Inspired oxygen fraction after cardiopulmonary bypass: effects on pulmonary function with regard to endothelin-1 concentrations and venous admixture

Twenty consecutive patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) were allocated at random to group I (n=10, high inspired oxyg en fraction (FIO2) after CPB), or group 2 (n= 10, moderate FIO2 after CPB). The effects of each FIO2 on arterial and mixed venous concentrations of en dothelin-1 (ET-1) and its precursor, Big ET-1, were measured. Venous admixt ure was calculated to assess the efficiency of pulmonary gas exchange. Pati ents whose lungs had been ventilated with a FIO2 Of 1.0 (exposure time 70 m in) after weaning from the CPB machine had significantly greater arterial a nd mixed venous Big ET-1 concentrations and venous admixture than patients whose lungs were ventilated with a FIO2 Of 0.35. In contrast, ET-1 concentr ations in the two groups were not significantly different. A reduction of F IO2 from 1.0 to 0.6 reduced venous admixture without lowering endothelial p eptide concentrations. On the first postoperative day all peptide concentra tions were similar in the two groups, whereas venous admixture remained non -significantly higher in group I. A short period of high FIO2 immediately a fter CPB increases endothelin concentrations and pulmonary venous admixture .