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 calclum-containing phosphate binders and calcitriol. However, patients using LCa must be carefully monitored for calcium homeostasis and bone turnover.

Reduced Complications during Hemodialysis by Automatic Blood Volume Controlled Ultrafiltration

Background

Intradialytic morbid events (IMEs, mostly hypotension) are frequent complications during hemodialysis (HD). This study investigated whether automatic feedback control via adjustment of the ultrafiltration rate reduces IME frequency.

Methods

In this multi-center cross-over study, 56 hypotension-prone patients were treated both with standard HD (sHD, applying a constant ultrafiltration rate) and HD applying a blood volume controlled ultrafiltration rate (cHD). The relative blood volume (RBV) was continuously monitored. The individual relative blood volume limit (RBVcrit) was determined from the measured RBV during initial sHD. During cHD, the ultrafiltration rate was automatically adjusted to keep the actual RBV above RBVcrit.

Results

In 3,081 HD treatments, slightly fewer IMEs were observed during cHD than during sHD (0.785±0.613 versus 0.695±0.547 per treatment, P=0.144). Less symptomatic events were seen during cHD: -13% for symptomatic hypotension (0.594 versus 0.685 per treatment, P=0.120), and -32% for cramps (0.049 versus 0.072 per treatment, P=0.009). Thirty-one patients with the highest IME rate (IME in at least every second treatment) especially benefited from cHD: 1.185±0.554 versus 0.979±0.543 IME per treatment (P=0.004). The reduction in blood pressure (BP) and the increase in heart rate were lower during the treatments with cHD than with sHD: systolic BP: -18.8±26.7 versus -22.2±28.9 mmHg (P=0.007), diastolic BP: -7.8±14.8 versus -9.1±15.3 mmHg (P=0.064), heart rate: 1.8±10.4 versus 2.3±11.6 per minute (P=0.014). Neither treatment duration nor ultrafiltration volume was significantly different between cHD and sHD.

Conclusion

For cHD, less intradialytic morbid events were observed than for sHD, and pre- to post-dialytic changes in blood pressure and heart rate were less pronounced.

Effects of an increase in time vs. frequency on cardiovascular parameters in chronic hemodialysis patients

Cardiovascular mortality is still high and many risk factors are inadequately controlled in patients on conventional chronic hemodialysis. Recent studies on intensified treatment schedules by either increasing length or frequency of dialysis sessions have shown promising results with better control of blood pressure, reduction of left ventricular hypertrophy and easier control of calcium/phosphate metabolism.

AIM

The present observational study compared the effect of different forms of "intensified dialysis treatment" i.e. either long nightly intermittent (LNHD, 3 x 7.5 - 8 h) or short daily dialysis sessions (DHD, 6 x 2.5 - 3 h) on cardiovascular parameters, phosphate and anemia control in comparison to standard treatment schedules (SHD, 3 x 4 - 5 h).

METHODS

All patients stable on hemodialysis between 18 and 80 years of age and with either uncontrolled hypertension and/or left ventricular hypertrophy and/or frequent intradialytic hypotension, were asked to participate in intensified dialysis therapy by either LNHD or DHD. Patients not willing to change their dialysis regime were asked to participate as control group (SHD). Primary end point was 24-h ambulatory blood pressure, secondary end points were predialysis blood pressure, left ventricular mass index (LVMI) and fractional shortening (FS), control of calcium, phosphate and anemia. Patients were followed up for 1 year.

RESULTS

17 patients opted for LNHD, 8 for DHD, 19 patients served as control group. After 1 year of treatment 24-h blood pressure was unchanged in all groups. Predialysis systolic blood pressure decreased in LNHD and DHD, but increased in SHD. Mean LVMI decreased in all treatment groups (DHD -20.1 +/- 24.0%, SHD -13.6 +/- 33.4%, LNHD -6.1 +/- 32.2%). The mean number of antihypertensive tablets/day was reduced in DHD by 3.3 tablet units, in LNHD by 1.2 tablet units, but increased in SHD patients. FS improved in patients on LNHD and DHD, but decreased in patients on SHD. Regression of LVMI was independent of dry weight which was unchanged in LNHD and SHD but increased in DHD. In contrast to SHD, phosphate control and Ca x P product improved in DHD and LNHD with less phosphate binding tablets. Intact PTH did not change in SHD, but decreased in DHD and LNHD. Hemoglobin increased in groups on intensified treatments, but fell in SHD. EPO resistance index fell in LNHD, but increased in DHD and SHD.

CONCLUSION

While reduction in 24-h blood pressure was not achieved by intensified dialysis, both schedules showed favourable effects on LVMI and FS with less antihypertensive medication. This was independent of reduction in dry weight. These effects were more pronounced in DHD patients. In contrast, in SHD patients, stable 24-h blood pressure and reduction in LVMI were achieved on the expense of an increasing amount of antihypertensive medication and with worsening of FS.

Influence of hemodialysis membrane permeability on serum levels of advanced glycation end products (AGEs) and homocysteine metabolites

BACKGROUND

[corrected] Advanced glycation end products (AGEs), total homocysteine (tHcy) and the homocysteine metabolites cystathionine (Cysta) and dimethylglycine (DMG) are increased in serum of patients with end-stage renal disease. The aim of this prospective randomized study was to compare the efficacy of polysulfone high-flux vs. polysulfone low-flux hemodialysis (HD) treatment regarding removal of AGEs, tHcy, Cysta and DMG.

PATIENTS AND METHODS

Twenty-nine patients on chronic HD treatment were randomly assigned to 2 groups in a 3-period 2-treatment design with low flux (A)--high flux (B)--low flux (A) for group I and B-A-B for group II, 6 weeks each period. The following parameters were measured in pre- and postdialytic serum samples at baseline and the end of each period: total serum fluorescence, Nepsilon-carboxymethyllysine (CML), free and protein-bound pentosidine, tHcy, Cysta and DMG.

RESULTS

There was increased removal of free pentosidine during high-flux HD treatment compared to low-flux HD treatment, attaining significance between the second and third treatment periods (group 1: 86.0 +/- 4.7% vs. 79.2 +/- 8.8%, p = 0.007; group II: 84.0 +/- 6.3% vs. 79.8 +/- 9.8%, p = 0.049 for high vs. low flux). The intradialytic reduction rates for total serum fluorescence, tHcy, Cysta, DMG did not differ between high- and low-flux HD treatment. Protein-bound pentosidine and CML did not decrease during the dialysis sessions, neither with high-flux nor with low-flux HD membrane. Despite a strong decrease during single HD session, the predialytic levels of free pentosidine, tHcy, Cysta and DMG remained unchanged during the study period both for high- and low-flux HD treatment.

CONCLUSION

The more pronounced effect of high-flux dialysis on the removal rate of free pentosidine, found in this randomized crossover study, could not translate into a significant difference in predialysis levels after a 6-week treatment period. We could not find any differences between polysulfone high- and low-flux membranes for lowering predialytic serum concentrations of the measured AGEs, which are mainly bound on albumin.

