Modeling the Dose of Home Dialysis

The growing interest in daily dialysis and combined continuous and intermittent dialysis treatments has created the need for a dialysis dosing model that is valid over a wide range of dosing frequency and intensity. Three models have been described for this purpose and are reviewed here. They have in common the concept of a continuous clearance value which is equivalent to the summed intermittent dialysis prescribed. The continuous clearance models all define a point on the saw-toothed blood urea nitrogen (BUN) concentration profile and calculate the continuous clearance required to achieve this at the same urea generation rate. The points modeled are the peak predialysis concentration (pkKt/V), the average Co (standard Kt/V, stdKt/V), and time-averaged urea concentration (TAC), which is termed equivalent renal clearance (EKRt/V). At the present time the only data for evaluation of clinical relevance of the three models is continuous ambulatory peritoneal dialysis (CAPD) outcome. The stdKt/V predicts that optimal CAPD outcome requires weekly stdKt/V 2.0, while the pkKt/V and EKRt/V models predict optimal doses of 1.8 and 3.0. These results suggest that the stdKt/V is the most realistic model, but data over much higher levels of therapy are not yet available to judge generalizability. The stdKt/V model was used to assess dose in two hemodialysis studies with 5 to 6 dialyses per week and showed that in one study the stdKt/V was only 2.0, while in the second study it was 5.6. These results show that dose can vary widely with a similar number of dialyses per week and point to the need for a generalized dosing model to guide and compare studies of daily home dialysis.