Calcium mass balances in bicarbonate hemodialysis

Calcium mass balance in adults during single hemodialysis and hemodiafiltration treatments using lower calcium dialysate concentrations

BACKGROUND

Debate continues as to the optimum hemodialysis (HD) dialysate calcium concentration. Although current guidelines advocate 1.25-1.5 mmol/L, some investigators have suggested these may cause calcium gains. As such we investigated whether using dialysate calcium of 1.25 mmol/L risked calcium gains, and whether there were differences between hemodiafiltration and high flux HD.

METHODS

We continuously collect an aliquot of effluent dialysate during dialysis sessions, and calculated dialysis calcium mass balance by the difference between the amount of calcium delivered as fresh dialysate and that lost in effluent dialysate.

RESULTS

We studied 106 stable outpatients, 64% male, mean age 64.4 ± 16.2 years, median dialysis vintage 32 (22-60) months. Most sessions (69%) used a 1.0 mmol/L calcium dialysate, with a median sessional loss of 13.7 (11.5-17.1) mmol, whereas using 1.25 mmol/L the median loss was 7.4 (4.9-10.1) mmol, but with 6.9% had a positive balance (p = 0.031 vs dialysate calcium 1.0 mmol/L). Most patients (85.8%) were treated by hemodiafiltration, but there was no difference in sessional losses (11.7 (8.4-15.8) vs 13.5 (8.1-16.8)) with high flux HD. Dialysis sessional calcium balance was associated with the use of lower dialysate calcium concentration (β -19.5, 95% confidence limits (95%CL) -27.7 to -11.3, p < 0.001), and sessional duration (β 0.07 (95% CL) 0.03-012, p = 0.002).

CONCLUSION

Ideally, the choice of dialysate calcium should be individualized, but clinicians should be aware, that even when using a dialysate calcium of 1.25 mmol/L, some patients are at risk of a calcium gain during hemodiafiltration and high-flux hemodialysis.

The Crosstalk between Calcium Ions and Aldosterone Contributes to Inflammation, Apoptosis, and Calcification of VSMC via the AIF-1/NF-κB Pathway in Uremia

Vascular calcification is a major complication of maintenance hemodialysis patients. Studies have confirmed that calcification mainly occurs in the vascular smooth muscle cells (VSMC) of the vascular media. However, the exact pathogenesis of VSMC calcification is still unknown. This study shows that the crosstalk between calcium and aldosterone via the allograft inflammatory factor 1 (AIF-1) pathway contributes to calcium homeostasis and VSMC calcification, which is a novel mechanism of vascular calcification in uremia. In vivo results showed that the level of aldosterone and inflammatory factors increased in calcified arteries, whereas no significant changes were observed in peripheral blood. However, the expression of inflammatory factors markedly increased in the peripheral blood of uremic rats without aortic calcification and gradually returned to normal levels with aggravation of aortic calcification. In vitro results showed that there was an interaction between calcium ions and aldosterone in macrophages or VSMC. Calcium induced aldosterone synthesis, and in turn, aldosterone also triggered intracellular calcium content upregulation in macrophages or VSMC. Furthermore, activated macrophages induced inflammation, apoptosis, and calcification of VSMC. Activated VSMC also imparted a similar effect on untreated VSMC. Finally, AIF-1 enhanced aldosterone- or calcium-induced VSMC calcification, and NF-κB inhibitors inhibited the effect of AIF-1 on VSMC. These in vivo and in vitro results suggest that the crosstalk between calcium ions and aldosterone plays an important role in VSMC calcification in uremia via the AIF-1/NF-κB pathway. Local calcified VSMC induced the same pathological process in surrounding VSMC, thereby contributing to calcium homeostasis and accelerating vascular calcification.

