Effect of dialyser membrane pore size on plasma homocysteine levels in haemodialysis patients

Flummoxed by flux: the indeterminate principles of haemodialysis

In haemodialysis (HD), unwanted substances (uraemic retention solutes or ‘uraemic toxins’) that accumulate in uraemia are removed from blood by transport across the semipermeable membrane. Like all membrane separation processes, the transport requires driving forces to facilitate the transfer of molecules across the membrane. The magnitude of the transport is quantified by the phenomenon of ‘flux’, a finite parameter defined as the volume of fluid (or permeate) transferred per unit area of membrane surface per unit time. In HD, as transmembrane pressure is applied to facilitate fluid flow or flux across the membrane to enhance solute removal, flux is defined by the ultrafiltration coefficient (KUF; mL/h/mmHg) reflecting the hydraulic permeability of the membrane. However, in HD, the designation of flux has come to be used in a much broader sense and the term is commonly used interchangeably and erroneously with other measures of membrane separation processes, resulting in considerable confusion. Increased flux is perceived to reflect more ‘porous’ membranes having ‘larger’ pores, even though other membrane and therapy attributes determine the magnitude of flux achieved during HD. Adjectival designations of flux (low-, mid-, high-, super-, ultra-) have found indiscriminate usage in the scientific literature to qualify a parameter that influences clinical decision making and prescription of therapy modalities (low-flux or high-flux HD). Over the years the concept and definition of flux has undergone arbitrary and periodic adjustment and redefinition by authors in publications, regulatory bodies (US Food and Drug Administration) and professional association guidelines (European Renal Association, Kidney Disease Outcomes Quality Initiative), with little consensus. Industry has stretched the boundaries of flux to derive marketing advantages, justify increased reimbursement or contrive new classes of therapy modalities when in fact flux is just one of several specifications that determine membrane or dialyser performance. Membranes considered as high-flux previously are today at the lower end of the flux spectrum. Further, additional parameters unrelated to the rate of diffusive or convective transport (flux) are used in conjunction with or in place of KUF to allude to flux: clearance (mL/min, e.g. of β₂-microglobulin) or sieving coefficients (dimensionless). Considering that clinical trials in nephrology, designed to make therapy recommendations and guide policy with economic repercussions, are based on the parameter flux they merit clarification—by regulatory authorities and scientists alike—to avoid further misappropriation.

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

Liposomes to Augment Dialysis in Preclinical Models: A Structured Review

In recent years, a number of groups have been investigating the use of “empty” liposomes with no drug loaded as scavengers both for exogenous intoxicants and endogenous toxic molecules. Preclinical trials have demonstrated that repurposing liposomes to sequester such compounds may prove clinically useful. The use of such “empty” liposomes in the dialysate during dialysis avoids recognition by complement surveillance, allowing high doses of liposomes to be used. The “reach” of dialysis may also be increased to molecules that are not traditionally dialysable. We aim to review the current literature in this area with the aims of increasing awareness and informing further research. A structured literature search identified thirteen papers which met the inclusion criteria. Augmenting the extraction of ammonia in hepatic failure with pH-gradient liposomes with acidic centres in peritoneal dialysis is the most studied area, with work progressing toward phase one trials. Liposomes used to augment the removal of exogenous intoxicants and protein-bound uraemic and hepatic toxins that accumulate in these organ failures and liposome-supported enzymatic dialysis have also been studied. It is conceivable that liposomes will be repurposed from the role of pharmaceutical vectors to gain further indications as clinically useful nanomedical antidotes/treatments within the next decade.

Assessing Plasma Total Homocysteine in Patients with End-Stage Renal Disease

Elevated plasma total homocysteine (tHcy) is a risk factor for cardiovascular disease; however, in light of several recent randomized trials, the issue of causality has been cast into doubt. Patients with end-stage renal disease are particularly interesting as they consistently have elevated tHcy and their leading causes of morbidity and mortality are related to cardiovascular disease. In the present article, we review the early evidence for the homocysteine theory of atherosclerosis, homocysteine metabolism, mechanisms of toxicity, and pertinent available clinical investigations. Where appropriate, the sparse evidence of homocysteine in peritoneal dialysis is reviewed. We conclude by addressing the difficulties associated with lowering plasma tHcy in patients with end-stage renal disease and suggest some novel methods for lowering tHcy in this resistant population. Finally, to address the issue of causality, we recommend that clinicians and scientists await the results of the FAVORIT trial before abandoning homocysteine as a modifiable risk factor for cardiovascular disease, as this study has recruited patients from a population with consistently elevated plasma tHcy who are known to respond to vitamin therapy.