Solutions for APD: special considerations

Automated peritoneal dialysis (APD) has become the fastest growing dialysis modality in Europe and the United States in recent years. Freedom from daytime exchanges, flexibility of prescription, performance in recumbent position leading to enhanced treatment efficacy, and a decreased incidence of peritonitis are the main advantages of APD over CAPD. Studies on new developments of glucose-based PD fluids were performed predominantly in CAPD patients. High volumes and frequent APD cycles in patients may aggravate the adverse effects of standard CAPD fluids on the peritoneal membrane with increasing time on PD. New, glucose-based PD fluids with neutral pH, very low concentrations of glucose degradation products (GDPs), containing either lactate or bicarbonate as buffering substances have been introduced into clinical use recently. With these new fluids, various in vitro, ex vivo, and in vivo studies could demonstrate a better preservation of peritoneal cell viability and growth, less inhibited secretory cell functions, a significant reduction in the formation of advanced glycation end products (AGEs), and clinical signs for an improved preservation of peritoneal mesothelial cells indicated by an increase in effluent CA125. One has to be aware, however, that uremia per se prior to initiation of PD, as well as during PD treatment itself, directly impacts on peritoneal membrane structural changes so that new, more biocompatible PD fluids may not be completely sufficient to prevent morphologic and functional changes of the membrane. Due to a strong sodium sieving during APD, PD fluids with sodium concentrations of 125-130 mmol/L may be beneficial. Systematic calcium kinetic studies have not yet been performed in APD patients. APD fluids should offer a calcium concentration range of 1.0-1.75 mmol/L in order to enable an individualized APD prescription. For long-term APD treatment, better knowledge of peritoneal membrane physiology and PD kinetics should promote individualization of prescriptions. New, pH-neutral PD solutions with minimized amounts of GDPs may be a significant step forward to improved membrane preservation during long-term APD treatment.

High glucose dialysis solutions increase synthesis of vascular endothelial growth factors by peritoneal vascular endothelial cells

OBJECTIVE

Increased peritoneal vasculature has been reported in long-term peritoneal dialysis (PD), and vascular endothelial growth factors (VEGFs) have been found in dialysate. High concentrations of glucose or lactate, glucose degradation products (GDPs), and low pH of dialysis solutions are all possible factors in increased peritoneal VEGF synthesis. In this study, we investigated the effects of high glucose dialysis solutions on VEGF synthesis by peritoneal vascular endothelial cells (PVECs).

METHODS

The PVECs were isolated from rat omentum and were incubated for 4 hours in three different culture media [M199 media (control), conventional dialysis solutions containing 4.25% glucose diluted with an equal volume of M199 media (HGD), and M199 media containing 118 mmol/L mannitol as an osmolar control (mannitol)]. Levels of VEGF protein in the culture supernatant were measured by ELISA, and mRNA expression was determined by Northern blot analysis. Data are presented as percent of control.

RESULTS

After incubation for 4 hours, the number of cells did not differ between the 3 groups. Levels of VEGF in culture supernatant were significantly higher in the HGD group (124% +/- 19%, p = 0.006) as compared with the control and mannitol (85% +/- 10%) groups. The mRNA expression of VEGF appeared to be higher in the HGD group (128% +/- 49%) than in the control and mannitol (94% +/- 18%) groups.

CONCLUSION

High glucose dialysis solutions increased VEGF synthesis by PVECs. The relationship between VEGF synthesis by PVECs and neovascularization of the peritoneum observed in long-term peritoneal dialysis patients has to be studied further.

Influence of neutral-pH dialysis solutions on the peritoneal membrane: a long-term investigation in rats

OBJECTIVE

Glucose degradation products (GDPs) and low pH are potential causes of bioincompatibility of peritoneal dialysis fluids (PDFs). The aim of the present study was to compare the effect of 6 weeks' exposure of the peritoneum in rats to two different PDFs: a standard PDF with a low pH and high level of GDPs (CAPD 3: Fresenius Medical Care, Bad Homburg, Germany), and a modified PDF with a low level of GDPs and a physiologic pH (CAPD 3 Balance: Fresenius Medical Care).

METHODS

After catheter implantation, rats were exposed twice daily for 6 weeks to CAPD 3 fluid or to CAPD 3 Balance. At the beginning and at the end of the study, a 4-hour dwell was performed in every rat to evaluate intraperitoneal inflammation and its effect on total collagen synthesis in the in vitro cultured rat mesothelial cells (ex vivo study). Additionally, after 6 weeks' exposure, the peritoneal cavity was opened, and macroscopic changes were evaluated according to a semiquantitative scale. Peritoneal samples were also taken for morphology study.

RESULTS

In rats treated with CAPD 3 fluid, intraperitoneal inflammation was comparable at the beginning and at the end of the experiment. In animals exposed to CAPD 3 Balance, the intensity of the intraperitoneal inflammation decreased during the study (cell count, p = 0.0781; neutrophil:macrophage ratio, p < 0.01; nitrite concentration, p < 0.05; hyaluronan level, p < 0.05). The capacity of effluent dialysate from CAPD 3 rats to activate collagen synthesis in in vitro-cultured mesothelial cells was the same at the beginning and at the end of the study. In the CAPD 3 Balance group, this capacity was statistically significantly lower at the end of the study than at the beginning (p < 0.05). The mean thickness of the visceral peritoneum was comparable in both groups of animals, but, macroscopically, more severe fibrosis was found in the peritoneum of rats exposed to CAPD 3 as compared with animals treated with CAPD 3 Balance (p < 0.05).

CONCLUSION

We showed that, in the rat model of peritoneal dialysis, chronic exposure of the peritoneum to PDFs with low GDPs and a physiologic pH diminished the intraperitoneal inflammatory reaction induced by dialysis, and reduced peritoneal fibrosis.

One-compartment model for amino acids and other biological molecules in peritoneal dialysis

OBJECTIVES

Investigation of the main factors determining the concentration-time course of amino acids and biological molecules in serum and dialysates.

METHODS

In a randomized, 3-period crossover study, 11 patients were treated once with each of 3 peritoneal dialysis solutions, 1 containing amino acids and bicarbonate, 1 containing glucose and bicarbonate and 1 containing glucose and lactate. Nineteen amino acids, 3 proteins, 2 metabolites and 2 ions were measured in serum and dialysate. A standard compartment model was fitted to the data.

RESULTS

The amino acids differed significantly in their kinetic characteristics (p < 0.001), mainly volume of distribution and elimination rate. Differences in absorption were small compared to the interpatient variation. The average transport rate from serum to dialysate was 0.50-1.14 h(-1), from dialysate to serum 0.33-0.41 h(-1), for elimination from the central compartment 0.35 to 2.27 h(-1), for volume of distribution 0.29 to 0.83 l/kg, for serum protein binding 19-47%, for amount in tissue 82 - 95%, for endogenous metabolic rate 16-151 micromol x kg(-1) x h(-1). The volume of distribution correlated with the R group (polar positive < aliphatic < polar uncharged). For the various proteins, the 2 bicarbonate solutions had higher serum-to-dialysate transport rates than the lactate solution (p = 0.018-0.601).

CONCLUSION

The compartment model demonstrated its usefulness. Accordance with literature data for healthy volunteers indicated the validity of the estimates.

Continuous flow peritoneal dialysis: solution formulation and biocompatibility

When peritoneal dialysis was introduced several years ago an important alternative dialysis therapy to hemodialysis was made available for the treatment of end-stage chronic disease. However, a continuous search for new developments and technologies is necessary to find the optimal peritoneal dialysis fluid (PDF) to preserve peritoneal membrane function as long as possible. Conventional PDFs are known to compromise the functional integrity of the peritoneal membrane as a consequence of their acidic pH in combination with their high lactate content, as well as the high concentrations of glucose and glucose degradation products (GDPs) present in currently used conventional solutions. Novel solutions such as bicarbonate-buffered PDF (at neutral pH) display improved in vitro biocompatibility as compared to conventional, acidic lactate-buffered PDF. Since these novel solutions are manufactured in dual-chambered bags they also contain fewer GDPs, thus further reducing their potential toxicity and protein glycation. Clinically the novel solutions reduce inflow pain and improve peritoneal membrane transport characteristics, ultrafiltration capacity, and effluent markers of peritoneal membrane integrity. The concept of continuous flow peritoneal dialysis (CFPD) is another approach to optimize PDF. The technique of CFPD not only enables the individualization of acid-base correction by variable concentrations of HCO3- but may also help to restore peritoneal cell functions by neutral pH, reduced glucose load, diminished GDP content, and reduced advanced glycation end product (AGE) formation, thereby potentially contributing to the improved preservation of peritoneal membrane function.

