Influence of varying inspired oxygen tensions on the pulmonary venous admixture (shunt) of mechanically ventilated patients.

Pulmonary venous admixture (shunt) was measured in 10 mechanically ventilated patients with respiratory failure at varying oxygen tensions. All patients manifested a drop in pulmonary shunt as FIO2 was increased from 0.21 to 0.4. Further increase in FIO2 led to a gradual increase in the calculated venous admixture. The clinical significance of the conventional measurements of pulmonary shunt at FIO2 = 1.0 is questionable because of the marked effect of FIO2 on pulmonary shunt. Consequently, shunt measurements should be performed with the clinically useful FIO2.