Renal resistive index by transesophageal and transparietal echo-doppler imaging for the prediction of acute kidney injury in patients undergoing major heart surgery

Background Acute kidney injury (AKI) following major heart surgery (MHS) is associated with early decrease in renal blood flow and worsened prognosis. Doppler-derived renal resistive index (RRI), which reflects renal vascular resistance, may predict the development of AKI in patients undergoing MHS. Methods We studied 60 consecutive patients (mean age 69.5 years, range 30-88, 41 males) undergoing MHS. We measured RRI, both at the renal sinus and intraparenchymally, by transesophageal echo-Doppler ultrasound (TE-EDus) at anesthesia induction and at the end of surgery in all patients. Additionally, we measured RRI by external transparietal echo-Doppler ultrasound (TP-EDus) at the following time points: anesthesia induction, end of surgery, 4 and 24 h from cardiopulmonary bypass (CPB) start. We also measured serum neutrophil gelatinase associated lipocalin (NGAL) at the same time points. Results AKI [serum creatinine (sCr) increase >= 0.3 mg/dl vs. baseline within 72 h] developed in 23/60 (38.3 %) patients, with two requiring dialysis. Systemic hemodynamic parameters were similar in the patients who developed AKI (AKI+) and in those who did not (AKI-). Intraparenchymal RRI at end-surgery was significantly higher in AKI+ compared to AKI- patients, both at TE-EDus and TP-EDus (TE-EDus mean difference, p = 0.004; TP-EDus mean difference, p = 0.013; difference between TE-EDus and TP-EDus results, p = 0.066), although the predictive performance was limited with both methods (area under the curve [AUC] of the receiver-operator characteristics: 0.71 and 0.70 for TE-EDus and TP-EDus, respectively). Serum NGAL values were higher in AKI + than in AKI- patients (anesthesia induction, p = 0.037; end-surgery, p = 0.007; 4 h from CPB start, p = 0.093; 24 h from CPB start, p = 0.024. However, combining RRI with serum NGAL at end-surgery did not provide a clear-cut advantage in predicting AKI. Conclusions In patients undergoing MHS, increased echo-Doppler ultrasound-derived RRI at end-surgery is significantly associated with the risk of AKI, but has limited practical utility for identifying the patients who will develop AKI.