First in vitro and in vivo experiences with Stay-Safe Balance, a pH-neutral solution in a dual-chambered bag

In addition to low pH and high osmolarity, glucose degradation products (GDPs) are considered to play a major role in the bioincompatibility of peritoneal dialysis fluids (PDFs). The formation of GDPs can be reduced by separating the glucose component of the solution (kept at very low pH) from the lactate component of the solution (kept at alkaline pH) during sterilization and storage. This development has been achieved by the use of a dual-chambered bag. Immediately before infusion, the seam between the two chambers is opened, and the contents are mixed. The result is a fluid with a more physiologic pH in the range 6.8 - 7.4. Concentrations of 3-deoxyglucosone (3-DG), methylglyoxal (MG), acetaldehyde (AA), and formaldehyde (FA) in Stay-Safe Balance (Fresenius Medical Care, Bad Homburg, Germany) were remarkably reduced when compared to conventional PD solution [conventional PDF (1.5% glucose): 172 micromol/L, 6 microLmol/L, 152 micromol/L, and 7 micromol/L respectively; Stay-Safe Balance (1.5% glucose): 42 micromolL, < 1 micromol/L, < 2 micromol/L, and < 3 micromol/L respectively; conventional PDF (4.25% glucose): 324 micromol/L, 10 micromol/L, 182 micromol/L, and 13 micromol/L respectively; Stay-Safe Balance (4.25% glucose): 60 micromol/L, < 1 micromol/L, < 2 micromol/L, and < 3 micromol/L respectively). Human peritoneal mesothelial cells (HPMCs) were exposed to a control solution, a conventional PDF [CAPD 2, 1.5% glucose (Fresenius Medical Care, Bad Homburg, Germany)], and Stay-Safe Balance, either in a co-incubation model (24-hour PDF exposure) or in a pre-incubation model (30-min PDF exposure), followed by 24-hour recovery in culture medium. Interleukin-1beta (IL-1beta)-stimulated (1 ng/mL) IL-6 secretion from HPMCs was assessed by ELISA. Exposure of HPMCs to conventional PDF resulted in a significant reduction in IL-6 release, which was fully restored following exposure to Stay-Safe Balance. In addition to the short-term investigations, long-term in vitro studies were also carried out. All fluids had near-neutral pH and were changed every second day. After 1, 3, 5, 7, 10, and 13 days of exposure, cell viability was assessed. Whereas exposure to conventional PDF resulted in a significant reduction in HPMC viability after just 3 - 5 days, no significant toxicity of filter-sterilized or dual-chambered fluid was observed for up to 13 days. An observational study with 9 patients suggested that the efficacy of Stay-Safe Balance is equivalent to that of conventional solution. However, even short-term treatment (8+/-1 weeks) with this more biocompatible solution seems to improve mesothelial cell mass as indicated by a rise in cancer antigen 125 (CA125) from a baseline of 47+/-37 U/min to 172+/-90 U/min. Our data indicate that Stay-Safe Balance may help to better preserve peritoneal membrane cell function. An ongoing European multicenter study is expected to confirm these results.

In vitro formation of N(epsilon)-(carboxymethyl)lysine and imidazolones under conditions similar to continuous ambulatory peritoneal dialysis

Conventional peritoneal dialysis fluids (PDFs) lead to formation of advanced glycation end-products (AGE) in the peritoneal membrane. In this study, we investigated in vitro the dependence of AGE formation on regular changes of PDFs, as performed during continuous ambulatory peritoneal dialysis (CAPD), and on the contribution of high glucose concentration versus glucose degradation products (GDPs). Under conditions similar to CAPD, protein glycating activity of a conventional single chamber bag PDF (CAPD 4.25%), two double chamber bag PDFs (CAPD Balance 4.25% and CAPD Bicarbonate 4.25%) and a sterile filtered control was measured in vitro by N(epsilon)-(carboxymethyl)lysine (CML) and imidazolones, two well characterized, physiologically relevant AGE structures. Regular changes of PDFs increased AGE formation (CML 3.3-fold and imidazolone 2.6-fold) compared to incubation without changes. AGE formation by CAPD 4.25% was increased compared to control (imidazolones 7.9-fold and CML 3.3-fold) and the use of double chamber bag PDFs led to a decrease of imidazolones by 79% (CAPD Bicarbonate 4.25%) and by 66% (CAPD Balance 4.25%) and to CML contents similar to the control. These results indicate that a major part of AGEs were formed by GDPs in PDFs, whereas only a minor part was due to high glucose concentration. The use of double chamber bag fluids can reduce AGE formation considerably.

The use of different buffers during continuous hemofiltration in critically ill patients with acute renal failure

OBJECTIVE

To determine the impact of different hemofiltration (HF) replacement fluids on the acid-base status and cardiovascular hemodynamics in patients with acute renal failure (ARF) and continuous veno-venous hemofiltration (CVVH).

DESIGN

Prospective, cohort study.

SETTING

Intensive Care Unit of the Heinrich Heine University Hospital, Düsseldorf, Germany.

SUBJECT AND METHODS

One hundred and thirty-two critically ill patients with acute renal failure and continuous veno-venous HF were studied. Fifty-two patients were subjected to lactate-based (group 1), and 32 to acetate-based hemofiltration (group 2) while 48 (group 3) were treated with bicarbonate-based buffer hemofiltration fluid. Fifty-seven had a septic, and 75 a cardiovascular, origin of the ARF. Creatinine, blood urea nitrogen (BUN), serum bicarbonate, arterial pH, lactate and Apache II scores were noted daily.

MAIN RESULTS

The mean CVVH duration was 9.8 +/- 8.1 days, mortality was 65%. No difference was present between the groups under investigation with regard to the main clinical parameters. Lactate- and bicarbonate-based hemofiltration led to significantly higher serum bicarbonate and arterial pH values as compared to the acetate-based hemofiltration. Serum bicarbonate values at 48 h after the initiation of CVVH treatment were 25.7 +/- 3.8 mmol/l (p < 0.001) in group 1, 20.6 +/- 3.1 mmol/l in group 2 and 23.3 +/- 3.9 mmol/l (p < 0.001) in group 3. While a lack of increase in serum bicarbonate and arterial pH was correlated to poor prognosis in lactate- and bicarbonate-based hemofiltration, no such observation was made in acetate-based hemofiltration. Cardiovascular hemodynamics were superior in patients treated with lactate- and bicarbonate-based buffer solution as compared to those treated with acetate-based buffer solution.

CONCLUSIONS

The degree of correction of acidosis during hemofiltration was determined by patient outcome in patients treated with lactate- and bicarbonate-based buffer solutions, but not in patients receiving acetate-buffered solution. Bicarbonate and lactate-based buffer solutions were found to be superior to acetate-based replacement fluid.

An amino acid-based peritoneal dialysis fluid buffered with bicarbonate versus glucose/bicarbonate and glucose/lactate solutions: an intraindividual randomized study

OBJECTIVE

In order to study acute metabolic changes and peritoneal transport, amino acids as osmotic agent and bicarbonate as buffer were tested as new agents in peritoneal dialysis (PD) solutions.

DESIGN

In a prospective, cross-over, randomized, intraindividual study, we investigated the acute metabolic changes following the application of three different PD fluids: (1) a 1% amino acid-based PD solution buffered with bicarbonate (34 mmol/L) (Amino/Bic); (2) a 1.5% glucose anhydrous-containing bicarbonate-buffered solution (34 mmol/L) (Glu/Bic); and (3) a conventional 1.5% glucose anhydrous-based dialysis solution with lactate (35 mmol/L) (Glu/Lac).

