Assessment of intradialysis calcium mass balance by a single pool variable‐volume calcium kinetic model

Introduction: A reliable method of intradialysis calcium mass balance quantification is far from been established. We herein investigated the use of a single‐pool variable‐volume Calcium kinetic model to assess calcium mass balance in chronic and stable dialysis patients. Methods: Thirty‐four patients on thrice‐weekly HD were studied during 240 dialysis sessions. All patients were dialyzed with a nominal total calcium concentration of 1.50 mmol/L. The main assumption of the model is that the calcium distribution volume is equal to the extracellular volume during dialysis. This hypothesis is assumed valid if measured and predicted end dialysis plasma water ionized calcium concentrations are equal. A difference between predicted and measured end‐dialysis ionized plasma water calcium concentration is a deviation on our main hypothesis, meaning that a substantial amount of calcium is exchanged between the extracellular volume and a nonmodeled compartment. Findings: The difference between predicted and measured values was 0.02 mmol/L (range ?0.08:0.16 mmol/L). With a mean ionized dialysate calcium concentration of 1.25 mmol/L, calcium mass balance was on average negative (mean ± SD ?0.84 ± 1.33 mmol, range ?5.42:2.75). Predialysis ionized plasma water concentration and total ultrafiltrate were the most important predictors of calcium mass balance. A significant mobilization of calcium from the extracellular pool to a nonmodeled pool was calculated in a group of patients. Discussion: The proposed single pool variable‐volume Calcium kinetic model is adequate for prediction and quantification of intradialysis calcium mass balance, it can evaluate the eventual calcium transfer outside the extracellular pool in clinical practice.     

Comparison between different dialysate calcium concentrations in nocturnal hemodialysis

Benefits of dialysate with greater calcium (Ca) concentration are reported in nocturnal hemodialysis (NHD) to prevent Ca depletion and subsequent hyperparathyroidism. Studies with patients dialyzing against 1.25 mmol/L Ca baths demonstrate increases in alkaline phosphatase (ALP) and parathyroid hormone (PTH) and increasing dialysate Ca subsequently corrects this problem. However, whether 1.5 or 1.75 mmol/L dialysate Ca is most appropriate for NHD is yet to be determined, and differences in the effect on mineral metabolism of daily vs. alternate daily NHD have also not been well defined. We retrospectively analyzed mineral metabolism in 48 patients, from 2 institutions (30 at Monash and 18 at Geelong), undergoing home NHD (8 hr/night, 3.5-6 nights/week) for a minimum of 6 months. Thirty-seven patients were dialyzed against 1.5 mmol/L Ca bath and 11 patients against 1.75 mmol/L. We divided patients into 4 groups, based on dialysate Ca and also on the hours per week of dialysis, <40 (1.5 mmol/L, n=29 and 1.75 mmol/L, n=8) or > or =40 (n=4 and 7). We compared predialysis and postdialysis serum markers, time-averaged over a 6-month period, and the administration of calcitriol and Ca-based phosphate binders between 1.5 and 1.75 mmol/L Ca dialysate groups. Baseline characteristics between all groups were similar, with a slightly longer, but nonsignificant, duration of NHD in both 1.75 mmol/L dialysate groups compared with 1.5 mmol/L. The mean predialysis Ca, phosphate, and Ca x P were similar between the 1.5 and 1.75 mmol/L groups, regardless of NHD hr/week. Postdialysis Ca was significantly greater, with 1.75 vs. 1.5 mmol/L in those dialyzing <40 hr/week (2.64+/-0.19 vs. 2.50+/-0.12 mmol/L, p=0.046), but postdialysis Ca x P were similar (2.25+/-0.44 vs. 2.16+/-0.29 mmol(2)/L(2), p=0.60). Parathyroid hormone was also lower with 1.75 vs. 1.5 mmol/L baths in the <40 hr/week groups (31.99+/-26.99 vs. 14.47+/-16.36 pmol/L, p=0.03), although this difference was not seen in those undertaking NHD > or =40 hr/week. Hemoglobin, ALP, and albumin were all similar between groups. There was also no difference in vitamin D requirement when using 1.75 mmol/L compared with the 1.5 mmol/L dialysate. Multivariate analysis to determine independent predictors of postdialysis serum Ca showed a statistically significant positive association with predialysis Ca, dialysate Ca, and total NHD hr/week. An elevated dialysate Ca concentration is required in NHD to prevent osteopenia but differences in serum markers of mineral metabolism between 1.5 and 1.75 mmol/L Ca dialysate in NHD in our study were few. This was similar for patients undertaking NHD <40 or > or =40 hr/week, although differences in the frequency of NHD may also be as important as dialysate Ca with regard to serum Ca levels. With concerns that prolonged higher Ca levels contribute to increased cardiovascular mortality, the optimal Ca dialysate bath is still unknown and further studies addressing bone metabolism with larger NHD numbers are required.     

