Clinical performance of a new high-flux synthetic membrane

Bisphenol A and Bisphenol S in Hemodialyzers

Bisphenol A (BPA)-based materials are used in the manufacturing of hemodialyzers, including their polycarbonate (PC) housings and polysulfone (PS) membranes. As concerns for BPA's adverse health effects rise, the regulation on BPA exposure is becoming more rigorous. Therefore, BPA alternatives, such as Bisphenol S (BPS), are increasingly used. It is important to understand the patient risk of BPA and BPS exposure through dialyzer use during hemodialysis. Here, we report the bisphenol levels in extractables and leachables obtained from eight dialyzers currently on the market, including high-flux and medium cut-off membranes. A targeted liquid chromatography-mass spectrometry strategy utilizing stable isotope-labeled internal standards provided reliable data for quantitation with the standard addition method. BPA ranging from 0.43 to 32.82 µg/device and BPS ranging from 0.02 to 2.51 µg/device were detected in dialyzers made with BPA- and BPS-containing materials, except for the novel FX CorAL 120 dialyzer. BPA and BPS were also not detected in bloodline controls and cellulose-based membranes. Based on the currently established tolerable intake (6 µg/kg/day), the resulting margin of safety indicates that adverse effects are unlikely to occur in hemodialysis patients exposed to BPA and BPS quantified herein. With increasing availability of new data and information about the toxicity of BPA and BPS, the patient safety limits of BPA and BPS in those dialyzers may need a re-evaluation in the future.

Clinical Safety of Expanded Hemodialysis Compared with Hemodialysis Using High-Flux Dialyzer during a Three-Year Cohort

Expanded hemodialysis (HD) equipped with a medium cut-off (MCO) membrane provides superior removal of larger middle molecules. However, there is still little research on the long-term benefits of expanded HD. Over a three-year period, this observational study evaluated the efficacy and safety profile of expanded HD for inflammatory cytokines, including IL-6. We conducted a prospective cohort study to investigate the inflammatory cytokine changes and a retrospective observational cohort study to investigate long-term clinical efficacy and safety over a three-year period. We categorized the patients according to dialyzer used: MCO and high-flux (HF) dialyzer. The inflammatory cytokines, including IFN-γ, IL-1β, IL-6, and TNF-α, were measured annually. The concentrations and changes of the four cytokines over time did not differ between the HF group (n = 15) and MCO group (n = 27). In both prospective and retrospective (HF group, n = 38; MCO group, n = 76) cohorts, there were no significant differences in either death, cardiovascular events, infections, or hospitalizations. Furthermore, the temporal changes in laboratory values, including serum albumin and erythropoietin prescriptions, did not differ significantly between the two groups in either the prospective or retrospective cohorts. In conclusion, clinical efficacy and safety outcomes, as well as inflammatory cytokines, did not differ with expanded HD compared with HF dialysis during a three-year treatment course, although the level of inflammatory cytokine was stable.

A Review of Commercial Developments and Recent Laboratory Research of Dialyzers and Membranes for Hemodialysis Application

Dialyzers have been commercially used for hemodialysis application since the 1950s, but progress in improving their efficiencies has never stopped over the decades. This article aims to provide an up-to-date review on the commercial developments and recent laboratory research of dialyzers for hemodialysis application and to discuss the technical aspects of dialyzer development, including hollow fiber membrane materials, dialyzer design, sterilization processes and flow simulation. The technical challenges of dialyzers are also highlighted in this review, which discusses the research areas that need to be prioritized to further improve the properties of dialyzers, such as flux, biocompatibility, flow distribution and urea clearance rate. We hope this review article can provide insights to researchers in developing/designing an ideal dialyzer that can bring the best hemodialysis treatment outcomes to kidney disease patients.