SETTING

University medical center.

PATIENTS

Ten nondiabetic patients stable on continuous ambulatory peritoneal dialysis (time on dialysis, 42.5 +/- 21.5 months) were treated and monitored with the test solutions over a 6-hour dwell. Three different study days followed in a randomized order for each patient (interval of 1-3 weeks). Blood and dialysate samples were taken at 0.25, 0.5, 1, 2, 4, and 6 hours. Immediately after the 1-hr dwell (and after sampling), the patients received a standardized breakfast, thereby simulating usual food intake.

RESULTS

Following the application of Amino/Bic a significant increase in plasma amino acids occurred, with peak levels (maximum 250% increase) after either the 1-hr or the 2-hr dwell. Before taking the standard meal (0.5 hr, 1 hr), the mean serum glucose level with Amino/Bic was 8% +/- 13% lower than with Glu/Bic (p = 0.06) and 14% +/- 8% lower than with Glu/Lac (p < 0.01). This difference was still significant after the standard breakfast and also for the whole dwell (average serum glucose 0.5-6 hr: Amino/Bic, 91 +/- 6 mg/dL; Glu/Bic, 100 +/- 8 mg/dL; Glu/Lac, 102 +/- 7 mg/dL; p < 0.01 MANOVA). The serum insulin profiles did not differ between the fluids. A transperitoneal protein- and amino acid-related nitrogen loss of 0.49 +/- 0.18 g and 0.48 +/- 0.12 g per dwell was measured using Glu/Bic and Glu/Lac, while a positive balance of 1.80 +/- 0.43 g was achieved with Amino/Bic. The parameters of acid-base status (pH, HCO3, pCO2) remained nearly unchanged in the blood, irrespective of the solution used, while dialysate values differed markedly. No significant differences with respect to ultrafiltration (Amino/Bic, -68 +/- 199 mL/6 hr; Glu/Bic, -51 +/- 89 mL/6 hr; Glu/ Lac, -2 +/- 134 mL/6 hr) and peritoneal creatinine clearance (Amino/Bic, 4.9 +/- 0.6 mL/min; Glu/Bic, 5.1 +/- 0.6 mL/min; Glu/ Lac, 4.8 +/- 0.5 mL/min) were measured.

CONCLUSIONS

Our results demonstrate that ultrafiltration and small solute clearance over a 6-hour dwell with a 1% Amino/Bic solution were comparable to those of 1.5% Glu/Bic and 1.5% Glu/Lac. Reduced serum glucose concentrations were found with Amino/Bic and this fluid compensated the transperitoneal protein-nitrogen loss of about three glucose dwells. Bicarbonate buffering (34 mmol/L) did not change blood acid-base status combined with either glucose or amino acids.

Liver cell reactive components in peritoneal dialysis fluids

Metabolic changes in peritoneal dialysis (PD) patients are an important aspect concerning long-term outcome. Liver plays the main role in regulating metabolism. The effects of peritoneal dialysis fluids (PDF) on liver cell function are scarcely investigated. Therefore, we investigated the effects of PDF, different in some components, on liver cell metabolism in vitro. Metabolic activity (MTT), cell integrity (LDH release), proliferation (BrdU incorporation) and synthesis of albumin and transferrin are measured by incubating HepG2 cells for 3 h and 24 h with six different PDFs: (a) lactate-buffered, pH5.5: PDF I (1.5% gluc.); PDF II (4.5% gluc. ); (b) bicarbonate-buffered, pH7.4: PDF III (1.5% gluc.), PDF IV (4. 5% gluc.); (c) amino acid-based solutions, pH 7.4: PDF V (low AA level) and PDF VI (high AA level). Metabolic activity of bicarbonate-treated cells is greatly enhanced in comparison to lactate-buffered PDFs. These findings are confirmed by proliferation data. Synthesis of albumin and transferrin is significantly enhanced by amino acid-based solutions. Our data demonstrate, that lactate-buffered PDF impair liver cells much stronger than bicarbonate-buffered PDF. pH is the parameter which contributes to cytotoxicity and impaired metabolism to a major extent. In contrast to glucose-containing solutions, amino acid-based PDF stimulate protein synthesis in liver cells.

Biocompatibility and buffers: effect of bicarbonate-buffered peritoneal dialysis fluids on peritoneal cell function

BACKGROUND

Conventional peritoneal dialysis fluids (PDF) have been shown to compromise the function of both leukocytes and human peritoneal mesothelial cells (HPMC). Various in vitro studies have identified the low initial pH in combination with high lactate content, as well as the hyperosmolality and high glucose concentration present in currently used solutions as the primary determinants of their bioincompatibility. Bicarbonate buffered PDF (at neutral pH) display improved in vitro biocompatibility as compared to conventional, lactate buffered PDF. However, little information is currently available regarding the potential impact of PDF on the function of human peritoneal fibroblasts (HPFB), the major cell population present in peritoneal interstitium.

METHODS

The current study compares the effect of bicarbonate and lactate buffered PDF in a model system of resting peritoneal mesothelial cells and fibroblasts cultured from human omentum. Interleukin-1 beta-stimulated IL-6 release from HPMC and HPFB was used as the cell functional parameter.

RESULTS

While short (30 min) pre-exposure to lactate buffered PDF significantly reduced the IL-1 beta-stimulated IL-6 release from HPMC during a subsequent recovery period (24 hr), a significant decrease in HPMC IL-6 secretion with bicarbonate buffered PDF was only observed after prolonged (> or = 60 min) exposure. In contrast, no significant IL-6 inhibition was detected with HPFB pre-exposed to PDF for up to 90 minutes. A significant suppression of HPFB IL-6 secretion was only observed in coincubation experiments (24 hr) with dilutions of both types of PDF.

CONCLUSIONS

These results indicate that (i) bicarbonate buffered PDF are less inhibitory to peritoneal cell function as compared to conventional, lactate buffered PDF; and (ii) HPFB may be more resistant than HPMC to bioincompatible PDF.

Randomized long-term evaluation of bicarbonate-buffered CAPD solution

BACKGROUND

Over the past 15 years, lactate has been used successfully as a buffer in peritoneal dialysis solutions, although its effectiveness in the correction of uremic acidosis and its biocompatibility on peritoneal resident cells have been questioned. In addition, some investigators have suggested other potential adverse metabolic effects resulting from the unphysiologically high lactate flux into the body during CAPD. These potential problems associated with lactate-containing CAPD solution prompted the search for alternative buffer-containing solutions. Bicarbonate, the physiological buffer, was considered when the problem of calcium and magnesium carbonate solubility was solved by the use of a two-compartment bag system, allowing the mixing of bicarbonate and divalent cations immediately before infusion. The long-term tolerance, safety, efficacy and therapeutic value of a bicarbonate-buffered peritoneal dialysis solution were evaluated in this study.

METHODS

This open, randomized, controlled, multicenter study comparing a 34 mmol/liter bicarbonate- with a 35 mmol/liter lactate-buffered peritoneal dialysis solution was performed in two consecutive 12-week-treatment phases. Fourteen Centers participated in this trial.

