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Publication:
Author Interview: Dr. Carlo Basile, MD

Effect of Dialysate Calcium Concentrations on Parathyroid Hormone and Calcium Balance During a Single Dialysis Session Using Bicarbonate Hemodialysis: A Crossover Clinical Trial

Carlo Basile, Pasquale Libutti, Anna Lucia Di Turo, Luigi Vernaglione

DOI: 10.1053/j.ajkd.2011.08.033

Our highly controlled single dialysis session studies using a crossover design and precise solute mass balances show that a dialysate total calcium concentration of 2.75 mEq/L (not yet commercially available) might be preferable to 2.5 or 3.0 mEq/L because it is able to give a mildly positive calcium mass balance, while maintaining normal plasma water ionized calcium levels and not stimulating short-term PTH secretion.

All ionized and total calcium mass balances were strongly positive (i.e. a gain of calcium for the patient because of a diffusion gradient from the dialysate to the patient) when using a dialysate total calcium concentration of 3.0 mEq/L. Only 6 out of 22 calcium mass balances were negative with a dialysate total calcium concentration of 2.5 mEq/L. Not many published data show strong positive calcium mass balances when using a dialysate total calcium concentration of 3.0 mEq/L and even more mean mildly positive calcium mass balances when using a dialysate total calcium concentration of 2.5 mEq/L.

A dialysate total calcium concentration of 3.0 mEq/L should be discouraged, or employed with caution in selected cases because of a large calcium load and a probably excessive short-term suppression of PTH secretion. A dialysate total calcium concentration of 2.5 mEq/L might be a good choice (slight calcium load), if it were not for the risk of secondary hyperparathyroidism, as shown by some long-term studies.

A dialysate total calcium concentration of 2.75 mEq/L could be a better choice because it is able to give a mildly positive calcium mass balance, while maintaining normal plasma water ionized calcium levels and not stimulating short-term PTH secretion.

Long-term studies are needed to confirm that the results we found in single dialysis sessions persist over multiple sessions and that they translate into improved clinical outcomes.

Background

In bicarbonate-based hemodialysis, dialysate total calcium (tCa) concentration may have effects on mineral metabolism.

Study Design

Randomized crossover trial of 3 dialysate tCa concentrations (2.5, 2.75, and 3.0 mEq/L).

Setting & Participants

22 stable anuric uremic patients underwent three 4-hour bicarbonate hemodialysis sessions with the 3 different dialysate tCa concentrations using a single-pass batch dialysis system.

Outcomes

Hourly measurements of plasma water ionized calcium (iCa) and plasma parathyroid hormone (PTH) concentrations. tCa mass balances were measured from the dialysate side.

Results

Hourly plasma water iCa concentrations were higher with a dialysate tCa concentration of 3.0 compared with 2.75 and 2.5 mEq/L (P < 0.05), as were iCa concentrations at the end of dialysis sessions (2.66 ± 0.1, 2.56 ± 0.12, and 2.4 ± 0.08 mEq/L, respectively; P < 0.001). Mean tCa mass balance values (diffusion gradient from the dialysate to the patient) were positive with all dialysate tCa concentrations and increased progressively with dialysate tCa concentration (75 ± 122, 182 ± 125, and 293 ± 228 mg, respectively; P < 0.001). Plasma PTH levels increased during dialysis using dialysate tCa concentration of 2.5 mEq/L (mean increase, 225 ± 312 pg/mL) and decreased with dialysate tCa concentrations of 2.75 and 3.0 mEq/L (mean decreases, 68 ± 325 and 99 ± 432 pg/mL, respectively).

Limitations

Small sample size and lack of measurement of total-body calcium mass balances.

Conclusions

A dialysate tCa concentration of 2.75 mEq/L might be preferable to 2.5 or 3.0 mEq/L because it is associated with mildly positive tCa mass balance values, plasma water iCa levels in the reference range, and stable PTH levels during dialysis.