Calcium Mass Transfer Research Articles

The Effects of Calcium Deactivation and Mass Transfer Limitations on the Measurement of Activation Energy in Char-Co2 Gasification

The Effects of Calcium Deactivation and Mass Transfer Limitations on the Measurement of Activation Energy in Char-Co2 Gasification

Skeletal and cardiovascular consequences of a positive calcium balance during hemodialysis.

Patients on hemodialysis are exposed to calcium via the dialysate at least three times a week. Changes in serum calcium vary according to calcium mass transfer during dialysis, which is dependent on the gradient between serum and dialysate calcium concentration (d[Ca]) and the skeleton turnover status that alters the ability of bone to incorporate calcium. Although underappreciated, the d[Ca] can potentially cause positive calcium balance that leads to systemic organ damage, including associations with mortality, myocardial dysfunction, hemodynamic tolerability, vascular calcification, and arrhythmias. The pathophysiology of these adverse effects includes serum calcium changes, parathyroid hormone suppression, and vascular calcification through indirect and direct effects. Some organs are more susceptible to alterations in calcium homeostasis. In this review, we discuss the existing data and potential mechanisms linking the d[Ca] to calcium balance with consequent dysfunction of the skeleton, myocardium, and arteries.

Evaluation of Renal Osteodystrophy and Serum Bone-Related Biomarkers in a Peritoneal Dialysis Population.

The spectrum of renal osteodystrophy (ROD) in peritoneal dialysis (PD) patients remains to be clarified. Ideal intact parathormone (iPTH) levels range is still not defined. The role of sclerostin, dickkopf-related protein 1, osteoprotegerin, and receptor activator for nuclear factor κB ligand for the diagnosis of ROD needs to be elucidated. In this cross-sectional study, tetracycline double-labeled bone biopsy was performed in 49 patients with histomorphometric analysis according Kidney Disease Improving Global Outcomes (KDIGO) guidelines. All patients were treated with biocompatible PD solutions, with calcium concentration of 1.25 mmol/L. Adynamic bone was the most frequent diagnosed pattern (42.9%) followed by hyperparathyroid-related bone disease (28.6%). Twenty-two percent of patients had normal bone. In patients with iPTH within the KDIGO recommended range for dialysis patients, adynamic bone was found in 59% of cases. Median (range) iPTH in patients with adynamic bone was 312 (60-631) pg/mL. Median (range) levels of sclerostin varied from 1511.64 (458.84-6387.70)pg/mL in patients with hyperparathyroid bone disease to 2433.1 (1049.59-11354.52)pg/mL in patients with adynamic bone. Sclerostin/iPTH ratio was the best marker of low turnover disease but iPTH performed best in the diagnosis of high turnover disease. Calcium mass transfer was positive in patients with low bone volume. Adynamic bone is the most frequent ROD pattern in contemporary PD. Our results suggest the need to review the iPTH target range for this population. The sclerostin/iPTH ratio showed improved performance compared to iPTH for the diagnosis of low turnover bone. © 2022 American Society for Bone and Mineral Research (ASBMR).

A prospective study of the influence of the skeleton on calcium mass transfer during hemodialysis.

BackgroundCalcium gradient, the difference between serum calcium and dialysate calcium d[Ca], is the main contributor factor influencing calcium transfer during hemodialysis. The impact, however, of bone turnover, on calcium mass transfer during hemodialysis is still uncertain.MethodsThis prospective cross-sectional study included 10 patients on hemodialysis for a 57.6±16.8 months, with severe hyperparathyroidism. Patients were submitted to 3 hemodialysis sessions using d[Ca] of 1.25, 1.5 and 1.75 mmol/l in three situations: pre-parathyroidectomy (pre-PTX), during hungry bone (early post-PTX), and after stabilization of clinical status (late post-PTX). Biochemical analysis and calcium mass transfer were evaluated and serum bone-related proteins were quantified.ResultsCalcium mass transfer varied widely among patients in each study phase with a median of -89.5, -76.8 and -3 mmol using d[Ca] 1.25 mmol/L, -106, -26.8 and 29.7 mmol using d[Ca] 1.50 mmol/L, and 12.8, -14.5 and 38 mmol using d[Ca] 1.75 mmol/L during pre-PTX, early post-PTX and late post-PTX, respectively, which was significantly different among d[Ca] (p = 0.0001) and among phases (p = 0.040). Ca gradient and delta of Ca also differed among d[Ca] and phases (p<0.05 for all comparisons), whether ultrafiltration was similar. Serum Osteocalcin decreased significantly in late post-PTX, whereas Sclerostin increased earlier, in early post-PTX.ConclusionsThe skeleton plays a key role in Ca mass transfer during dialysis, either by determining pre-dialysis serum Ca or by controlling the exchangeable Ca pool. Knowing that could help us to decide which d[Ca] should be chosen in a given patient.

