title: Risk associated with preoperative anemia in cardiac surgery: a multicenter cohort study.
abstract: BACKGROUND
  Preoperative anemia is an important risk factor for perioperative red blood cell transfusions, which are associated with postoperative morbidity and mortality. Whether preoperative anemia also is an independent risk factor for adverse outcomes after cardiac surgery, however, has not been fully elucidated.
  
  
  RESULTS
  In this multicenter cohort study, data were collected on 3500 consecutive patients who underwent cardiac surgery during 2004 at 7 academic hospitals. The prevalence of preoperative anemia, defined as hemoglobin <12.5 g/dL, and its unadjusted and adjusted relationships with the composite outcome of in-hospital death, stroke, or acute kidney injury were obtained. The overall prevalence of preoperative anemia was 26%, with values ranging from 22% to 30% at the participating hospitals. After the exclusion of patients who had severe preoperative anemia (hemoglobin <9.5 g/dL) or preoperative kidney failure and those who underwent emergency surgery, the composite outcome was observed in 7.5% of patients (247 of 3286). The unadjusted odds ratio for the composite outcome in anemic versus nonanemic patients was 3.6 (95% confidence interval, 2.7 to 4.7). The risk-adjusted odds ratios, obtained by multivariable logistic regression and propensity-score matching to control for important confounders (including comorbidities, institution, surgical factors, and blood transfusion), were 2.0 (95% confidence interval, 1.4 to 2.8) and 1.8 (95% confidence interval, 1.2 to 2.7), respectively.
  
  
  CONCLUSIONS
  Preoperative anemia is independently associated with adverse outcomes after cardiac surgery. Future studies should determine whether therapies aimed at treating preoperative anemia would improve the outcomes of patients undergoing cardiac surgery.
authors.affiliation: Department of Anesthesia, University Health Network, University of Toronto, Toronto, Ontario, Canada, M5G 2C4. keyvan.karkouti@uhn.on.ca
authors.forename: Keyvan
authors.initials: K
authors.lastname: Karkouti
authors.forename: Duminda N
authors.initials: DN
authors.lastname: Wijeysundera
authors.forename: W Scott
authors.initials: WS
authors.lastname: Beattie
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000740:Anemia / Q000150:complications* / Q000628:therapy; D002170:Canada; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D016022:Case-Control Studies; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D017707:Erythrocyte Transfusion; D006801:Humans; D008875:Middle Aged; D019990:Perioperative Care; D015995:Prevalence; D012189:Retrospective Studies; D012307:Risk Factors; D016896:Treatment Outcome