A Bifunctional Adsorber Particle for the Removal of Hydrophobic Uremic Toxins from Whole Blood of Renal Failure Patients

Hydrophobic uremic toxins accumulate in patients with chronic kidney disease, contributing to a highly increased cardiovascular risk. The clearance of these uremic toxins using current hemodialysis techniques is limited due to their hydrophobicity and their high binding affinity to plasma proteins. Adsorber techniques may be an appropriate alternative to increase hydrophobic uremic toxin removal. We developed an extracorporeal, whole-blood bifunctional adsorber particle consisting of a porous, activated charcoal core with a hydrophilic polyvinylpyrrolidone surface coating. The adsorption capacity was quantified using analytical chromatography after perfusion of the particles with an albumin solution or blood, each containing mixtures of hydrophobic uremic toxins. A time-dependent increase in hydrophobic uremic toxin adsorption was depicted and all toxins showed a high binding affinity to the adsorber particles. Further, the particle showed a sufficient hemocompatibility without significant effects on complement component 5a, thrombin-antithrombin III complex, or thrombocyte concentration in blood in vitro, although leukocyte counts were slightly reduced. In conclusion, the bifunctional adsorber particle with cross-linked polyvinylpyrrolidone coating showed a high adsorption capacity without adverse effects on hemocompatibility in vitro. Thus, it may be an interesting candidate for further in vivo studies with the aim to increase the efficiency of conventional dialysis techniques.

Flux and Passage Enhancement in Hemodialysis by Incorporating Compound Additive into PVDF Polymer Matrix

In this study, Polyvinylidene fluoride (PVDF) hollow fiber hemodialysis membranes were prepared by non-solvent induced phase separation (NIPS) with compound addtive. The compound additive was made with polyvinyl pyrrolidone (PVP) and Poly ethylene glycol (PEG). The results showed that the modified PVDF membrane had better separation performance than virgin PVDF membrane. The UF flux of modified PVDF membrane can reach 684 L·h⁻¹·m⁻² and lysozyme (LZM) passage is 72.6% while virgin PVDF membrane is 313 L·h⁻¹·m⁻² and 53.2%. At the same time, the biocompatibility of PVDF membranes was also improved. Compared with commercial polysulfone hemodialysis membrane (Fresenius F60S membrane), the modified PVDF membrane had better mechanical and separation performance. The stress and tensile elongation of modified PVDF membrane was 0.94 MPa and 352% while Fresenius F60S membrane was 0.79 MPa and 59%. The LZM passage reached 72.6% while Fresenius F60S membrane was 54.4%. It was proven that the modified PVDF membrane showed better hydrophilicity, antithrombogenicity, less BSA adsorption, and lower hemolytic ratio and adhesion of platelets. Water contact angle and BSA adsorption of the modified PVDF membrane are 38° and 45 mg/m² while Fresenius F60S membrane are 64° and 235 mg/m². Prothrombin time (PT) and activated partial thromboplastin time (APTT) of the modified PVDF membrane are 56.5 s and 25.8 s while Fresenius F60S membrane is 35.7 s and 16.6 s. However, further biocompatibility evaluation is needed to obtain a more comprehensive conclusion.

High-flux versus low-flux membranes for end-stage kidney disease

BACKGROUND

Clinical practice guidelines regarding the use of high-flux haemodialysis membranes vary widely.

OBJECTIVES

We aimed to analyse the current evidence reported for the benefits and harms of high-flux and low-flux haemodialysis.

SEARCH METHODS

We searched Cochrane Renal Group's specialised register (July 2012), the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1948 to March 2011), and EMBASE (1947 to March 2011) without language restriction.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that compared high-flux haemodialysis with low-flux haemodialysis in people with end-stage kidney disease (ESKD) who required long-term haemodialysis.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two authors for study characteristics (participants and interventions), risks of bias, and outcomes (all-cause mortality and cause-specific mortality, hospitalisation, health-related quality of life, carpal tunnel syndrome, dialysis-related arthropathy, kidney function, and symptoms) among people on haemodialysis. Treatment effects were expressed as a risk ratio (RR) or mean difference (MD), with 95% confidence intervals (CI) using the random-effects model.

