Participants and randomization
Adult patients (aged ≥ 19 years) scheduled for elective OPCAB were included in this study. Exclusion criteria comprised robot-assisted surgery, minimally invasive direct coronary artery bypass grafting, concomitant major surgery, primary pulmonary morbidity requiring oxygen therapy before surgery, mechanical ventilation (MV) prior to surgery, preoperative mechanical circulatory support (e.g., extracorporeal membrane oxygenation, intra-aortic balloon pump), and refusal to participate.In this study, month-by-month cluster randomization was performed; participants were assigned to receive either 30% or 80% oxygen (the 30% and 80% oxygen groups, respectively) during OPCAB, based on the month in which the surgery was performed. As FiO