Calcium‐phosphate and parathyroid intradialytic profiles: A potential aid for tailoring the dialysate calcium content of patients on different hemodialysis schedules

Abstract

Severe hyperparathyroidism is a challenge on hemodialysis. The definition of dialysate calcium (Ca) is a pending issue with renewed importance in cases of individualized dialysis schedules and of portable home dialysis machines with low-flow dialysate. Direct measurement of calcium mass transfer is complex and is imprecisely reflected by differences in start-to-end of dialysis Ca levels. The study was performed in a dialysis unit dedicated to home hemodialysis and to critical patients with wide use of daily and tailored schedules. The Ca-phosphate (P)-parathyroid hormone (PTH) profile includes creatinine, urea, total and ionized Ca, albumin, sodium, potassium, P, PTH levels at start, mid, and end of dialysis. "Severe" secondary hyperparathyroidism was defined as PTH > 300 pg/mL for ≥3 months. Four schedules were tested: conventional dialysis (polysulfone dialyzer 1.8-2.1 m(2) ), with dialysate Ca 1.5 or 1.75 mmol/L, NxStage (Ca 1.5 mmol/L), and NxStage plus intradialytic Ca infusion. Dosages of vitamin D, calcium, phosphate binders, and Ca mimetic agents were adjusted monthly. Eighty Ca-P-PTH profiles were collected in 12 patients. Serum phosphate was efficiently reduced by all techniques. No differences in start-to-end PTH and Ca levels on dialysis were observed in patients with PTH levels < 300 pg/mL. Conversely, Ca levels in "severe" secondary hyperparathyroid patients significantly increased and PTH decreased during dialysis on all schedules except on Nxstage (P < 0.05). Our data support the need for tailored dialysate Ca content, even on "low-flow" daily home dialysis, in "severe" secondary hyperparathyroid patients in order to increase the therapeutic potentials of the new dialysis techniques.

Phosphate and Calcium Control in Short Frequent Hemodialysis with the NxStage System One Cycler: Mass Balance Studies and Comparison with Standard Thrice-Weekly Bicarbonate Dialysis

“…A first explanation of this increase is intradialytic weight loss (i.e., hemoconcentration), acting to increase Ca binding to albumin, as indicated by the direct correlation between total plasma Ca changes and weight loss. A lower increase in NSO (also described by others) [24], appears mostly related to lower intradialytic weight loss, almost half as in BHD. A second component of plasma Ca change was related to trans-membrane Ca exchanges as indicated by the direct relationship between total plasma Ca change and dialysate to blood Ca gradient.…”

“…We did not observe a lesser decrease of PTH as described by others [24], but start and end-session PTH values were available in a small number of our patients. It has to be expected that intra-dialytic PTH changes depend upon several factors, including the degree of changes in plasma iCa, basal PTH levels, and degree of functional autonomy of hyperplasic parathyroids [25].…”