Preoperative and intraoperative risk factors for impaired pulmonary oxygenation after cardiopulmonary bypass: a single-center retrospective analysis

Postoperative pulmonary dysfunction is a frequent complication after cardiopulmonary bypass (CPB). Identifying preoperative and intraoperative risk factors for impaired oxygenation is essential for perioperative optimization. A retrospective analysis was conducted on 202 patients who underwent open-heart surgery with CPB at Kumamoto University Hospital between June 2022 and October 2024. Patients were categorized into two groups on the basis of the partial pressure of oxygen (PaO2)/ Fraction of Inspired Oxygen (FiO₂) ratio (P/F ratio) from arterial blood gas analysis under FiO₂ 1.0 at intensive care unit (ICU) admission: impaired oxygenation (P/F < 300) and normal oxygenation (P/F ≥ 300). Multivariate logistic regression was used to identify risk factors for impaired pulmonary oxygenation. Of the 202 patients, 53 (26%) developed impaired oxygenation. Multivariate analysis revealed high preoperative body mass index (BMI), a history of hypertension, and an elevated preoperative respiratory index (RI) as independent predictors. The model showed good discrimination (Area Under the Curve (AUC) = 0.746, 95% CI: 0.669–0.823) and calibration. Preoperative RI, BMI, and hypertension are significant predictors of impaired oxygenation after CPB. RI, a readily accessible metric derived from arterial blood gas analysis, may be integrated into routine preoperative assessments to identify high-risk patients and guide tailored lung-protective strategies. The study was approved by the Ethics Committee of Kumamoto University Hospital (Approval No. 3040). The approval date is August 30, 2024.