Reduction in β2-Microglobulin With Super-flux Versus High-flux Dialysis Membranes: Results of a 6-Week, Randomized, Double-blind, Crossover Trial

The Efficacy and Safety of Continuous Veno-Venous Hemodiafiltration With High Cutoff Membrane Versus High Flux Membrane in Septic Acute Kidney Injury: A Randomized Controlled Study

BACKGROUND

The application of high cutoff (HCO) membranes for continuous renal replacement therapy remains unclear in septic acute kidney injury (S-AKI) patients.

METHODS

S-AKI patients who received continuous veno-venous hemodiafiltration (CVVHDF) were randomly assigned to the experimental group (HCO membrane) and the control group (high flux membrane, HF membrane). Interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in serum and waste fluid were measured at 0, 2, 12, and 24 h after CVVHDF initiation and the 28-day mortality.

RESULTS

Eleven patients were randomized to the HCO group, and 9 patients in the HF group, with a mean age of 54.9 ± 3.2 years and 6 patients (30%) being female. After 24 h of treatment with CVVHDF, there were significant reductions in serum IL-6 and TNF-α concentrations in the HCO group (p = 0.001, 0.015) and HF group (p = 0.004, 0.031). The serum IL-6 reduction rate of the HCO group was significantly higher than that of the HF group (79.21% vs. 42.69%, p = 0.025), while serum TNF-α reduction rates were comparable between the 2 groups. There were no significant changes in serum albumin after 24 h using either HCO membrane (28.7 ± 1.7 g/L vs. 32.7 ± 1.6 g/L, p = 0.138) or HF membrane (29.6 ± 1.1 g/L vs. 32.6 ± 1.3 g/L, p = 0.055). The two groups had similar 24-h filter clotting rates and 28-day mortality.

CONCLUSION

While CVVHDF with the HCO membrane and HF membrane both achieved significant reductions in serum cytokine levels, the HCO membrane was associated with a greater reduction rate in IL-6 but not in TNF-α. No difference was observed in serum albumin, mortality, or filter clotting.

TRIAL REGISTRATION

Registry number: ChiCTR2000039725.

Thyroid hormone replacement therapy in dialysis/renal insufficiency patients

Dialysis/renal insufficiency patients are often accompanied by hypothyroidism due to renal damage, the mechanisms of which are complex. The use of thyroid hormone replacement therapy in such patients has become an important clinical issue. This article reviews the mechanism of hypothyroidism in dialysis/renal insufficiency patients and describes the importance and precautions of thyroid hormone replacement therapy to provide a reference for clinical diagnosis and treatment.

The Pathogenesis of CKD-Associated Pruritus: A Theoretical Model and Relevance for Treatment

Our understanding of the pathogenesis of uremic pruritus (also known as CKD-associated pruritus [CKD-aP]) remains elusive. Although multiple discrete changes in the immunochemical milieu of the skin of patients with CKD-aP have been described, a coherent theory of mechanism is absent. This article proposes a theoretical model of mechanism. It concentrates on the initiation phase of CKD-aP and its three parts: ( 1 ) genesis, triggered by first precipitants; ( 2 ) cascade of cytokine release that follows and the cross-talking of multiple skin cells with each other and afferent nerve fibers; and ( 3 ) enhancement. The limitation of the model will be described and ideas for future research proposed. Implications for management shall be examined.

High cut-off membranes in patients requiring renal replacement therapy: a systematic review and meta-analysis

BACKGROUND

Whether high cut-off (HCO) membranes are more effective than high-flux (HF) membranes in patients requiring renal replacement therapy (RRT) remains controversial. The aim of this systematic review was to investigate the efficacy of HCO membranes regarding the clearance of inflammation-related mediators, β2-microglobulin and urea; albumin loss; and all-cause mortality in patients requiring RRT.

METHODS

We searched all relevant studies on PubMed, Embase, Web of Science, the Cochrane Library, and China National Knowledge Infrastructure, with no language or publication year restrictions. Two reviewers independently selected studies and extracted data using a prespecified extraction instrument. Only randomized controlled trials (RCTs) were included. Summary estimates of standardized mean differences (SMDs) or weighted mean differences (WMDs) and risk ratios (RRs) were obtained by fixed-effects or random-effects models. Sensitivity analyses and subgroup analyses were performed to determine the source of heterogeneity.

