Oxygen therapy after abdominal surgery.

Arterial blood was sampled from 10 patients, on the day after upper abdominal surgery, breathing air, and during oxygen therapy from 24, 28 and 35% venturi masks. PaO2 during breathing each concentration of oxygen correlated with PaO2 during air breathing. The difference between pulmonary end-capillary and arterial oxygen content was used as an index of the impairment of oxygen transfer in the lung. This difference was reduced by oxygen therapy. The response to oxygen therapy did not correspond to predictions based on an iso-shunt lung model. These findings suggest that hypoxaemia in these patients is predominantly caused by ventilation/perfusion mismatching.