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Calcium kinetics and the long-term effects of lowering dialysate calcium concentration
A Argilés1, P G Kerr, B Canaud
1LP9008 CNRS, Centre de Recherches en Biochimie Macromoléculaire, Montpellier, France.
Insights
Lowering dialysate calcium (dCa) to 1.25 mM during hemodialysis prevents hypercalcemia without altering long-term calcium or phosphate levels. This adjustment also maintained similar parathyroid hormone (PTH) levels compared to higher dCa concentrations.
Area of Science:
- Nephrology
- Mineral Metabolism
- Dialysis Therapy
Background:
- Classical hemodialysis calcium (Ca) levels are 1.75 mM.
- High dialysate Ca and CaCO3 use can cause hypercalcemia.
- Lowering dialysate Ca is proposed to prevent hypercalcemia.
Purpose of the Study:
- Assess acute and long-term effects of reduced dialysate Ca.
- Investigate i.v. 1-alpha vitamin D3 effectiveness in lowering PTH with different dialysate Ca levels.
Main Methods:
- Studied Ca kinetics in 9 patients using hemodialysis (HD) and hemodiafiltration (HDF) with sequential 1.75, 1.5, and 1.25 mM dialysate Ca.
- Measured blood and dialysate electrolytes, weight, blood pressure, and heart rate.
- Followed 7 patients for 1 year on 1.25 mM dCa vs. 6 controls on 1.5 mM dCa, monitoring Total Ca, phosphate, ALP, and PTH.
Main Results:
- Dialysate Ca reduction significantly altered intradialytic ionized calcium (iCa) kinetics.
- Post-dialysis iCa increased with 1.75 and 1.5 mM dCa, but not with 1.25 mM dCa.
- Long-term, low dCa (1.25 mM) required doubled CaCO3 intake but maintained similar Total Ca, phosphate, ALP, and PTH levels compared to 1.5 mM dCa.
Conclusions:
- Lowering dialysate Ca to 1.25 mM effectively prevents intradialytic calcium accumulation.
- This concentration is safe for long-term use, maintaining mineral balance and PTH levels.
- Dialysate Ca adjustment is a viable strategy to manage calcium balance in hemodialysis patients.
Abstract:
The optimal dialysate calcium (Ca) content for hemodialysis has been classically fixed at 1.75 mM. However, this dialysate Ca concentration (dCa) with its positive intradialytic Ca balance combined with the use of CaCO3 as a phosphate binder may result in hypercalcemia. To prevent or treat hypercalcemia, a decrease in dCa has been proposed. In the present study both the acute and the long-term effects of lowering dCa were assessed. Additionally, given the results obtained after one year with low dCa the effectiveness of i.v. 1 alpha vitamin D3 in lowering PTH serum levels in two groups of patients dialyzed with different dCa was also studied. (a) Ca kinetics during hemodialysis (HD) and on line hemodiafiltration (HDF) were studied in a group of nine stable patients who were sequentially treated with 1.75, 1.5 and 1.25 mM dCa. Dialysate was the same but for the dCa which was lowered stepwise. Na, K, tCa, ionized Ca (iCa), proteins, phosphate and pH were measured from blood inlet and outlet and dialysate outlet at the start, one hour, two hours and after the treatments. At the same time weight, blood pressure and heart rate were recorded. The sieving of iCa was significantly different in HDF versus HD (F = 6.73; P < 0.01); intravenous infusion of 18 liters of filtered ultrapure dialysate compensated the Ca loss due to the convective component of HDF, as iCa was similar at the blood inlet in HD and HDF in the three dCa tested (F = 2.59; NS). Intradialytic iCa kinetics measured in the blood inlet were significantly different with different dCa (P < 0.001 for 1.75 mM vs. 1.5 mm and P < 0.001 for 1.5 mM vs. 1.25 mM). A significant increase in post-dialysis iCa was observed with dCa of 1.75 and 1.5 while no modification was observed with 1.25 mM dCa. (b) Regarding long-term effects of lowering dCa, seven of the nine patients acutely studied were followed for a one year period after changing from dCa = 1.5 to dCa = 1.25 mM. A control group of six patients was maintained with dCa = 1.5 for the same period of time and with the same treatment schedule but for dCa. Total Ca, phosphate and alkaline phosphatase were assessed monthly, and phosphate binders and oral vitamin D derivative doses were adapted accordingly. Intact PTH was determined quarterly. CaCO3 oral intake was more than doubled in the low dCa group. Total Ca, phosphate and ALP were similar in both groups over the assessed year.(ABSTRACT TRUNCATED AT 400 WORDS)