Pulmonary dysfunction is a known complication of cardiac surgery. High fractions of inspired oxygen (FiO₂) during the critical pulmonary reperfusion phase of cardiopulmonary bypass (CPB) weaning is a proposed pathophysiological contributor yet remains sparsely investigated.

Predefined, exploratory substudy of the GLORIOUS randomized, clinical trial.

Single tertiary center with cardiothoracic surgery expertise.

Adult patients undergoing nonemergent coronary artery bypass grafting (CABG) and/or surgical aortic valve replacement.

Restrictive (FiO₂ 50%) versus liberal (FiO₂ 100%) oxygenation during CPB and the first hour after weaning or until patient transfer from the operating table. Pulmonary function (forced expired volume in 1 second [FEV₁], forced vital capacity [FVC], FEV₁/FVC, and diffusion capacity of carbon monoxide) was measured preoperatively and 3 months postoperatively.

A total of 878 patients were included in the study. Postoperatively, at the 3-month mark, pulmonary function declined across all parameters in the overall study population (median FEV₁ [% predicted] by 8.3 percentage points [95% CI 6.6 to 8.3], FVC [% predicted] by 6.1 percentage points [95% CI 5.2 to 7.0], FEV₁/FVC by 1.6 percentage points [95% CI 1.0 to 2.1], and diffusion capacity of carbon monoxide [% predicted corrected] by 7.7 percentage points [95% CI 6.2 to 9.1], all p< 0.001). However, no significant between-group differences in decline were observed (all p > 0.3), including in subgroup analyses.

While pulmonary function exhibited a mild-to-moderate decline 3 months after cardiac surgery, a restrictive (FiO₂ 50%) oxygenation strategy during CPB did not attenuate this decline compared with a liberal (FiO₂ 100%) strategy. Findings are hypothesis-generating.