Non‑traumatic cardiac arrest, or sudden cardiac arrest, is caused by a loss of heart function. The heart stops pumping blood around the body, reducing the blood flow to the brain which may lead to unconsciousness. If blood flow and oxygen are not restored, brain damage and eventually death will occur.
In the UK, the overall incidence of adult in‑hospital cardiac arrest has been estimated at 1.6 per 1000 hospital admissions with an overall unadjusted survival to hospital discharge of 18.4% (Nolan et al. 2014). Out‑of‑hospital cardiac arrest affects approximately 60,000 people in the UK each year (Malhotra and Rakhit 2013), with an estimated survival to discharge rate of 2.2 to12% (Perkins and Cooke 2012). Non‑modifiable risk factors for sudden cardiac arrest include coronary heart disease, a family history of coronary heart disease, age (incidence increases with age) and sex (men are at higher risk of sudden cardiac arrest). Modifiable risk factors include smoking, obesity, diabetes, a sedentary lifestyle, increased low‑density lipoprotein cholesterol levels and hypertension (Zipes et al. 2006). Heart conditions such as coronary heart disease, heart attack, cardiomyopathy, valvular heart disease, congenital heart disease and electrical problems in the heart (such as Brugada syndrome and long QT syndrome) can lead to sudden cardiac arrest. Common non‑cardiac causes of cardiac arrest include trauma, non‑traumatic bleeding, intoxication, near drowning and pulmonary embolism (Kuisma and Alaspää 1997).
Cardiopulmonary resuscitation (CPR) is carried out when a person has a cardiac arrest. In manual CPR, 1 or more rescuers manually compress the person's chest and give rescue breaths. The purpose of CPR is to help the blood and oxygen to keep circulating in the body after the heart has stopped pumping. Rescuer fatigue can reduce the effectiveness of manual chest compressions. Although fatigue may not directly affect chest compression rate or rescue breath volume, the proportion of correctly delivered chest compressions has been shown to decrease from 52% in minute 1 to 39% in minute 5 (McDonald et al. 2013). There should be as little delay as possible during the changeover of rescuers, and chest compressions should not be interrupted; even short interruptions can result in a poorer neurological outcome or reduced chance of survival (Resuscitation Council UK 2010).