Ca Kinetics in Dialysis Therapy

The primary purposes of Ca kinetic modeling during dialysis are: (1) to quantitatively assess Ca mass balance during dialysis with current therapy; (2) to determine the feasibility of predicting Ca mass balance from key dialysis prescription parameters so that it can be prospective-ly prescribed and controlled in dialysis therapy, and (3) to minimize accumulation and inhibit vascular calcification and mortality. There are no reported studies that we are aware of attempting to develop a model to analyze Ca mass balance during dialysis. A review of this subject in PubMed for the past 30+years indicated the most complete balance data were contained in a paper by Hou et al. [1] published in the American Journal of Kidney Disease in 1991. They reported mean serial blood levels and total net dialysate flux every 30 min in 6 patients on three different concentrations of CdiCa - 3.50, 2.50 and 1.50 mEq/l. These mass balance data are extremely useful but the authors did not attempt to formulate a model for kinetic analysis of the data. Ca mass balance measurements were reported by Nolph et al. [2] in 1974 for continuous ambulatory peritoneal dialysis (CAPD) with CdiCa = 0. The Nolph data were combined with the Hou data to provide data sets covering a very wide range of Ca dialysance for purposes of initial model development. Two other useful


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Dr. Frank Gotch

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Fig. 1. Ca mass balance in dialysis therapy is undefined. Can we inhibit vascular calcification by minimizing Ca accumulation?

Net gut intake Ca Gnca

Interdialytic interval

Dietary Ca + CaCo3

Secreted gut Ca


Bone cation

Vascular Calcification t(CCa * CPO4)


Complex hormonal control?

Net dialyzer removal Ca Jdc

During dialysis


CdiCa > CPiCa

CdiCa < CpiC

Ca data sets were found [3, 4] and used for the development of the model described below. Several other reports of mass balance in the literature were found but most reporting measurements of ionized Ca (CCa2+) which, as will be shown below, do not yield reproducible mass balance calculations. The initial formulation of a Ca mass balance model reported here was evaluated by the feasibility of closing mass balance on reported data [1-4].

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