Effect of positive end-expiratory pressure on intrapulmonary shunt at different levels of fractional inspired oxygen

Abstract

In 10 patients undergoing ventilation, venous admixture was measured at different values of positive end-expiratory pressure (PEEP). The measurements were performed at the level of fractional inspired oxygen (F(IO)2) at which each patient was ventilated, and at F(IO)2=1. In patients ventilated at F(IO)2 between 0.21 and 0.3 venous admixture was not modified by PEEP, while in patients ventilated with F(IO)2 between 0.4 and 0.6, venous admixture decreased significantly (p<0.01). With F(IO)2=1, increased PEEP produced a reduction in venous admixture in all cases (p <0.05). These observations suggest that in patients similar to ours, PEEP does not reduce venous admixture at low levels of F(IO)2 (0.21-0.3), and the observed reduction with PEEP at F(IO)2=1 may be misinterpreted.