MAIN RESULTS

We included 33 studies that involved 3820 participants with ESKD. High-flux membranes reduced cardiovascular mortality (5 studies, 2612 participants: RR 0.83, 95% CI 0.70 to 0.99) but not all-cause mortality (10 studies, 2915 participants: RR 0.95, 95% CI 0.87 to 1.04) or infection-related mortality (3 studies, 2547 participants: RR 0.91, 95% CI 0.71 to 1.14). In absolute terms, high-flux membranes may prevent three cardiovascular deaths in 100 people treated with haemodialysis for two years. While high-flux membranes reduced predialysis beta-2 microglobulin levels (MD -12.17 mg/L, 95% CI -15.83 to -8.51 mg/L), insufficient data were available to reliably estimate the effects of membrane flux on hospitalisation, carpal tunnel syndrome, or amyloid-related arthropathy. Evidence for effects of high-flux membranes was limited by selective reporting in a few studies. Insufficient numbers of studies limited our ability to conduct subgroup analyses for membrane type, biocompatibility, or reuse. In general, the risk of bias was either high or unclear in the majority of studies.

AUTHORS' CONCLUSIONS

High-flux haemodialysis may reduce cardiovascular mortality in people requiring haemodialysis by about 15%. A large well-designed RCT is now required to confirm this finding.

Dialyzer and machine technologies: application of recent advances to clinical practice

Although hemodialysis is a mature therapy, a growing population of patients with more complex medical problems and limitations on resources will require technological innovations to improve the safety, reliability and efficiency of the therapy. The past several years have seen design changes to dialyzers that have provided incremental improvements in small solute clearance and more substantial improvements in the clearance of large solutes. New functions have been added to dialysis machines that help ensure reliable delivery of the dialysis prescription and enable full advantage to be taken of improvements in dialyzer clearance of large molecules. In addition, feedback control systems have been developed that may help reduce the untoward side effects which many patients experience during hemodialysis. Whether or not a particular innovation enters routine clinical use will depend on demonstrating that it improves clinical outcomes, its cost, and, in some cases, on a more enlightened approach by regulatory authorities.

Acute effects of hemodialysis on lung function in patients with end-stage renal disease

Impaired lung function in hemodialysis patients may be caused by an underlying pulmonary disease; however, the impact of uremia and the effects of dialysis treatment are not well understood. Our investigation aimed to characterize the acute effects of bicarbonate hemodialysis using membranes differing in biocompatibility on various parameters of lung function in unselected uremic patients maintained on regular hemodialysis. Fourteen clinically stable hemodialysis patients without acute lung disease were included in the study. Restrictive lung disease was present in eight of 14 cases and obstructive lung disease in one patient. A cellulose dialyzer membrane and a synthetic high-flux dialyzer membrane were each tested twice (two sessions one week apart). Spirometry (VCmax, FEV1, FEF(25-75%), PEF) was carried out before and after hemodialysis. Resistance was determined with the interrupter technique and with the impulse oscillation system (R5Hz, R20Hz) before, during and after hemodialysis. Our comparative investigation of two dialyzer membranes found that bioincompatibility of dialysis had no acute adverse effects on lung function in our heterogeneous population of dialysis patients. None of our patients experienced bronchoconstriction or aggravation of obstructive lung disease as a result of poor biocompatibility of the dialyzer membrane. Spirometric data and resistance measurements by two different methods showed no relevant changes during the dialysis procedure. There was no correlation between lung function parameters and interdialytic changes in body weight or duration on hemodialysis. Regardless of the membrane used, the hemodialysis procedure does not acutely affect lung function in uremic patients on maintenance hemodialysis. Hemodialysis is a safe procedure even in uremic patients with pre-existing lung disease.

