Perioperative Changes in Renal Resistive Index as a Predictor of Acute Kidney Injury After Cardiac Surgery: A Prospective Cohort Study.

Cardiac surgery-associated acute kidney injury (CSA-AKI) is common and various tools are proposed to identify patients at risk of AKI. The determination of the Doppler-derived renal resistance index (RRI) is useful for detecting the occurrence of tubular necrosis or allograft rejection. This study questions the value of RRI in identifying CSA-AKI, defined according to the renal risk, injury, failure, loss of kidney function, and end-stage kidney disease (RIFLE) classification. We conducted a prospective, unblinded, observational study in patients undergoing open heart surgery. Clinical and surgical data were collected from the electronic medical files and the Cleveland score was calculated for each patient. Before the surgery and upon admission to the intensive care unit (ICU), blood flow in the renal cortical or arcuate arteries was measured and the RRI was computed. The capability of preoperative serum creatinine, the Cleveland score, and the preoperative and postoperative change in RRI were investigated with the area under the receiver operating characteristic curve (ROC-AUC) to predict the AKI. Within the first five postoperative days, 31.4% developed CSA-AKI. All patients with stage 1 AKI recovered normal creatinine levels before ICU discharge while those with stage 2 or 3 (AKI 2/3) exhibited persistent changes. To discriminate AKI 2/3, the ROC-AUC was less than 0.7 for the preoperative serum creatinine and RRI, 0.879 for the Cleveland score, and 0.710 for the postoperative RRI. The change between the preoperative and postoperative RRI (dRRI) provided a ROC-AUC of 0.825 (sensitivity 72.7% and specificity 96.6%) with an optimal cut-off point at 9.4%. Noninvasive determination of RRI is helpful for detecting PO-AKI and provides additional information to clinical markers.