Body build and preoperative arterial oxygen tensions.

Arterial oxygen tensions were determined in 35 supine unpremedicated surgical patients. Correlations were sought for age, weight, and weight/height, and Pao2. A definite, clear cut linear reduction of Po2 with age was found but not for weight alone. A relationship with weight/height ratio was found. If the weight/height related reduction in FRC following induction is added to that, two potential factors can be seen to contribute to intra-operative hypoxaemia. In a further 20 patients who received phenobarbitone premedication only, arterial oxygen tensions were found to be above the predicted line for their age. This is taken as evidence against respiratory depression due to premedication with barbiturates.