RESULTS

Nineteen RCTs involving 710 participants were included in this systematic review. Compared with HF membranes, HCO membranes were more effective in reducing the plasma level of interleukin-6 (IL-6) (SMD -0.25, 95% confidence interval (CI) -0.48 to -0.01, P   =  0.04, I2  = 63.8%); however, no difference was observed in the clearance of tumor necrosis factor-α (TNF-α) (SMD 0.03, 95% CI -0.27 to 0.33, P  = 0.84, I2  = 4.3%), IL-10 (SMD 0.22, 95% CI -0.12 to 0.55, P  = 0.21, I2  = 0.0%), or urea (WMD -0.27, 95% CI -2.77 to 2.23, P  = 0.83, I2  = 19.6%). In addition, a more significant reduction ratio of β 2 -microglobulin (WMD 14.8, 95% CI 3.78 to 25.82, P  = 0.01, I2  = 88.3%) and a more obvious loss of albumin (WMD -0.25, 95% CI -0.35 to -0.16, P  < 0.01, I2  = 40.8%) could be observed with the treatment of HCO membranes. For all-cause mortality, there was no difference between the two groups (risk ratio [RR] 1.10, 95% CI 0.87 to 1.40, P  = 0.43, I2  = 0.0%).

CONCLUSIONS

Compared with HF membranes, HCO membranes might have additional benefits on the clearance of IL-6 and β 2-microglobulin but not on TNF-α, IL-10, and urea. Albumin loss is more serious with the treatment of HCO membranes. There was no difference in all-cause mortality between HCO and HF membranes. Further larger high-quality RCTs are needed to strengthen the effects of HCO membranes.

The membrane perspective of uraemic toxins: which ones should, or can, be removed?

Informed decision-making is paramount to the improvement of dialysis therapies and patient outcomes. A cornerstone of delivery of optimal dialysis therapy is to delineate which substances (uraemic retention solutes or 'uraemic toxins') contribute to the condition of uraemia in terms of deleterious biochemical effects they may exert. Thereafter, decisions can be made as to which of the accumulated compounds need to be targeted for removal and by which strategies. For haemodialysis (HD), the non-selectivity of membranes is sometimes considered a limitation. Yet, considering that dozens of substances with potential toxicity need to be eliminated, and targeting removal of individual toxins explicitly is not recommended, current dialysis membranes enable elimination of several molecules of a broad size range within a single therapy session. However, because HD solute removal is based on size-exclusion principles, i.e. the size of the substances to be removed relative to the mean size of the 'pores' of the membrane, only a limited degree of selectivity of removal is possible. Removal of unwanted substances during HD needs to be weighed against the unavoidable loss of substances that are recognized to be necessary for bodily functions and physiology. In striving to improve the efficiency of HD by increasing the porosity of membranes, there is a greater potential for the loss of substances that are of benefit. Based on this elementary trade-off and availability of recent guidance on the relative toxicity of substances retained in uraemia, we propose a new evidence-linked uraemic toxin elimination (ELUTE) approach whereby only those clusters of substances for which there is a sufficient body of evidence linking them to deleterious biological effects need to be targeted for removal. Our approach involves correlating the physical properties of retention solutes (deemed to express toxicity) with key determinants of membranes and separation processes. Our analysis revealed that in attempting to remove the relatively small number of 'larger' substances graded as having only moderate toxicity, uncontrolled (and efficient) removal of several useful compounds would take place simultaneously and may compromise the well-being or outcomes of patients. The bulk of the uraemic toxin load comprises uraemic toxins below <30 000 Da and are adequately removed by standard membranes. Further, removal of a few difficult-to-remove-by-dialysis (protein-bound) compounds that express toxicity cannot be achieved by manipulation of pore size alone. The trade-off between the benefits of effective removal of the bulk of the uraemic toxin load and risks (increased loss of useful substances) associated with targeting the removal of a few larger substances in 'high-efficiency' HD treatment strategies needs to be recognized and better understood. The removability during HD of substances, be they toxic, inert or beneficial, needs be revised to establish the pros and cons of current dialytic elimination strategies.  .

