Inverse Association Between Preoperative Cardiac Output and Postoperative Kidney Function in Off-Pump Coronary Artery Bypass Grafting

Background The relationship between cardiac output and kidney function following cardiac surgery remains poorly defined. We aimed to evaluate the association between preoperative cardiac output and postoperative acute kidney injury (AKI) in patients undergoing off-pump coronary artery bypass grafting (CABG), a setting without exposure to cardiopulmonary bypass. Methods This cohort study included 1,949 patients aged ≥ 60 years from the Bottomline-CS trial who underwent elective off-pump CABG. Preoperative cardiac output was measured under standardized resting conditions, 1–2 days prior to surgery. The primary outcome was AKI within the postoperative 7 days, defined according to KDIGO serum creatinine criteria. Propensity score-matched analyses were performed to compare the risk of AKI between patients with low and high baseline cardiac output. Restricted cubic spline models were used to examine the continuous relationship between cardiac output and the risk of AKI. The findings were validated in an external cohort to assess their robustness. Results Overall AKI incidence was 11% (213/1,949). In matched analyses, a preoperative cardiac index (CI) ≥ 3.0 L/min/m² was associated with higher AKI than CI < 3.0 (14.3% vs 9.0%; OR 1.69; 95% CI, 1.15–2.48). A similar association was observed for cardiac output ≥ 5.0 L/min versus < 5.0 (13.3% vs 8.9%; OR 1.56; 95% CI, 1.09–2.23). Spline analyses showed a J-shaped relationship, with rising risk above CI about 3.0 L/min/m² and cardiac output about 5.0 L/min. High-output patients had lower systemic vascular resistance with similar mean arterial pressure. Mediation analyses found no explanatory effect of intraoperative hypotension, vasopressor use, oxygenation deficits, fluid balance, or intraoperative cardiac output change. Findings were supported in an external cohort. Conclusions Higher, not lower, preoperative cardiac output is independently associated with increased risk of postoperative AKI in patients undergoing off-pump CABG.