Phosphate binders and metabolic acidosis in patients undergoing maintenance hemodialysis—sevelamer hydrochloride,calcium carbonate,and bixalomer

The serum bicarbonate (HCO₃^–) levels are decreased in chronic hemodialysis (HD) patients treated with sevelamer hydrochloride (SH). We assessed the effects of bixalomer on the chronic metabolic acidosis in these patients. We examined 12 of the 122 consecutive Japanese patients with end‐stage renal disease on HD, who orally ingested a dose of SH (≥2250 mg), and an arterial blood gas analysis and biochemical analysis were performed before HD. Patients whose serum HCO₃^– levels were under 18 mmol/L were changed from SH to the same dose of bixalomer. A total of 12 patients were treated with a large amount of SH. Metabolic acidosis (a serum HCO₃^– level under 18 mmol/L) was found in eight patients. These patients were also treated with or without small dose of calcium carbonate (1.2 ± 1.1 g). The dose of SH was changed to that of bixalomer. After 1 month, the serum HCO₃^– levels increased from 16.3 ± 1.4 to 19.6 ± 1.7 mmol/L (P < 0.05). Metabolic acidosis was not observed in four patients (serum HCO₃^– level: 20.3 ± 0.7 mmol/L) likely because they were taking 3 g of calcium carbonate with SH. In the present study, the development of chronic metabolic acidosis was induced by HCl containing phosphate binders, such as SH, and partially ameliorated by calcium carbonate, then subsequently improved after changing the treatment to bixalomer.     

Treating mineral metabolism disorders in patients undergoing long hemodialysis: A search for an optimal strategy

In hemodialysis (HD) patients, mineral metabolism (MM) disorders have been associated with an increased mortality rate. We report the evolution of MM parameters in a stable HD population undergoing long hemodialysis by performing an annual cross-sectional analysis for every year from 1994 to 2008. The therapeutic strategy has changed: the dialysate calcium concentration has decreased from a mean of 1.7 ± 0.1 to 1.5 ± 0.07 mmol/L and has been adapted to parathyroid hormone serum levels (from 1 to 1.75 mmol/L). The use of calcium-based and aluminum-based phosphate binders has decreased and they have been replaced by sevelamer; alfacalcidol has partly been replaced by native vitamin D. The percentage of patients with a parathyroid hormone serum level between 150 and 300 pg/mL has increased from 9% to 67% (P<0.001); the percentage of patients with phosphataemia between 1.15 and 1.78 mmol/L has increased from 39% to 84% (P<0.001). The percentage of those with albumin-corrected calcemia between 2.1 and 2.37 mmol/L has increased from 29% to 61% (P<0.001), and that of patients with a calcium-phosphorous product (Ca × P) level >4.4 mmol/L decreased from 8.8% to 2% (P=0.02). Although patients undergo long and intensive HD treatment, MM disorders are common. However, an appropriate strategy, mostly consisting of native vitamin D supplementation, progressive replacement of calcium-based phosphate binders with non–calcium-based ones, and individualization of dialysis session duration and dialysate calcium concentration, would result in a drastic improvement.     

Marked improvement in bone metabolism parameters after increasing the dialysate calcium concentration from 2.5 to 3 mEq/L in nonhypercalcemic hemodialysis patients

