Renal Resistive Index Measurement by Transesophageal Echocardiography: Comparison With Translumbar Ultrasonography and Relation to Acute Kidney Injury Alper Kararmaz, MD,* Mustafa Kemal Arslantas, MD,† and Ismail Cinel, MD, PhD* Objectives: The aim of this study was to evaluate the relationship between transesophageal ultrasonography- derived renal resistive index values (RRI TEE ) and a standard translumbar renal ultrasound-derived RRI (RRI TLUSG ). The effectiveness of each method to predict acute kidney injury (AKI) after cardiac surgery also was compared. Design: A prospective observational study. Setting: A teaching university hospital. Participants: Sixty patients undergoing cardiac surgery. Interventions: First, RRI was measured with both meth- ods after anesthesia induction. Second, another measure- ment was performed with TEE after cardiopulmonary bypass and immediately following the surgery with trans- lumbar ultrasound. To test the correlation between the 2 methods and to plot a Bland-Altman graph, preoperative RRI values measured by both techniques were used. Receiver operating characteristic curves also were plotted to compare the diagnostic values of RRI measured intraoperatively by TEE after cardiopulmonary bypass and by RRI TLUSG after surgery. Measurements and Main Results: There was a statistically significant correlation between the 2 RRI measurement approaches (r ¼ 0.86, p o 0.0001). The Bland-Altman plot indicated good agreement between the methods. The area under the curve (AUC) of RRI TEE in predicting AKI was 0.82 (95% confidence interval [CI] ¼ 0.64-0.9, p ¼ 0.001), and the AUC of RRI TLUSG after surgery was 0.85 (95% CI ¼ 0.7-0.98, p o 0.0001). In predicting AKI, an uncertainty zone for RRI TEE values between 0.68 and 0.71 was computed by the gray-zone approach. Conclusions: RRI TEE showed clinically acceptable agree- ment with RRI TLUSG . Indeed, RRI measured intraoperatively with TEE was comparable to RRI TLUSG in terms of detecting postoperative AKI. & 2014 Elsevier Inc. All rights reserved. KEY WORDS: transesophageal echocardiography, Doppler, renal resistive index, acute kidney injury, cardiac surgery D ESPITE IMPROVEMENTS in monitoring technology and therapeutic strategies, cardiac surgery-associated acute kidney injury (AKI) remains a common and serious postoperative complication. After cardiac surgery, the inci- dence of AKI has been reported to be 3% to 30%, depending on its definition. 1–4 Even in patients who do not require dialysis, AKI is associated with increased morbidity and mortality. 2 In clinical practice, the diagnosis of AKI is based on serum creatinine and urinary output. The relationship between a minimal increase in creatinine and 30-day mortality has been well documented in previous studies. 2,5 However, both serum creatinine and urinary output are relatively insensi- tive and unreliable markers in detecting AKI because serum creatinine levels can vary widely with age, sex, muscle mass, muscle metabolism, medications, and hydration status, and serum creatinine does not depict accurately kidney function until steady-state equilibrium has been achieved during acute changes in glomerular filtration. 6,7 Moreover, they can be altered by several factors during the perioperative period. 8 Park et al 9 proposed that the failure of prior interventional trials is, in part, attributable to delays in the diagnosis of AKI on the basis of early changes in serum creatinine. However, optimal preventative and therapeutic interventions require expeditious diagnosis of AKI, as for any other disease state. Several biologic and physiologic early AKI markers have been investigated. 10 However, most of these novel biomarkers are impractical for use at the bedside and intra- operatively because of their cost, predictability, and delayed results. 10,11 Renal blood flow is decreased at an early stage during acute tubular necrosis as a consequence of protracted intrarenal vasoconstriction. 12 The Doppler-based renal resistive index (RRI ¼ [peak systolic velocity – end-diastolic velocity]/peak systolic velocity), measured with ultrasonography, is a non- invasive, practical, and inexpensive method of predicting AKI in the early phase. 13–15 Renal resistive index values (RRI) usually is obtained by transabdominal or translumbar renal Doppler ultrasonography (RRI TLUSG ), but these approaches are impractical during cardiac surgery. Transesophageal echocar- diography (TEE) also can be used to measure renal arterial blood flow Doppler velocities and RRI (RRI TEE ) in patients undergoing cardiac surgery. 16,17 However, data regarding the utility of TEE in monitoring RRI, the concordance between RRI TEE and RRI TLUSG , and the prognostic value of RRI TEE in predicting AKI are insufficient. In this prospective study, it was hypothesized that there would be a good correlation and agreement between RRI TEE and RRI TLUSG in patients undergoing cardiac surgery. The effectiveness of the 2 methods in predicting AKI also was compared. METHODS After obtaining institutional ethics committee approval and informed consent, 60 patients scheduled for elective cardiovascular surgery with cardiopulmonary bypass (CPB) were examined in this prospective, observational study. The exclusion criteria were any renal or renal artery disease, nonsinus cardiac rhythm, use of an intraaortic balloon pump, severe aortic insufficiency, and any contraindication to From the *Department of Anesthesiology and Reanimation, School of Medicine; and the †Pendik Education and Research Hospital, Marmara University, Istanbul, Turkey. Address reprint requests to Alper Kararmaz, MD, Department of Anesthesiology and Reanimation, Marmara University Pendik Educa- tion and Research Hospital, Mimar Sinan Caddesi No: 41 Ust Kay- narc, Fevzi Cakmak Mah., Pendik, Istanbul, Turkey. E-mail: akararmaz@hotmail.com © 2014 Elsevier Inc. All rights reserved. 1053-0770/2601-0001$36.00/0 http://dx.doi.org/10.1053/j.jvca.2014.11.003 Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2014: pp ]]]–]]] 1