Platelet activation through interaction with hemodialysis membranes induces neutrophils to produce reactive oxygen species

The intradialytic activation of leukocytes is one of the major causes of hemodialysis-associated complications. During hemodialysis, the formation of microaggregates consisting of platelets and neutrophils has been observed to accompany the production of reactive oxygen species (ROS) by leukocytes. In this study, we investigated the interaction of platelets and neutrophils with hemodialysis membranes in vitro to elucidate the mechanism underlying microaggregate formation and its relevance to leukocyte activation. The production of ROS in neutrophils was induced by the coincubation of neutrophils with polysulfone (PS) membranes, and was increased when platelets were present in the neutrophil suspension. Neutrophils that were incubated with polymethylmethacrylate (PMMA) membranes in the presence of platelets also produced significant levels of ROS, suggesting that the presence of platelets augmented ROS production in neutrophils. Platelets adhered more firmly to hydrophobic membranes such as PS and PMMA membranes than to hydrophilic membranes, such as those composed of regenerated cellulose (RC) or ethylene vinylalcohol copolymer (EVAL). The adhesion of platelets to dialysis membranes composed of different materials was correlated with those membranes' ability to induce platelet activation as assessed by the cell surface expression of P-selectin. Moreover, coincubation of neutrophils with platelets that had been treated with hydrophobic membranes induced a higher level of superoxide anion relative to those treated with hydrophilic membranes in association with the P-selectin-mediated microaggregate formation. These results suggest that platelets activated through interaction with hemodialysis membranes stimulate neutrophils to produce ROS via P-selectin-mediated adhesion, and that this property of adhesion to platelets is critical for the biocompatibility of hemodialysis membranes.

Cellulose, modified cellulose and synthetic membranes in the haemodialysis of patients with end-stage renal disease

BACKGROUND

When the kidney fails the blood-borne metabolites of protein breakdown and water cannot be excreted. The principle of haemodialysis is that such substances can be removed when blood is passed over a semipermeable membrane. Natural membrane materials include cellulose or modified cellulose, more recently various synthetic membranes have been developed. Synthetic membranes are regarded as being more "biocompatible" in that they incite less of an immune response than cellulose-based membranes.

OBJECTIVES

To assess the effects of different haemodialysis membrane material in patients with end-stage renal disease (ESRD).

SEARCH STRATEGY

We searched MEDLINE, EMBASE, PreMEDLINE, HealthStar CINAHL, the Cochrane Central Register of Controlled Trials (CENTRAL), Biosis, SIGLE, CRIB, UK National Research Register and reference lists of relevant articles. We contacted biomedical companies, known investigators and handsearched selected journals and conference proceedings. Date of most recent search: June 2004.

SELECTION CRITERIA

All randomised controlled trials (RCTs) or quasi-RCTs comparing different haemodialysis membrane material in patients with ESRD.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the methodological quality of studies. Data was abstracted onto a standard form by one reviewer and checked by another. Relative Risk (RR) and weighted mean difference (WMD) with 95% confidence intervals (CI)) MAIN RESULTS: Thirty two studies were identified. Pre-dialysis ss(2) microglobulin concentrations were not significantly lower in patients treated with synthetic membranes (WMD -14.67, 95% CI -33.10 to 4.05). When analysed for change in ss(2) microglobulin, a fall was only noted with high-flux membranes. The incidence of amyloid was less in patients who were dialysed for six years with high-flux synthetic membranes (one study, RR 0.03, 95% CI 0.00 to 0.54). There was a significant difference in favour of the synthetic (high-flux) membrane in comparison to cellulose membranes for triglycerides (WMD -0.66; 95% CI -1.18 to -0.14) but not for modified cellulose membranes. Dialysis adequacy measured by Kt/V was marginally higher when cellulose membranes were used (WMD -0.10; 95% CI -0.16 to 0.04), whereas synthetic membranes achieved significantly higher Kt/V values when compared with modified cellulose membranes (WMD 0.20, 95% 0.11 to 0.29) . There were no data on quality of life measures.

AUTHORS' CONCLUSIONS

We found no evidence of benefit when synthetic membranes were compared with cellulose/modified cellulose membranes in terms of reduced mortality no reduction in dialysis-related adverse symptoms. Despite the relatively large number of RCTs undertaken in this area none of the included studies reported any measures of quality of life.

A randomized, controlled study of the consequences of hemodialysis membrane composition on erythropoietic response

BACKGROUND

Membrane biocompatibility has long been thought to be relevant to hemodialysis outcomes and, possibly, renal anemia.

