Impact of dialysate calcium concentration on the progression of aortic stiffness in patients on haemodialysis.

BACKGROUND Higher dialysate calcium (DCa) can result in an acute and transient increase in arterial stiffness. The aim of the present study is to evaluate the impact of DCa on the progression of arterial stiffness, calcium balance and bone metabolism in haemodialysis (HD) patients over a 6-month period. Method. We randomly assigned 30 patients on chronic HD to be dialysed with a DCa of 1.12 or 1.37 mmol/L for a period of 6 months. Aortic stiffness and brachial stiffness were respectively measured by carotid-femoral pulse wave velocities (cf-PWV) and carotid-radial pulse wave velocity (cr-PWV) at baseline and at 3 and 6 months. Central pulse pressure (PP) and augmentation index were determined by radial artery tonometry. Dialysis calcium balance and parathyroid hormone (PTH) were measured monthly. Procollagen type-1 amino-terminal propeptide (P1NP) and C-terminal telopeptide of type-I collagen (CTX) were measured as markers of bone formation and resorption, respectively. Data was analysed by linear mixed model. RESULTS Twenty-seven patients (66 ± 13 years old) with a mean duration of HD of 5.8 ± 3.6 months completed the study. At baseline, the groups were similar with respect to age, serum levels of calcium, phosphate and PTH, blood pressure (BP), cf-PWV and cr-PWV. The cf-PWV at baseline and 3 and 6 months were, respectively, 13.4 ± 4.2, 14.7 ± 3.31 and 13.6 ± 2.5 m/s in the DCa 1.12 group and 14.6 ± 5.9, 15.8 ± 7.8 and 17.0 ± 7.0 m/s in the DCa 1.37 group. After correction for mean BP, cf-PWV increased with DCa 1.37 as compared to DCa 1.12 (Time-DCa interaction P = 0.002). However, there were no significant effects of DCa on progression of cr-PWV, central PP or augmentation index. During the intervention period, the mean PTH was slightly higher in the DCa 1.12 group as compared to the DCa 1.37 group (325 ± 185 versus 211 ± 128 ng/L, P = 0.054), and dialysis calcium balance was -8.1 ± 4.4 versus -0.2 ± 4.7 mmol/session, respectively, in groups with DCa 1.12 and DCa 1.37 (P = 0.0001). Treatment with DCa 1.12 mmol/L resulted in increasing levels of CTX as compared to DCa 1.37 (P = 0.02), whereas the P1NP levels did not change significantly in either group. CONCLUSIONS In this study, aortic stiffness progressed with DCa 1.37, while it remained stable with DCa 1.12 over a 6-month period. These results suggest that higher DCa concentrations could be a risk factor for the progression of aortic stiffness in HD patients. In the context of limited oral calcium, the long-term safety of DCa 1.12 on bone metabolism remains to be established.