title: The association of blood transfusion with mortality after cardiac surgery: cause or confounding? (CME).
abstract: BACKGROUND
  Bleeding into the chest is a life-threatening complication of cardiac surgery. Blood transfusion has been implicated as an important cause of harm associated with bleeding, based largely on studies demonstrating an independent association between transfusion and mortality. These studies did not, however, consider the possibility that bleeding may in itself be harmful, inasmuch as drains are inefficient at clearing blood from the chest and retained blood may compromise cardiac and lung function.
  
  
  METHODS
  We undertook a multivariate logistic regression analysis of the risk factors associated with mortality in 2599 consecutive patients undergoing cardiac surgery. Unlike previous studies the risk factors examined included the volume of chest tube drainage at 24 hours. A stratified analysis was also undertaken that compared the adjusted risk of death for patients exposed or not exposed to a postoperative blood transfusion.
  
  
  RESULTS
  Blood transfusion was not an independent predictor of mortality (p=0.4). Chest tube drainage was the strongest independent predictor of mortality (p<0.001). In the stratified analysis, chest tube drainage remained an independent predictor of mortality for patients not exposed to a blood transfusion (p<0.01). Furthermore, the risk of death of these patients was no different from patients exposed to a blood transfusion (p=0.7 for interaction).
  
  
  CONCLUSIONS
  Our results argue that for patients undergoing cardiac surgery bleeding contributes to mortality through mechanisms unrelated to blood transfusion.
authors.affiliation: Department of Intensive Care, St Vincent's Institute of Medical Research, the Department of Medicine, University of Melbourne, Australia. barry.dixon@svhm.org.au
authors.forename: Barry
authors.initials: B
authors.lastname: Dixon
authors.forename: John D
authors.initials: JD
authors.lastname: Santamaria
authors.forename: David
authors.initials: D
authors.lastname: Reid
authors.forename: Marnie
authors.initials: M
authors.lastname: Collins
authors.forename: Thomas
authors.initials: T
authors.lastname: Rechnitzer
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Newcomb
authors.forename: Ian
authors.initials: I
authors.lastname: Nixon
authors.forename: Michael
authors.initials: M
authors.lastname: Yii
authors.forename: Alexander
authors.initials: A
authors.lastname: Rosalion
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Campbell
mesh_terms: D000368:Aged; D006348:Cardiac Surgical Procedures / Q000401:mortality*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D065227:Transfusion Reaction