Agreement between the Classical Urea Kinetic Model and Direct Dialysis Quantification: Importance of Urea Rebound

Abstract

From a review of the literature regarding kinetic models used for assessing the adequacy of hemodialysis, no definite conclusions can be drawn as to whether the classical urea kinetic model (UKM) or modified direct dialysis quantification (mDDQ) is more reliable. We compared mDDQ with classical UKM and with a modified UKM that employs an equilibrated urea value. From the theoretical viewpoint, no substantial conflict is found between the two models as regards the dialysis dose, if urea rebound is considered. From the practical viewpoint, in our opinion direct quantification lends itself better for experimental purposes whereas for routine K_t/V evaluation UKM is easier and accurate enough, provided that rebound is taken into account.

Assessment of the Length of Each Hemodialysis Session by On-Line Dialysate Urea Monitoring

“…Whole body urea clearance (K) was calculated as the removed urea divided by the product of the length of the session and log mean urea concentration [16](see ‘Appendix’). To evaluate the variability of the time required to attain the target dose of dialysis, the duration of the midweek session of the second study week (HD 5 in fig.…”

“…G week was compared with the total urea removed during the three hemodialysis sessions of the second study week. Simultaneously to G 1 , G 2 and G 3 calculations, V was determined in each treatment from an intradialytic mass balance equation by the single-pool or by the double-pool model, according to DDQ [8], using a variable-volume modified formula [16]. The V was also obtained using the anthropometric Watson formulas [17].…”

“…Ur = urea removal, Td = length of the hemodialysis session, C 1 and C rebound = predialysis and rebound serum urea concentrations, respectively [16]. …”

“…(2) Urea generation rate was calculated between every two hemodialysis sessions of the second study week (G 1 , G 2 and G 3 ) [16]:…”

“…For single-pool V calculation, Td = length of dialysis in minutes and C 2 = postdialysis serum urea concentration. For double-pool V calculation, Td = length of dialysis + 45 and C 2 = serum urea concentration 45 min after the end of the dialysis session [16]. …”