Human Oxygenation by Air during Anaesthesia: the Relation of Ventilatory Volume and Arterial Oxygen Saturation.

Ventilation and arterial oxygen saturation have been measured in 18 patients during anaesthesia with ether or halothane carried in air. All patients were ventilated artificially with a Jefferson ventilator at a frequency of 16 breaths per minute and variable tidal volume. Ventilation has been expressed as a percentage of Radford's standard, Nunn's standard and the patient's pre-operative resting ventilation. 110 per cent of both Radford's and Nunn's standard ventilation and 98 per cent of the patient's own resting ventilation were found to yield a mean arterial oxygen saturation of 95 per cent. Below this the mean saturation fell sharply with decreasing ventilation. Cyanosis was never visible even with a saturation as low as 70 per cent, although desaturation was evident in the colour of the arterial blood when sampled.