title: Fluid balance, change in serum creatinine and urine output as markers of acute kidney injury post cardiac surgery: an observational study.
abstract: BACKGROUND
  Acute kidney injury (AKI) is defined as oliguria or rise in serum creatinine but oliguria alone as a diagnostic criterion may over-diagnose AKI.
  
  
  OBJECTIVE
  Given the association between fluid overload and AKI, we aimed to determine if positive fluid balance can complement the known parameters in assessing outcomes of AKI.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  Teaching hospital in Vancouver, Canada.
  
  
  METHODS
  111 consecutive patients undergoing elective cardiac surgery from January to April 2012.
  
  
  METHODS
  Outcomes of cardiac surgery intensive care unit (CSICU) and hospital length of stay (LOS) in relation to fluid balance, urine output and serum creatinine.
  
  
  METHODS
  All fluid input and output was recorded for 72 hours post-operatively. Positive fluid balance was defined as >6.5 cc/kg. Daily serum creatinine and hourly urine output were recorded and patients were defined as having AKI according to the AKIN criteria.
  
  
  RESULTS
  Of the patients who were oliguric, those with fluid overload trended towards longer LOS than those without fluid overload [CSICU LOS: 62 and 39 hours (unadjusted p-value 0.02, adjusted p-value 0.58); hospital LOS: 13 and 9 days (unadjusted p-value: 0.05, adjusted p-value: 0.16)]. Patients with oliguria who were fluid overloaded had similar LOS to patients with overt AKI (change in serum creatinine ≥ 26.5 µmol/L), [CSICU LOS: 62 and 69 hours (adjusted p value: 0.32) and hospital LOS: 13 and 14 days (adjusted p value: 0.19)]. Patients with oliguria regardless of fluid balance had longer CSICU LOS (adjusted p value: 0.001) and patients who were fluid overloaded in the absence of AKI had longer hospital LOS (adjusted p value: 0.02).
  
  
  CONCLUSIONS
  Single centre, small sample, LOS as outcome.
  
  
  CONCLUSIONS
  Oliguria and positive fluid balance is associated with a trend towards longer LOS as compared to oliguria alone. Fluid balance may therefore be a useful marker of AKI, in addition to urine output and serum creatinine.
authors.affiliation: Division of Nephrology, Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Katrina
authors.initials: K
authors.lastname: Chau
authors.affiliation: Department of Anesthesiology, Pharmacology and Therapeutics, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Travis
authors.initials: T
authors.lastname: Schisler
authors.affiliation: Division of Nephrology, Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Lee
authors.initials: L
authors.lastname: Er
authors.affiliation: Division of Nephrology, Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Dharmvir
authors.initials: D
authors.lastname: Jaswal
authors.affiliation: Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Christopher
authors.initials: C
authors.lastname: Cheung
authors.affiliation: Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Amanda
authors.initials: A
authors.lastname: Israel
authors.affiliation: Department of Anesthesiology, Pharmacology and Therapeutics, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: John
authors.initials: J
authors.lastname: Bowering
authors.affiliation: Division of Nephrology, Faculty of Medicine, The University of British Columbia, St Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z1Y6 Canada.
authors.forename: Adeera
authors.initials: A
authors.lastname: Levin
keywords: Acute kidney injury; Cardiac surgery; Diagnosis; Fluid resuscitation