LAUSR

To the Editor: We have read with great interest the excellent review of Basile et al and would like to add two more potential adverse effects of high dialysate bicarbonsate. We have recently published a pilot study evaluating the influence of dialysate bicarbonate concentration on intradialytic calcium balance and plasma PTH level changes in chronic dialysis patients. We found that dialysate bicarbonate influences plasma calcium, calcium balance, and intradialytic PTH levels. A higher dialysate bicarbonate decreases intradialytic losses of calcium and can result in actual calcium gains. These effects are primarily a result of the influence of alkalinization on plasma ionized calcium. As a patient is alkalized, plasma ionized calcium decreases which increases the diffusive gradient of ionized calcium from dialysate to the patient during the treatment. At the same time, intradialytic alkalinization leads to increased PTH secretion, also a consequence of the decreased plasma ionized calcium associated with the increased blood pH (Figure 1). Paradoxically, despite the alkalinization‐induced decrease in plasma ionized calcium observed after dialysis, the amount of calcium transferred from the dialysate to the patient increases. This may favor progression of extraosseal calcification, probably a leading cause of morbidity and mortality in patients undergoing dialysis. The quantitative significance of the described phenomenon is illustrated in Figure 2, where we compared our measurements using dialysate bicarbonate concentrations 26 and 32 mmol/L with the study of Basile et al, where a concentration of 35 mmol/L was used (dialysate calcium concentration was 1.25 mmol/L for all measurements). It is apparent that dialysate bicarbonate concentration is associated with a clinically important effect on calcium mass balance.