Total dialysate calcium effects on calcium balance during dialysis

Total dialysate calcium concentration has an important influence on calcium metabolism in bicarbonate high-flux dialysis. The aim of the study is to investigate the influence of different dialysate calcium concentrations on serum concentration of ionised calcium and on the balance of total dialysate calcium.

A total of 20 stable aneuric patients on chronic bicarbonate high-flux haemodialysis with a frequency of 4 hours, 3 times per week with two different concentrations of total dialysate calcium (tdCa) were included in the study. Dialysis in the first session was performed with total dialysate calcium of 1.25 mmol/L, and at the next session with dialysate calcium of 1.5 mmol/L. The serum concentrations of total and ionized calcium were determined before and after each dialysis session. The balance of total dialysate calcium was measured on the dialysate side.

Serum concentration of total calcium before and after haemodialysis did not show any significant difference in HD with a total dialysate calcium of 1.25 mmol/L (2.40 ± 0.19 mmol/L before HD and 2.46 ± 0.15 mmol/L after HD). Serum ionized calcium in HD with tdCa 1.25 significantly decreased after HD (1.16 ± 0.09 mmol/L before HD to 1.08 ± 0.04 mmol/after HD, p < 0.05). The total serum calcium significantly increased after HD in comparison to HD with tdCa of 1.5 mmol/L (2.40 ± 0.15 mmol/L to 2.65 ± 0.16 mmol/L, p < 0.05). The concentration of serum ionized calcium did not increase significantly in HD with tdCa 1.50 mmol/L (1.16 ± 0.08 mmol/L to 1.20 ± 0.05 mmol/L). Average values of total dialysate calcium balance (gradient of diffusion between dialysate and patient) were negative in tdCa 1.25 (1.38 ± 0.08 mmol/L versus 1.48 ± 0.43 mmol/L), but in HD with tdCa 1.5 were slightly positive (1.56 ± 0.07 mmol/L versus 1.52 ± 0.07).

The use of total dialysate calcium of 1.5 mmol/L is beneficial because balance values of total dialysate calcium are slightly positive, but serum concentration of ionized calcium stays in the normal range.