After a minute, the PaO2 will have fallen to zero. In the case of ventricular fibrillation, myocardial metabolism continues at an approximately normal rate, exhausting oxygen and high energy phosphate supplies. Acidosis then arises as the result of increased anaerobic metabolism and the accumulation of carbon dioxide in the tissues. The degree of acidosis developing in the brain, even with basic life support, will threaten tissue survival within 5 - 6 minutes. Also, in the heart, even with the restoration of a perfusing rhythm, acidosis depresses contractility and there is a higher risk of further arrhythmias.
Cardiovascular collapse prompts a massive stress response.
Catecholamines are released in large amounts, together with adrenal corticosteroids, anti-diuretic hormone and other hormonal responses. The possible detrimental effects of these changes include hyperglycaemia, hypokalaemia, increased lactate levels and a tendency towards further arrhythmias. There are many causes of cardiac arrest. In the developed world most are related to ischaemic heart disease. Table 1 lists other common causes.