To analyze the dynamic lactate trajectory characteristics within 72 hours after ICU admission in patients with acute kidney injury (AKI) following cardiac surgery, and to explore their association with clinical outcomes.

A retrospective cohort study was conducted using the Medical Information Mart for Intensive Care-Ⅳ database (2008-2022), enrolling 1 297 postoperative AKI patients. Group-based trajectory modeling (GBTM) was employed to identify lactate trajectory patterns. Multivariable Cox proportional hazards regression and logistic regression models were used to analyze the association between trajectory groups and clinical outcomes including in-hospital mortality and major adverse kidney events at 30 days (MAKE30). Predictive performance was evaluated using receiver operating characteristic (ROC) curves.

Three distinct lactate trajectories were identified: a low-level stable group (n = 743), a partial clearance group (n = 452), and a rebound hyperlactate group (n = 102). Compared with the low-level stable group, both the partial clearance group and the rebound hyperlactate group showed significantly higher rates of in-hospital mortality, MAKE30 incidence, mechanical ventilation lasting ≥ 2 days, and ICU stay of ≥ 7 days (all P < 0.05). Multivariate Cox regression analysis showed that the risk of in-hospital mortality in the rebound hyperlactate group was 12.40 times of the low-level stable group [adjusted hazard ratio = 12.40, 95% confidence interval (CI) (6.04, 25.46), P < 0.001]. Multivariate logistic regression analysis indicated that the risk of MAKE30 in the rebound hyperlactate group was 4.01 times of the low-level stable group [adjusted odds ratio = 4.01, 95%CI (2.19, 7.35), P < 0.001]. The lactate trajectory model demonstrated an area under the curve (AUC) of 0.869 for predicting in-hospital mortality, which was superior to that of a single lactate measurement (AUC = 0.835, P = 0.017).

Early dynamic lactate trajectories represent strong independent predictors of in-hospital mortality and other adverse outcomes in AKI patients with post-cardiac surgery. Early monitoring of lactate changes holds significant clinical value for identifying their adverse outcomes.