title: The Unintended Consequences of Over-Reducing Cardiopulmonary Bypass Circuit Prime Volume.
abstract: BACKGROUND
  The Society of Thoracic Surgeon blood conservation guidelines recommend minimizing cardiopulmonary bypass circuit prime volume (PV) as an integral, evidence-based (Class I, Level A) blood conservation strategy. We used a large, multiinstitutional registry to evaluate the effectiveness of restricting cardiopulmonary bypass PV on intraoperative red blood cell (RBC) transfusion.
  
  
  METHODS
  We reviewed 47,273 isolated coronary artery bypass graft procedures performed among 189 institutions between April 2012 and May 2015. The primary outcome was intraoperative transfusion of at least 1 unit RBC; the secondary outcome was intraoperative transfusion of 4 or more units RBC. We estimated the adjusted odds of each transfusion type using separate multivariable logistic regression models that controlled for 13 confounding factors. The effect of PV on odds of transfusion was modeled using restricted cubic splines to assess possible nonlinearity.
  
  
  RESULTS
  We found a statistically significant nonlinear pattern in the relation between PV and odds of transfusion of both 1 or more units RBC (χ2= 116.3, df = 4, p < 0.001) and 4 or more units RBC (χ2= 25.9, df = 4, p < 0.001). The lowest probability of transfusion of 1 or more units RBC was estimated at a ratio of PV to estimated blood volume of 0.152 (p < 0.001).
  
  
  CONCLUSIONS
  Efforts to minimize PV below 15% of a patient's estimated blood volume do not protect patients from intraoperative RBC transfusion, and may increase exposure. Prime volume can affect both patient morbidity and the economic impact associated with blood utilization. Further studies on the effect of PV on blood transfusion are warranted.
authors.affiliation: Minneapolis Heart Institute, Minneapolis, Minnesota. Electronic address: benjamin.sun@allina.com.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Sun
authors.affiliation: Mayo Clinic Rochester, Rochester, Minnesota.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Dickinson
authors.affiliation: SpecialtyCare, Nashville, Tennessee.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Tesdahl
authors.affiliation: Center for Health Outcomes and Policy, University of Michigan, Ann Arbor, Michigan.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Likosky
authors.affiliation: SpecialtyCare, Nashville, Tennessee.
authors.forename: Christopher
authors.initials: C
authors.lastname: Wells
authors.affiliation: SpecialtyCare, Nashville, Tennessee.
authors.forename: Samuel
authors.initials: S
authors.lastname: Weinstein
mesh_terms: D000368:Aged; D001803:Blood Transfusion / Q000706:statistics & numerical data*; D002315:Cardiopulmonary Bypass / Q000379:methods*; D001026:Coronary Artery Bypass; D005260:Female; D006355:Heart-Lung Machine; D006438:Hemodilution; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011183:Postoperative Complications