A Multilayer Model for Alumina Inclusion Transformation by Calcium in the Ladle Furnace

Calcium wire injection is widely used for modification of solid alumina inclusions to liquid or partially liquid calcium aluminate. In the present work, a multilayer growth model is proposed for modification of alumina inclusions. Diffusion through a multiphase product layer and mass transfer of solute through the boundary layer to the inclusion are taken into account in this model. It is assumed that the outer surface of the inclusion is thermodynamically in equilibrium with the local steel composition. The results show that the mass transfer of calcium through the boundary layer and within the inclusion is complete in a matter of seconds; furthermore, once the liquid calcium aluminate forms, it quickly consumes the other solid calcium aluminate phases. Because the calcium is so rapidly consumed by the inclusions, the rate of transformation in a calcium treatment process is controlled by the rate that calcium is supplied to the steel by the calcium bubbles.

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.

Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena

Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 °C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

A Brief Review of External Mass Balance and Internal Calcium Redistribution in Dialysis Patients—Is Calcium a Uremic Toxin?

Recent debates between 2 schools of thought on calcium mass balance in dialysis patients and its relevance to disease--one emphasizing external calcium mass balance, and the other, internal calcium redistribution--have created controversy. Due to decreased ability to excrete calcium and loss of endocrine function by the kidney, patients suffering from chronic kidney disease, particularly when requiring dialysis, demonstrate varying degrees of positive or negative calcium balance, vitamin D deficiency, and secondary hyperparathyroidism. Consequently, patients are prone to bone demineralization, with diminished bone strength, and are thus prone to fractures that substantially worsen morbid outcomes in this population. However, intra- and interdialytic positive calcium mass balance creates complications of a different kind, which include the occurrence of vascular and cardiac disease and reduced survival. This review aims to shed light on the mechanisms of and relationships between external calcium mass balance and internal calcium redistribution and their consequences. It also discusses the potential to improve current regimens by means of diffusive and convective calcium mass transfer for the achievement of neutral calcium mass balance.

Effects of bone remodelling on calcium mass transfer during haemodialysis

During haemodialysis, calcium balance can affect, or be affected by, mineral metabolism. However, when dialysate calcium concentration (d[Ca]) is chosen or kinetic models are employed to calculate calcium balance, bone remodelling is rarely considered. In this study, we examined whether bone remodelling affects calcium mass transfer during haemodialysis. We dialysed 23 patients using a d[Ca] of 1.0, 1.25, 1.5 or 1.75 mmol/L. Calcium mass transfer was measured and associated with remodelling bone factors. Calcium balance varied widely depending on the d[Ca]. Calcium removal was -578 +/- 389, -468 +/- 563, +46 +/- 400 and +405 +/- 413 mg when a d[Ca] of 1.0, 1.25, 1.5 or 1.75 mmol/L was used, respectively (1.0 and 1.25 vs 1.5 and 1.75 mmol/L, P < 0.001; 1.5 vs 1.75 mmol/L, P < 0.05). Univariate analysis showed that calcium balance correlated with calcium gradient, parathyroid hormone (PTH), osteocalcin and dialysis vintage. Multivariate analysis revealed that calcium balance was dependent on calcium gradient, PTH and osteocalcin. These results suggest that bone remodelling could affect calcium mass transfer during haemodialysis.

