Temperature variations during cardiopulmonary bypass (CPB) may significantly contribute to the development and progression of acute kidney injury (AKI) after cardiac surgery. We tested the hypothesis that temperature time-series variables during CPB are associated with AKI after cardiac surgery.

We conducted a retrospective analysis of the data from 2041 patients. The primary outcome of interest in this study was cardiac surgery-associated AKI. By analyzing time-series nasopharyngeal temperature (Tnp) monitored intraoperatively with multiple categories, we obtained indicators reflecting the duration and depth of hypothermia. We used univariate and multivariate logistic regression analyses to identify perioperative factors associated with the outcome and construct a prediction model, which was evaluated in terms of discrimination and calibration.

Mild hypothermia (32–34 °C) was independently associated with a reduced risk of AKI compared to other temperature categories. The proportion of the duration with temperature at 32–34 °C during CPB (CPB_32–34 °C_DurProp) demonstrated the greatest predictive value for AKI compared to other temperature-related characteristics. We found age, preoperative creatinine, history of hypertension, intraoperative blood loss, intraoperative transfusion of allogeneic blood, and the use of left ventricular assist device (LVAD) were risk factors for the development of AKI. In contrast, preoperative hemoglobin, intraoperative urine output, and CPB_32–34 °C_DurProp were protective factors.

The proportion of duration of mild hypothermia (32–34 °C) during CPB was identified as an independent risk factor for AKI after cardiac surgery. A prediction model incorporating this factor demonstrated good predictive performance. This emphasizes the importance of maintaining mild hypothermia during CPB in reducing the risk of AKI in postoperative cardiac surgery patients.