Although hyperthermic perfusion (arterial outlet temperature >37°C) during cardiopulmonary bypass (CPB) is associated with acute kidney injury (AKI), the impact of body temperature at the time of separation from CPB (CPB separation temperature) remains unclear. This study evaluated this association in adult patients undergoing cardiac surgery.

A retrospective observational study.

University hospital.

A total of 261 adults who underwent cardiac surgery with CPB between January 2022 and February 2024.

None.

Univariate analyses assessed perioperative variables associated with AKI, followed by multivariate logistic regression to identify independent risk factors. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal CPB separation temperature cutoff. Patients were then stratified, and propensity score matching was applied to compare AKI incidence. Multivariate analysis identified higher body mass index (odds ratio [OR], 1.13; p = 0.009), lower baseline hematocrit (OR, 0.93; p = 0.031), higher baseline serum creatinine (OR, 1.14; p = 0.006), longer CPB time (OR, 1.13; p < 0.001), and higher CPB separation temperature (OR, 1.13; p = 0.002) as independent risk factors for AKI. ROC analysis identified 36.2°C as the optimal cutoff. After matching, patients with CPB separation temperatures ≥36.2°C had a significantly higher incidence of AKI than those with temperatures <36.2°C (30.9% v 14.8%, p = 0.014).

Higher CPB separation temperature was independently associated with AKI. Given the small absolute temperature differences, these findings should be interpreted cautiously and may reflect cumulative thermal exposure during rewarming rather than a direct temperature effect.