Comparison of the removal of uraemic toxins with medium cut-off and high-flux dialysers: a randomized clinical trial

BACKGROUND

Accumulation of middle-weight uraemic toxins in haemodialysis (HD) patients results in increased morbidity and mortality. Whether medium cut-off HD (MCO-HD) improves removal of middle-weight uraemic toxins remains to be demonstrated.

METHODS

This cross-over prospective study included 40 patients randomly assigned to receive either 3 months of MCO-HD followed by 3 months of high-flux HD (HF-HD), or vice versa. The primary endpoint was myoglobin reduction ratio (RR) after 3 months of MCO-HD. Secondary endpoints were the effect of MCO-HD on other middle-weight toxins and protein-bound toxins, and on parameters of nutrition, inflammation, anaemia and oxidative stress.

RESULTS

Compared with HF-HD, MCO-HD provided higher mean RR of myoglobin (36 ± 8 versus 57 ± 13%, P < 0.0001), beta2-microglobulin (68 ± 6 versus 73 ± 15%, P = 0.04), prolactin (32 ± 13 versus 59 ± 11%, P < 0.0001), fibroblast growth factor 23 (20 ± 21 versus 41 ± 22%, P = 0.0002), homocysteine (43 ± 7 versus 46 ± 9%, P = 0.03) and higher median RR of kappa [54 (48-58) versus 70 (63-74)%, P < 0.0001] and lambda free light chain (FLC) [15 (9-22) versus 44 (38-49)%, P < 0.0001]. Mean ± SD pre-dialysis levels of beta2-microglobulin (28.4 ± 5.6 versus 26.9 ± 5.1 mg/L, P = 0.01) and oxidized low-density lipoprote (6.9 ± 4.4 versus 5.5 ± 2.5 pg/mL, P = 0.04), and median (interquartile range) kappa FLC [145 (104-203) versus 129 (109-190) mg/L, P < 0.03] and lambda FLC [106 (77-132) versus 89 (62-125) mg/L, P = 0.002] were significantly lower. Mean albumin levels decreased significantly (38.2 ± 4.1 versus 36.9 ± 4.3 g/L, P = 0.004), without an effect on nutritional status as suggested by unchanged normalized protein catabolic rate and transthyretin level.

CONCLUSIONS

Compared with HF-HD, MCO-HD provides higher myoglobin and other middle molecules RR and is associated with moderate hypoalbuminemia. The potential benefits of this strategy on long-term clinical outcomes deserve further evaluation.

Urea removal strategies for dialysate regeneration in a wearable artificial kidney

The availability of a wearable artificial kidney (WAK) that provides dialysis outside the hospital would be an important advancement for dialysis patients. The concept of a WAK is based on regeneration of a small volume of dialysate in a closed-loop. Removal of urea, the primary waste product of nitrogen metabolism, is the major challenge for the realization of a WAK since it is a molecule with low reactivity that is difficult to adsorb while it is the waste solute with the highest daily molar production. Currently, no efficient urea removal technology is available that allows for miniaturization of the WAK to a size and weight that is acceptable for patients to carry. Several urea removal strategies have been explored, including enzymatic hydrolysis by urease, electro-oxidation and sorbent systems. However, thus far, these methods have toxic side effects, limited removal capacity or slow removal kinetics. This review discusses different urea removal strategies for application in a wearable dialysis device, from both a chemical and a medical perspective.

Albumin handling in different hemodialysis modalities

Hypoalbuminemia is a major risk factor for morbidity and mortality in dialysis patients. With increasing interest in highly permeable membranes and convective therapies to improve removal of middle molecules, transmembrane albumin loss increases accordingly. Currently, the acceptable upper limit of albumin loss for extracorporeal renal replacement therapies is unknown. In theory, any additional albumin loss should be minimized because it may contribute to hypoalbuminemia and adversely affect the patient's prognosis. However, hypoalbuminemia-associated mortality may be a consequence of inflammation and malnutrition, rather than low albumin levels per se. The purpose of this review is to give an overview of albumin handling with different extracorporeal renal replacement strategies. We conclude that the acceptable upper limit of dialysis-related albumin loss remains unknown. Whether enhanced middle molecule removal outweighs the potential adverse effects of increased albumin loss with novel highly permeable membranes and convective therapies is yet to be determined.

