Doppler renal resistance index for the prediction of response to passive leg-raising following cardiac surgery

Abstract

Purpose: Doppler-based renal resistance index (RI) can be measured at the bedside of critically illpatients. This study was designed to assess if the RI predicted an increase in cardiac output (CO)following passive leg-raising (PLR) in patients admitted to the intensive care unit after cardiacsurgery.Methods: During this single center prospective study, Doppler assessment of RI and measure-ments of CO using the thermodilution method were performed, after surgery, in the intensive careunit before and after PLR. A positive response to PLR was defined as a 10% increase in CO.Results: We included 30 patients. The mean RI was higher before (0.694 60.069) than after PLR(0.679 6 0.069) (P 5 .02) with a median change of 20.012 (IQR: 20.042;0.000). Following PLR, 9patients (30%) had a >10% increase in CO. In patients with a positive PLR response, the decreasein the RI during PLR was more pronounced than in patients who did not respond to PLR (PLR 60.042 (IQR: 20.051; 20.040) vs PLR 620.008 (IQR: 20.032; 0.015) (P 5 .004). There was a sig-nificant negative association between RI change in response to PLR and a 10% increase in COfollowing PLR (OR: 1.63 (CI:1.07–2.47) (P 5 .02) per 20.01 change).Conclusion: An increase in CO following PLR was associated with a significant decrease in RI. Var-iations of RI in response to PLR should be further studied as a tool to predict fluid responsiveness.However, their clinical utility could be limited by the small magnitude of the variations.