RESULTS

A total of 69 out of initially 123 randomized patients completed the six-month study period (36 patients in the bicarbonate group and 33 in the lactate group). While the arterial acid base status of the total study population did not change during the study period and no significant difference was observed between the two treatment groups, the acid-base status of patients in the bicarbonate group entering the study with a metabolic acidosis significantly improved (mean +/- SD; blood pH: baseline = 7.361 +/- 0.05, week 12 = 7.380 +/- 0.04, P < 0.05; week 24 = 7.388 +/- 0.03 P < 0.05; plasma bicarbonate: baseline = 19.49 +/- 3.01 mmol/liter, week 12 = 21.16 +/- 2.63 mmol/liter, P < 0.01; week 24 = 21.51 +/- 2.42 mmol/liter, P < 0.01). No significant changes were recorded in acidotic patients treated with the conventional lactate-buffered solution. The changes in plasma bicarbonate from baseline during the study was significantly different between the groups (week 12: lactate = +0.11 +/- 2.21 mmol/liter, bicarbonate = +1.69 +/- 2.55 mmol/liter, P < 0.05, 95% confidence interval for the difference 0.21 to 2.94 mmol/liter; week 24: lactate = +0.03 +/- 2.48 mmol/liter, bicarbonate = +1.82 +/- 2. 96 mmol/liter, P < 0.05, 95% confidence interval for the difference 0.16 to 3.42 mmol/liter). The normalized protein catabolic rate (nPCR) slightly but significantly decreased in the lactate group (baseline -0.90 +/- 0.23 g/kg/day, week 24 -0.83 +/- 0.21 g/kg/day, P < 0.01) and increased in the bicarbonate group (baseline +0.89 +/- 0.28 g/kg/day, week 24 +0.92 +/- 0.26 g/kg/day, P < 0.05). Changes from baseline between groups were significant (week 24, lactate = -0. 099 +/- 0.15 g/kg/day, bicarbonate = 0.049 +/- 0.12 g/kg/day, P < 0. 01, 95% confidence interval for the difference 0.068 to 0.229 g/kg/day). Other evaluated parameters (biochemical profile, peritoneal function parameters, dialysate protein loss) did not differ significantly between the two groups. No adverse effects related to the study solution were recorded.

CONCLUSIONS

These results support the efficacy and safety of bicarbonate-buffered peritoneal solutions in a controlled randomized comparison for up to six months. Peritoneal dialysis solutions containing the physiological buffer bicarbonate might effectively replace conventional lactate-buffered CAPD solutions.

LDL hemoperfusion--a new procedure for LDL apheresis: first clinical application of an LDL adsorber compatible with human whole blood

To date, lipid apheresis procedures can remove low-density lipoprotein (LDL) cholesterol (LDL-C) only from plasma. Thus, initially plasma has to be separated from the blood cells, which increases the costs and complexity of the extracorporeal circuit. This paper describes the first clinical application of a new LDL adsorber that eliminates LDL directly from whole blood. The goal of this pilot study was to test the efficacy, safety, and feasibility of direct lipoprotein adsorption in patients. In a 2 center Phase II clinical trial, 12 hypercholesterolemic patients suffering from overt coronary or peripheral artery disease were treated once with LDL hemoperfusion. The new LDL adsorber (DALI, Fresenius, St. Wendel, Germany) contained 480 ml of polyacrylate coated polyacrylamide gel. The anticoagulation consisted of an initial heparin bolus followed by an acid citrate dextrose (ACD)-A infusion during the treatment. The processing of nearly 1 patient blood volume resulted in a reduction of LDL-C by 45 +/- 8% and triglycerides by 23 +/- 20%. HDL-C, fibrinogen, and cell counts were not significantly influenced. In a subgroup of 5 patients who exhibited elevated lipoprotein (a) (Lp[a]) levels, Lp(a) reduction was 43 +/- 15% (all results corrected for plasma volume shifts). The sessions were clinically uneventful; the system was technically safe and easily handled. In conclusion, short-term LDL hemoperfusion by the DALI proved to be a safe, effective, and simple procedure for the treatment of patients suffering from symptomatic recalcitrant hypercholesterolemia. The present study represents a solid basis for the clinical long-term evaluation of this new technique in the future.

In vivo and in vitro effects of amino-acid-based and bicarbonate-buffered peritoneal dialysis solutions with regard to peritoneal transport and cytokines/prostanoids dialysate concentrations

BACKGROUND

Increasing evidence suggests that conventional PD solutions are detrimental to host defence mechanisms of peritoneal cells. We tested a new amino-acid-based and bicarbonate-buffered PD solution under in vivo and in vitro conditions.

METHODS

During a prospective, cross-over randomized, intraindividual study 10 CAPD patients were investigated with three different solutions: Amino/Bic, 1% amino acid, 34 mmol/l bicarbonate; Glu/Bic, 1.5% glucose, 34 mmol/l bicarbonate; and Glu/Lac, 1.5% glucose, 35 mmol/l lactate. A PET was performed and transport properties (clearance, D/P ratio, MTAC) were calculated. Prostanoid and cytokine concentrations were measured in serum and the 6 h effluent. Using an in vitro model, mononuclear leukocytes of healthy donors were also incubated with the test fluids. In vivo results. Peritoneal clearance and MTAC of small solutes (creatinine, urea) were not significantly altered by amino acids or bicarbonate. Peritoneal permeability and transperitoneal excretion of higher-weight protein molecules (beta 2-microglobulin, albumin, IgG) were increased with Amino/Bic compared to Glu/Lac (P < 0.05) (D/P ratio albumin: Amino/Bic, 0.027 +/- 0.003; Glu/Bic, 0.023 +/- 0.003; Glu/Lac, 0.022 +/- 0.002). Application of Amino/Bic was accompanied by an increased effluent concentration of Il-6, Il-8, TNF alpha, PGE2, and 6-keto-PGF1a (P < 0.05). Dialysate nitrite/nitrate and cGMP concentrations (as indicators of NO generation) did not differ between the solutions. In vitro results. Both bicarbonate fluids demonstrated a better preservation of the mitochondrial dehydrogenases activity (MTT assay) compared to Glu/ Lac (P < 0.01) (Amino/Bic: 80.6 +/- 3.2%; Glu/Bic: 86.0 +/- 1.8%; Glu/Lac, 64.9 +/- 2.3%, referred to RPMI as control). Constitutive and LPS stimulated release of Il-1 beta and Il-6 was less suppressed with both bicarbonate fluids (P < 0.05) (LPS-stim. Il-6 release: Amino/Bic, 33.0 +/- 6.6%; Glu/Bic, 65.5 +/- 10.3%; Glu/Lac, 1.5 +/- 0.7% referred to RPMI).

CONCLUSION

Application of an amino-acid/bicarbonate solution resulted in a small but significant increase in peritoneal permeability. Also increased concentrations of various cytokines/prostanoids were measured in the effluent. According to in vitro testing with mononuclear phagocytes both bicarbonate-buffered fluids were to the same extent less inhibitory to certain cell functions than lactate-buffered solution.

Improved cytosolic free calcium mobilization and superoxide production in bicarbonate-based peritoneal dialysis solution

BACKGROUND

Intraperitoneal phagocytes play an important role in local host defence to prevent CAPD peritonitis. The intracellular calcium [Ca2+]i is thought to be involved in the regulation of various cell functions. This study therefore investigates the effect of lactate-based dialysis solution (LBDS) and bicarbonate-based dialysis solution (BBDS) on cytosolic free calcium mobilization and superoxide production (SP) as important steps in signal transduction and bacterial killing.

METHODS

We studied changes in [Ca2+]i and SP following stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) in polymorphonuclear neutrophils (PMNs) incubated in either LBDS-pH 5.2, LBDS adjusted to pH 7.4, 1:10 diluted spent and fresh LBDS or BBDS-pH 7.4 with different glucose concentrations, comparing the data with cells treated with Hanks buffer (HBSS) pH 7.4 as control. To elucidate the effect of glucose and lactate PMNs were additionally incubated in HBSS-pH 7.4, containing glucose (HBSS-Glu-pH 7.4) or lactate (HBSS-Lact-pH 7.4) in the same concentrations as contained in CAPD solutions and tested as above. PMNs were isolated from healthy blood donors and incubated with dialysis solution 10 min prior to stimulation with fMLP.

