Neutrophil activation is correlated with acute kidney injury after cardiac surgery under cardiopulmonary bypass

[Objective] To explore the relationship between neutrophil activation under cardiopulmonary bypass (CPB) and the incidence of cardiac surgery-associated acute kidney injury (CS-AKI). [Methods] This prospective cohort study enrolled adult patients who scheduled for cardiac surgery under CPB at West China Hospital between May 1, 2022 and March 31, 2023. The primary outcome was acute kidney injury (AKI). Blood samples (5 mL) were obtained from the central vein before surgery, at rewarming, at the end of CPB, and 24 hours after surgery. Neutrophils were labeled with CD11b, CD54 and other markers. To assess the effect of neutrophils activation on AKI, propensity score matching (PSM) was employed to equilibrate covariates between the groups. [Results] A total of 120 patients included into the study, and 17 (14.2%) developed AKI. Both CD11b+ and CD54+ neutrophils significantly increased during the rewarming phase and the increases were kept until 24 hours after surgery. During rewarming, the numbers of CD11b+ neutrophils were significantly higher in AKI compared to non-AKI (4.71×109/L vs 3.31×109/L, Z=-2.14, P<0.05). Similarly, the CD54+ neutrophils counts were also significantly higher in AKI than in non-AKI before surgery (2.75×109/L vs 1.79×109/L, Z=-2.99, P<0.05), during rewarming (3.12×109/L vs 1.62×109/L, Z=-4.34, P<0.05), and at the end of CPB (4.28×109/L vs 2.14×109/L, Z=-3.91, P<0.05). An analysis of 32 matched patients (16 in each group) revealed that CD11b+ and CD54+ neutrophil levels of AKI were 1.74 folds (4.83×109/L vs 2.77×109/L, Z=-2.72, P<0.05) and 2.34 folds (3.32×109/L vs 1.42×109/L, Z=-4.12, P<0.05), respectively, of non-AKI at rewarming phase. [Conclusion] Neutrophils are activated during CPB, and they can be identified by CD11b/CD54 markers. The activated neutrophils of AKI patients are approximately 2 folds of non-AKI during the rewarming phase, with disparity reached peak between groups during rewarming. These findings suggest the removal of 50% of activated neutrophils during the rewarming phase may be effective to reduce the risk of AKI.