Abstract

In 18 patients who were undergoing upper laparotomies the alveolo-arterial oxygen difference and right-to-left shunt were measured before the operation, on the first post-operative day, and in some cases also later in the post-operative period. The arterial oxygen tension was found to be considerably reduced post-operatively. The right-to-left shunt estimated by the hydrogen isotope technique was moderately increased in most instances, but the increase was far from large enough to account for the observed hypoxaemia. It is concluded that uneven distribution of ventilation relative to perfusion is the main cause of post-operative hypoxaemia, whereas veno-arterial shunt through atelectatic areas is of minor importance.