title: Acute normovolemic hemodilution does not reduce antithrombin concentration for cardiac surgery.
abstract: BACKGROUND
  Acute normovolemic hemodilution (ANH) is used to reduce allogeneic blood transfusion with cardiac surgery. This procedure involves pre-operatively removing and storing a volume of whole blood and replacing the volume with crystalloid. The stored blood is then available for transfusion, if required. Hemodilution associated with ANH may reduce the effectiveness of heparin anticoagulation due to dilution of antithrombin. The aim of this study was to determine if antithrombin concentrations are reduced in patients who undergo one unit of ANH during cardiac surgery.
  
  
  METHODS
  Patients scheduled for cardiac surgery (n = 71) were grouped according to whether they did or did not undergo ANH pre-operatively. Antithrombin concentrations were measured before and after ANH. This study had 80% power to detect a difference in reduction of antithrombin concentration of 6% between groups following ANH with an alpha error of <0.05. The effect of one unit ANH was expected to cause a difference of 12% or greater.
  
  
  RESULTS
  No significant difference in the concentration of antithrombin between ANH patients and those that did not have ANH, nor was there a difference in the decrease in antithrombin between groups.
  
  
  CONCLUSIONS
  The results indicate that one unit of ANH does not significantly reduce the concentration of antithrombin prior to cardiac surgery. Thus patients who undergo one unit of ANH are not at increased risk due to dilution of antithrombin.
authors.affiliation: Department of Pathology, University of Western Australia, Nedlands, Western Australia, Australia. matthew.linden@umassmed.edu
authors.forename: Matthew Dean
authors.initials: MD
authors.lastname: Linden
authors.forename: Mark
authors.initials: M
authors.lastname: Schneider
authors.forename: Wendy Naomi
authors.initials: WN
authors.lastname: Erber
mesh_terms: D000368:Aged; D000990:Antithrombin III / Q000032:analysis*; D006348:Cardiac Surgical Procedures / Q000379:methods*; D002315:Cardiopulmonary Bypass; D000077324:Crystalloid Solutions; D005260:Female; D006438:Hemodilution / Q000009:adverse effects*; D006801:Humans; D007552:Isotonic Solutions; D008297:Male; D008875:Middle Aged; D010952:Plasma Substitutes / Q000627:therapeutic use; D011300:Preoperative Care
chemical_list: D000077324:Crystalloid Solutions; D007552:Isotonic Solutions; D010952:Plasma Substitutes; D000990:Antithrombin III