Prognostic value of renal resistive index for predicting renal recovery in critically ill patients with acute kidney injury

Background: Renal recovery after acute kidney injury is a clinical outcome that influences prognosis in critically ill patients. The renal resistive index was measured by Doppler ultrasound and has been proposed as a potential predictor of renal recovery; however, its prognostic value remains inconsistent. Methods: This prospective study included acute kidney injury patients admitted to the intensive care unit at Cho Ray Hospital from November 2021 to July 2022. Renal resistive index was measured by Doppler ultrasound at intensive care unit admission, after 24 hours, and after 48 hours. Renal recovery was assessed on days 2 and 7 and at hospital discharge. Results: Among 95 patients with acute kidney injury, renal recovery occurred in 16.8% at day 2, 37.9% at day 7, and 47.4% at hospital discharge. Renal resistive index measured at day 2 (renal resistive index 2) was significantly higher in the non-recovery group than in the recovery group (0.755 ± 0.071 vs. 0.692 ± 0.091; p = 0.001). Both renal resistive index 2 and its percentage change (% renal resistive index 2) demonstrated moderate discriminative ability for predicting renal recovery at day 7. In multivariable analysis, acute kidney injury stage 3, cumulative fluid balance >5%, renal resistive index 2 >0.722, and a reduction in percentage renal resistive index 2 <5% were independently associated with impaired renal recovery at day 7. Conclusion: Renal resistive index on day 2 and its dynamic changes were associated with renal recovery in critically ill patients with acute kidney injury. Repeated renal resistive index assessment may provide complementary prognostic information when integrated with clinical factors. Further multicentre studies are needed to validate its clinical utility and to combine the renal resistive index with clinical and biochemical parameters.