Myoglobin clearance with continuous veno-venous hemodialysis using high cutoff dialyzer versus continuous veno-venous hemodiafiltration using high-flux dialyzer: a prospective randomized controlled trial

Background

Myoglobin clearance in acute kidney injury requiring renal replacement therapy is important because myoglobin has direct renal toxic effects. Clinical data comparing different modalities of renal replacement therapy addressing myoglobin clearance are limited. This study aimed to compare two renal replacement modalities regarding myoglobin clearance.

Methods

In this prospective, randomized, single-blinded, single-center trial, 70 critically ill patients requiring renal replacement therapy were randomized 1:1 into an intervention arm using continuous veno-venous hemodialysis with high cutoff dialyzer and a control arm using continuous veno-venous hemodiafiltration postdilution with high-flux dialyzer. Regional citrate anticoagulation was used in both groups to maintain the extracorporeal circuit. The concentrations of myoglobin, urea, creatinine, β2-microglobulin, interleukin-6 and albumin were measured before and after the dialyzer at 1 h, 6 h, 12 h, 24 h and 48 h after initiating continuous renal replacement therapy.

Results

Thirty-three patients were allocated to the control arm (CVVHDF with high-flux dialyzer) and 35 patients to the intervention arm (CVVHD with high cutoff dialyzer). Myoglobin clearance, as a primary endpoint, was significantly better in the intervention arm than in the control arm throughout the whole study period. The clearance values for urea and creatinine were higher in the control arm. There was no measurable albumin clearance in both arms. The clearance data for β₂-microglobulin and interleukin-6 were non-inferior in the intervention arm compared to those for the control arm. Dialyzer lifespan was 57.0 [38.0, 72.0] hours in the control arm and 70.0 [56.75, 72.0] hours in the intervention arm (p = 0.029).

Conclusions

Myoglobin clearance using continuous veno-venous hemodialysis with high cutoff dialyzer and regional citrate anticoagulation is better than that with continuous veno-venous hemodiafiltration with regional citrate anticoagulation.

Trial registration

German Clinical Trials Registry (DRKS00012407); date of registration 23/05/2017. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00012407.

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.

Middle molecule clearance with high cut-off dialyzer versus high-flux dialyzer using continuous veno-venous hemodialysis with regional citrate anticoagulation: A prospective randomized controlled trial

BACKGROUND

Regional anticoagulation with citrate during renal replacement therapy (RRT) reduces the risk of bleeding, extends dialyzer lifespan and is cost-effective. Therefore, current guidelines recommend its use if patients are not anticoagulated for another reason and if there are no contraindications against citrate. RRT with regional citrate anticoagulation has been established in critically ill patients as continuous veno-venous hemodialysis (CVVHD) to reduce citrate load. However, CVVHD is inferior regarding middle molecule clearance compared to continuous veno-venous hemofiltration (CVVH). The use of a high cut-off dialyzer in CVVHD may thus present an option for middle molecule clearance similar to CVVH. This may allow combining the advantages of both techniques.

METHODS

In this prospective, randomized, single-blinded single-center-trial, sixty patients with acute renal failure and established indication for renal replacement therapy were randomized 1:1 into two groups. The control group was put on CVVHD using regional citrate anticoagulation and a high-flux dialyzer, while the intervention group was on CVVHD using regional citrate anticoagulation and a high-cut-off dialyzer. The concentrations of urea, creatinine, β2-microglobulin, myoglobin, interleukin 6 and albumin were measured pre- and post-dialyzer 1, 6, 12, 24 and 48 hours after initiating CVVHD.

RESULTS

Mean plasma clearance for β2-microglobulin was 19.6±5.8 ml/min in the intervention group vs. 12.2±3.6 ml/min in the control group (p<0.001). For myoglobin (8.0±4.5 ml/min vs. 0.2±3.6 ml/min, p<0.001) and IL-6 (1.5±4.3 vs. -2.5±3.5 ml/min, p = 0.002) a higher mean plasma clearance using high-cut-off dialyzer could be detected too, but no difference for urea, creatinine and albumin could be observed concerning this parameter between the two groups.