The optimal dialysate calcium (Ca) concentration for hemodialysis (HD) patients is set at 2.5 mEq/L according to Kidney Disease Outcomes Quality Initiative (K-DOQI) guidelines. This recommendation is opinion-based and could negatively affect secondary hyperparathyroidism. Studies have suggested that a dialysate Ca of 3.0 mEq/L is a compromise between bone protection and cardiovascular risk. The aim of our study was to investigate the effect on bone metabolism parameters after increasing the dialysate Ca concentration from 2.5 to 3.0 mEq/L. The dialysate Ca concentration in our patients was increased from 2.5 to 3.0 mEq/L. Patients with hypercalcemia, normal-high Ca levels with a high Ca-Phosphorus product (Ca x P), excessively suppressed parathyroid hormone (PTH), or a past medical history of calciphylaxis were excluded. Twenty-two patients were studied over 20 weeks. Parathyroid hormone levels decreased significantly (442 +/- 254 vs. 255 +/- 226 pg/mL; p=0.000), without significant changes in serum Ca, P, and Ca x P levels at any sampling point. Better control of secondary hyperparathyroidism allowed us to decrease the paracalcitol dosage in 6 of the 12 patients who had been treated with this drug at the beginning of the study. Other potential factors involved in PTH secretion were not modified. A significant improvement in the rate of patients with 3 or more K-DOQI parameters within the target ranges (8 [36%] vs. 12 [55%]; p=0.026) was observed. In the absence of hypercalcemia or excessively suppressed PTH, an increase from 2.5 mEq to 3.0 mEq/L in dialysate Ca concentration resulted in better control of secondary hyperparathyroidism without affecting Ca, P, and Ca x P levels, thus enabling us to reduce the dosage of vitamin D metabolites.     

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 m²), 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.     

Citrate vs. acetate dialysate on intradialytic heparin dose: A double blind randomized crossover study

Introduction Citrate containing dialysate has a calcium‐binding anticoagulant effect compared to standard acetic acid containing dialysate. We performed a randomized, double‐blind, crossover trial in maintenance HD patients to determine if citrate dialysate (“citrate”) safely allows for a lower cumulative heparin dose (“heparin dose”). Methods Intradialytic heparin was adjusted to the minimum during a 2‐week run‐in phase. Patients remaining on heparin at the end of the run‐in phase were then randomized to two weeks of HD with acetate dialysate (“acetate”) followed by two weeks of citrate (sequence 1) or two weeks of citrate followed by two weeks of acetate (sequence 2). We estimated a minimum of 14 patients are required to show a 30% reduction in heparin dose per HD session with citrate compared with acetate. Twenty‐five patients entered the run‐in phase, 20 were randomized, and 19 completed the study. Findings The mean heparin dose was reduced by 19% (656 units, 95% CI ?174 to ?1139 units, P = 0.011) in the acetate group, and 30% (1046 units 95% CI ?498 to 1594 units, P < 0.001) in the citrate group. There was no difference in the mean heparin dose reduction between the two dialysates (P > 0.05). The intradialytic ionized calcium in the citrate group was lowered by 0.10 mmol/L (95% CI 0.07 to 0.14 mmol/L, P < 0.001), and remained unchanged in the acetate group. Discussion Although citrate is a safe alternative to acetate, it does not result in additional heparin dose reduction.     

Determination of free calcium and calcium-containing species in human plasma by capillary electrophoresis-inductively coupled plasma optical emission spectrometry

A new method for the determination of free calcium concentration in human plasma was developed by online coupling capillary electrophoresis (CE) with inductively coupled plasma optical emission spectrometry (ICP-OES). Baseline separation of calcium-containing species was achieved by CE-ICP-OES in a 120-cm-long capillary with 100-microm internal diameter, at 20 kV applied voltage, with a 30 mmol/L Tris-HCl buffer at pH 7.4. A total of eight calcium-containing species were found in human plasma; the concentration of free calcium ion was found to be 41.9 mg/L. The concentrations of calcium for other seven calcium species, estimated from the calibration against Ca(2+) standard, were 3.14-15.6 mg/L. The precision (RSD, n = 10) ranged from 1.2 to 2.7% for the migration time and 2.8 to 3.9% for the peak area. The developed method was also applied to analyze plasma samples with recovery ranged from 94.5 to 102% for samples spiked with 40 mg/L free Ca(2+) ion.     