RESULTS

[Ca2+]i mobilization and SP were completely inhibited in PMNs incubated in LBDS pH 5.2. pH adjustment of LBDS to 7.4 and 1:10 dilution of spent and fresh LBDS corrected some of the suppression of the calcium influx and superoxide production. BBDS pH 7.4, however, preserved physiological cell function significantly better at low (1.5 and 2.3%) glucose concentrations.

CONCLUSION

In comparison to conventional lactate-based dialysis solution, pH adjusted and 1:10 diluted LBDS, bicarbonate-based dialysis solution is more biocompatible since it preserves significantly better neutrophil cell functions.

In vitro biocompatibility evaluation of a novel bicarbonate-buffered amino-acid solution for peritoneal dialysis

BACKGROUND

Conventional lactate-buffered peritoneal dialysis fluids containing glucose as the osmotic agent have been shown to compromise important peritoneal host defence functions. The current study employed an in vitro model using activated peripheral blood mononuclear leukocytes (PBMC) for the preclinical biocompatibility assessment of a novel bicarbonate-buffered peritoneal dialysis fluid containing 1.0% amino acids as the osmotic agent.

METHODS

PBMC (5 x 10(6)/ml) were pre-exposed (10-30 mm, 37 degrees C) to bicarbonate-buffered 1% amino-acid solution, bicarbonate- or lactate-buffered 1.5% glucose fluid, or control medium (RPMI). The cells were then washed and stimulated for 2 h at 37 degrees C in RPMI containing 100 ng/ml E.coli endotoxin from strain O55:B5. The cytokines IL-6 and TNF alpha in cell supernatants were assessed using specific enzyme immunoassays, cytokine mRNA expression by reverse transcription polymerase chain reaction.

RESULTS

Short, i.e. 10 min, exposure to conventional, lactate-buffered glucose fluid resulted in a significant and time-dependent inhibition of cytokine release and mRNA expression by activated PBMC, whereas the cytokine response was improved even following prolonged (up to 2 h) exposure to bicarbonate-buffered 1% amino-acid solution or bicarbonate-buffered 1.5% glucose fluid.

CONCLUSIONS

Our results suggest that very short, i.e. potentially clinically relevant, exposure to conventional dialysis fluid impairs the cytokine response by activated leukocytes. In this respect, the use of bicarbonate-buffered solutions containing 1.0% amino acids or 1.5% glucose may result in improved biocompatibility properties.

In vitro effects of glucose polymer-containing peritoneal dialysis fluids on phagocytic activity

Commercially available peritoneal dialysis fluids (PDFs) are known to impair peritoneal cellular defense mechanisms. We have investigated the influence of glucose polymer-containing PDFs on phagocytic function in vitro. Polymorphonuclear neutrophils (PMNLs) and monocytes (MNs) from 10 continuous ambulatory peritoneal dialysis patients and 10 healthy donors were incubated in PDFs containing either 7.5% icodextrin (glucose polymer) or 1.5% glucose at original pH and pH 7.4. Chemiluminescence response and H202 production were measured following stimulation with preopsonized Staphylococcus epidermidis or phorbol myristate acetate. Phagocytosis of radiolabeled bacteria and killing capacity of the cells were determined. A comparison of the impact of glucose polymer versus glucose-containing solutions at their original pH on the oxidative metabolism of the cells showed a highly significant difference (P < 0.0001) in favor of glucose polymers for H202 production of PMNLs (7.78 +/- 4.5 nmol cytochrome C reduction/10(6) cells/min v 1.11 +/- 0.67 nmol cytochrome C reduction/10(6) cells/min) and MNs (7.66 +/- 3.6 nmol cytochrome C reduction/10(6) cells/min v 1.29 +/- 0.86 nmol cytochrome C reduction/10(6)cells/min). Correspondingly, PMNLs and MNs incubated in glucose polymers showed a significantly higher chemiluminescence response irrespective of the stimulant used (P < 0.0001). Applying the killing assay on PMNLs also revealed a significantly higher percentage of inactivated bacteria (45.5% +/- 11.0% v 29.2% +/- 15.5%; P < 0.05). After adjustment of pH to 7.4, a significant difference could only be found for H202 production of PMNLs in favor of glucose polymers (16.73 +/- 6.98 nmol cytochrome C reduction/10(6) cells/min v 11.65 +/- 5.37 nmol cytochrome C reduction/10(6) cells/min; P < 0.05). In addition, we compared the glucose-polymer solution to an otherwise equally composed equiosmolar solution that contained 0.274% glucose instead of glucose polymers. No significant differences were detected with any of the tests applied. Our data suggest that glucose polymer solutions are comparatively less suppressive to phagocytic function than currently used glucose-containing PDFs. This effect may be attributed to the low osmolarity of these solutions.

Clinical experience with a 39 mmol/L bicarbonate-buffered peritoneal dialysis solution

OBJECTIVE

To investigate the effect on the patient's acid-base status of a 39 mmol/L bicarbonate-buffered continuous ambulatory peritoneal dialysis (CAPD) solution.

DESIGN

This was an open, controlled, cross-over, two-center study in 9 patients. After three months of treatment with a 34 mmol/L bicarbonate-buffered solution (t0) patients were switched to a 39 mmol/L bicarbonate-containing solution for four weeks. At the end of the study period (t4) patients were again treated with a 34 mmol/L bicarbonate-buffered CAPD solution for one month (t8).

RESULTS

Mean venous plasma bicarbonate level significantly increased during the study and decreased at the baseline level during the control period (t0 = 22.94 +/- 2.54, t1 = 26.74 +/- 3.07, t2 = 28.47 +/- 2.68, t3 = 28.11 +/- 3.56, t4 = 28.71 +/- 3.27, t8 = 24.94 +/- 2.56). Arterial blood pH and plasma bicarbonate significantly increased during the study and significantly decreased at the end of the control period (pH: t0 = 7.37 +/- 0.04, t4 = 7.42 +/- 0.04, t8 = 7.37 +/- 0.06. Bicarbonate: t0 = 21.97 +/- 2.57, t4 = 25.85 +/- 2.02, t8 = 21.87 +/- 2.89). The changes in plasma bicarbonate during the study period were inversely correlated with the metabolic acid production calculated from the protein catabolic rate and with the apparent distribution space for bicarbonate (ABS) of patients.

CONCLUSIONS

The 39 mmol/L bicarbonate-buffered CAPD solution improved the patient's acid-base status. Potential undesirable metabolic alkalosis could be prevented by analyzing the ABS and the metabolic acid production of patients.

Comparison of a lactate-versus acetate-based hemofiltration replacement fluid in patients with acute renal failure

The objective of the study was to determine the impact of a lactate- and an acetate-based hemofiltration replacement fluid (HF) on the acid-base status in patients with acute renal failure (ARF) and continuous venovenous hemofiltration (CVVH). The prospective, cohort study was carried out in the intensive care unit of the Heinrich-Heine University Hospital, Düsseldorf, FRG. Subjects were 84 critically ill patients with ARF and CVVH. Fifty-two patients were subjected to lactate-based (group 1) and 32 to acetate-based hemofiltration (group 2). Thirty-eight patients had a septic, 46 a cardiovascular origin of the ARF. Creatinine, BUN, serum bicarbonate, arterial pH, lactate and APACHE II score were noted daily. Mean CVVH duration was 9.8 +/- 8.1 days; mortality was 65%. The groups did not differ with regard to the main clinical parameters. Lacate-based hemofiltration led to significantly higher serum bicarbonate and arterial pH values as compared to the acetate-based hemofiltration. Baseline serum bicarbonate values were 23.3 +/- 8.3 mmol/L in group 1 and 21.6 +/- 4.3 mmol/L in group 2 (NS); values at 48 h after initiating CVVH treatment were 25.7 +/- 3.8 mmol/L and 20.6 +/- 3.1 mmol/L, respectively (p < 0.001). Arterial pH prior to CVVH treatment was 7.36 +/- 0.1 in group 1 and 7.34 +/- 0.1 in group 2 (NS), and 7.43 +/- 0.07 versus 7.37 +/- 0.06 (p < 0.001) on day 2. These findings were maintained throughout therapy. While a lack of increase in serum bicarbonate and arterial pH was correlated to a poor prognosis in lactate-based hemofiltration, no such observation could be made in acetate-based hemofiltration. Septic patients did not differ in their acid-base status from nonseptic patients. Lactic acidosis occurred in 8 septic patients irrespective of the substitution fluid. All 8 patients died. There was a significant increase in HCO3 and arterial pH values in lactate-based as compared to acetate-based HF.