Relationship between plasma levels of homocysteine and the related B vitamins in patients with hemodialysis adequacy or inadequacy

OBJECTIVES

Hemodialysis (HD) with dialysis adequacy could increase the excretion of B vitamins (folate, vitamin B₆, and B₁₂) and raise the plasma level of homocysteine. Here we determined the associations of plasma homocysteine with B vitamins in patients with HD adequacy or inadequacy.

METHODS

We recruited 68 patients who had received HD treatments (three times a week, 4 h each). Based on the individual's hemogram and quarterly urea reduction rate (Kt/V), patients were pooled into one of the following two groups: the first group with dialysis adequacy (Kt/V > 1.2, n = 48) and the second with dialysis inadequacy (Kt/V ≤ 1.2, n = 20). We also recorded the anthropometric date of each patient and their biochemical data and dietary intakes. Plasma levels of homocysteine, cysteine, folate, pyridoxal 5'-phosphate (PLP), and vitamin B₁₂ were measured twice, once before and once after HD.

RESULTS

The plasma levels of homocysteine, cysteine, folate, PLP, and vitamin B₁₂ dropped significantly at the end of HD. The plasma levels of vitamin B₁₂ were negatively correlated with the plasma levels of homocysteine, both pre- and post-HD, and in both groups regardless of dialysis adequacy or inadequacy. In contrast, plasma levels of folate and PLP were not correlated with homocysteine at both pre- or post-HD in both groups.

CONCLUSIONS

The plasma level of vitamin B₁₂, but not folate or vitamin B₆, was negatively correlated with that of homocysteine both before and after HD treatment, and regardless of dialysis adequacy or inadequacy.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

Interventions for lowering plasma homocysteine levels in dialysis patients

BACKGROUND

People with end-stage kidney disease (ESKD) have high rates of cardiovascular events. Randomised controlled trials (RCTs) of homocysteine-lowering therapies have not shown reductions in cardiovascular event rates in the general population. However, people with kidney disease have higher levels of homocysteine and may have different mechanisms of cardiovascular disease. We performed a systematic review of the effect of homocysteine-lowering therapies in people with ESKD.

OBJECTIVES

To evaluate the benefits and harms of established homocysteine lowering therapy (folic acid, vitamin B6, vitamin B12) on all-cause mortality and cardiovascular event rates in patients with ESKD.

SEARCH METHODS

We searched Cochrane Kidney and Transplant's Specialised Register to 25 January 2016 through contact with the Information Specialist using search terms relevant to this review.

SELECTION CRITERIA

Studies conducted in people with ESKD that reported at least 100 patient-years of follow-up and assessed the effect of therapies that are known to have homocysteine-lowering properties were included.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data using a standardised form. The primary outcome was cardiovascular mortality. Secondary outcomes included all-cause mortality, incident cardiovascular disease (fatal and nonfatal myocardial infarction and coronary revascularisation), cerebrovascular disease (stroke and cerebrovascular revascularisation), peripheral vascular disease (lower limb amputation), venous thromboembolic disease (deep vein thrombosis and pulmonary embolism), thrombosis of dialysis access, and adverse events. The effects of homocysteine-lowering therapies on outcomes were assessed with meta-analyses using random-effects models. Prespecified subgroup and sensitivity analyses were conducted.

MAIN RESULTS

We included six studies that reported data on 2452 participants with ESKD. Interventions investigated were folic acid with or without other vitamins (vitamin B6, vitamin B12). Participants' mean age was 48 to 65 years, and proportions of male participants ranged from 50% to 98%.Homocysteine-lowering therapy probably leads to little or no effect on cardiovascular mortality (4 studies, 1186 participants: RR 0.93, 95% CI 0.70 to 1.22). There was no evidence of heterogeneity among the included studies (I² = 0%). Homocysteine-lowering therapy had little or no effect on all-cause mortality or any other of this review's secondary outcomes. All prespecified subgroup and sensitivity analyses demonstrated little or no difference. Reported adverse events were mild and there was no increase in the incidence of adverse events from homocysteine-lowering therapies (3 studies, 1248 participants: RR 1.12, 95% CI 0.51 to 2.47; I(2) = 0%). Overall, studies were assessed as being at low risk of bias and there was no evidence of publication bias.

AUTHORS' CONCLUSIONS

Homocysteine-lowering therapies were not found to reduce mortality (cardiovascular and all-cause) or cardiovascular events among people with ESKD.