METHODS

We performed a randomized, controlled, single-center study comparing the consequences on renal anemia of 2 dialyzers of equivalent performance, but different composition, during 7 months. Two hundred eleven patients of an unselected dialysis population of 235 patients gave informed consent to undergo random assignment to either group A (SF170E; modified cellulose triacetate/midflux membrane; Nipro, Osaka, Japan) or group B (HF80LS; polysulfone/high-flux membrane; Fresenius, Bad Homburg, Germany). Anemia management was identical in both treatment groups and followed strict clinical protocols managed by computer algorithms. Dialysis adequacy, hemoglobin (Hb) level, ferritin level, percentage of red blood cell hypochromicity, C-reactive protein (CRP) level, and intravenous iron and epoetin doses were monitored monthly.

RESULTS

One hundred seventy-seven patients completed the 7-month study. Equilibrated Kt/V increased in both groups. Hb outcome improved overall, but did not differ between the 2 study groups. Epoetin dose was not significantly different after 7 months compared with baseline in either group. Hb level, epoetin dose, iron status, CRP level, dialysis Kt/V, and residual renal function did not differ between the 2 groups. A slight but significant negative correlation was identified between dialysis Kt/V and Hb level in the population as a whole (Spearman's correlation, -0.16; P = 0.04).

CONCLUSION

No significant epoetin-sparing effect was identified through the use of the high-flux polysulfone HF80LS membrane over the modified cellulose triacetate SF170E membrane. Although not a primary outcome for this study, there was a suggestion of benefit of improved Hb level, without increased need for epoetin, through increasing delivered dialysis dose.

Preparation of blood-compatible hollow fibers from a polymer alloy composed of polysulfone and 2-methacryloyloxyethyl phosphorylcholine polymer

Blood-compatible hollow fibers were successfully prepared from a polymer alloy composed of polysulfone (PSf) and the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. To improve the hydrophilicity, fouling-resistance characteristics, and blood compatibility of the PSf hollow fiber in a hemodialyzer, an MPC polymer that can be blended with PSf was synthesized in order to prepare the polymer alloy (PSf/MPC polymer). The contents of the MPC polymer blended in the PSf were 7 and 15 wt%. The PSf/MPC polymer hollow fiber could be prepared by both wet and dry-wet processing methods. The hollow fiber took an asymmetric structure, that is, the hollow-fiber membrane had a dense skin layer on the porous sponge-like structure. The mechanical strength was higher than that of conventional PSf hollow fibers for hemodialysis. The surface characterization of the PSf/MPC polymer hollow fiber by x-ray photoelectron spectroscopy revealed that the MPC units were concentrated at the surface. The permeability for solutes through the PSf/MPC polymer hollow fibers was measured for 4 h. The permeabilities of both a low-molecular-weight compound and protein were greater than those of the PSf hollow fibers. The amount of adsorbed protein was lower on the PSf/MPC polymer hollow fiber when compared to that of the PSf hollow fiber. Moreover, platelet adhesion was also effectively inhibited on the PSf/MPC polymer hollow fiber. Based on these results, the addition of the MPC polymer to the PSf is a very useful method to improve the functions and blood compatibility of the hollow fiber.

Solute clearances during continuous venovenous haemofiltration at various ultrafiltration flow rates using Multiflow-100 and HF1000 filters

BACKGROUND

In continuous venovenous haemofiltration (CVVH), high ultrafiltration rates provide survival benefits in acute renal failure. This study measured clearances obtained at ultrafiltration rates of up to 4.5 l/h.

METHODS

Clearances of small solutes (urea, creatinine, phosphate and urate) and of beta(2)-microglobulin (beta(2)-M) were measured during CVVH. Five preset Multiflow-100 (M-100) and five HF1000 hollow-fibre filters were compared. For the M-100, clearances obtained by haemofiltration were compared with those obtained by haemodiafiltration at similar total effluent rates from a previous study.

