The nadir oxygen delivery index (DO₂i) during cardiopulmonary bypass (CPB) is reportedly associated with acute kidney injury (AKI) in patients undergoing cardiac surgery. However, there are few reports on the relationship between patient sex and the nadir DO₂i threshold to prevent AKI. The aim of this study was to seek and evaluate the optimal DO₂i threshold differences between males and females to avoid AKI during on-pump cardiac surgery.

We retrospectively analyzed a total of 430 patients who underwent cardiac surgery between March 2017 and February 2023. A receiver operating characteristic analysis and univariable and multivariable regression analyses were performed to evaluate the association between perioperative variables, including the nadir DO₂i and incidence of AKI, in males and females.

The nadir DO₂i was significantly lower (median, 294 [interquartile range (IQR), 272-317] mL/min/m² versus 277 [IQR, 262-295] mL/min/m²; P < .001) and cumulative time below the DO₂i of 270 mL/min/m² was longer (0.3 [IQR, 0-4.2] minutes vs 3.0 [IQR, 0-11.7] minutes; P < .001) in the female patients. However, the incidence rate of AKI was similar in males and females (15.2% [n = 39/256] vs 16.7% [n = 29/174]; P = .68). The best cut-off values of nadir DO₂i for AKI were <301 mL/min/m² (sensitivity, 82.1%; specificity, 39.5%) in males and <273 mL/min/m² (sensitivity, 69.0%; specificity, 61.4%) in females.

The optimal DO₂i to prevent AKI during cardiac surgery differs between males and females. Therefore, CPB management should be adjusted by sex based on the different cut-off values of nadir DO₂i.