Background: In septic patients, the interplay between macro-microcirculatory dysfunction and acute kidney injury (AKI) remains elusive. This study aimed to explore the association between hemodynamics and endothelial damage in sepsis associated AKI (SA-AKI) by evaluating the combined predictive value of renal resistive index (RRI) and plasma syndecan-1.

Methods: This prospective observational study enrolled 80 septic patients admitted to the intensive care unit of a tertiary hospital from May to December 2024. AKI was diagnosed according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. Plasma syndecan-1 levels were measured at admission and RRI was assessed within 24 hours of ICU admission. Diagnostic performance was evaluated using receiver operating characteristic (ROC) curve analysis by calculating the area under the curve (AUC). Univariate and multivariate logistic regression models were applied to identify independent risk factors of SA-AKI. Predictive models were constructed to validate the effectiveness.

Results: Among 80 septic patients, 41 (51.25%) developed AKI. Syndecan-1 levels were significantly higher in the AKI group [109.95 (73.67,221.40) vs. 73.67（54.59,109.95）ng/ml, P =0.007], and RRI values were markedly elevated (0.69±0.08 vs. 0.60±0.06, P <0.001) compared to non-AKI patients. Univariate analysis revealed syndecan-1 (OR=2.68, 95%CI 1.29-5.59) and RRI (OR=1.18, 95%CI 1.09-1.28) as predictors of AKI. In multivariate models adjusted for confounders, both plasma syndecan-1 (OR=3.57, 95%CI 1.01-12.64, P =0.048) and RRI (OR=1.19, 95% CI 1.07-1.33, P =0.002) retained significance. The Predictive Model using a combination of plasma syndecan-1 and RRI achieved superior diagnostic performance (AUC 0.859, sensitivity 87.8%, specificity 92.3%).

Conclusions: In patients with SA-AKI, elevated plasma syndecan-1 and RRI were identified as independent risk factors for SA-AKI. The combination of syndecan-1 and RRI can serve as synergistic biomarkers for prediction of SA-AKI.