title: Harms associated with single unit perioperative transfusion: retrospective population based analysis.
abstract: OBJECTIVE
  To determine whether perioperative transfusion of as little as one unit of packed red blood cells in the operating room or the day after surgery is associated with measurably increased odds for perioperative ischemic stroke and myocardial infarction.
  
  
  METHODS
  Retrospective cohort study of hospital administrative data.
  
  
  METHODS
  346 hospitals in the United States participating in the claims based Premier Perspective database from 1 January 2009 to 31 March 2012.
  
  
  METHODS
  1,583,819 adults who underwent non-cardiac, non-intracranial, non-vascular surgery and required a stay of at least one night in hospital and did not receive packed red blood cells on days two to seven after surgery.
  
  
  METHODS
  Transfusion of packed red blood cells on the day of surgery or one day after by exposure categories (none or one, two, three or four or more units).
  
  
  METHODS
  The composite outcome of stroke/myocardial infarction was defined as ischemic stroke, ST elevation myocardial infarction, ventricular tachycardia, or ventricular fibrillation during index admission or as a primary diagnosis for readmission within 30 days. Ventricular tachycardia/ventricular fibrillation were included as a surrogate for myocardial infarction.
  
  
  RESULTS
  41,421 (2.6%) patients received at least one unit of packed red blood cells within 48 hours of surgery, and 8044 (0.51%) experienced the composite outcome of stroke/myocardial infarction. Patients who were transfused were older, more likely to be women, and had more comorbid disease. Hierarchical logistic regression adjusted for comorbidities and demographics with random effects by hospital showed that transfusion of as little as one unit was associated with an odds ratio of 2.33 (95% confidence interval 1.90 to 2.86) for perioperative stroke/myocardial infarction, and the odds of stroke/myocardial infarction markedly increased with transfusion of four or more units. Subgroup analysis limiting the cohort to one of several common surgical procedures, excluding those who received two or more units, or excluding who received transfusion on postoperative day one showed substantially similar results, as did a matched propensity score analysis. Two methods of modeling unmeasured confounders suggest an odds ratio of >10 with imbalance of up to 47% between patients who did and did not receive transfusion would be required to invalidate our results.
  
  
  CONCLUSIONS
  A perioperative transfusion of one unit of packed red blood cells is associated with increased odds of perioperative ischemic stroke and/or myocardial infarction, even after adjustment for a wide range of factors in our data and despite extensive sensitivity analyses.
authors.affiliation: Department of Anesthesia and Perioperative Care, University of California, CA 94143-0648, USA elizabeth.whitlock@ucsf.edu.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Whitlock
authors.affiliation: Department of Anesthesia and Perioperative Care, University of California, CA 94143-0648, USA.
authors.forename: Helen
authors.initials: H
authors.lastname: Kim
authors.affiliation: Division of Hospital Medicine, Department of Medicine, University of California, San Francisco, CA 94143, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Auerbach
mesh_terms: D017707:Erythrocyte Transfusion / Q000009:adverse effects; D017052:Hospital Mortality; D006801:Humans; D016015:Logistic Models; D009203:Myocardial Infarction / Q000209:etiology / Q000401:mortality*; D016017:Odds Ratio; D017063:Outcome Assessment, Health Care; D062645:Percutaneous Coronary Intervention / Q000401:mortality*; D010818:Practice Patterns, Physicians'; D057216:Propensity Score; D012189:Retrospective Studies; D018570:Risk Assessment; D020521:Stroke / Q000209:etiology / Q000401:mortality*; D014481:United States / Q000453:epidemiology