RESULTS

For small solutes, the effluent to plasma ratio (E/P) remained close to 1.0 at all ultrafiltration rates; filter clearances were thus equal to Quf for both filters. Increasing Quf from 1.0 to 4.5 l/h did not significantly modify E/P. Convective clearances of beta(2)-M were lower than those obtained for small solutes. For the M-100, average beta(2)-M E/P was 0.62+/-0.10 and did not significantly change while increasing Quf. For the HF1000, average beta(2)-M E/P were significantly lower compared with the M-100 (0.42+/-0.09 at 1.0 l/h) and decreased progressively to 0.26+/-0.06 while increasing Quf to 4.5 l/h. With pre-dilution, progressive decreases in clearances delivered to patients were observed reaching 40% at a Quf rate of 4.5 l/h. There was no clinically significant adsorption of beta(2)-M. For the M-100, at similar total effluent flow rates, clearances delivered to patients using haemodiafiltration were significantly higher for small solutes but lower for beta(2)-M in comparison to haemofiltration only.

CONCLUSIONS

Filter clearance for small solutes equalled Quf at evaluated rates. At high ultrafiltration rates there was significant loss of clearances with pre-dilution. At similar total effluent rates with the use of pre-dilution, haemodiafiltration is superior to haemofiltration for small solute clearance but inferior for beta(2)-M.

Properties of membranes used for hemodialysis therapy

Recent trends show a progressive increase in the use of modified cellulosic and synthetic dialyzers and a corresponding decrease in the utilization rate of unmodified cellulosic dialyzers. The purpose of this article is to describe current membrane and dialyzer technology, with the focus almost entirely on modified cellulosic and synthetic membranes. A general overview of membrane-related determinants of dialyzer performance is first presented, followed by a discussion of specific characteristics of some of the more commonly used membranes and dialyzers.

Albumin loss in on-line hemodiafiltration

BACKGROUND

Based on the increased hydraulic permeability of the new high permeability polyethersulfone membrane, DIAPES HF-800, we investigated the kinetics and handling of albumin in high volume on-line hemodiafiltration (HDF).

METHODS

Seven patients on predilutional HDF were studied in two consecutive sessions. Blood flow rate and transmembrane pressure were continuously monitored. Spent dialysate was spilled at 20 ml/h every hour. Albumin was measured in blood and dialysate by immunonephelometry. Albumin and proteins adsorbed onto the dialyzer membrane were eluted after treatment with Triton X. Ultrafiltrates collected at 1 and 2 hours of treatment were pooled from different patients and incubated for 24 hours at 37 degrees C with bovine serum albumin (BSA). Total sulphydryl groups were evaluated using Ellmann's reagent [5, 5'-dithio-bis(2-nitrobenzoic acid)].

RESULTS

In all 7 patients, the total loss of albumin was 3.99 +/- 1.81 g, ranging between 1.09 and 6.82 g/session. Most albumin loss occurred in the first 60 min of pre-dilutional hemodiafiltration (1.92+0.83 g). There was no correlation between transmembrane pressure, urea clearance and the loss of albumin. Plasma water urea clearance values were stable over the treatment (234 +/- 14.3 ml/min). Plasma albumin concentration did not decrease during HDF sessions. Albumin adsorbed onto the dialyzers was 0.7 +/- 1.6 mg but the total amount of adsorbed proteins was much higher (130 + 90 mg). In addition, the ultrafiltrate collected during HDF sessions was able to induce oxidation of bovine serum albumin as measured by total protein sulfhydryl groups: bovine serum albumin incubated in the presence of ultrafiltrate collected at 1 hour had a sulfhydryl loss of 56.3 +/- 5.7% (p < 0.0001 vs control), and bovine serum albumin incubated with ultrafiltrate collected at 2 hours had a loss of 67.5 +/- 3.8% (p < 0.003 vs control).

CONCLUSION

The present study shows the high inter- and intra-patient variability of transmembrane passage of albumin in chronically uremic patients undergoing pre-dilutional HDF. Factors involved do not seem to be correlated to transmembrane pressure but rather to an interaction with the polymer surface. Albumin adsorption was minimal and was significantly lower than that of other plasma proteins. Albumin loss during HDF seemed to have no acute impact on plasma albumin. In addition, we demonstrated the presence of prooxidative compounds able to oxidize albumin, of which extracorporeal removal by HDF procedure could be beneficial for HD patients.