Simulation of Mass Transfer of Calcium in Concrete by the Lattice Kinetic Scheme for a Binary Miscible Fluid Mixture

The lattice kinetic scheme (LKS) for a binary miscible fluid mixture was applied to the simulation of the mass transfer of calcium in concrete. Cement paste, a major component of concrete, is a porous medium with a complicated three-dimensional geometry. The structure of the model concrete was selected on the basis of experimental data obtained by high-intensity X-ray computed tomography. The LKS, an improved version of the original lattice Boltzmann method, was used to save computational memory and to maintain numerical stability. First, an unsteady convection-diffusion problem was examined, and the accuracy of the method and the error norms with various lattice resolutions were investigated. Next, the problem of the calcium current in concrete was simulated. Pressure drops in the concrete were calculated for various Reynolds numbers, and the results were compared with those of an empirical equation based on experimental data. Also, velocity fields and concentration profiles were obtained at a pore scale for a structure with inhomogeneous mass diffusivities. These simulations showed that the present method might be useful for predicting calcium leaching in concrete from the microscopic point of view.

Mass transfer of calcium across the peritoneum at three different peritoneal dialysis fluid Ca2+ and glucose concentrations

In peritoneal dialysis, the rate of ultrafiltration has been predicted to be a major determinant of peritoneal calcium (Ca2+) removal. Hence, dialysis fluid glucose concentration should be an important factor governing the transperitoneal Ca2+ balance. The aim of this study was to test the effect of various dialysate glucose levels and selected dialysate Ca2+ levels on Ca2+ removal in peritoneal dialysis patients. Patients (N = 8) received, during a 7-week period, 2 L of lactate (30 mmol/L)/bicarbonate (10 mmol/L)-buffered peritoneal dialysis solutions containing either 1.5% glucose and 1.0 mmol/L Ca2+ or 2.5% glucose and 1.6 mmol/L Ca2+, or 4% glucose and 2.5 mmol/L Ca2+, respectively, provided in a three-compartment bag (trio system). Patients underwent standardized (4-hour) dwells, one for each of the three dialysates to assess permeability-surface area product (PS) or mass transfer area coefficients (MTAC) for ionized and "freely diffusible" Ca2+, lactate, glucose, bicarbonate, phosphate, creatinine, and urea. There was a clear-cut dependence of peritoneal Ca2+ removal on the rate of ultrafiltration. For large peritoneal to dialysate Ca2+ gradients (2.5 mmol/L Ca2+ in 4% glucose) a close fit of measured to simulated data was predicted by the three-pore model using nonelectrolyte equations. For low transperitoneal Ca2+ concentration gradients, however, directly measured Ca2+ data agreed with the simulated ones only when the peritoneal Ca2+ PS was set lower than predicted from pore theory (6 mL/min). There was a marked ultrafiltration dependence of transperitoneal Ca2+ transport. Nonelectrolyte equations could be used to simulate peritoneal ion (Ca2+) transport provided that the transperitoneal ion concentration gradients were large. Based on our data 1.38 mmol/L Ca2+ in the dialysis fluid would have created zero net Ca2+ gain during a 4-hour dwell for 1.5% glucose, whereas 1.7 and 2.2 mmol/L Ca2+ would have been needed to produce zero Ca2+ gain for 2.5% glucose and 3.9% glucose, respectively.

Mineralogical and microstructural changes accompanying the interaction of Boom Clay with ordinary Portland cement

The results of in situ tests conducted at the HADES underground laboratory, Mol, Belgium, indicate significant reaction between Boom Clay and ordinary Portland cement over a period of 18 months. Mass transfer of calcium, magnesium, aluminium, iron, silicon and sulphur leads to the development of a distinct zonal structure extending 100–250 μm into both the cement and the clay. The associated mineralogical changes have modified the microstructure of the altered region and there is clear evidence of increased porosity in the zone of portlandite dissolution. Additionally, experiments conducted at 85°C show the presence of a narrow Mg-Al-Si rich band in the clay close to the contact. Analyses indicate the formation of a di-phasic (Mg-aluminate hydroxide and Mgsilicate hydroxide) gel with low crystallinity and compositions close to hydrotalcite and sepiolite, respectively. Reactive transport modelling has been used to simulate phase transformations within the active region and relate these to porosity changes based on simple molar volume considerations. Given the close coupling of mineral chemistry and microstructure in cement±clay systems, such an approach is regarded as essential if reliable estimates are to be made of long-term reactivity.

