain guidance on basic and advanced life support.
After cardiac arrest, people in a coma who have a return of spontaneous circulation (ROSC) can have their core body temperature actively controlled. This is done to:
prevent fever (by maintaining a core temperature between 36.5°C and 37.5°C), or
induce therapeutic hypothermia (by cooling to a core temperature typically between 32°C and 36°C).
The aim is to reduce brain injury and improve neurological outcomes. The exact mechanism by which cooling may protect against brain injury is unclear. Possible mechanisms include reductions in metabolic demand, release of excitatory neurotransmitters and inflammation after ischaemia.
Temperature control is done using either:
surface techniques (for example, heat exchange cooling pads, cooling blankets and ice packs), or
internal techniques (for example, an endovascular cooling device).
Core body temperature is monitored using a temperature probe (such as a bladder, rectal or nasopharyngeal temperature probe) and is controlled to a preset point determined by the clinician.
If therapeutic hypothermia is induced, controlled rewarming is usually done over several hours. In addition, people who have had cardiac arrest generally have standard critical care measures, and may need intravenous sedation and muscle relaxants, to prevent shivering.