Oxygen delivery during cardiopulmonary bypass and postoperative mortality: A retrospective cohort study

BACKGROUND: Oxygen delivery during cardiopulmonary bypass reflects the balance between pump flow, hemoglobin concentration, and arterial oxygenation and is a key determinant of tissue oxygen transport. While inadequate oxygen delivery has been linked to postoperative organ dysfunction, its association with mortality remains unclear. METHODS: We conducted a retrospective cohort study including 4,358 adult patients undergoing cardiac surgery with cardiopulmonary bypass at a tertiary center between 2018 and 2024. Time-weighted average indexed oxygen delivery (DO2i) was calculated from pump flow, arterial oxygen saturation, hemoglobin concentration, and body surface area. The primary outcome was 30-day mortality. Secondary outcomes included postoperative acute kidney injury (AKI), stroke, and intensive care unit (ICU) and hospital length of stay. Associations were evaluated using multivariable regression models adjusted for demographic, clinical, and procedural factors. RESULTS: Lower intraoperative DO2i was associated with higher 30-day mortality. Overall, 75 patients (1.7%) died within 30 days. Each 10 ml · min -1 · m -2 decrease in DO2i was associated with increased odds of mortality (adjusted odds ratio [ORadj] 1.16; 95% CI 1.09-1.23; P < 0.001). The adjusted 30-day mortality was 1.69% (95% CI 1.32-2.05%) at the 25th percentile of DO2i (226.2 ml · min⁻¹ · m⁻²), compared with 0.74% (95% CI 0.41-1.07%) at the 75th percentile (295.6 ml · min⁻¹ · m⁻²). Lower DO2i was also associated with AKI (ORadj 1.05; 95% CI 1.03-1.07; P < 0.001), longer ICU (adjusted incidence rate ratio [IRRadj] 1.02; 95% CI 1.01-1.03; P < 0.001) and hospital length of stay (IRRadj 1.01; 95% CI 1.01-1.02; P < 0.001), but not with stroke (ORadj 1.00; 95% CI 0.95-1.06; P = 0.877). CONCLUSIONS: Patients receiving lower intraoperative DO2i during cardiopulmonary bypass had a higher risk of postoperative mortality, AKI, and prolonged recovery. These findings support the clinical relevance of oxygen delivery during bypass and provide a rationale for future mechanistic and interventional studies.