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

Background: Cardiac surgery associated acute kidney injury (CSA-AKI) is com-mon and various tools are proposed to identify patients at risk for AKI. Determi-nation of Doppler derived renal resistance index (RRI) is useful to detect the oc-currence 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, end-stage of kidney disease (RIFLE) classification. Methods: We conducted a prospective, unblinded, observational in patients scheduled for cardiac surgery. Clinical and surgical data were collected from the electronic medical files and the Cleveland score was calculated for each patient. Before surgery and on admission in the intensive care unit (ICU), blood flow in renal cortical or arcuate arteries was measured and RRI was computed. The ca-pability of preoperative serum creatinine, the Cleveland score as well as pre-operative, postoperative and change in RRI in predicting PO-AKI was investigat-ed with the area under the receiver operating characteristic curve (ROC-AUC). Results: Within the first 5 postoperative days, 31.4 % developed CSA-AKI. All patients with stage 1 AKI recovered normal creatinine levels before ICU dis-charge 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 both preoperative se-rum creatinine and RRI, 0.879 for the Cleveland score, 0.710 for postoperative RRI. The change between 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%. Conclusions Noninvasive determination of RRI is helpful to detect AKI and pro-vides additional information to clinical markers.