Copyright © European Society of Anaesthesiology. Unauthorized reproduction of this article is prohibited. ORIGINAL ARTICLE Doppler renal resistive index for early detection of acute kidney injury after major orthopaedic surgery A prospective observational study Philippe Marty, Simon Szatjnic, Fabrice Ferre, Jean-Marie Conil, Nicolas Mayeur, Olivier Fourcade, Stein Silva and Vincent Minville BACKGROUND Postoperative acute kidney injury (AKI) is a cause of morbidity and mortality. Its diagnosis requires better markers than variations in diuresis or postoperative serum creatinine. OBJECTIVES The aim of this study was to evaluate the accuracy of Doppler renal resistive index for early detection of AKI after hip or knee arthroplasty. DESIGN A prospective observational study. SETTING A single-centre study in a university hospital. PATIENTS Fifty men and women older than 65 years, requiring hip or knee replacement with at least two periopera- tive AKI risk factors, including diabetes, arteritis, chronic heart or renal dysfunction, and prescription of angiotensin-convert- ing enzyme (ACE) inhibitors. Exclusion criteria were poor abdominal echogenicity, arrhythmia, respiratory failure or agitation. INTERVENTION Renal resistive index was measured pre- operatively and in the postanaesthesia care unit. RESULTS Sixteen patients presented with AKI in the postoperative period. Resistive index was increased in this group in both the preoperative [0.72 (0.69 to 0.73) vs. 0.66 (0.58 to 0.71); P ¼ 0.01] and postoperative periods [0.75 (0.71 to 0.75) vs. 0.67 (0.62 to 0.72); P ¼ 0.0001]. Resistive index evaluated by ROC curves and AUC to detect AKI was 0.862 [95% confidence interval (95% CI) 0.735 to 0.943]. The most accurate cut-off value was a postoperative resistive index of 0.705 (sensitivity ¼ 94%, specificity ¼ 71%, LRR ¼ 3.19 and LR– ¼ 0.09). The grey area between 0.705 and 0.73, corresponding to the inconclusive zone, included 26% (13/50) of all the patients. CONCLUSION Postoperative resistive index appears to be effective for early detection of AKI after major orthopaedic surgery. Resistive index can be measured in the postopera- tive care unit in patients at risk of AKI. TRIAL REGISTRATION NUMBER 29-0512. Published online 10 July 2014 Introduction Detecting acute kidney injury (AKI) in the perioperative period is of major interest in the management of high-risk surgical patients 1,2 because of its impact on both morbid- ity 3,4 and mortality. 5 Although various tests are available, despite numerous studies, an early, accurate and easy-to- use marker of AKI in clinical practice is still lacking. Serum creatinine concentration (sCr) remains a popular marker despite its known limitations. 6 Another AKI marker, the urine output, lacks specificity. Numerous biomarkers (Ngal, 7 cystatin C 8 ) are available, but in the context of postoperative AKI, their clinical significance remains to be clarified. Among the predictors of AKI, Doppler renal resistive index (RI) is of interest. It can be measured quickly, with low intra- and interobserver variability. 9,10 Bossard et al. 11 showed that RI measure- ment in the immediate postoperative period after cardiac surgery predicted delayed AKI. Its usefulness in other clinical settings should now be clarified. Major orthopae- dic surgery is known to be haemorrhagic 12 and might precipitate AKI in patients with perioperative risk factors. The aim of this study was to assess the usefulness of preoperative resistive index, postoperative resistive Eur J Anaesthesiol 2015; 32:37–43 From the De ´ partement Anesthe ´ sie-Re ´ animation, CHU Toulouse, Universite ´ Toulouse III Paul Sabatier, Faculte ´ de Me ´ decine Toulouse-Rangueil, EA 4564-MATN, Institut Louis Bugnard (IFR 150), Toulouse, France Correspondence to Philippe Marty, De ´ partement Anesthe ´ sie-Re ´ animation, CHU Toulouse, 31059 Toulouse, France E-mail: philippemarty@hotmail.com 0265-0215 ß 2014 Copyright European Society of Anaesthesiology DOI:10.1097/EJA.0000000000000120