Monitoring Oxygen Saturation Levels in the Early Recovery Phase of General Anaesthesia

Abstract

There has been interest in the detection of postoperative hypoxaemia for nearly 40 years. Clinical observation of cyanosis is a rather gross method of detecting hypoxaemia. For patients with a normal or relatively normal level of haemoglobin to appear cyanotic, blood oxygen tensions have to be at or below the range of 48–56 mmHg. This equates with a haemoblobin saturation of around 80%. This point lies on the beginning of the steepest part of the oxygen/haemoglobin dissociation curve and once overt signs of hypoxaemia are apparent, any further fall in the arterial oxygen tension will lead not only to a dramatic decline in the oxygen carried by the blood but also to a reduction in the terminal blood/tissue gradient that determines oxygen entry into the cells.