Mineralogical and microstructural changes accompanying the interaction of Boom Clay with ordinary Portland cement

The results of in situ tests conducted at the HADES underground laboratory, Mol, Belgium, indicate significant reaction between Boom Clay and ordinary Portland cement over a period of 18 months. Mass transfer of calcium, magnesium, aluminium, iron, silicon and sulphur leads to the development of a distinct zonal structure extending 100–250 μm into both the cement and the clay. The associated mineralogical changes have modified the microstructure of the altered region and there is clear evidence of increased porosity in the zone of portlandite dissolution. Additionally, experiments conducted at 85°C show the presence of a narrow Mg-Al-Si rich band in the clay close to the contact. Analyses indicate the formation of a di-phasic (Mg-aluminate hydroxide and Mgsilicate hydroxide) gel with low crystallinity and compositions close to hydrotalcite and sepiolite, respectively. Reactive transport modelling has been used to simulate phase transformations within the active region and relate these to porosity changes ...

Are we mismanaging calcium and phosphate metabolism in renal failure?

Secondary hyperparathyroidism and renal osteodystrophy are the consequences of abnormal calcium, phosphate, and calcitriol metabolism ensuing from renal failure. Evidence suggests that calcium balance tends to become negative as we grow older than 35 years of age; however, the current dialysis modalities provide patients regardless of age with excessive calcium during dialysis. Administration of calcitriol in the management of hyperparathyroidism further increases the calcium and phosphate absorption. Furthermore, the current thrice-weekly renal replacement therapies fail to remove the daily absorbed phosphate, and we have to use calcium carbonate as a primary phosphate-binding agent to reduce intestinal phosphate absorption. The large calcium mass transfer and phosphate retention could lead to soft tissue calcification, especially in older end-stage renal disease (ESRD) patients. Consequently, only by maintaining a negative calcium balance during renal replacement therapy can we safely use calcitriol and calcium carbonate for the management of secondary hyperparathyroidism. Recent studies have indicated that phosphate restriction alone independent of plasma calcitriol or calcium can lower plasma parathyroid hormone (PTH) in renal failure and prevent hyperplasia of parathyroid glands. Therefore, phosphate control perhaps is the most important means to prevent secondary hyperparathyroidism. Previous studies have shown that ferric compounds are potent phosphate-binding agents; hence, these compounds warrant further trial in the management of phosphate metabolism in renal failure.

The Influence of Dialysate Calcium Concentration on the Pth Level in Children Undergoing Capd

In 12 children aged four-and-a-half to 18 years (mean 11 +/- 4.2) undergoing continuous ambulatory peritoneal dialysis (CAPD), serum intact parathyroid hormone (iPTH), ionized calcium (iCa) levels, and calcium mass transfer (CaMT) were measured on three consecutive days: day 1, after a four-hour interval between dialyses; on day 2, after four hours dwell time with peritoneal dialysis (PD) Ca 3.5 mEq/L; and on day 3, after four hours dwell time with PD Ca 2.5 mEq/L. A significantly more negative CaMT was found when PD Ca 2.5 mEq/L was used, as compared with values obtained using PD Ca 3.5 mEq/L. Significantly lower parathyroid hormone (PTH) values were found after the interval between exchanges. We conclude that in order to properly evaluate parathyroid gland function and to decide whether or not to give vitamin D metabolites, a protocol for determining PTH should be standardized.