Calcium phosphate metabolism and bone mineral density with nocturnal hemodialysis

An elevated calcium x phosphate product (Ca x P) is an independent risk factor for vascular calcification and cardiovascular death in dialysis patients. More physiological dialysis in patients undergoing nocturnal hemodialysis (NHD) has been shown to produce biochemical advantages compared with conventional hemodialysis (CHD) including superior phosphate (P) control. Benefits of dialysate with greater calcium (Ca) concentration are also reported in NHD to prevent Ca depletion and subsequent hyperparathyroidism, but there are concerns that a higher dialysate Ca concentration may contribute to raised serum Ca levels and greater Ca x P and vascular disease. The NHD program at our unit has been established for 4 years, and we retrospectively analyzed Ca and P metabolism in patients undergoing NHD (8-9 h/night, 6 nights/week). Our cohort consists of 11 patients, mean age 49.3 years, who had been on NHD for a minimum of 12 months, mean 34.3 months. Commencement was with low-flux (LF) NHD and 1.5 mmol/L Ca dialysate concentration, with conversion to high-flux (HF) dialyzers after a period (mean duration 18.7 months). We compared predialysis serum albumin, intact parathyroid hormone, P, total corrected Ca, and Ca x P at baseline on CHD, after conversion to LF NHD and during HF NHD. We also prospectively measured bone mineral density (BMD) on all patients entering the NHD program. Bone densitometry (DEXA) scans were performed at baseline (on CHD) and yearly after commencement of NHD. With the introduction of HF dialyzers, the Ca dialysate concentration was concurrently raised to 1.75 mmol/L after demonstration on DEXA scans of worsening osteopenia. Analysis of BMD, for all parameters, revealed a decrease over the first 12 to 24 months (N = 11). When the dialysate Ca bath was increased, the median T and Z scores subsequently increased (data at 3 years, N = 6). The mean predialysis P levels were significantly lower on LF NHD vs. CHD (1.51 vs. 1.77 mmol/L, p = 0.014), while on HF NHD P was lower again (1.33 mmol/L, p = 0.001 vs. CHD). Predialysis Ca levels decreased with conversion from CHD to LF NHD (2.58 vs. 2.47 mmol/L, p = 0.018) using a 1.5 mmol/L dialysate Ca concentration. The mean Ca x P on CHD was 4.56 compared with a significant reduction of 3.74 on LF NHD (p = 0.006) and 3.28 on HF NHD (p = 0.001 vs. CHD), despite the higher dialysate Ca in the latter. We conclude that an elevated dialysate Ca concentration is required to prevent osteopenia. With concerns that prolonged higher Ca levels contribute to increased cardiovascular mortality, the optimal Ca dialysate bath is still unknown. Better P control on NHD, however, reduces the overall Ca x P, despite the increased Ca concentration, therefore reducing the risk of vascular calcification.     

Quality of hemodialysis water in a resource‐poor country: The Nigerian example

Hemodialysis (HD) patients are exposed to large volumes of water, separated from patients' blood by semipermeable membrane of dialyzers. Chemical contaminants in poorly treated water impact negatively on quality of life of these patients. This survey was carried out to assess the HD water quality in Lagos, Nigeria. Ten milliliters of feed and treated water from all six HD centers in Lagos were tested for aluminum, copper, zinc, magnesium, calcium using atomic absorption spectrometry; sodium and potassium were tested using flame photometry, fluoride with molecular photoluminescence method; sulfate using turbidimetry, nitrates measured by cadmium column reduction method, chloramines and free chlorine were measured using N, N‐diethyl‐1‐P‐phenylenediamine colorimetric method. Information on sources of feed water, frequency of testing of HD water, methods of water treatment, type of water purification system and maintenance was also obtained. All centers used borehole as main source of water supply. None of the centers met Association for the Advancement of Medical Instrumentation (AAMI) guidelines for most chemical contaminants. Only chlorine (0.48 ± 0.07 mg/L) and potassium (3.9 ± 0.95 mg/L) levels met AAMI standards after treatment. Mean levels of chemical contaminants in treated water were as follows: aluminum 0.04 ± 0.01 mg/L, zinc 0.27 ± 0.08 mg/L, chloramines 0.16 ± 0.03 mg/L, fluoride 1.83 ± 0.40 mg/L, sulfate 117 ± 86.1 mg/L which were mildly elevated; calcium 126.00 ± 22.7 mg/L, sodium 179 ± 25.6 mg/L, and nitrate 70.5 ± 50.8 mg/L, which were markedly elevated; and magnesium 8.3 ± 3.38 mg/L, which was moderately elevated above AAMI recommended levels. HD water quality is poor in our environment. Concerted efforts are required to ensure good quality water for HD.     

Glucose variability in maintenance hemodialysis patients with type 2 diabetes: Comparison of dialysis and nondialysis days

Introduction

Hemodialysis (HD) induces several physiological changes that can affect plasma glucose levels in patients with diabetes and in turn their glycemic control. Studies using continuous glucose monitoring (CGM) to assess glucose variations on dialysis days compared with nondialysis days report conflicting results. Here, we used CGM to examine glucose variations induced by HD in patients with type 2 diabetes.

