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 (KIDt/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 KIDt/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 KIDt/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 (VWatson; VChertow), double-pool urea kinetic modelling (VUKM) and by ionic dialysance (VIOD) [Diascan; Hospal®]. Results. The use of VUKM or VIOD instead of VWatson or VChertow improved the relation between eKt/V and KIDt/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), KIDt/VUKM (1.19±0.30) and KIDt/ VIOD (1.21±0.25) were comparable. Intra-class correlation coefficient of VIOD was 0.87 with a 1-month interval and <0.75 after 2 and 3 months. Intra-class correlation coefficient of VDP was 0.79 with a 1-month interval and <0.75 after 2 and 3 months. Inter-treatment variation in KIDt/V during six consecutive dialysis sessions was 6.1%±0.6%. Changes in blood flow were the main determinant of variations in KIDt/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 intradialytic change in ionic dialysance (P<0.05). Conclusion. The use of VIOD and VUKM results in better agreement between eKt/V and KIDt/V compared with anthropometric formulae. KIDt/V was comparable with eKt/V and thus lower than expected for a single-pool method. VIOD and VUKM, should be assessed at least monthly. KIDt/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. © The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.