Hindawi Publishing Corporation Case Reports in Critical Care Volume 2013, Article ID 103450, 4 pages http://dx.doi.org/10.1155/2013/103450 Case Report Urine Biochemistry in the Early Postoperative Period after Cardiac Surgery: Role in Acute Kidney Injury Monitoring Alexandre Toledo Maciel and Daniel Vitório Intensimed Research Group, Adult Intensive Care Unit, Hospital S˜ ao Camilo, Pomp´ eia Avenue, 1178 Pomp´ eia, 05022-001 S˜ ao Paulo, SP, Brazil Correspondence should be addressed to Alexandre Toledo Maciel; alexandre.toledo@intensimed.com Received 10 June 2013; Accepted 7 July 2013 Academic Editors: C. Lazzeri and G. Pichler Copyright © 2013 A. T. Maciel and D. Vit´ orio. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We have recently suggested that sequential urine electrolyte measurement in critically ill patients may be useful in monitoring kidney function. Cardiac surgery is one of the leading causes of acute kidney injury (AKI) in the intensive care unit (ICU). In this paper, we describe the sequential behavior of urine electrolytes in three patients in the early (irst 60 hours) postoperative period ater cardiac surgery according to AKI status: no AKI, transient AKI, and persistent AKI. We have found that the patient with no AKI had stable and high concentrations of sodium (NaU) and chloride (ClU) in sequential spot samples of urine. AKI development was characterized in the other two patients by decreases in NaU and ClU, which have started early ater ICU admission. Transient AKI was marked by also transient and less severe decreases in NaU and ClU. Persistent AKI was marked by the less favorable clinical course with abrupt and prolonged declines in NaU and ClU values. hese electrolytes in urine had a behavior like a “mirror image” in comparison with that of serum creatinine. We suggest that sequential urine electrolytes are useful in monitoring acute kidney injury development in the early postoperative period ater cardiac surgery. 1. Introduction Acute kidney injury (AKI) is frequent among patients under- going cardiac surgery [1, 2]. It seems to be an independent risk factor for increased intensive care and hospital mortality [3]. Serum creatinine level and urine output are still the cornerstones for AKI diagnosis in all settings, including postoperative AKI. Urine biochemistry, although a major tool in AKI diagnosis and management in the past, is nowadays considered not useful [4] especially due to evidence showing its dissociation from renal hemodynamics [5]. However, sequential evaluation of urine electrolytes (basically, sodium, potassium, and chloride) in the course of early postoperative period has never, to our knowledge, been performed. We have recently observed that alterations in the concentration of these electrolytes measured in spot urine samples may be related to kidney function and AKI development, sometimes preceding elevations in serum creatinine [6, 7]. In this paper, we report the sequential behavior of urine electrolytes in a 60 h period in three patients ater undergoing cardiac surgery. 2. Case Presentation We will briely present the 3 cases separately. In all cases, there was no previous history of kidney disease, and the surgical procedure consisted in on-pump coronary artery bypass grat (CABG), and all patients had their serum creatinine as well as urine sodium (NaU), chloride (ClU), and potassium (KU) measured at 0 (T 0 ), 6 (T 6 ), 12 (T 12 ), 24 (T 24 ), 36 (T 36 ), 48 (T 48 ), and 60 (T 60 ) hours ater ICU admission. hese measurements are part of a research protocol in our ICU of which these patients were the irst three included. All patients were admitted in the ICU immediately ater the surgery. An indwelling urinary catheter was in place during the entire observation period. AKIN creatinine-based criteria were used to deine AKI [8]. Baseline creatinine was considered the creatinine value at ICU admission. Oliguria was deined as a urine output less than 0.5 mL/kg/h in a 6 h period. AKI reversal was deined as a creatinine value lower than baseline creatinine +0.3 (mg/dL). Day 1 (D1) is the day of ICU admission.