Methods

Patients with type 2 diabetes undergoing maintenance HD were included. CGM (Ipro2®, Medtronic) was performed at baseline and Week 4, 8, 12, and 16 for up to 7 days at each visit. CGM profiles on days where participants received HD were compared with days without HD using a linear mixed model.

Findings

Twenty-seven patients were included. The median number of CGM days performed was 8 (interquartile range [IQR] 6–10) for dialysis days and 16 (IQR 12–17) for nondialysis days. The median sensor glucose was 9.4 (95% confidence interval [CI] 8.8–10.2) mmol/L on dialysis days compared with 9.5 (95% CI 8.9–10.2) mmol/L on nondialysis days (p = 0.58). Nocturnal mean sensor glucose was higher on dialysis days compared with nondialysis days: 8.8 (95% CI 8.0–9.6) mmol/L versus 8.4 (95% CI 7.7–9.2) mmol/L (p = 0.029).

Discussion

Similar median sensor glucose values were found for days on and off HD. Nocturnal glucose levels were modestly increased on dialysis days. Our findings indicate that antidiabetic treatment does not need to be differentiated on dialysis versus nondialysis days in patients with type 2 diabetes undergoing maintenance HD.     

Regional Anticoagulation with Sodium Citrate in Pediatric Patients on Intermittent Hemodialysis Therapy with Bleeding Risks

Heparin‐free anticoagulation in hemodialysis (HD) is advocated for patients with clotting abnormalities and risk of bleeding. Objective: First publication on regional citrate anticoagulation (RCA) in children. RCA is free from systemic effects, guarantees excellent dialyzer life, but requires careful monitoring. Methods: We report on 3 patients treated by intermittent RCA HD (4 h each, high‐flux dialyzer F40, Fresenius): (1) 17‐year‐old boy (renal transplant failure, access via cubital Cimino fistula) after hypertensive intra‐cerebral hemorrhage (2 sessions); (2) 13‐year‐old girl (hemolytic uremic syndrome, access via jugular vein Shaldon catheter) after abdominal surgery and bleeding (8 sessions); and (3) 7‐year‐old boy (hyperoxaluria, access via PermCath^® jugular vein catheter) after renal transplant biopsy (3 sessions). Sodium citrate 30% was infused into the extra corporeal circuit (blood flow 150 mL/min) before dialyzer (initial flow 30 mL/min) and calcium gluconate 10% for antidote into venous line near of catheter or fistula (initial flow 40 mL/min). Post‐dialyzer extracorporeal serum Ca⁺⁺ (aim < 0.3 mmol/L) and pre‐dialyzer intra‐corporeal Ca⁺⁺ (aim > 0.9) were measured for every 30 min. Serum Na⁺, K⁺, base excess (BE), blood flow, blood pressure, heart rate, and blood out‐flow and in‐flow pressure were also monitored. Results: For adequate RCA (mean extracorporeal serum Ca⁺⁺ 0.24 ± 0.04 mmol/L), a mean citrate flow of 36.1 ± 5.9 mL/h and a mean calcium substitution rate of 40.8 ± 3.4 mL/h were needed. Intra‐corporeal Ca⁺⁺ was kept at 1.10 ± 0.07 mmol/L. Extracorporeal activated clotting time (ACT) was 194 ± 41 and intra‐corporeal ACT 90 ± 12 sec. Serum Na⁺, K⁺, and BE during HD were 138 ± 2, 3.5 ± 0.3, and ?0.6 ± 1.1 mmol/L, respectively. Mean arterial blood pressures of patients 1–3 were 117 ± 5, 103 ± 5, and 102 ± 6 mmHg. All patients were stable and without any bleeding during HD. The only adverse event was 1 episode of hypocalcemia (Ca⁺⁺ < 0.6 mmol/L) cured by stopping dialysis. Conclusions: Local anticoagulation with sodium citrate during intermittent HD can be applied safely in children and adolescents.     

