title: Defining oliguria during cardiopulmonary bypass and its relationship with cardiac surgery-associated acute kidney injury.
abstract: BACKGROUND
  While urine flow rate ≤0.5 ml kg-1h-1is believed to define oliguria during cardiopulmonary bypass (CPB), it is unclear whether this definition identifies risk for acute kidney injury (AKI) . The purpose of this retrospective study was to evaluate if urine flow rate during CPB is associated with AKI.
  
  
  METHODS
  Urine flow rate was calculated in 503 patients during CPB. AKI in the first 48 h after surgery was defined by the Kidney Disease: Improving Global Outcomes classification. Adjusted risk factors associated with AKI and urine flow rate were assessed.
  
  
  RESULTS
  Patients with AKI [n=149 (29.5%)] had lower urine flow rate than those without AKI (P<0.001). The relationship between urine flow and AKI risk was non-linear, with an inflection point at 1.5 ml kg-1h-1Among patients with urine flow <1.5 ml kg-1h-1, every 0.5 ml kg-1h-1higher urine flow reduced the adjusted risk of AKI by 26% (95% CI 13-37; P<0.001). Urine flow rate during CPB was independently associated with the risk for AKI. Age up to 80 years and preoperative diuretic use were inversely associated with urine flow rate; mean arterial pressure on CPB (when <87 mmHg) and CPB flow were positively associated with urine flow rate.
  
  
  CONCLUSIONS
  Urine flow rate during CPB <1.5 ml kg-1h-1identifies patients at risk for cardiac surgery-associated AKI. Careful monitoring of urine flow rate and optimizing mean arterial pressure and CPB flow might be a means to ensure renal perfusion during CPB.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00769691 and NCT00981474.
authors.affiliation: Division of Cardiac Surgery, Department of Surgery.
authors.forename: D
authors.initials: D
authors.lastname: Hori
authors.affiliation: Division of Cardiac Surgery, Department of Surgery.
authors.forename: N M
authors.initials: NM
authors.lastname: Katz
authors.affiliation: Division of Nephrology, Department of Medicine.
authors.forename: D M
authors.initials: DM
authors.lastname: Fine
authors.affiliation: Texas Heart Institute, Houston, TX, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ono
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: V M
authors.initials: VM
authors.lastname: Barodka
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: L C
authors.initials: LC
authors.lastname: Lester
authors.affiliation: Biostatistics Consulting Center, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
authors.forename: G
authors.initials: G
authors.lastname: Yenokyan
authors.affiliation: Division of Cardiac Surgery, Department of Surgery choguetwo@gmail.com.|Department of Anesthesiology, Northwestern University Feinberg School of Medicine, Chicago, IL.
authors.forename: C W
authors.initials: CW
authors.lastname: Hogue
mesh_terms: D058186:Acute Kidney Injury / Q000209:etiology* / Q000652:urine; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D002315:Cardiopulmonary Bypass; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009846:Oliguria / Q000175:diagnosis* / Q000209:etiology* / Q000652:urine; D011183:Postoperative Complications / Q000209:etiology* / Q000652:urine; D012189:Retrospective Studies; D012307:Risk Factors
keywords: acute kidney injury; cardiac surgery; cardiopulmonary bypass; oliguria