Convective therapies versus low-flux hemodialysis for chronic kidney failure: a meta-analysis of randomized controlled trials

BACKGROUND

Although convective therapies have gained popularity for the optimal removal of uremic solutes, their benefits and potential risks have not been fully elucidated. We conducted a meta-analysis of all randomized controlled trials comparing convective therapies with low-flux hemodialysis in patients with chronic kidney failure.

METHODS

We performed a literature search using MEDLINE (inception-December 2012), Cochrane Central Register of Controlled Trials, ClinicalTrials.gov, scientific abstracts from meetings and bibliographies of retrieved articles. Randomized controlled trials comparing the effect of convective therapies including high-flux hemodialysis, hemofiltration or hemodiafiltration versus low-flux hemodialysis were included. Random-effects model meta-analyses were used to examine continuous and binary outcomes.

RESULTS

Sixty-five (29 crossover and 36 parallel-arm) trials were identified (n = 12 182). Convective therapies resulted in a decrease in all-cause mortality [relative risk (RR) 0.88; 95% confidence interval (CI) 0.76, 1.02, P = 0.09], cardiovascular mortality (RR 0.84; 95% CI 0.71, 0.98, P = 0.03), all-cause hospitalization (RR 0.91; 95% CI 0.82, 1.01; P = 0.08) and therapy-related hypotension (RR 0.55, 95% CI 0.35, 0.87, P = 0.01). Convective therapies also resulted in an increase in the clearance of several low-molecular-weight (urea, creatinine and phosphate), middle-sized (β-2 microglobulin and leptin) and protein-bound (homocysteine, advanced glycation end-products and pentosidine) solutes and a decrease in inflammatory markers (interleukin-6). There was no impact of convective therapies on cardiac morphological and functional parameters, and blood pressure and anemia parameters.

CONCLUSIONS

Although convective therapies are associated with improved clearance of uremic solutes, the potential long-term benefits of specific convective modalities require further study.

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.

Mesna for treatment of hyperhomocysteinemia in hemodialysis patients: a placebo-controlled, double-blind, randomized trial

BACKGROUND AND OBJECTIVES

Increased plasma total homocysteine is a graded, independent risk factor for the development of atherosclerosis and thrombosis. More than 90% of patients with end-stage renal disease have hyperhomocysteinemia despite vitamin supplementation. It was shown in previous studies that a single intravenous dose of mesna 5 mg/kg caused a drop in plasma total homocysteine that was significantly lower than predialysis levels 2 d after dosing. It was hypothesized 5 mg/kg intravenous mesna administered thrice weekly, before dialysis, for 8 wk would cause a significant decrease in plasma total homocysteine compared with placebo.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with end-stage renal disease were randomly assigned to receive either intravenous mesna 5 mg/kg or placebo thrice weekly before dialysis. Predialysis plasma total homocysteine concentrations at weeks 4 and 8 were compared between groups by paired t test.

RESULTS

Mean total homocysteine at 8 wk in the placebo group was 24.9 micromol/L compared with 24.3 micromol/L in the mesna group (n = 22 [11 pairs]; mean difference 0.63). Interim analysis at 4 wk also showed no significant difference between mesna and placebo (n = 32 [16 pairs]; placebo 26.3 micromol/L, mesna 24.5 micromol/L; mean difference 1.88). Multivariable adjustments for baseline characteristics did not alter the analysis. Plasma mesna seemed to reach steady-state concentrations by 4 wk.

CONCLUSIONS

It is concluded that 5 mg/kg mesna does not lower plasma total homocysteine in hemodialysis patients and that larger dosages may be required.

The Effect of Mesna on Plasma Total Homocysteine Concentration in Hemodialysis Patients

BACKGROUND

Plasma total homocysteine (tHcy) level is an independent risk factor for the development of atherosclerosis. The degree of risk in most of the population is decreased by using dietary vitamin supplementation; however, more than 90% of patients with end-stage renal disease have increased tHcy levels despite supplementation. Only a small fraction of tHcy is removed by hemodialysis because of extensive disulfide bonding to albumin. The objective of this study is to determine whether a single intravenous dose of mesna, a thiol-containing drug analogue of taurine, facilitates tHcy clearance during hemodialysis.

METHODS

Initial in vitro thiol exchange tests were performed with mesna in plasma from dialysis patients. Mesna, 300 micromol/L (49.2 mg/L), was incubated with plasma at 37 degrees C, and free homocysteine was measured at various times. In vivo, mesna activity was tested in 10 hemodialysis patients by administering 2.5 or 5.0 mg/kg of mesna intravenously at the beginning of a treatment cycle. Blood samples were drawn throughout dialysis, and plasma tHcy levels were compared with those obtained from a previous dialysis session in which mesna was not administered.

