Changes in Venous Admixture with Alterations of Inspired Oxygen Concentration

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Abstract
To assess the change in venous admixture during breathing of 100% O2 (FIO2 1.0), shunt fraction (.ovrhdot.Qs/.ovrhdot.Qt) was calculated at a maintenance FIO2(FIO2m: 0.27-0.70) and at FIO2 1.0 in 40 studies of 34 patients with acute respiratory failure. At FIO2 1.0, .ovrhdot.Qs/.ovrhdot.Qt increased in 26 studies, but did not increase in 14 studies. Patients in whom .ovrhdot.Qs/.ovrhdot.Qt increased during breathing O2 had mild respiratory failure, as indicated by low .ovrhdot.Qs/.ovrhdot.Qt values at FIO2m and a low incidence of diffuse parenchymal infiltrates on chest roentgenograms. All patients who recently had cardiovascular surgical procedures were in this group. Respiratory failure was more severe in those whom .ovrhdot.Qs/.ovrhdot.Qt decreased with O2, as indicated by high .ovrhdot.Qs/.ovrhdot.Qt values at FIO2m, evidence of diffuse pulmonary disease by roentgenography and signs of adult respiratory distress syndrome. Changes in .ovrhdot.Qs/.ovrhdot.Qt in response to FIO2 1.0 in acute respiratory failure are related to the severity of respiratory insufficiency.