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      Dialysis membrane: from convection to adsorption

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          Abstract

          Although patients undergoing dialysis have a complex illness, there are compelling reasons to believe that the inadequate removal of organic waste is an important contributing factor to the illness itself. This paper focuses on the transport phenomena that occur within a dialyser. An attempt is made to clarify how transport phenomena are related to the performance of a dialysis session and how they depend on the membrane characteristics. Our study offers some discussion points on the complex issue of defining what the best parameters could be in comparing the efficiency of different membranes. The new high-flux dialysers have improved larger-molecule clearance and biocompatibility. Membrane performance is a very hard process to evaluate, and different membranes can only be compared by establishing adequate points of comparison. At the same time, the points of comparison themselves may change depending on the type of co-morbidities of the specific patient who is considered for membrane selection. This editorial (together with all the papers presented in this issue) seeks to focus on the membrane's own merits in improving the dialysis therapy.

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          Most cited references41

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          Hemodialysis membrane with a high-molecular-weight cutoff and cytokine levels in sepsis complicated by acute renal failure: a phase 1 randomized trial.

          Sepsis is the leading cause of acute renal failure. Intermittent hemodialysis (IHD) is a common treatment for patients with acute renal failure. However, standard hemodialysis membranes achieve only little diffusive removal of circulating cytokines. Modified membranes may enable both successful IHD treatment and simultaneous diffusive cytokine removal. Double-blind, crossover, randomized, controlled, phase 1 trial. Tertiary intensive care unit. 10 septic patients with acute renal failure according to RIFLE class F. Each patient was treated with 4 hours of high-cutoff (HCO)-IHD and 4 hours of high-flux (HF)-IHD. We chose relative change in plasma interleukin 6 (IL-6) concentrations from baseline to 4 hours as the primary outcome for effective cytokine removal. We measured plasma and effluent concentrations of cytokines (IL-6, IL-8, IL-10, and IL-18) and albumin. Median age was 53 years (25(th) to 75(th) percentiles, 43 to 71 years). Both treatments achieved equal control of uremia. Four hours of HCO-IHD accomplished a greater decrease in plasma IL-6 levels (-30.3%) than 4 hours of HF-IHD (1.1%; P = 0.05). HCO-IHD, but not HF-IHD, achieved substantial diffusive clearance of several cytokines (IL-6, 14.1 mL/min; IL-8, 75.2 mL/min; and IL-10, 25.5 mL/min). Such clearance also was associated with greater relative decreases in plasma IL-8 and IL-10 levels in favor of HCO-IHD (P = 0.02, P = 0.04). We found significantly greater relative changes from prefilter to postfilter plasma IL-6, IL-8, and IL-10 values in favor of HCO-IHD (P = 0.02, P = 0.01, P < 0.01). During HCO-IHD, cumulative albumin loss into the effluent was 7.7 g (25(th) to 75(th) percentiles, 4.8 to 19.6) versus less than 1.0 g for HF-IHD (P < 0.01). Small phase 1 trial. In septic patients with acute renal failure, HCO-IHD achieved simultaneous uremic control and diffusive cytokine clearances and a greater relative decrease in plasma cytokine concentrations than standard HF-IHD.
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            Change from conventional haemodiafiltration to on-line haemodiafiltration.

