Evaluation of arterial oxygenation during anaesthesia.

The clinical or physiological signs of hypoxaemia have limited value during anaesthesia. In the absence of surgical bleeding, the best signs are probably cyanosis and/or bradycardia-although neither is sensitive or specific. A moderate degree of hypoxaemia can be present without clinical signs! In the presence of surgical bleeding, the best sign may be darkening of fresh blood in the surgical field. The only reliable indicators of arterial oxygenation available for routine anaesthesia are the laboratory measurements of PaO2 and SaO2. Unfortunately, these measurements are intermittent and delayed. The modern Hewlett Packard and Biox ear oximeters can provide an immediate and continuous estimate of arterial oxygen saturation in anaesthetized humans. These instruments are extremely useful in clinical practice when the risks of hypoxaemia or hypoxaemic injury are high. Unfortunately, cost precludes their general use. The safety of anaesthesia would no doubt be improved with an inexpensive reliable monitor of arterial oxygenation.