Calcium balance in hemodialysis: More uncertainty than certainty

There is controversy about the choice of dialysate calcium concentration (DCa), with strong arguments both in favor of and against the use of a low or high DCa, as they can both be potentially harmful. Evidence suggests that calcium mass balance is positive with a DCa 3.5 mEq/L, negative or neutral with the use of DCa 2.5 mEq/L, whereas both positive and negative balances have been observed with the use of DCa 3.0 mEq/L. Overall, the use of DCa >2.5 mEq/L is usually associated with an increase in serum calcium level and a decrease in serum PTH level and use of lower vitamin D analogue dose, with the opposite effects usually observed with the use of lower DCa. Most of the available evidence is from small-sized and crossover studies; hence, evidence should be regarded with caution and applied in a patient-specific manner. As there are a lot of significant unanswered questions regarding calcium balance and the optimal DCa in hemodialysis patients, further high-quality research is needed to clarify many still unclear aspects of calcium homeostasis and balance in these patients. In conclusion, with the existing evidence the choice of DCa needs to be individualized and contextualized in the setting of each patient's calcium balance needs and homeostatic response, taking also into account oral calcium intake (dietary and medicinal), any other relevant therapy administered, such as vitamin D analogues, the type of renal mineral bone disorder, and associated cardiovascular comorbidity.

The Strategy to Prevent and Regress the Vascular Calcification in Dialysis Patients

The high prevalence of arterial calcification in end-stage renal disease (ESRD) is far beyond the explanation by common cardiovascular risk factors such as aging, diabetes, hypertension, and dyslipidemia. The finding relies on the fact that vascular and valvular calcifications are predictors of cardiovascular diseases and mortality in persons with chronic renal failure. In addition to traditional cardiovascular risk factors such as diabetes mellitus and blood pressure control, other ESRD-related risks such as phosphate retention, excess calcium, and prolonged dialysis time also contribute to the development of vascular calcification. The strategies are to reverse "calcium paradox" and lower vascular calcification by decreasing procalcific factors including minimization of inflammation (through adequate dialysis and by avoiding malnutrition, intravenous labile iron, and positive calcium and phosphate balance), correction of high and low bone turnover, and restoration of anticalcification factor balance such as correction of vitamin D and K deficiency; parathyroid intervention is reserved for severe hyperparathyroidism. The role of bone antiresorption therapy such as bisphosphonates and denosumab in vascular calcification in high-bone-turnover disease remains unclear. The limited data on sodium thiosulfate are promising. However, if calcification is to be targeted, ensure that bone health is not compromised by the treatments.

Calcium Mass Balance during Citrate Hemodialysis: A Randomized Controlled Trial Comparing Normal and Low Ionized Calcium Target Ranges

BACKGROUND

Regional citrate anticoagulation (RCA) during hemodialysis interferes with calcium homeostasis. Optimal ionized calcium (iCa) target range during RCA and consequent calcium balance are unknown.

METHODS

In a randomized controlled trial (ACTRN12613001029785) 30 chronic hemodialysis patients were assigned to normal (1.1-1.2 mmol/) or low (0.95-1.05 mmol/l) iCa target range during a single hemodialysis with RCA. The primary outcome was calcium mass balance during the procedure, using a partial spent dialysate collection method; magnesium mass balance was also measured. Intact parathormone (iPTH), total calcium (tCa) and magnesium were measured before and after procedures.

RESULTS

Mean iCa during procedures was significantly different in the two groups (1.12±0.06 in normal and 1.06±0.07 mmol/l in low iCa group, p <0.001), resulting in different tCa (2.18±0.22 vs. 1.95±0.17, p = 0.003) after the procedure. Mean delivered calcium during the procedure was 58.3±4.8 mmol in the normal and 51.5±8.2 mmol in the low iCa group (p = 0.010), which resulted in a significantly higher mean positive calcium mass balance of 14.6±8.3 mmol (584±333 mg) per procedure in normal as compared to 7.2±8.5 mmol (290±341 mg) in low iCa group (p = 0.024). Linear mixed effects model showed a significant interaction effect of time and iCa target range group on iPTH, i.e. a significant increase in iPTH in the low as compared to normal iCa target group (p = 0.008). Magnesium mass balance was mildly negative and comparable in both groups.

CONCLUSIONS

Low iCa target range resulted in a significantly less positive calcium mass balance, but in a significant increase in iPTH. To achieve a more neutral calcium balance, we recommend allowing a mild hypocalcemia during hemodialysis with RCA, especially when it is used for prolonged periods.

