A kinetic model of calcium mass balance during dialysis therapy

A kinetic model of Ca mass balance during dialysis has been developed. It is a single-compartment, variable-volume model to compute Ca mass balance during dialysis in its volume of distribution, the extracellular fluid. The model was used to analyze literature data which were suitable for the assessment of Ca mass balance over the course of dialysis. The modeled analyses predicted the serial plasma Ca concentrations very well. The mass balance analyses revealed a pool of rapidly diffusible Ca beyond the extracellular fluid distribution volume where Ca could be mobilized (M+(Ca)) or sequestered (M-(Ca)) very rapidly at rate equal but opposite in sign to dialyzer flux and thus effectively maintain near constant plasma Ca in the face of dialyzer Ca concentration gradients. This pool is likely the large pool of diffusible (miscible) Ca in connective tissue and on bone surfaces. Analysis of net Ca flux during dialysis with Cdi(Ca) = 2.50 mEq/l suggests that 80% of patients are in positive Ca balance during dialysis. Further studies are required to verify the model and to develop a model of interdialytic Ca mass balance.