Prescribing Hemodialysis Using a Weekly Urea Mass Balance Model

Abstract

Prescribing hemodialysis by monitoring only predialysis BUN concentrations is not sufficient to guarantee adequate therapy. Results from the National Cooperative Dialysis Study have suggested that hemodialysis therapy is adequate if the protein catabolic rate is maintained greater than 1 g/day/kg body weight and simultaneously if sufficient hemodialysis is prescribed to maintain either a time-averaged BUN concentration (TACurea) less than 50 mg/dl or a value of Kt/V greater than unity. In the present study mathematical relationships were derived from a weekly urea mass balance model that permit an evaluation of TACurea and of protein catabolism via the urea generation rate (G) without the need for conventional urea kinetic modeling. The parameters TACurea and G were simply calculated from a midweek predialysis BUN concentration (BUNMw) by:TACurea = 0.7 BUNMw G =0.7BUNMw(Kr+Kdτ/T) where Kr, Kd,τ and T denote residual renal urea clearance, dialyzer urea clearance, number of minutes of hemodialysis per week, and number of minutes total in a week, respectively. Clinical results from 139 modeling sessions on 91 patients demonstrated that TACurea and G derived from urea kinetic modeling correlated highly with those calculated from the above equations (r = 0.96 and 0.94, respectively). It is concluded that individualized hemodialysis prescription and adequacy of therapy can be assessed by monitoring TACurea and G by calculation from a weekly urea mass balance model.

The Modeling Game

“…He may change his equations or add additional ones, as needed, to provide better and better predictions until he is content that his model achieves a suitable level of accura cy. This exercise is well illustrated in the arti cle by Vonesh et al [2].…”

“…Ripple and Stelin [8] postu late more than one pore size to make this reconciliation. The modeling by Vonesh et al [2] of peritoneal dialysis falls toward the curve fitting side of the spectrum.…”

“…This level of qualifi cation has not as yet happened. Vonesh et al [2] have taken a crucial step in the first level of qualification (model validation) and this model may now be used to establish levels of treatment adequacy. We have, at present, satisfactory clinical guidelines developed empirically by clinician scientists that call for certain levels of weekly clearance for urea and creatinine [10].…”

“…The first by Vonesh et al [1] applies UKM to the patient undergoing CAPD. The second by Leypoldt et al [2] offers a user-friendly modification of the urea kinetic modeling (UKM) equa tions for hemodialysis prescription. Kinetic modeling of dialysis therapy is not a new game and reaches back at least to work by Babb et al and their dialysis index [3].…”

A Bayesian approach for the identification of patient-specific parameters in a dialysis kinetic model

“…Moreover, a need for treatment customization emerged over the years, to reduce the associated comorbidities, because the individual tolerance to HD may vary from patient to patient also in the presence of similar treatment conditions. 7,8 Instruments that simulate and predict the patient-specific response to HD treatment in terms of electrolyte and catabolite kinetics are a necessary step toward customization, in order to identify the most suitable therapy for reducing intra-dialysis complications and associated long-term dysfunctions.…”