title: Acute surgical anemia influences the cardioprotective effects of beta-blockade: a single-center, propensity-matched cohort study.
abstract: BACKGROUND
  Despite decreasing cardiac events, perioperative beta-blockade also increases perioperative stroke and mortality. Major bleeding and/or hypotension are independently associated with these outcomes. To investigate the hypothesis that beta-blockade limits the cardiac reserve to compensate for acute surgical anemia, the authors examined the relationship between cardiac events and acute surgical anemia in patients with and without beta-blockade.
  
  
  METHODS
  The records of all noncardiac, nontransplant surgical patients between March 2005 and June 2006 were retrospectively retrieved. The primary outcome was a composite that comprised myocardial infarction, nonfatal cardiac arrest, and in-hospital mortality (major adverse cardiac event). The lowest recorded hemoglobin in the first 3 days defined nadir hemoglobin. Propensity scores estimating the probability of receiving a perioperative beta-blocker were used to match (1:1) patients who did or did not receive beta-blockers postoperatively. The relationship between nadir hemoglobin and major adverse cardiac event was then assessed.
  
  
  RESULTS
  This analysis identified 4,387 patients in whom nadir hemoglobin could be calculated; 1,153 (26%) patients were administered beta-blockers within the first 24 h of surgery. Propensity scores created 827 matched pairs that were well balanced for all measured confounders. Major adverse cardiac event occurred in 54 (6.5%) beta-blocked patients and in 25 (3.0%) beta-blocker naive patients (relative risk 2.38; 95% CI 1.43-3.96; P = 0.0009). The restricted cubic spline relationship demonstrated that this difference was restricted to those patients in whom the hemoglobin decrease exceeded 35% of the baseline value.
  
  
  CONCLUSIONS
  beta-Blocked patients do not seem to tolerate surgical anemia when compared with patients who are naive to beta-blockers. Prospective studies are required to validate these findings.
authors.affiliation: Department of Health Policy Management and Evaluation, University of Toronto, Toronto, Ontario, Canada. scott.beattie@uhn.on.ca
authors.forename: W Scott
authors.initials: WS
authors.lastname: Beattie
authors.forename: Duminda N
authors.initials: DN
authors.lastname: Wijeysundera
authors.forename: Keyvan
authors.initials: K
authors.lastname: Karkouti
authors.forename: Stuart
authors.initials: S
authors.lastname: McCluskey
authors.forename: Gordon
authors.initials: G
authors.lastname: Tait
authors.forename: Nicholas
authors.initials: N
authors.lastname: Mitsakakis
authors.forename: Gregory M T
authors.initials: GM
authors.lastname: Hare
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D000465:Algorithms; D000740:Anemia / Q000209:etiology / Q000503:physiopathology*; D016063:Blood Loss, Surgical / Q000503:physiopathology*; D002316:Cardiotonic Agents; D015331:Cohort Studies; D016208:Databases, Factual; D006323:Heart Arrest / Q000209:etiology; D006454:Hemoglobins / Q000378:metabolism; D017052:Hospital Mortality; D006801:Humans; D007431:Intraoperative Complications / Q000503:physiopathology*; D007511:Ischemia / Q000503:physiopathology; D008875:Middle Aged; D009203:Myocardial Infarction / Q000517:prevention & control; D011446:Prospective Studies; D012189:Retrospective Studies; D012307:Risk Factors; D016019:Survival Analysis; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000319:Adrenergic beta-Antagonists; D002316:Cardiotonic Agents; D006454:Hemoglobins