Long-term dialysis with low-calcium solution (1.0 mmol/L) in CAPD: effects on bone mineral metabolism. Collaborators of the Multicenter Study Group

OBJECTIVE

Peritoneal dialysate solutions with conventionally high-calcium (Ca) concentrations (1.75 mmol/L) are now widely replaced by solutions with a lower, more physiological calcium content to prevent hypercalcemia in patients treated with oral calcium-containing phosphate binders and/or calcitriol. While there is still debate on how far the dialysate calcium should be lowered (1.25 mmol/L or less), little information is available concerning the effects of a long-term treatment with low-calcium solutions on secondary hyperparathyroidism and bone mineral metabolism in general.

DESIGN

A prospective, randomized, controlled multicenter study to compare the effects of low-calcium (LCa, dialysate calcium 1.0 mmol/L) versus standard-calcium dialysate solution (SCa, dialysate calcium 1.75 mmol/L) on bone mineral metabolism in continuous ambulatory peritoneal dialysis (CAPD) patients over 2 years of treatment.

SETTING

Nephrology and dialysis units of primary and tertiary hospitals in Germany and Switzerland.

PATIENTS

All CAPD patients in the participating centers between 18 and 80 years of age, stable on CAPD for at least 1 month, free of aluminium bone disease or prior parathyroidectomy were invited to enter the study. Sixty-four patients could be randomly allotted to LCa (n = 35) or SCa (n = 29) treatment in a 2-year protocol; 34 finished the study as planned.

INTERVENTIONS

Calcium carbonate (CaCO3) was given as oral phosphate binder to maintain serum phosphate < 2.0 mmol/L. If hypercalcemia supervened, CaCO3 was exchanged stepwise for aluminium hydroxide (Al(OH)3), until normocalcemia was obtained. Patients received calcitriol (0.25 microgram/day per os) if parathyroid hormone (PTH) exceeded the upper limit of normal by a factor of 2 or more.

MAIN OUTCOME MEASURES

We assessed total and ionized serum calcium, phosphate, serum aluminum, alkaline phosphatase, osteocalcin, PTH (intact molecule), and phosphate binder intake at regular intervals. Measurements of bone mineral density and hand skeleton x-rays were obtained at the start and after 6 months and 2 years, respectively.

RESULTS

With LCa, mean total and ionized serum calcium levels were within the normal range (total Ca: 2.0-2.6 mmol/L; ionized Ca: 1.19-1.32 mmol/L), but throughout the treatment period were significantly lower than with SCa. The incidence of hypercalcemia (> 2.8 mmol/L) was three times higher in patients on SCa, despite the significantly higher amount of Al(OH)3 and less CaCO3 given in this group. In parallel, serum aluminum increased with SCa throughout the study, whereas it was slowly decreasing with LCa. Median PTH levels remained stable at about two times the upper limit of normal over the 2 years of study with LCa. However, 23% of the patients on LCa developed severe hyperparathyroidism, with PTH levels exceeding ten times the upper limit of normal compared to only 10.3% of the patients on SCa. With SCa, median PTH decreased towards near normal levels. Alkaline phosphatase and serum osteocalcin correlated positively with PTH levels. Bone mineral density was in the lower normal range in both groups and remained unchanged at the end of the study. Skeletal x-ray films showed only minor alterations in very few patients in both groups with no correlation to serum PTH or treatment modality.

CONCLUSION

In CAPD patients low-calcium dialysate solutions can be used successfully over prolonged periods of time with stable control of serum calcium. The risk of hypercalcemia resulting from calcium-containing phosphate binders and the need to use aluminum-containing phosphate binders is markedly diminished. However, there is a certain risk that severe secondary hyperparathyroidism with long-term LCa therapy will develop, even if normocalcemia is maintained. Thus, LCa dialysis requires close and continuous monitoring of PTH and bone metabolism.

Biocompatibility of bicarbonate buffered peritoneal dialysis fluids: influence on mesothelial cell and neutrophil function

The present study compares the effects of lactate and bicarbonate buffered PDF on human neutrophil (PMN) and human peritoneal mesothelial cell (HPMC) viability and function. Acute exposure of PMN to lactate buffered PDF at pH 5.5 (CAPD 2, 1.5% and CAPD 3, 4.25% glucose) resulted in significant reductions in cellular ATP levels, the phagocytosis of serum treated zymosan (STZ) and respiratory burst activation (CL). Exposure of PMN to bicarbonate buffered PDF (BIC 20, 1.5% glucose and BIC 30, 4.25% glucose both at pH 7.2) had no significant effect on cell viability or the CL response. Phagocytosis was, however, depressed significantly more following exposure to BIC 30 than BIC 20. PMN cellular ATP levels and phagocytosis were significantly better in cells exposed to BIC 30 than to CAPD 3 at pH 7.4 (P = 0.043 for both). Pre-exposure of HPMC to CAPD 2, CAPD 3 or BIC 30 for 30 minutes resulted in a significant reduction in cellular ATP content compared to control medium. Pre-exposure to BIC 20 did not result in a reduction in HPMC ATP levels. HPMC synthesis of IL-6 was unaffected by 15 or 30 minutes pre-exposure to BIC 20 or BIC 30, in contrast pre-exposure to CAPD 2 or CAPD 3 for 15 or 30 minutes resulted in a significant reduction in stimulated IL-6 synthesis (24.5 +/- 3.01 and 32.3 +/- 5.0 vs. 43.9 +/- 10 pg/microgram cell protein in M199, N = 6; P = 0.02). Neutralization of the pH of CAPD 2 and CAPD 3 resulted in normalization of HPMC IL-6 secretion. Analysis of IL-6 mRNA expression in control, BIC 20 and 30 pre-treated HPMC subsequently stimulated with IL-1 beta revealed no differences in the expression of the IL-6 specific 465 base pair transcripts. The improved cellular function in bicarbonate buffered PDF indicates potentially improved host defence status and preservation of the peritoneal membrane in CAPD patients.

Correction of acidosis in CAPD decreases whole body protein degradation

Correction of acidosis in CAPD decreases protein degradation and synthesis but has no effect on leucine oxidation. The effect of the correction of metabolic acidosis in CRF patients treated with CAPD was determined from the kinetics of infused L-[1-13C]leucine. Seven CAPD patients were studied before (acid) and after correction of acidosis (bicarbonate) (pH:acid 7.39 +/- 0.01, bicarbonate 7.41 +/- 0.01, P = 0.005). Leucine appearance from body protein (PD) [corrected] and leucine disappearance into body protein (PS) [corrected] decreased significantly with correction of acidosis. (PS: acid 211.7 +/- 9.8, bicarbonate 142.3 +/- 4.2 micromol x kg-1 x hr-1, P < 0.001; PD: acid 200.6 +/- 8.5, bicarbonate 132.4 +/- 3.7 micromol x kg-1 x hr-1, P < 0.001). There was no significant change in leucine oxidation or plasma amino acid concentrations. These results demonstrate that optimal correction of acidosis in CAPD is beneficial in terms of protein turnover.

What is the appropriate dialysate calcium concentration for the dialysis patient?