CONCLUSION

CVVHD using a high cut-off dialyzer results in more effective middle molecule clearance than that with high-flux dialyzer.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00005254, registered 26th November 2013).

Extracorporeal Treatment in the Management of Acute Poisoning: What an Intensivist Should Know?

Extracorporeal treatment (ECTR) represents a treatment modality promoting removal of endogenous or exogenous poisons and supporting or temporarily replacing a vital organ. This article aims to provide a brief overview of the technical aspects and the potential indications and limitations of the different ECTRs, highlighting the important characteristics of poison amenable to ECTR and the most appropriate prescriptions used in the setting of acute poisoning. The various principles that govern poison elimination by ECTR (diffusion, convection, adsorption, and centrifugation) and how components of the ECTR can be adjusted to maximize clearance have also being discussed.

Super High-Flux Continuous Venovenous Hemodialysis Using Regional Citrate Anticoagulation: Long-Term Stability of Middle Molecule Clearance

Continuous renal replacement therapy is a standard treatment in critically ill patients with acute kidney injury. All CRRT techniques provide a high low-molecular weight clearance but even with hemofiltration, clearance of middle molecules is low. We investigated whether a new super high-flux hemofilter provides effective and sustained middle molecule clearance during citrate-anticoagulated continuous venovenous hemodialysis for up to 72 h. We included 14 critically ill patients with AKI-KDIGO-III in a prospective observational trial. We measured/calculated blood and urine concentrations, clearances and sieving coefficients of eight molecules with molecular weights from 60 to 66 kDa, hemodynamic parameters and SAPS-II scores. All filters were patent at 72 h. Clearance and sieving coefficients of small solutes were high and sustained over time, those for larger solutes decreased over 72 h but remained high enough to decrease blood concentrations of solutes up to 25 kDa. Albumin serum levels remained unaffected. Catecholamine doses and SAPS-II scores decreased significantly. This new hemofilter may improve blood purification in critically ill patients with AKI.

Precise Quantitative Assessment of the Clinical Performances of Two High-Flux Polysulfone Hemodialyzers in Hemodialysis: Validation of a Blood-Based Simple Kinetic Model Versus Direct Dialysis Quantification

Highly permeable dialysis membranes with better design filters have contributed to improved solute removal and dialysis efficacy. However, solute membrane permeability needs to be well controlled to avoid increased loss of albumin that is considered to be detrimental for dialysis patients. A novel high-flux dialyzer type (FX CorDiax; Fresenius Medical Care) incorporating an advanced polysulfone membrane modified with nano-controlled spinning technology to enhance the elimination of a broader spectrum of uremic toxins has been released. The aim of this study was to compare in the clinical setting two dialyzer types having the same surface area, the current (FX dialyzer) and the new dialyzer generation (FX CorDiax), with respect to solute removal capacity over a broad spectrum of markers, including assessment of albumin loss based on a direct dialysis quantification method. We performed a crossover study following an A1-B-A2 design involving 10 patients. Phase A1 was 1 week of thrice-weekly bicarbonate hemodialysis with the FX dialyzer, 4 h per treatment; phase B was performed with a similar treatment regimen but with a new FX CorDiax dialyzer and finally the phase A2 was repeated with FX dialyzer as the former phase. Solute removal markers of interest were assessed from blood samples taken before and after treatment and from total spent dialysate collection (direct dialysis quantification) permitting a mass transfer calculation (mg/session into total spent dialysate/ultrafiltrate). On the blood side, there were no significant differences in the solute percent reduction between FX CorDiax 80 and FX 80. On the dialysate side, no difference was observed regarding eliminated mass of different solutes including β₂ -microglobulin (143.1 ± 33.6 vs. 138.3 ± 41.9 mg, P = 0.8), while the solute mass removal of total protein (1.65 ± 0.51 vs. 2.14 ± 0.75 g, P = 0.04), and albumin (0.41 ± 0.21 vs. 1.22 ± 0.51 g, P < 0.001) were significantly less for FX CorDiax 80 compared to the FX 80 dialyzer. The results of this cross-over study indicate that the new FX CorDiax dialyzer has highly effective removal of middle molecules, without any concomitant increase in total protein and albumin loss. The clinical relevance and potential benefit of this finding needs to be determined.

