Dialysate calcium study in alternate night nocturnal haemodialysis

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Elevated calcium phosphate product (Ca x P) is an independent risk factor for vascular calcification and cardiovascular death in the end-stage renal disease (ESRD) population (Block et al, 1998). Conventional haemodialysis (4hrs x 3) may not successfully correct the profound disturbances in calcium and phosphate metabolism of ESRD, characterised by hyperphosphatemia and abnormal serum calcium levels. In general a low calcium dialysate (1.3 mmol/L) is used for patients on conventional haemodialysis in North West Dialysis Service (NWDS), at Monash Medical Centre (MMC) and Geelong Hospital and throughout Australia. The calcium and phosphate balance achieved with Quotidian Nocturnal Haemodialysis (8 hours x 6 days) differs significantly from conventional haemodialysis and is associated with marked improvements in the reduction of elevated serum phosphate levels. An observational study by Lindsay et al demonstrated that patients on quotidian haemodialysis utilising 1.25 mmol/L dialysate calcium exhibited calcium depletion and hypocalcemia thus exacerbating secondary hyperparathyroidism (Lindsay et al, 2003). In the same study they demonstrated that an increase in dialysate calcium concentration was associated with a return of bone alkaline phosphatase levels to baseline and a gradual fall of parathyroid hormone (PTH) levels to target range. In association with the increase in dialysate calcium, the use of activated vitamin D compounds fell. Based on the results of this study, it has been common practice to dialyse all nocturnal haemodialysis patients, regardless of whether they dialyse for 8 hrs x 6 or 8 hrs x 3.5, on higher calcium baths (>1.6 mmol/L). It is not clear however, what should be the optimal calcium bath for patients on 8 x 3.5nights/week, particularly as serum phosphate levels are not as tightly controlled with quotidian haemodialysis, and unlike the 6 nights/week group, many patients still require the use of calcium based phosphate binders. Ideally the optimal calcium bath should be such that the overall Ca x P product is <4mmol2/l2 and the PTH 15-30pmol/l, however the concern is that the use of a higher calcium bath in the alternate night group will lead to relative hypercalcemia and an overall increase in Ca x P. Recent evidence also supports the importance of the pleiotropic effects of Vitamin D in addition to its well-recognised role in bone metabolism. It is conceivable that patients being dialysed with a higher calcium bath may not be able to tolerate the addition of Vitamin D due to the development of hypercalcemia. In order to establish the optimal calcium bath in patients on alternate night haemodialysis, we propose a prospective observational study comparing predefined outcomes using >1.6mmol/L and 1.3mmol/L dialysate calcium.

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