Recently, there has been a trend to lower dialysate calcium concentrations because of the frequent occurrence of hypercalcaemia with the use of calcium-containing phosphate binders. No single dialysate calcium concentration is available which suits all dialysis patients. The risk of hypercalcaemia depends on intradialytic (diffusive and convective) calcium transport and interdialytic calcium balance (negative or positive intestinal balance). Low dialysate calcium concentrations expose the patient to the risks of negative calcium balance and increase in parathyroid hormone concentration, particularly if patients are non-compliant with the intake of calcium-containing phosphate binders.

Factors affecting bicarbonate transfer with bicarbonate-containing CAPD solution

OBJECTIVE

To evaluate bicarbonate fluxes across the peritoneal membrane and bicarbonate gain in patients treated with continuous ambulatory peritoneal dialysis (CAPD) using dialysis solutions with different bicarbonate concentrations.

PATIENTS AND DESIGN

Ninety-seven exchanges, using different dwell times and glucose and bicarbonate concentrations were performed in 43 stable CAPD patients. Dialysate effluent bicarbonate concentration and volumes were measured at different dwell times. Net dialytic bicarbonate gain was calculated. Patients' acid-base status was determined at the middle of the dwell.

RESULTS

In prolonged dwells (6-12 hours) the dialysate effluent bicarbonate concentration correlated with arterial plasma bicarbonate concentration (F = 129, p < 0.0001), but not with ultrafiltration rate or dialysis solution bicarbonate concentration. In 4-hour dwells, effluent bicarbonate concentration correlated with both plasma bicarbonate concentration and ultrafiltration rate (F = 32.52, p < 0.0001 and F = 4.4, p < 0.05, respectively). The effluent bicarbonate concentration may be predicted from the patient's plasma bicarbonate concentration and net ultrafiltration rate for either a 4-hour or prolonged (6-12 hours) dwell time. Net bicarbonate gain by the patient correlated with ultrafiltration rate, plasma bicarbonate, and dialysis solution bicarbonate concentration (F = 100.56, p < 0.0001 at 4 hours and F = 108.08, p < 0.0001 at 6-12 hours), with the ultrafiltration rate being the predominant parameter.

CONCLUSIONS

The effluent bicarbonate concentration is related to plasma bicarbonate concentration, with ultrafiltration playing a marginal role only during short dwells. However, the ultrafiltration rate has a profound effect on net patient bicarbonate gain. Multiple linear regression analysis allows the prediction of the effect of acid-base status, ultrafiltration, dwell time, and dialysis solution bicarbonate content on net patient bicarbonate gain. It seems that bicarbonate content in the CAPD dialysis solution should be progressively increased with increasing solution osmolality.

In vitro effects of low-calcium peritoneal dialysis solutions on peritoneal macrophage functions

The use of low-calcium peritoneal dialysis solutions (PDS) for continuous ambulatory peritoneal dialysis is becoming widely accepted to reduce the risk of serum hypercalcemia in patients taking calcium salts as phosphate binders. We compared the in vitro effects of low-calcium PDS (1,000 mumol calcium/L), calcium-free buffer, and buffers with increasing calcium concentrations (500 to 5,000 mumol calcium/L) on peritoneal macrophage (PMO) functions. Peritoneal macrophages isolated from 10 continuous ambulatory peritoneal dialysis patients were incubated in the different solutions and tested for phagocytic and killing capacity, superoxide generation (cytochrome-C reduction and lucigenin-enhanced chemiluminescence), and the rate of myeloperoxidase-dependent oxidative metabolism (luminol-enhanced chemiluminescence). All functions of the PMO incubated in calcium-free buffer were significantly suppressed compared with the PMO incubated in calcium buffers. No dose-dependent increase of a single PMO function could be found after incubating the PMO in calcium buffer with increasing concentrations. Incubation of PMO in otherwise identical PDS containing 1,000, 1,450, or 1,750 mumol calcium/L did not result in significantly different PMO functions. Acidic PDS (pH 5.3 to 5.5) suppressed all measured PMO functions as compared with their neutralized counterparts (pH 7.4), irrespective of the calcium concentration. Results of our in vitro study show that low-calcium PDS does not suppress PMO functions any more than standard-calcium PDS (1,750 mumol calcium/L) does.

Low dialysate calcium in continuous ambulatory peritoneal dialysis: a randomized controlled multicenter trial. The Peritoneal Dialysis Multicenter Study Group

Hypercalcemia is a common complication in continuous ambulatory peritoneal dialysis (CAPD) patients treated with calcium-containing phosphate binders and using the standard dialysate calcium concentration of 3.5 mEq/L (SCa). Lowering the dialysate calcium was proposed to overcome this problem. The current randomized controlled multicenter study was designed to investigate efficiency and safety of a low calcium dialysate (2.00 mEq/L; LCa) compared with SCa (3.5 mEq/L) in CAPD patients. After an 8-week run-in period, 103 stable CAPD patients, 68 men, 35 women, aged 54.5 years (range, 20 to 77)) were randomly allotted to treatment with either LCa or SCa. All patients received calcium carbonate as oral phosphate binder to achieve serum phosphate levels < 6.2 mg/dL. If persistent hypercalcemia arose, CaCO3 was replaced by Al(OH)3 until normocalcemia was achieved. All patients received 0.25 microgram calcitriol/d. Parameters monitored included total and ionized serum calcium, serum phosphate, phosphate binder intake, incidence of hypercalcemia, serum aluminium, intact parathyroid hormone (1,84PTH), osteocalcin, alkaline phosphatase, bone mineral density and hand skeletal x-ray. Primary end points were (a) number of hypercalcemic episodes, (b) tolerated doses of calcium-containing phosphate binders, and (c) 1,84PTH. After 6 months of therapy, total and ionized calcium were lower in LCa patients (total Ca:9.6 v 10.08 mEq/L, P = 0.005; iCa: 4.76 v 5.15 mg/dL; P = 0.013). In the LCa group, significantly fewer episodes of hypercalcemia were recorded (total S-calcium > 10.8 mg/dL: LCa 24 v SCa 86 episodes; P < 0.005). Use of LCa permitted the administration of more CaCO3 (mean daily tablet number: LCa, 5.9 v SCa, 4.2; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro effects of amino-acid-based versus glucose-based continuous ambulatory peritoneal dialysis fluids on peritoneal macrophage function

We studied the in vitro effects of peritoneal dialysis fluids (PDF) containing 1 and 1.5% amino acids (AA) as compared to approximately equiosmolar glucose (GLU)-based PDF (1.5 and 4.25%) and control buffer, respectively, on peritoneal macrophage (PMO) function. The media were tested at original pH (5.3-5.5) and after pH adjustment to 7.4. PMO were isolated from the effluents of 10 on continuous ambulatory peritoneal dialysis (CAPD) patients and tested for luminol- and lucigenin-enhanced chemiluminescence (CL), superoxide generation measured by cytochrome c reduction, killing capacity and phagocytosis after incubation (30 min, 37 degrees C) in the PDF used. All AA-based PDF exhibited a statistically significant depressive effect on integral CL response, O2- production and bacterial killing of PMO at pH 7.4 in comparison with pH-adjusted GLU-based PDF of similar osmolality and buffer. Exposure of PMO to acidic AA-based media did not result in a significantly different suppression of the oxidative metabolism and the killing capacity as compared to fresh GLU-based fluids. Phagocytosis of PMO did not show significant differences after incubation in the solutions studied. Thus, the AA-based PDF employed compromise the oxidative metabolism and the killing capacity of PMO at pH 7.4 in vitro significantly more than GLU-based fluids. Since pH-identical and almost equiosmolar PDF were compared, the specific composition of the AA-based fluids, especially the high content of lactate and several essential AA, could be responsible for this detrimental impact.