Effect of Treatment Duration and Frequency on Uremic Solute Kinetics, Clearances and Concentrations

The kinetics of uremic solute clearances are discussed based on two categories of uremic solutes, namely those that are and those that are not derived directly from nutrient intake, particularly dietary protein intake. This review highlights dialysis treatments that are more frequent and longer (high-dose hemodialysis) than conventional thrice weekly therapy. It is proposed that the dialysis dose measures based on urea as a marker uremic solute, such as Kt/V and stdKt/V, be referred to as measures of dialysis inadequacy, not dialysis adequacy. For uremic solutes derived directly from nutrient intake, it is suggested that inorganic phosphorus and protein-bound uremic solutes be considered as markers in the development of alternative measures of dialysis dose for high-dose hemodialysis prescriptions. As the current gap in understanding the detailed kinetics of protein-bound uremic solutes, it is proposed that normalization of serum phosphorus concentration with a minimum (or preferably without a) need for oral-phosphorus binders be targeted as a measure of dialysis adequacy in high-dose hemodialysis. For large uremic solutes not derived directly from nutrient intake (middle molecules), use of extracorporeal clearances for β₂ -microglobulin that are higher than currently available during thrice weekly therapy is unlikely to reduce predialysis serum β₂ -microglobulin concentrations. High-dose hemodialysis prescriptions will lead to reductions in predialysis serum β₂ -microglobulin concentrations, but such reductions are also limited by significant residual kidney clearance. Kinetic data regarding middle molecules larger than β₂ -microglobulin are scarce; additional studies on such uremic solutes are of high interest to better understand improved methods for prescribing high-dose hemodialysis prescriptions to improve patient outcomes.

Dialyzer Reuse and Outcomes of High Flux Dialysis

Background

The bulk of randomized trial evidence for the expanding use of High Flux (HF) hemodialysis worldwide comes from two randomized controlled trials, one of which (HEMODIALYSIS, HEMO) allowed, while the other (Membrane Outcomes Permeability, MPO) excluded, the reuse of membranes. It is not known whether dialyzer reuse has a differential impact on outcomes with HF vs low flyx (LF) dialyzers.

Methods

Proportional Hazards Models and Joint Models for longitudinal measures and survival outcomes were used in HEMO to analyze the relationship between β2-microglobulin (β2M) concentration, flux, and reuse. Meta-analysis and regression techniques were used to synthesize the evidence for HF dialysis from HEMO and MPO.

Findings

In HEMO, minimally reused (< 6 times) HF dialyzers were associated with a hazard ratio (HR) of 0.67 (95% confidence interval, 95%CI: 0.48–0.92, p = 0.015), 0.64 (95%CI: 0.44 – 0.95, p = 0.03), 0.61 (95%CI: 0.41 – 0.90, p = 0.012), 0.53 (95%CI: 0.28 – 1.02, p = 0.057) relative to minimally reused LF ones for all cause, cardiovascular, cardiac and infectious mortality respectively. These relationships reversed for extensively reused membranes (p for interaction between reuse and flux < 0.001, p = 0.005) for death from all cause and cardiovascular causes, while similar trends were noted for cardiac and infectious mortality (p of interaction between reuse and flux of 0.10 and 0.08 respectively). Reduction of β2M explained only 1/3 of the effect of minimally reused HF dialyzers on all cause mortality, while non-β2M related factors explained the apparent attenuation of the benefit with more extensively reused dialyzers. Meta-regression of HEMO and MPO estimated an adjusted HR of 0.63 (95% CI: 0.51–0.78) for non-reused HF dialyzers compared with non-reused LF membranes.

Conclusions

This secondary analysis and synthesis of two large hemodialysis trials supports the widespread use of HF dialyzers in clinical hemodialysis over the last decade. A mechanistic understanding of the effects of HF dialysis and the reuse process on dialyzers may suggest novel biomarkers for uremic toxicity and may accelerate membrane technology innovations that will improve patient outcomes.

