title: The influence of baseline hemoglobin concentration on tolerance of anemia in cardiac surgery.
abstract: BACKGROUND
  Current red blood cell (RBC) transfusion guidelines assume that most acutely anemic patients can tolerate hemoglobin (Hb) concentrations as low as 6.0 to 7.0 g per dL and recommend that range as the transfusion threshold in patients who have no overt signs of organ dysfunction. Nonetheless, "normal" Hb concentrations vary widely in the population, and this variability may influence patients' tolerance of acute anemia. This retrospective cohort study was carried out to test this hypothesis.
  
  
  METHODS
  Data were analyzed on 10,179 consecutive patients who had normal Hb concentrations (12.0-16.0 g/dL in women and 13.0-18.0 g/dL in men) and underwent on-pump cardiac surgery from 1999 to 2006 at an academic hospital. The relationships of lowest intraoperative Hb concentration and maximum decrease in Hb concentration (from baseline) with the composite outcome of in-hospital death, stroke, or kidney failure were determined in various patient subgroups.
  
  
  RESULTS
  The relationship between lowest Hb concentration and adverse outcomes was not independently associated with increased risk. In contrast, the relationship between maximum decrease in Hb concentration and adverse outcomes was independently associated with increased risk, with a 50 percent decrease being the threshold beyond which risk was increased (adjusted odds ratio, 1.53; 95% confidence interval, 1.12-2.08; p = 0.007).
  
  
  CONCLUSIONS
  The degree of acute anemia that patients can safely tolerate during cardiac surgery is inversely related to their baseline Hb concentration. Current transfusion guidelines do not account for this relationship.
authors.affiliation: Department of Anesthesia, University Health Network, University of Toronto, Toronto, Ontario, Canada. 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: Terrence M
authors.initials: TM
authors.lastname: Yau
authors.forename: Stuart A
authors.initials: SA
authors.lastname: McCluskey
authors.forename: Adriaan
authors.initials: A
authors.lastname: van Rensburg
authors.forename: W Scott
authors.initials: WS
authors.lastname: Beattie
mesh_terms: D000368:Aged; D000740:Anemia / Q000097:blood*; D005260:Female; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012307:Risk Factors; D013903:Thoracic Surgery / Q000379:methods*
chemical_list: D006454:Hemoglobins