The effects of dialysate acids and divalent ions on calcification and cardiovascular outcomes: old wisdom and new developments.

Dialysate calcium (DCa) and magnesium (DMg) and the organic acid used in the acid concentrate have a profound combined influence on intradialytic mineral balance and may influence vascular calcification progression and treatment-related symptoms. Whereas Kidney Disease: Improving Global Outcomes recommends a DCa between 1.25 (DCa 1.25) and 1.50 mmol/l (DCa 1.50), the optimal DCa for an individual patient remains uncertain. No consistent mortality difference between DCa 1.50 and 1.25 has been observed. However, DCa 1.50 may induce a positive calcium balance, raising concerns about vascular calcification progression. Conversely, DCa below 1.25 mmol/l has been associated with a higher risk of sudden cardiac death. Compared with acetic acid (acetate dialysate, Acet-D), citric acid (citrate dialysate, Cit-D) reduces calcification propensity of serum, although the effect on vascular calcification progression is inconclusive. Whenever feasible, DCa should be individualized, ideally using estimates of calcium mass balance (CaMB). Because Cit-D generally results in a more negative CaMB than Acet-D solutions at the same nominal DCa, this difference should be considered when prescribing DCa. Increasing DMg from 0.50 to 0.75 mmol/l may improve surrogate cardiovascular outcomes although its effect on clinical outcomes remains to be defined. Overall, Acet-D with DCa 1.25 is a reasonable standard especially when using calcium-containing phosphate binders and in patients at risk for adynamic bone disease, whereas in patients with a high risk of sudden cardiac death, frequent intradialytic hypotension or with severe secondary hyperparathyroidism, DCa 1.50 may be a reasonable alternative. Regarding the choice of acid, the use of Cit-D represents a promising alternative pending further clinical evidence.