Principles and operational parameters to optimize poison removal with extracorporeal treatments

A role for nephrologists in the management of a poisoned patient involves evaluating the indications for, and methods of, enhancing the elimination of a poison. Nephrologists are familiar with the various extracorporeal treatments (ECTRs) used in the management of impaired kidney function, and their respective advantages and disadvantages. However, these same skills and knowledge may not always be considered, or applicable, when prescribing ECTR for the treatment of a poisoned patient. Maximizing solute elimination is a key aim of such treatments, perhaps more so than in the treatment of uremia, because ECTR has the potential to reverse clinical toxicity and shorten the duration of poisoning. This manuscript reviews the various principles that govern poison elimination by ECTR (diffusion, convection, adsorption, and centrifugation) and how components of the ECTR can be adjusted to maximize clearance. Data supporting these recommendations will be presented, whenever available.

Engineering perspective on the evolution of push/pull-based dialysis treatments

The incidence of kidney disease is rapidly increasing worldwide, and techniques and devices for treating end-stage renal disease (ESRD) patients have been evolving. Better outcomes achieved by convective treatment have encouraged the use of synthetic membranes with high water permeability in clinical setups, and high-flux hemodialysis (HD) and hemodiafiltration (HDF) are now preferred forms of convective therapy in ESRD patients. Push/pull-based dialysis strategies have also been examined to increase convective mass transfer in ESRD patients. The push/pull technique uses the entire membrane as a forward filtration domain for a period of time. However, backfiltration must accompany the forward filtration to compensate for the fluid depletion resulting from the forward filtration, making it necessary to switch the membranes to a backfiltration domain. This paper attempts to describe the advancement of push/pull-based renal supportive treatments in terms of their technical description, hemodialytic efficacy including fluid management accuracy and applicability for clinical use. How the optimization of push and pull actions could translate into better convective efficiency will also be discussed in depth.

New high-cutoff dialyzer allows improved middle molecule clearance without an increase in albumin loss: a clinical crossover comparison in extended dialysis

BACKGROUND

Accumulation of middle molecules is thought to have adverse effects in patients with acute kidney injury (AKI). Elimination of middle molecules by non-convective means, i.e. hemodialysis, remains difficult. The aim of the study was to investigate the removal characteristics of a new high permeability membrane in AKI patients undergoing extended dialysis (ED).

PATIENTS AND METHODS

We performed a prospective, crossover study comparing the EMiC2 dialyzer (1.8 m(2), FMC, Germany) and AV 1000S (1.8 m(2), FMC) in 11 critically ill patients with AKI. β2-Microglobulin, cystatin c, creatinine, and urea were measured before and after 0.5, 5.0 and 10 h of ED. Serum reduction ratios, dialyzer clearances, and mass in the total collected dialysate were determined.

RESULTS

Dialyzer clearance of β2-microglobulin (EMiC2: 52 ± 1.7 ml/min, AV 1000S: 41.7 ± 1.5 ml/min, p = 0.0002) and cystatin c (EMiC2: 47.2 ± 1.2 ml/min, AV 1000S: 34.2 ± 2.3 ml/min, p < 0.0001) was markedly different, as was the reduction of serum levels of β2-microglobulin (EMiC2: 54.3 ± 3.6%, AV 1000S: 39.1 ± 4.5%, p = 0.025) and cystatin c (EMiC2: 38.9 ± 2.6%, AV 1000S: 28.0 ± 3.9%, p = 0.043). Additionally, we observed a higher total amount of these substances in the collected dialysate. There was no significant difference in the total amount of albumin eliminated per treatment.

CONCLUSION

The new EMiC2 dialyzer enhances removal of middle molecules without an increase in albumin loss. The clinical relevance of this finding needs to be determined.

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.

Review: membranes for haemodialysis

Haemodialysis, by design, uses a semipermeable membrane to separate blood from dialysate. The qualities of this membrane determine the nature of the 'traffic' between the blood and dialysate. In this sense, the qualities of the membrane determine what size molecules move from one compartment to the other, the amount and rate at which they might move and the amount and rate of water movement across the membrane. In addition, the nature of the membrane influences the biological response of the patient both in terms of what is or is not removed by the dialysis process and by way of the reaction to the biocompatibility of the membrane. This brief review will explore aspects of dialysis membrane characteristics.