title: Ultrafiltration method for measuring vascular access flow rates during hemodialysis.
abstract: BACKGROUND
  The vascular access blood flow rate (QA) has been shown to be an important predictor of vascular access failure; therefore, the routine measurement of QA may prove to be a useful clinical method of vascular access assessment.
  
  
  METHODS
  We have developed a new ultrafiltration (UF) method for determining QA during HD from changes in arterial hematocrit (H) after abrupt changes in the UF rate with the dialysis blood lines in the normal (DeltaHn) and reverse (DeltaHr) configurations. This method accounts for cardiopulmonary recirculation and requires neither intravenous saline injections nor accurate knowledge of the dialyzer blood flow rate. Clinical studies were conducted in 65 chronic HD patients from three different dialysis programs to compare QA determined by the UF method with that determined by saline dilution using an ultrasound flow sensor.
  
  
  RESULTS
  Arterial H increased (P<0.0001) after abrupt increases in the UF rate when the lines were in the normal and reverse configurations. An increase in the UF rate from the minimum setting to 1.8 liter/hr resulted in a DeltaHn of 0.3+/-0.2 (mean +/- SD) H units and a DeltaHr of 1.6+/-1.0 H units. Q(A) values determined by the UF method (1050+/-460 ml/min) were 16+/-25% higher (P<0.001) than those determined by saline dilution (950+/-440 ml/min); the calculated QA values by the UF and saline dilution methods correlated highly with each other (R = 0.92, P<0.0001). The average coefficient of variation for duplicate measurements of QA determined by the UF method in a subset of these patients (N = 21) was approximately 10% when assessed in either the same dialysis session or consecutive sessions.
  
  
  CONCLUSIONS
  The results from this study show that changes in arterial H after abrupt changes in the UF rate can be used to assess Q(A).
authors.affiliation: Research and Medical Services, Salt Lake City VA Medical Center, and Department of Internal Medicine, University of Utah, USA.
authors.forename: D
authors.initials: D
authors.lastname: Yarar
authors.forename: A K
authors.initials: AK
authors.lastname: Cheung
authors.forename: P
authors.initials: P
authors.lastname: Sakiewicz
authors.forename: R M
authors.initials: RM
authors.lastname: Lindsay
authors.forename: E P
authors.initials: EP
authors.lastname: Paganini
authors.forename: R R
authors.initials: RR
authors.lastname: Steuer
authors.forename: J K
authors.initials: JK
authors.lastname: Leypoldt
mesh_terms: D001783:Blood Flow Velocity; D002408:Catheters, Indwelling; D005069:Evaluation Studies as Topic; D005260:Female; D006400:Hematocrit; D006438:Hemodilution / Q000379:methods / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008955:Models, Cardiovascular; D006435:Renal Dialysis; D015203:Reproducibility of Results; D014462:Ultrafiltration / Q000379:methods*