Calcium and Magnesium Mass Transfer in Peritoneal Dialysis Patients Using 1.25 Mmol/L Calcium, 0.25 Mmol/L Magnesium Dialysis Fluid

To examine the effect of a reduced calcium/magnesium dialysis fluid (1.25/0.25 mmol/L, respectively) on calcium and magnesium mass transfer in both 1.36% and 3.86% glucose solutions. Each patient underwent four test exchanges, two with a standard dialysis fluid containing 1.36% and 3.86% glucose, and two with a reduced calcium/magnesium fluid containing 1.36% and 3.86% glucose. Calcium and magnesium were measured in dialysate and serum at 0 and 240 minutes. Single renal unit of a university teaching hospital. Sixteen patients established on CAPD, and peritonitis-free, for at least 3 months. A lower dialysate calcium results in negative mass transfer when serum-ionized calcium exceeds dialysate calcium (mean -0.21 +/- 0.15 mmol/exchange), and positive mass transfer when serum-ionized calcium is less than dialysate calcium in 1.36% glucose solutions (mean 0.57 +/- 0.18 mmol/exchange). A negative correlation was found between serum-ionized calcium level and calcium mass transfer. With a 3.86% reduced calcium/magnesium solution, calcium mass transfer is always negative (-0.88 +/- 0.18 mmol/exchange) due to ultrafiltration and solute drag. Fifteen patients were found to be hypermagnesemic at the time of the study. Magnesium mass transfer was neutral with the standard 1.36% glucose fluid (mean -0.01 mmol/exchange), but negative with the reduced calcium/magnesium 1.36% glucose fluid (mean -0.58 +/- 0.13 mmol/exchange). With the 3.86% glucose solution, both fluids produced negative magnesium mass transfer (mean -0.32 +/- 0.11 and -1.07 +/- 0.11 mmol/exchange for standard and reduced calcium/magnesium fluids, respectively). We conclude that this fluid formulation should reduce hypercalcemia and hypermagnesemia in CAPD patients.

Transperitoneal Calcium Mass Transfer using Dialv Sate with a Low Calcium Concentration (1.0 mM)

Lower dialysate calcium concentrations were recently proposed to overcome the risk of hypercalcemia in continuous ambulatory peritoneal dialysis (CAPD) patients on calcium-containing phosphate binders and/or vitamin D metabolites using the standard dialysate calcium concentration (SCa) of 1.75 mM. To assess transperitoneal calcium mass transfer (CaMT) in CAPD patients using a dialysate with a low calcium concentration (LCa, 1.00 mM), 18 stable patients were randomly allocated to receive either LCa or SCa. CaMT was assessed over 4 hours using 2L dialysate bags with three different dialysate glucose concentrations (1.5%, 2.3%, 4.25%). Total serum calcium (tCa), ionized calcium (iCa), and the exact dialysate volume were measured before and after the 4-hour dwell. A sample of the drained dialysate was obtained to measure the dialysate calcium concentration. The tCa and iCa levels were not significantly different in both groups prior to and did not change throughout the test. CaMT (median/range) was -0.64 mmol/exchange (-0.35(-)-1.29 mmol/exchange) using LCa with 1.5% glucose compared to 0.23 mmol (-0.18-0.87 mmol) with SCa (p < 0.0001). CaMT was negatively correlated to iCa and ultrafiltration volume [4.25%: LCa-1.22 (-0.84(-)-1.9); SCa -0.43 (-1.35-0.13); p < 0.001]. In summary, LCa results in a loss of calcium into the dialysate even at low ultrafiltration volumes and serum iCa levels. This might facilitate the prevention and therapy of renal osteodystrophy with calcium-containing phosphate binders and calcitriol. However, patients using LCa must be carefully monitored for calcium homeostasis and bone turnover.

