Doppler-based renal resistive index can assess progression of acute kidney injury in patients undergoing cardiac surgery

Abstract

Objectives: The objective of this study was to test whether assessment of renal resistive index measured after cardiac surgery (RRI(T0)) can diagnose persistent acute kidney injury (AKI). The predictive value was evaluated using a gray-zone approach.

Design: A prospective observational study.

Setting: A teaching university hospital.

Participants: Eighty-two patients following cardiac surgery with cardiopulmonary bypass.

Interventions: Measurements of hemodynamic parameters and RRI were obtained before surgery, on admission to the intensive care unit, 6 hours after admission, and on the first postoperative day. AKI was defined according to the renal risk, injury, failure, loss of kidney function, end-stage of kidney disease (RIFLE) classification during the first postoperative week. Persistent AKI was defined as AKI lasting >3 days.

Measurements and main results: Out of the 82 patients, 15 (18%) developed persistent AKI, and 6 (7%) developed transient AKI. The median value and time-course of RRI were significantly different between patients with transient AKI and persistent AKI. Doppler-based RRI(T0) predicted persistent AKI with an area under the receiver-operating characteristic curve of 0.93 (95% confidence interval: 0.85-0.98, p<0.0001). The optimal cut-off of RRI was 0.73 (95% confidence interval: 0.73-0.75). The gray-zone approach identified a range of RRI values between 0.72 and 0.75 in 14% of patients.

Conclusions: Doppler-based RRI can be helpful for noninvasive assessment of renal function recovery after cardiac surgery by using RRI(T0) to predict persistent AKI. The optimal cut-off was 0.73 with a gray zone ranging between 0.72 and 0.75.

Keywords: Doppler; acute kidney injury; cardiac surgical procedures; postoperative period; ultrasonography.