AN OPTIMAL POTASSIUM, CALCIUM, AND MAGNESIUM DIALYSATE FOR GENERAL USE

Because of the increasing lee of calcium (Ca) and magnesium (Mg) salts as phosphate (PO4) binders and the increased use of active vitamin D metabolites, combined with patient compliance problems related to low- potassium (K) diets, the concentrations of K, Ca, and Mg found in dial ysates are now often lowered to avoid problems of hyperkalemia, hyperc alcemia, and hypermagnesemia. While recent studies have evaluated chan ges in a particular electrolyte this study was performed to evaluate t he effects of reducing all 3 electrolytes over a 3-month period. Patie nts aged 19 to 72 years were randomly allocated to either continue wit h their usual bicarbonate dialysate (K, 2.0 mmol/L; Ca, 1.8 mmol/L; Mg , 0.5 mmol/L) or commence dialysis with a low-electrolyte dialysate (K , 1.0 mmol/L, Ca, 1.45 mmol/L, Mg, 0.25 mmol/L). Blood samples were co llected at the study's commencement and then monthly thereafter. Patie nt groups were comparable, including the use of Ca2CO3, Mg trisilicate , and calcitriol. Mean plasma K concentration fell significantly withi n 1 month in the low-electrolyte dialysate group, and at the third mon th the post-dialysis concentration was 2.9 +/- 0.12 mmol/L. While the pre-dialysis plasma Ca concentration did not change in the low-electro lyte dialysate group over the 3-month period, serum intact parathyroid hormone (iPTH) was significantly increased (35%) at 3 months. A subgr oup analysis showed that those patients with plasma Ca concentrations greater than 2.70 mmol/L did demonstrate a fall in mean plasma Ca over the 3-month period but without a concomitant fall in iPTH. Plasma Mg concentrations fell in a similar fashion to those of K. Plasma PO4 con centrations were unaltered by the low-electrolyte dialysate, yet the p ost-dialysis fall at 3 months was greatest in this patient group. This study suggests that dialysate composition should be tailored to meet the needs of individual patients rather than target a large group. In addition, dialysate Ca concentrations lower than 1.5-1.6 mmol/L can le an to significant worsening of hyperparathyroidism, and the lower the dialysate Ca concentration the greater the need for Ca2CO3 and active vitamin D metabolites, possibly in large doses.