Calcium mass transfer in CAPD: the role of convective transport

One hundred and fifty calcium (Ca) balance studies were performed in 50 patients treated with CAPD using dialysate with a 1.75 mmol/l (7 mg/dl) Ca content, in order to calculate the peritoneal balance of Ca by measuring the Ca in all the effluent for a 24-h period, and looking at the influence of serum ionized Ca and the ultrafiltration rate in the calcium balance. Of the 150 balance studies, 77 were made using four exchanges of dialysate per day and 73 using three exchanges per day. The serum ionized Ca was 1.17 +/- 0.09 mmol/l, the ultrafiltration 844 +/- 723 ml/day and the peritoneal Ca transfer 39 +/- 46 m/day. The net Ca abortion with four exchanges was less than that with three exchanges per day. There was a strong negative correlation between the peritoneal Ca absorption and the ultrafiltration (r = -0.7, P < 0.00001) and with the ionized Ca (r = -0.49, P < 0.0001). Thirty-three peritoneal balance studies showed a negative Ca balance and in all 33 cases ultrafiltration was greater than 350 ml/day. We conclude that the peritoneal balance of Ca depends not only on the serum ionized Ca, but also on ultrafiltration. The lesser Ca gain observed with four dialysis exchanges per day is due to greater ultrafiltration rates present in this setting.

Calcium Mass Transfer With Dialysate Containing 1.25 and 1.75 mmol/L Calcium in Peritoneal Dialysis Patients

Studies with 1.75 mmol/L calcium dialysate have shown that patients gain calcium from dialysate. Thus, hypercalcemia, especially when calcium compounds are used for phosphate control, is a commonly seen complication. Dialysate with 1.25 mmol/L calcium has been available since 1989. Little is known about calcium mass transfer (CMT) with dialysate of this calcium concentration. CMT was measured in 20 stable adult peritoneal dialysis patients. Each CMT study consisted of a 2-L continuous ambulatory peritoneal dialysis (CAPD) exchange with a dwell time of 4 hours. CMT studies were performed using 1.25 and 1.75 mmol/L calcium dialysate with 1.5, 2.5, and 4.25 g/dL dextrose concentrations. CMT with 1.25 mmol/L calcium dialysate was compared to that with 1.75 mmol/L for each dextrose concentration. With a dextrose concentration of 1.5 g/dL, the mean CMT for 1.25 mmol/L calcium dialysate was —0.1 ± 0.3 mmol versus 0.6 ± 0.3 mmol for 1.75 mmol/L calcium dialysate (P < 0.0001). A dextrose concentration of 2.5 gl dL resulted in a mean CMT of —0.4 ± 0.2 mmol for 1.25 mmol/L calcium versus 0.45 ± 0.25 mmol for 1.75 mmol/L calcium (P < 0.0001). Using a dextrose concentration of 4.25 g/dL, the mean CMT was —0.7 ± 0.25 mmol for 1.25 mmol/L calcium versus —0.05 ± 0.35 mmol for 1.75 mmol/L calcium (P < 0.0001). Mean serum ionized calcium (SiCa) was between 1.15 and 1.20 mmol/L for all study groups. CMT inversely correlated with SiCa for each type of dialysate used. CMT was dependent on the concentrations of calcium and dextrose in the dialysate and the SiCa level at the time of the exchange. The use of 1.25 mmol/L calcium dialysate, which does not result in calcium gain to the patient, may prove to be useful in preventing hypercalcemia when peritoneal dialysis patients are using calcium salts as phosphate binders.

Factors influencing transperitoneal calcium balance during CAPD.

A dialysate containing a calcium concentration of 1.75 mmol/L has been the standard in CAPD for a long time. This concentration was chosen to achieve a positive calcium balance to suppress hyperparathyroidism. In the measurement of peritoneal calcium mass transfer, conflicting results have been published, with positive and negative calcium balances reported. These differences have been explained by differences in the filtration rate, and a negative correlation between the filtration rate and the peritoneal calcium mass transfer can be found. Whereas nearly all patients in this study had a negative calcium balance using a glucose solution of 3.86%, a wide variation was found for the 1.36% glucose solution. There were several patients who had a positive calcium balance despite a positive filtration rate. The explanation for this finding lay in differences in serum concentrations of calcium, and especially differences in the size of the total exchangeable calcium pool that contains the plasma calcium compartment. A negative correlation between peritoneal calcium balance and the size of the total exchangeable calcium pool could be demonstrated. This finding may explain the differences in the peritoneal calcium flux reported in the literature. As an enlargement of the exchangeable calcium pool correlates with the progression of vascular calcification, therapeutic efforts should be directed toward prevention of an enlargement of this pool.