title: Ionic dialysance and the assessment of Kt/V: the influence of different estimates of V on method agreement.
abstract: BACKGROUND
  Ionic dialysance was recently introduced as a means to assess Kt/V (K(ID)t/V). With this method, urea distribution volume (V) has to be estimated. The primary aim of the present study was to assess the agreement between equilibrated Kt/V assessed by urea kinetic modelling (eKt/V) with K(ID)t/V taking into account different estimates of V, and to assess the monthly variation in V. Secondly, the mechanisms behind the intra-treatment changes in ionic dialysance and inter-treatment variability of K(ID)t/V were assessed.
  
  
  METHODS
  Sixty-six patients were included. eKt/V was estimated using 30 min post-treatment sampling in the second generation Daugirdas equation. V was assessed by the formulae of Watson and Chertow (V(Watson); V(Chertow)), double-pool urea kinetic modelling (V(UKM)) and by ionic dialysance (V(IOD)) [Diascan; Hospal(R)].
  
  
  RESULTS
  The use of V(UKM) or V(IOD) instead of V(Watson) or V(Chertow) improved the relation between eKt/V and K(ID)t/V (both r = 0.93; P < 0.001 vs r = 0.84 and r = 0.81; P < 0.001). Mean values of eKt/V (1.19 +/- 0.21), K(ID)t/V(UKM) (1.19 +/- 0.30) and K(ID)t/V(IOD) (1.21 +/- 0.25) were comparable. Intra-class correlation coefficient of V(IOD) was 0.87 with a 1-month interval and <0.75 after 2 and 3 months. Intra-class correlation coefficient of V(DP) was 0.79 with a 1-month interval and <0.75 after 2 and 3 months. Inter-treatment variation in K(ID)t/V during six consecutive dialysis sessions was 6.1% +/- 0.6%. Changes in blood flow were the main determinant of variations in K(ID)t/V (P < 0.05). During treatment, ionic dialysance decreased by 12 +/- 13 ml/min (P < 0.001). The decline in blood volume was the major determinant of the intra-dialytic change in ionic dialysance (P < 0.05).
  
  
  CONCLUSIONS
  The use of V(IOD) and V(UKM) results in better agreement between eKt/V and K(ID)t/V compared with anthropometric formulae. K(ID)t/V was comparable with eKt/V and thus lower than expected for a single-pool method. V(IOD) and V(UKM), should be assessed at least monthly. K(ID)t/V varies widely between consecutive dialysis sessions, mainly due to differences in blood flow. During treatment, ionic dialysance decreases, which is related to the relative decline in blood volume.
authors.affiliation: Department of Internal Medicine, Máxima Medical Centre, Veldhoven, The Netherlands.
authors.forename: Karin
authors.initials: K
authors.lastname: Moret
authors.forename: Charles H
authors.initials: CH
authors.lastname: Beerenhout
authors.forename: A Warmold L
authors.initials: AW
authors.lastname: van den Wall Bake
authors.forename: Paul G
authors.initials: PG
authors.lastname: Gerlag
authors.forename: Frank M
authors.initials: FM
authors.lastname: van der Sande
authors.forename: Karel M
authors.initials: KM
authors.lastname: Leunissen
authors.forename: Jeroen P
authors.initials: JP
authors.lastname: Kooman
mesh_terms: D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007477:Ions / Q000737:chemistry*; D007668:Kidney / Q000378:metabolism / Q000502:physiology; D007700:Kinetics; D008297:Male; D015233:Models, Statistical; D008962:Models, Theoretical; D015203:Reproducibility of Results; D013997:Time Factors; D014508:Urea / Q000737:chemistry
chemical_list: D007477:Ions; D014508:Urea