Early detection of postoperative acute kidney injury by Doppler renal resistive index in cardiac surgery with cardiopulmonary bypass

Background. Acute kidney injury (AKI) is common after cardiac surgery, affecting outcome. Early detection of an AKI marker is likely to speed diagnosis and implementation of measures to preserve renal function. In septic shock and unselected ventilated subjects, an increased Doppler renal resistive index (RRI) is a predictor of AKI. This study aims to determine whether RRI would act similarly in the postoperative setting of cardiac surgery. Methods. This study included 65 subjects aged more than 60 yr undergoing elective heart surgery with cardiopulmonary bypass (CPB) and at risk of AKI. All presented at least one AKI risk factor [arteritis, diabetes, or serum creatinine (sCr) clearance of 30-60 ml min(-1)] and were haemodynamically stable without arrhythmia. Doppler RRI was measured in the immediate postoperative period (POP) while subjects were ventilated and sedated. AKI was assessed when sCr increased 30% above the preoperative baseline. Results. Eighteen subjects developed AKI between days 1 and 4, with six requiring dialysis. RRI in the POP was increased in AKI [RRI: 0.79 (0.08) with AKI vs 0.68 (0.06) without AKI, P < 0.001], correlating to AKI severity [0.68 (0.06) without AKI, 0.77 (0.08) with AKI but no dialysis, and 0.84 (0.03) with AKI and dialysis, P, 0.001]. RRI was similar in subjects receiving catecholamines. RRI. >0.74 in the POP predicted delayed AKI with high sensitivity and specificity (0.85 and 0.94, respectively). Multivariate analysis showed that AKI was associated with increased RRI and transfusion. Conclusions. RRI used in the immediate POP after cardiac surgery with CPB enabled prediction of delayed AKI and anticipation of its severity.