Optimization of haemodialysis frequency and duration. A computer simulation study.

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Haemodialysis (HD) is a specific treatment for The aims of the present study were to forecast the uraemia, consisting of multiple doses administered urea concentration profile and TAC urea over time by rhythmically at time intervals not all equally spaced. computer simulation in a single-compartment variable It can be used for only 5‐9% of the lifetime of the volume (SPVV ) model. The eVects on TAC urea and uraemic patients and, therefore, it must be properly Kd*t/V of two HD schedules, the traditional alternate planned to ensure acceptable relief of the uraemic day HD and daily HD, each with three diVerent HD syndrome. However, the design of a good HD schedule durations, were compared at the steady state condition. is empirical, since the concepts of HD dose and The importance of achieving the steady state for adequacy are not completely agreed upon. adequate comparisons is emphasized. The importance of the urea kinetic modelling approach in evaluation of HD was the main conclusion of the National Cooperative Dialysis Study (NCDS) [1], as perhaps should have been expected, considering the fluctuating profiles of urea in the blood of uraemic Subjects and methods patients. The NCDS conclusions emphasized the importance of the time-averaged plasma urea concen- The patient‐haemodialysis system was described as a onetration ( TAC ) as a predictor of a good outcome. TAC compartment variable volume ( V t ) system, in which a diVusive first-order process takes place intermittently for a fixed urea includes removal of urea from the body and its time interval (t d ) and at a fixed frequency. The assumptions production, and thus may be considered a measure of of instantaneous and complete mixing inside the compartthe urea balance, provided that body volumes are not ment are assured by definition. The equations of the model grossly changed. In the following mechanistic analysis are shown in the Appendix. The analytical solutions of the of the NCDS data [2], Kd*t/V was proposed as a model equations are detailed in [3]. The initial compartment quantitative estimation of HD dose, in which Kd is volume ( V 0 ) was set at 38 l. During two consecutive HD, the urea clearance of the haemodialyser, t is the time the V t increased at a constant rate so that the same V 0 was duration of HD, and V is the volume distribution of reached at the end of the interval (t id ). The initial plasma the urea. Kd*t/V is a dimensionless number which urea concentration (C 0 ) was 180 mg/dl. A urea generation arises from analytical solution of ordinary diVerential rate (G u ) of 8.0 mg/min was assumed to follow zero-order kinetics. The HD filter was modelled as a subsystem with equations of the single-pool urea model and has clinical concentrated parameters, characterized by a clearance ( Kd ) meaning on its own. Neither TAC urea nor Kd*t/V of 160 ml/min and an ultrafiltration rate ( UFR) of 10 ml/min enable us to separate production of urea (represented during HD. Two HD regimens were planned, as follows: one by the protein catabolic rate in patients on nitrogen daily regimen with t