Early Renal Microcirculatory Perfusion Patterns in Sepsis: Associations with SA-AKI Trajectories in the Emergency Department

Background/Objectives: Sepsis-associated acute kidney injury (SA-AKI) involves complex disturbances in renal microcirculation that may precede overt biochemical evidence of renal dysfunction. This study aimed to characterize early renal perfusion patterns during the emergency department (ED) phase of sepsis, as assessed by the renal resistive index (RRI) and the semiquantitative power Doppler ultrasonography score (SPDUS), and to explore their relationship with subsequent SA-AKI trajectories. Methods: In this prospective observational study, adult ED patients who met the Sepsis-3 criteria were enrolled. Renal perfusion was evaluated using the RRI and SPDUS at ED admission and repeated at the fourth hour. SA-AKI was classified as transient or non-transient based on renal recovery patterns. Trajectory comparisons were performed to identify early physiological differences. Receiver operating characteristic (ROC) analyses were conducted for descriptive and exploratory assessment of perfusion pattern separation between injury trajectories. Results: Fifty-four patients were included, with 35 classified as transient and 19 as non-transient SA-AKI. Patients with non-transient injury exhibited lower baseline SPDUS0 grades and higher RRI0 values compared with those with transient injury. These differences were evident at ED presentation, prior to the initiation of advanced organ support, and persisted at the fourth hour, with the non-transient group continuing to show lower SPDUS4 and higher RRI4 values than the transient group. These findings reflect distinct early renal microcirculatory perfusion patterns across SA-AKI trajectories. Sensitivity, specificity, and cut-off values are reported for descriptive and exploratory purposes only and should not be interpreted as validated clinical thresholds. Conclusions: Early alterations in renal microcirculatory perfusion are detectable during the ED phase of sepsis and differ between transient and non-transient SA-AKI trajectories. Baseline RRI and SPDUS values provide physiological insight into early renal perfusion abnormalities and evolving microcirculatory dysfunction in sepsis, but should not be interpreted as predictive tools.