Acute calcium kinetics in haemodialysis patients

INTRODUCTION

To avoid excessive calcium loading in haemodialysis (HD) patients, current guidelines suggest a dialysate calcium concentration (dCa) of 2·5 mEq/L based on relatively stable intradialytic serum calcium levels. However, the latter do not account for possible calcium storage in acutely accessible pools. A rapidly exchangeable calcium pool located at the bone level has been previously proposed to be involved in acute (minute-to-minute) extracellular calcium regulation.

DESIGN

To evaluate the contribution of this pool in the maintenance of serum calcium levels, acute calcium buffer capacity was assessed by measuring intradialytic dialysate-sided ionized calcium mass balance (iCa_MB ) and change in extracellular fluid calcium mass in chronic HD patients using a dCa of 3·5 (n = 28) and 2·5 (n = 10) mEq/L. Serum osteocalcin, the most abundant noncollagenous bone protein, was measured before the HD session.

RESULTS

iCa_MB was invariably positive for both 2·5 and 3·5 mEq/L dCa, with a mean of 434 (±125) and 725 (±162) mg/HD, respectively (P < 0·001). Buffered intradialytic calcium load was 410 (±116) and 565 (±130) mg/HD, and acute calcium buffer capacity was 95 (±8)% and 78 (±7)% (mean values at 2·5 and 3·5 mEq/L dCa, respectively) (P < 0·001). Using 3·5 mEq/L dCa, an independent association of acute calcium buffer capacity with undercarboxylated osteocalcin (β = 0·512, P = 0·002) was demonstrated.

CONCLUSIONS

Our data strongly suggest the existence of a rapidly exchangeable calcium pool that counteracts acute serum calcium deviations in HD patients. This study provides, for the first time, experimental evidence for the involvement of bone in acute extracellular calcium regulation in vivo.

Quantification of Dialytic Removal and Extracellular Calcium Mass Balance during a Weekly Cycle of Hemodialysis

Objectives

The removal of calcium during hemodialysis with low calcium concentration in dialysis fluid is generally slow, and the net absorption of calcium from dialysis fluid is often reported. The details of the calcium transport process during dialysis and calcium mass balance in the extracellular fluid, however, have not been fully studied.

Methods

Weekly cycle of three dialysis sessions with interdialytic breaks of 2-2-3 days was monitored in 25 stable patients on maintenance hemodialysis with calcium concentration in dialysis fluid of 1.35 mmol/L. Total and ionic calcium were frequently measured in blood and dialysate. The volume of fluid compartments was measured by bioimpedance.

Results

Weekly dialytic removal of 12.79 ± 8.71 mmol calcium was found in 17 patients, whereas 9.48 ± 8.07 mmol calcium was absorbed per week from dialysis fluid in 8 patients. Ionic calcium was generally absorbed from dialysis fluid, whereas complexed calcium (the difference of total and ionic calcium in dialysis fluid) was removed from the body. The concentration of total calcium in plasma increased slightly during dialysis. The mass of total and ionic calcium in extracellular fluid decreased during dialysis in patients with the dialytic removal of calcium from the body and did not change in patients with the absorption of calcium from dialysis fluid.

Conclusions

We conclude that about one third of patients on dialysis with calcium 1.35 mmol/L in dialysis fluid may absorb calcium from dialysis fluid and therefore individual prescriptions of calcium concentration in dialysis fluid should be considered for such patients.

Dialysate Calcium Concentration, Mineral Metabolism Disorders, and Cardiovascular Disease: Deciding the Hemodialysis Bath

Patients with end-stage kidney disease treated with dialysis are at increased risk to experience fractures and cardiovascular events than similar-aged people from the general population. The enhanced risk for these outcomes in dialysis patients is not completely explained by traditional risk factors for osteoporosis and cardiovascular disease. Mineral metabolism abnormalities are almost universal by the time patients require dialysis therapy, with most patients having some type of renal osteodystrophy and vascular calcification. These abnormalities have been linked to adverse skeletal and cardiovascular events. However, it has become clear that the treatment regimens used to modify the serum calcium, phosphate, and parathyroid hormone levels almost certainly contribute to the poor outcomes for dialysis patients. In this article, we focus on one aspect of mineral metabolism management; dialysate calcium concentration and the relationships among dialysate calcium concentrations, mineral and bone disorder, and cardiovascular disease in hemodialysis patients.

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

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.