Indexed Delivery of Oxygen Predicts In-hospital Mortality and Morbidity in Reoperative Adult Cardiac Surgery Patients: A Retrospective Cohort Study

Objectives: To evaluate the association between intraoperative indexed oxygen delivery (DO₂i) during cardiopulmonary bypass (CPB) and postoperative outcomes in patients undergoing reoperative cardiac surgery. Design: Retrospective cohort study. Setting: A tertiary academic cardiac surgery center. Participants: A total of 343 patients who underwent reoperative cardiac procedures between January 2011 and January 2021. Interventions: Patients were stratified by the median DO₂i threshold predictive of in-hospital mortality, identified using Youden's Index. Measurements and Main Results: Median DO₂i was 300.8 ± 52.3 mL/min/m². In-hospital mortality was 14.6%. A median DO₂i <289.4 mL/min/m² predicted mortality (area under the curve = 0.756, sensitivity 78%, specificity 64%). Multivariable analysis showed that each 1 mL/min/m² decrease in DO₂i increased mortality risk by 1.6% (odds ratio [OR] 1.016, 95% confidence interval [CI] 1.007-1.024). DO₂i below the threshold was associated with a fourfold higher mortality risk (OR 4.12, 95% CI 1.18-9.49). After inverse-probability-of-treatment weighting, patients with low DO₂i had higher mortality (21.6% v 6.6%; p < 0.001), acute kidney injury (p = 0.042), cardiac morbidity (51.1% v 38.5%; p < 0.001), and prolonged ventilation (14.3% v 8.3%; p = 0.015). Conclusions: Reduced intraoperative DO₂i was independently associated with increased risk of mortality and major morbidity following reoperative cardiac surgery. Incorporating continuous DO₂i monitoring and optimization into CPB management may improve outcomes in this high-risk population.