Association of mineral metabolism factors with all-cause and cardiovascular mortality in hemodialysis patients: the Japan dialysis outcomes and practice patterns study

Abnormalities in mineral metabolism have been linked to mortality in hemodialysis (HD) patients. We postulated that these abnormalities would have a particularly large deleterious impact on deaths due to cardiovascular causes in Japan. This study describes the recent status of abnormal mineral metabolism, significant predictors, and potential consequences in the Dialysis Outcomes and Practice Patterns Study (DOPPS), Phases 1 and 2, in Japan. Major predictor variables were patient demographics, comorbidities, and laboratory markers of mineral metabolism such as albumin-adjusted serum calcium (calciumAlb), phosphorus, and intact PTH (iPTH). In a cross section of 3973 Japanese HD patients in DOPPS I and II, a large faction had laboratory values outside of the recommended Kidney Disease Outcomes Quality Initiative (K/DOQI) guideline range for serum concentrations of phosphorus (51% of patients above upper target range), calciumAlb (43.7% above), calcium-phosphorus (Ca x P) product (41.1% above), and iPTH (18.6% above). All-cause mortality was significantly and independently associated with calciumAlb (relative risk [RR]=1.22 per 1 mg/dL, p=0.0005) and iPTH (RR=1.04 per 100 pg/mL, p=0.04). Cardiovascular mortality was significantly associated with calciumAlb (RR=1.28, p=0.02), phosphorus (RR=1.13 per 1 mg/dL, p=0.008), Ca x P product (RR=1.07 per 2 mg(2)/dL(2), p=0.002), and PTH (RR=1.08, p=0.0001). This study expands our understanding of the relationship between altered mineral metabolism and mortality outcomes, showing slightly stronger associations with cardiovascular causes than observed for all-cause mortality. These findings have important therapeutic implications for Japanese HD patients.     

Surfactant assisted synthesis of precipitated calcium carbonate nanoparticles using dolomite: Effect of pH on morphology and particle size

Synthesis of nanomaterials from readily available minerals for industrial applications is a growing research area. Understanding the causes of their properties becomes handy in utilization. In this study, an effective sucrose solution based method was employed for the extraction of calcium from dolomite to synthesize precipitated calcium carbonate nanostructures with different morphologies and sizes. It was found that 30% (w/v) sucrose solution extracted approximately 91% of calcium from dolomite forming a calcium-sucrate complex. Carbonation was achieved by CO₂ bubbling and aqueous sodium carbonate addition. Precipitation was performed under different pH values of 7.5, 10.5 and 12.5 in the absence of an anionic surfactant and in the template of sodium dodecyl sulfate (SDS)/calcium-sucrate at pH 12.5. It was found that CO₂ bubbling slightly promotes smaller particles. The anionic surfactant enables particle size and agglomeration reduction while introducing some hydrophobicity. The smallest particles were achieved at a range of 40–55 nm in the presence of SDS/sucrose template and were of spherical morphology. By changing the pH, a tendency to form different polymorphs and shapes of calcium carbonate was observed.     

Measurement of Refractive Nonlinearities in GaAs Above Bandgap Energy

We present a technique for single-beam measurement of the optical nonlinearity in GaAs for photon energies above the bandgap. We measured the real and the imaginary parts of the nonlinear refractive index of a bulk crystal by using the change in reflection of dye laser pulses (10 ns, 538 nm). The values obtained, n(2) = (7.8 ? 0.6) x 10(-8) cm(2)/W and kappa(2) = (-2.8 ? 0.7) x 10(-8) cm(2)/W, are discussed.     

Is there an association between intradialytic hypotension and serum magnesium changes?

Intradialytic hypotension (IDH) is the most common complication of hemodialysis (HD). The aim of this study was to investigate the significance of intradialytic changes of serum magnesium (sMg) and its relation to IDH. We considered 58 patients undergoing HD. Serum magnesium was measured at start, after 2 hours, and at the end of the HD sessions. Total sMg concentration corrected for albumin was according to Krolles proposed formula. Blood pressure was measured every 30 min. Data were analyzed by SPSS.15. A P value of less than 0.05 was considered as significant. Occurrence of IDH among HD patients was 27.6% (16/58). Serum magnesium decreased significantly during HD session (P<0.05). Comparing corrected sMg in IDH group with non-IDH group showed that: corrected sMg was 0.66 ± 0.14 mmol/L vs. 0.84 ± 0.26 mmol/L at the start of dialysis (P=0.43), 0.62 ± 0.17 mmol/L vs. 0.74 ± 0.23 mmol/L (P=0.04) at 2 hours, and 0.61 ± 0.12 mmol/L vs. 0.72 ± 0.22 mmol/L (P=0.03) at the end of dialysis. Intradialytic hypotension episodes were significantly related to a decrease in sMg during dialysis (P=0.02). There was a significant decrease in sMg levels during dialysis. Intradialytic hypotension was significantly related to lowered sMg levels during dialysis.     

