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Fluid balance and urine volume are independent predictors of mortality in acute kidney injury

Catarina Teixeira1, Francesco Garzotto12, Pasquale Piccinni3, Nicola Brienza4, Michele Iannuzzi5, Silvia Gramaticopolo3, Francesco Forfori6, Paolo Pelaia7, Monica Rocco8, Claudio Ronco12, Clara Belluomo Anello9, Tiziana Bove10, Mauro Carlini11, Vincenzo Michetti12, Dinna N Cruz12* and NEFROlogia e Cura INTensiva (NEFROINT) investigators

Author Affiliations

1 International Renal Research Institute Vicenza (IRRIV), Viale Rodolfi 37, Vicenza, 36100, Italy

2 Department of Nephrology, Dialysis and Transplantation, St. Bortolo Hospital, Viale Rodolfi 37, Vicenza, 36100, Italy

3 Department of Intensive Care and Anesthesiology, St. Bortolo Hospital, Viale Rodolfi 37, Vicenza, 36100, Italy

4 Department of Anesthesia and Intensive Care, Emergency and Organ Transplantation - University of Bari, Pizza G. Cesare 11, Bari, 70124, Italy

5 Intensive Care Unit, Department of Anesthesia and Resuscitation, Federico II University Hospital, Via S. Pansini 5, Naples, 80131, Italy

6 Division of Anesthesiology and Intensive Care, Department of Surgery, University of Pisa, Via Roma 67, Pisa, 56100, Italy

7 Intensive Care Unit, University Hospital Umberto I - G.M. Lancisi - G. Salesi, Via Tronto 10/A, Torrette di Ancona, 60020, Italy

8 Department of Anesthesiology and Intensive Care, University of Rome "La Sapienza", Viale del Policlinico 155, Rome, 00161, Italy

9 Intensive Care Unit, Emergency Department of Anesthesiological and Surgical Science 2 (SUN), University Hospital, Via Santa Maria di Costantinopoli 104, Naples, 80138, Italy

10 Department of Cardiothoracic Anesthesia and Intensive Care, Vita-Salute San Raffaele University, San Raffaele Scientific Institute, Via Olgettina 60, Milan, 20132, Italy

11 Department of Anesthesia and Intensive Care, A.O.U.I. University of Verona, Piazzale Scuro, Verona, 37134, Italy

12 Department of Intensive Care and Anesthesiology - Catholic University of Sacred Heart, Largo A. Gemelli 8, Rome, 00168, Italy

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Critical Care 2013, 17:R14  doi:10.1186/cc12484

Published: 24 January 2013



In ICUs, both fluid overload and oliguria are common complications associated with increased mortality among critically ill patients, particularly in acute kidney injury (AKI). Although fluid overload is an expected complication of oliguria, it remains unclear whether their effects on mortality are independent of each other. The aim of this study is to evaluate the impact of both fluid balance and urine volume on outcomes and determine whether they behave as independent predictors of mortality in adult ICU patients with AKI.


We performed a secondary analysis of data from a multicenter, prospective cohort study in 10 Italian ICUs. AKI was defined by renal sequential organ failure assessment (SOFA) score (creatinine >3.5 mg/dL or urine output (UO) <500 mL/d). Oliguria was defined as a UO <500 mL/d. Mean fluid balance (MFB) and mean urine volume (MUV) were calculated as the arithmetic mean of all daily values. Use of diuretics was noted daily. To assess the impact of MFB and MUV on mortality of AKI patients, multivariate analysis was performed by Cox regression.


Of the 601 included patients, 132 had AKI during their ICU stay and the mortality in this group was 50%. Non-surviving AKI patients had higher MFB (1.31 ± 1.24 versus 0.17 ± 0.72 L/day; P <0.001) and lower MUV (1.28 ± 0.90 versus 2.35 ± 0.98 L/day; P <0.001) as compared to survivors. In the multivariate analysis, MFB (adjusted hazard ratio (HR) 1.67 per L/day, 95%CI 1.33 to 2.09; <0.001) and MUV (adjusted HR 0.47 per L/day, 95%CI 0.33 to 0.67; <0.001) remained independent risk factors for 28-day mortality after adjustment for age, gender, diabetes, hypertension, diuretic use, non-renal SOFA and sepsis. Diuretic use was associated with better survival in this population (adjusted HR 0.25, 95%CI 0.12 to 0.52; <0.001).


In this multicenter ICU study, a higher fluid balance and a lower urine volume were both important factors associated with 28-day mortality of AKI patients.