RESULTS

In vitro, mesna liberated 36.5% +/- 2.5% of protein-bound homocysteine in 30 minutes. In vivo, a single 2.5-mg/kg dose of mesna was ineffective; however, at 5.0 mg/kg, it caused a 55.2% +/- 3.9% decrease in plasma tHcy levels postdialysis compared with a 34.2% +/- 5.3% decrease with dialysis alone (P < 0.001).

CONCLUSION

Intravenous mesna causes a rapid decrease in plasma tHcy levels during hemodialysis.

Homocysteine-Lowering Vitamin B Treatment Decreases Cardiovascular Events in Hemodialysis Patients

BACKGROUND

Dialysis patients have higher cardiovascular events rate than patients with normal renal function. Hyperhomocysteinemia, a risk factor for cardiovascular disease, is frequently detected in dialysis patients. Vitamin B supplementation lowers hyperhomocysteinemia, but it is unknown whether it reduces cardiovascular events rate. We planned a long-term study to analyze the effects of homocysteine-lowering vitamin B therapy on cardiovascular disease in hemodialysis patients.

METHODS

We performed a single center open prospective trial. Patients, just on folate therapy at enrolment, were left out from randomization and maintained folate therapy according to study's protocol (group A). Patients, untreated with folic acid at recruitment, were randomly assigned to other 2 groups: patients submitted to folate supplementation according to study's protocol (group B), and untreated ones (group C). We instructed patients to take 5 mg oral daily folic acid or 5 mg every other day whether serum folate levels were up the normal high limit. We measured homocysteine, folate and vitamin B12 plasma levels at baseline and every 4 months. We chose the appearance of fatal and nonfatal cardiovascular events as end-points.

RESULTS

We analyzed data of 114 patients for a median follow-up time of 871 days. Stepwise regression analysis demonstrated that baseline homocysteine levels were related to folate (coefficient: -1.02; F: 64.5), creatinine (coefficient: 0.98; F: 11.3), and C reactive protein (coefficient: -0.64; F: 4.3). Patients ended the study for the following reasons: cardiovascular morbidity (n = 44), death (n = 25), renal transplant (n = 9), moved away (n = 4). Cardiovascular events occurred in 58 of 114 patients (51%), in 26 of 63 (41%) treated patients (both group A and group B) and in 32 of 51 (63%; chi2 = 6.0; p = 0.05) untreated patients (group C). Kaplan-Meier survival analysis showed that cardiovascular events were less frequent in treated patients with low homocysteine levels (chi2 24.1; p < 0.0001). Cox regression analysis showed that cardiovascular events were explained by homocysteine, dialysis vintage, past cardiovascular accidents, and age. We noticed not only lower homocysteine levels, but also higher protein catabolic rate values in events-free patients as compared with patients with nonfatal cardiovascular events. After having divided patients into 4 subgroups according to high and low, split at median, Hcy and protein catabolic rate values, we observed in Kaplan-Meier survival curves for cardiovascular events by these subgroups that patients with low Hcy and high protein catabolic rate values showed a significant lower hazard rate than patients with high Hcy and low protein catabolic rate levels (chi2 = 21.7; p < 0.0001).

CONCLUSIONS

This trial shows for the first time that homocysteine-lowering folate therapy decreases cardiovascular events in dialysis patients. It is necessary to perform large prospective studies to confirm our results.

Resolving controversies regarding hemodiafiltration versus hemodialysis: the Dutch Convective Transport Study

Hemodialysis patients suffer from a high incidence of cardiovascular disease. Among the many predisposing factors, such as high blood pressure, dyslipidemia, and fluid overload, the accumulation of high molecular weight uremic toxins, the so-called middle molecules, may play an important role. Since convective therapies such as online hemodiafiltration have a better clearance profile for these compounds than standard hemodialysis, it has been suggested that these dialysis strategies may reduce cardiovascular morbidity and mortality. As reliable data on these issues are not available, the Dutch Convective Transport Study (CONTRAST) was recently initiated. This prospective randomized trial was designed to compare online hemodiafiltration with low-flux hemodialysis with respect to cardiovascular morbidity and mortality.

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.