Calcium Fluoride Precipitation and Deposition From 12 mmol/L Fluoride Solutions With Different Calcium Addition Rates

The effects of different Ca-addition rates on calcium fluoride (CaF₂) precipitation and deposition were investigated in 12 mmol/L sodium fluoride solutions to which 0.1 mol/L calcium chloride solution was continuously added at average rates of (5, 7.5, 10, 12.5, 15 or 20) mmol L⁻¹ min⁻¹. The changes in ionic fluoride and calcium concentrations, as well as turbidity, were continuously recorded by F and Ca electrodes, and a fiber optic based spectrophotometer, respectively. The F⁻ concentration decreased and turbidity increased with time indicating precipitation of CaF₂. For the systems with Ca-addition rates of (5, 7.5, 10, 12.5, 15, and 20) mmol L⁻¹ min⁻¹, the 1 min CaF₂ depositions in the model substrate (cellulose filter paper, pores 0.2 µm) expressed as mean ± SD of deposited F per substrate surface area were (3.78 ± 0.31, 11.45 ± 0.89, 9.31 ± 0.68, 8.20 ± 0.56, 6.63 ± 0.43, and 2.09 ± 0.28) µg/cm², respectively (n = 10 for each group). The 1-min F depositions did not show positive correlation to Ca-addition rates. The lowest 1-min F deposition was obtained in the systems with the highest Ca-addition rate of 20 mmol L⁻¹ min⁻¹ for which CaF₂ precipitation rate reached the maximum value of 0.31 mmol L⁻¹ s⁻¹ almost immediately after beginning of reaction (6 s). The largest 1-min F depositions were obtained from the systems with Ca addition rates of (7.5 to 12.5) mmol L⁻¹ min⁻¹ in which CaF₂ precipitation rates continuously increased reaching the maximum values of (0.13 to 0.20) mmol L⁻¹ s⁻¹ after (18 to 29) s, respectively. The 1-min F depositions were greatly enhanced in comparison with the control F solutions that did not have continuous Ca-addition. This indicates that continuous Ca addition that controls the rate of CaF₂ formation could be a critical factor for larger F depositions from F solutions. The efficacy of conventional F mouthrinses could be improved with addition of a substance that continuously releases Ca.     

Metformin intoxication requiring dialysis

Metformin (MTF) is one of the most common oral agents used to treat diabetes mellitus. Intoxication is associated with lactic acidosis and has significant clinical consequences. We report 12 cases requiring dialytic intervention. Twelve patients were analyzed from 2005 to 2010; 10 of these patients were treated with dialysis. Conventional hemodialysis (HD) and continuous veno-venous hemodialysis treatments with bicarbonate dialysis were used, and the results were presented as mean and standard deviation. The results are as follows: 33% of the patients were male, hospital stay was 9.3 (± 12) days, average MTF dose 1.7 g/day, mortality was 25%. Baseline glomerular filtration rate for these patients was 51.5?mL/min, with an average age of 64 (± 11) years. On presentation, all had acute kidney injury with blood urea nitrogen/creatinine 75 (± 30)/8.1 (± 3.7) mg/dL, lactic acid 12.4 (± 8.1) mmol/L, pH?7.04 (± 0.19), bicarbonate 7.2 (± 4.5) mmol/L. Metformin level was 25 (± 17) μg/mL; anion gap was 28 (± 9), and serum potassium was 5.4 (± 1.3) mEq/L. Seventy percent of patients were treated with conventional HD. Patients required 4 (± 5) dialysis treatments at blood flow QB 330 (± 53), dialysis flow QD 571 (± 111) for 305 (± 122) minutes. Postdialysis, the acidosis parameters improved: bicarbonate 19.2 (± 4.1) mmol/L, lactic acid 6 (± 4) mmol/L and MTF levels decreased 8.9 (± 5.7) μg/mL. Metformin percentage removal was calculated to be 60% (± 24). No difference was found between HD and continous veno-venous hemodialysis. The only difference between survivors was the age 53 (± 7) vs. 78 (± 10) (P?相似文献