BACKGROUND: The optimal fluid management strategy for patients undergoing on-pump cardiac surgery was controversial regarding the fluid types. This study aimed to compare the impact of hydroxyethyl starch (HES) and succinylated gelatin on postoperative acute kidney injury (AKI). METHODS: This is a single-center, retrospective study. Adult patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) between 2018 and 2022 were included. Patients were grouped by the priming solution used: HES (the HES group) or succinylated gelatin (the gelatin group). The primary outcome was the incidence of postoperative AKI, and secondary outcomes included continuous renal replacement therapy (CRRT), blood transfusions, myocardial infarction, lung infection, cerebrovascular events, chest drainage, duration of mechanical ventilation, intensive care unit (ICU) stay, in-hospital mortality, and associated costs. Propensity score matching (PSM) was conducted to adjust for characteristic differences between the two groups. RESULTS: A total of 14,443 patients were included. After 1:1 propensity score matching, 1880 pairs were analyzed. Baseline characteristics were comparable between the matched groups. The incidence of AKI was significantly lower in the gelatin group (3.0% vs. 5.1%, P = 0.001). No significant differences were found in transfusion requirements after score-matching. The use of HES was independently associated with increased odds of AKI (adjusted odds ratio [aOR], 1.785
95% CI, 1.262-2.526
P = 0.001). The effects of HES use on the occurrence of postoperative AKI were greater in elderly and female patients. CONCLUSION: The use of HES as a priming solution in on-pump cardiac surgery was associated with an increased risk of postoperative AKI compared to gelatin, although it did not affect transfusion requirements. These findings highlight the importance of considering the priming solution type in fluid management during cardiac surgery.