Correlation between rewarming rate during cardiopulmonary bypass and postoperative acute kidney injury : a retrospective analysis

Abstract Objective : To investigate the correlation between the rewarming rate during cardiopulmonary bypass (CPB) and the incidence of acute kidney injury (AKI) following open heart surgery. Methods : Clinical data from 348 patients who underwent open heart surgery with CPB at the Department of Cardiac and Vascular Surgery, Nanjing Hospital Affiliated to Nanjing Medical University, between January 2020 and December 2023 were retrospectively analyzed. Patients were divided into slow rewarming (≤ 0.09 °C/min) and rapid rewarming (> 0.09 °C/min) groups based on the rewarming rate during CPB. The primary endpoint was the incidence and severity of AKI within 7 days postoperatively. Preoperative baseline characteristics, intraoperative variables, and postoperative outcomes were collected and compared between the two groups. Univariate analysis and multivariate logistic regression were performed to identify independent risk factors for postoperative AKI. A nomogram for predicting postoperative AKI risk was subsequently developed. Model discrimination was assessed using receiver operating characteristic (ROC) curves, calibration was evaluated via the Hosmer–Lemeshow test and calibration plots, and clinical net benefit was examined using decision curve analysis (DCA). Results :A total of 348 patients were included, of whom 58 developed postoperative AKI, yielding an incidence of 16.7%. Compared with the slow rewarming group, the rapid rewarming group had a significantly higher incidence of AKI (23.1% vs. 10.8%, P<0.01) and more severe AKI clinical stages. Multivariate logistic regression revealed that rapid rewarming rate (OR=2.15, 95% CI:1.52–3.04), prolonged CPB time (per 10‑minute increase, OR=1.18, 95% CI:1.05–1.33), decreased preoperative estimated glomerular filtration rate (per 10 mL/min/1.73 m² decrease, OR = 1.32, 95% CI: 1.12–1.56), and increased intraoperative red blood cell transfusion (per 1‑unit increase, OR=1.09, 95% CI:1.02–1.17) were independent risk factors for postoperative AKI. Conclusion :Rapid rewarming during CPB is an independent risk factor for AKI after cardiac surgery. The risk prediction model constructed from key indicators can effectively identify patients at high risk for postoperative AKI and enable early recognition of such patients.