Pulmonary function after prolonged mechanical ventilation with high concentrations of oxygen.

The mortality and morbidity resulting from mechanical ventilation with high concentrations of inspired oxygen has been investigated in two groups of patients. Ninety-one patients requiring mechanical ventilation for pulmonary disease included six (group 1) in whom death was attributed directly to respiratory failure but only three in whom oxygen toxicity might have been relevant. Review of the clinical and postmortem findings suggests that oxygen was probably not a contributory factor in two of these three. A second group of 16 patients who survived prolonged mechanical ventilation with oxygen in excess of 40% (average 14.5 days) included five who had been ventilated with 75% oxygen or more for an average of 38 hours. Lung function studies carried out on this second group of patients approximately one year later demonstrated that all but three had significant defects in either ventilation, gas transfer, or both. Oxygen toxicity was thought to be a likely cause in one and a possible contributory factor in three more. It is suggested that the adverse effects of oxygen on the alveolar epithelium are rarely of practical importance in hypoxaemic patients requiring mechanical ventilation but disturbance to the pulmonary defences against infection may well be of greater importance. The fear of inducing oxygen toxicity should not be allowed to interfere with the relief of arterial hypoxaemia in ventilated patients.