A consecutive series of patients undergoing cardiac surgery for valve replacement was divided into two groups. The first underwent postoperative artificial ventilation using the oxygen-driven Bird ventilator. The inspiratory oxygen concentration was 83%. In the second group a Bird ventilator was also used but with an oxygen concentration of 40%. In the first group the intrapulmonary right-to-left shunt rose to an average of 17% during the first two postoperative daysand in the second group to an average of 9%. The study supports the view that the inspiratory oxygen concentration should only be kept high enough to achieve a normal oxygen saturation of arterial blood
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