title: Blood volume measurement by hemodilution: association with valve disease and re-evaluation of the Allen Formula.
abstract: BACKGROUND
  Total blood volume (TBV) assessment is central to the management of cardiac surgical patients with cardiopulmonary bypass (CPB). The widely accepted Allen Formula lacks accuracy in estimating TBV in these patients. Moreover, the impact of commonly encountered cardiac disease states on TBV has not been systematically investigated. The aim of this study was to determine TBV by hemodilution (TBVHD) for patients with valve disease, compare TBVHD to algorithms frequently used during cardiac surgery and to modify the Allen Formula to better fit today's patient population.
  
  
  METHODS
  TBVHD was prospectively measured upon initiation of CPB. Ninety-six patients were grouped into 4 cohorts by preoperative diagnosis and compared to Allen and weight-based formulae in a univariate analysis: mitral regurgitation (MR), coronary artery disease requiring bypass surgery (CABG) and aortic stenosis (AS) ± CABG. The independent effects of height and weight on TBV were correlated to the original Allen Formula by multiple linear regression.
  
  
  RESULTS
  Patients with MR had significantly larger TBVHD compared to patients with AS, CABG or both. The smallest TBVHD was found in the patients with AS and CABG. The modified Allen Formula had an excellent model fit (R(2) = 0.88 and R(2) = 0.95 for males and females, respectively; p<0.001) while the classic formula overestimated TBV by 30% in males and females. For males, height impacted TBV calculations the most whereas weight was the predominant determinant in females.
  
  
  CONCLUSIONS
  Blood volume assessment via the Allen Formula or bodyweight overestimated TBV in cardiac surgical patients, with potential implications on their management. The assumption that MR frequently presents with increased intravascular volume was confirmed whereas AS patients with coronary disease had a relatively smaller TBV. Lastly, a modified Allen Formula to better reflect today's patient population was derived to reproducibly improve accuracy in mathematical estimates of TBV.
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, USA jhilberath@partners.org.
authors.forename: J N
authors.initials: JN
authors.lastname: Hilberath
authors.affiliation: Department of Anesthesiology, Warren Alpert School of Medicine, Rhode Island Hospital, Providence, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Thomas
authors.affiliation: Department of Cardiac Perfusion, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
authors.forename: T
authors.initials: T
authors.lastname: Smith
authors.affiliation: Department of Cardiovascular Perfusion, Duke University Medical Center, Durham, USA.
authors.forename: C
authors.initials: C
authors.lastname: Jara
authors.affiliation: Department of Cardiac Perfusion, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Fitzgerald
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
authors.forename: K
authors.initials: K
authors.lastname: Wilusz
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Muehlschlegel
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001024:Aortic Valve Stenosis / Q000503:physiopathology / Q000601:surgery*; D001810:Blood Volume; D002315:Cardiopulmonary Bypass; D001026:Coronary Artery Bypass; D003324:Coronary Artery Disease / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006438:Hemodilution; D006801:Humans; D008875:Middle Aged; D008944:Mitral Valve Insufficiency / Q000503:physiopathology / Q000601:surgery*
keywords: Allen Formula; cardiac surgery; cardiopulmonary bypass; hemodilution; total blood volume measurement