Randomized trial of FX high flux vs standard high flux dialysis for homocysteine clearance

BACKGROUND

Cardiovascular disease is the major cause of death in the end-stage renal disease population. Novel risk factors such as homocysteine (Hcy) are of considerable interest in this group as hyperhomocysteinaemia is highly prevalent in the setting of renal impairment. Folic acid-vitamin B group therapies are only partially effective treatments. Hcy is highly protein-bound and thus poorly dialysed. Dialyzers with albumin-leaking properties have been shown to result in lowering of plasma Hcy. As the FX-class (Advanced Fresenius Polysulfone dialyzer) has greater clearance of larger molecular weight substances but is non-albumin-leaking, we explored the capacity of this new technology membrane to reduce plasma Hcy levels.

METHODS

A prospective randomized cross-over trial in 35 prevalent haemodialysis patients, one group receiving 12 weeks dialysis using FX dialyzer then 12 weeks with standard high flux dialysis (SHF) and the other group SHF followed by FX dialyzer. All patients received vitamin B(6) 25 mg and folic acid 5 mg daily throughout the study.

RESULTS

The primary outcome was plasma Hcy pre-dialysis at week 12. FX vs SHF showed no significant difference, 25+/-6.6 vs 25.9+/-5.8 microg/l, Delta95% CI = -2.77 to 4.59, P = 0.31. There was a non-significant trend toward a decrease in Hcy in both groups (27.43+/-7.68 to 25.91+/-5.78 micromol/l for SHF, P = 0.23 and 26.0+/-4.58 to 25.0+/-6.61 micromol/l for FX, P = 0.28). Analysis by repeated measures method demonstrated a statistically significantly lower Hcy with FX vs SHF dialyzer (adjusted beta = -1.30, 95% CI = -2.41 to -0.19, P = 0.022). K(t)/V(urea) was higher in FX vs SHF (1.35+/-0.18 vs 1.22+/-0.2; P = 0.013). Folate and B(6) levels did not change.

CONCLUSIONS

The primary outcome analysis did not show any significant difference in pre-Hcy comparing FX and SHF membranes. Although our secondary analysis demonstrated a statistically significant difference between membranes, the magnitude of the difference (1.3 mumol/l) is not clinically significant. Thus the use of the FX dialyzer did not result in a clinically significant benefit in relation to improving pre-dialysis Hcy compared with standard high-flux dialysis.

Protein-Leaking Membranes for Hemodialysis: A New Class of Membranes in Search of an Application?

A new class of membranes that leak protein has been developed for hemodialysis. These membranes provide greater clearances of low molecular weight proteins and small protein-bound solutes than do conventional high-flux dialysis membranes but at the cost of some albumin loss into the dialysate. Protein-leaking membranes have been used in a small number of clinical trials. The results of these trials suggest that protein-leaking membranes improve anemia correction, decrease plasma total homocysteine concentrations, and reduce plasma concentrations of glycosylated and oxidized proteins. However, it is not clear yet that routine use of protein-leaking membranes is warranted. Specific uremic toxins that are removed by protein-leaking membranes but not conventional high-flux membranes have not been identified. It is also unclear whether protein-leaking membranes offer benefits beyond those obtained with conventional high-flux membranes used in convective therapies, such as hemofiltration and hemodiafiltration. Finally, the amount of albumin loss that can be tolerated by hemodialysis patients in a long-term therapy has yet to be determined. Protein-leaking membranes offer a new approach to improving outcomes in hemodialysis, but whether their benefits will outweigh their disadvantages will require more basic and clinical research.

Neurological complications in renal failure: a review

Neurological complications whether due to the uremic state or its treatment, contribute largely to the morbidity and mortality in patients with renal failure. Despite continuous therapeutic advances, many neurological complications of uremia, like uremic encephalopathy, atherosclerosis, neuropathy and myopathy fail to fully respond to dialysis. Moreover, dialytic therapy or kidney transplantation may even induce neurological complications. Dialysis can directly or indirectly be associated with dialysis dementia, dysequilibrium syndrome, aggravation of atherosclerosis, cerebrovascular accidents due to ultrafiltration-related arterial hypotension, hypertensive encephalopathy, Wernicke's encephalopathy, hemorrhagic stroke, subdural hematoma, osmotic myelinolysis, opportunistic infections, intracranial hypertension and mononeuropathy. Renal transplantation itself can give rise to acute femoral neuropathy, rejection encephalopathy and neuropathy in graft versus host disease. The use of immunosuppressive drugs after renal transplantation can cause encephalopathy, movement disorders, opportunistic infections, neoplasms, myopathy and progression of atherosclerosis. We address the clinical, pathophysiological and therapeutical aspects of both central and peripheral nervous system complications in uremia.