            On-line haemodiafiltration (HDF) is a technique which combines diffusion with elevated convection and uses pyrogen-free dialysate as a replacement fluid. The purpose of this study was to evaluate the difference between conventional HDF (1-3 l/h) and on-line HDF (6-12 l/h). The study included 37 patients, 25 males and 12 females. The mean age was 56.5 +/- 13 years and duration of dialysis was 62.7 +/- 49 months. Three patients dropped out for transplantation, three patients died and three failed to complete the study period. Initially all patients were on conventional HDF with high-flux membranes over the preceding 34 +/- 32 months. Treatment was performed with blood flow (QB) 402 +/- 41 ml/min, dialysis time (Td) 187 min, dialysate flow (QD) 654 +/- 126 ml/min and replacement fluid (Qi) 4.0 +/- 2 l/session. Patients were changed to on-line HDF with the same filtre and dialysis time, QD 679 +/- 38 ml/min (NS), QB 434 +/- 68 ml/min (P < 0.05) and post-dilutional replacement fluid 22.5 +/- 4.3 l/session (P < 0.001). We compared conventional HDF with on-line HDF over a period of 1 year. Dialysis adequacy was monitored according to standard clinical and biochemical criteria. Kinetic analysis of urea and beta2-micro-globulin (beta2m) was performed monthly. Tolerance was excellent and no pyrogenic reactions were observed. Pre-dialysis sodium increased 2 mEq/l during on-line HDF. Plasma potassium, pre- and post-dialysis bicarbonate, uric acid, phosphate, calcium, iPTH, albumin, total proteins, cholesterol and triglycerides remained stable. The mean plasma beta2m reduction ratio increased from 56.1 +/- 8.7% in conventional HDF to 71.1 +/- 9.1% in on-line HDF (P < 0.001). The pre-dialysis plasma beta2m decreased from 27.4 +/- 8.1 to 24.2 +/- 6.5 mg/l (P < 0.01). Mean Kt/V (Daugirdas 2nd generation) was 1.35 +/- 0.21 in conventional HDF compared with 1.56 +/- 0.29 in on-line HDF (P < 0.01), Kt/Vr (Kt/V taking into consideration post-dialysis urea rebound) 1.12 +/- 0.17 vs 1.26 +/- 0.20 (P < 0.01), BUN time average concentration (TAC) 44.4 +/- 9 vs 40.6 +/- 10 mg/dl (P < 0.05) and protein catabolic rate (PCR) 1.13 +/- 0.22 vs 1.13 +/- 0.24 g/kg (NS). There was a significant increase in haemoglobin (10.66 +/- 1.1 vs 11.4 +/- 1.5) and haematocrit (32.2 +/- 2.9 vs 34.0 +/- 4.4%), P < 0.05, during the on-line HDF period, which allowed a decrease in the erythropoietin doses (3861 +/- 2446 vs 3232 +/- 2492 UI/week), (P < 0.05). Better blood pressure control (MAP 103.8 +/- 15 vs 97.8 +/- 11 mmHg, P < 0.01) and a lower percentage of patients requiring antihypertensive drugs were also observed. The change from conventional HDF to on-line HDF results in increased convective removal and fluid replacement (18 l/session). During on-line HDF treatment, dialysis dose was increased for both small and large molecules with a decrease in uraemic toxicity level (TAC). On-line HDF provided a better correction of anaemia with lower dosages of erythropoietin. Finally, blood pressure was easily controlled.
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              Effect of the super-flux cellulose triacetate dialyser membrane on the removal of non-protein-bound and protein-bound uraemic solutes.

              Uraemic solutes accumulate in haemodialysis (HD) patients and interfere with physiological functions. Low-flux (LF) HD does not efficiently remove all uraemic compounds. We investigated whether large pore super-flux (SF) cellulose triacetate membranes (CTA) result in a better removal of uraemic solutes. Eleven patients were dialysed consecutively with LF-CTA and SF-CTA during 3 weeks. Urea (UR), creatinine (CR), uric acid (UA), 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), indole-3-acetic acid (IAA), indoxyl sulfate (IS), hippuric acid (HA), pentosidine (PENT), low-molecular weight (MW) AGEs (AGEs) and albumin were determined in pre-HD, post-HD blood and in dialysate. Reduction rate (RR), dialytic clearance and mass transfer-area coefficient (KoA) were calculated. SF-HD resulted in a higher RR than LF-HD for IS and AGEs. Urea RR correlated with HA (r=0.59), IS (r=0.68) and IAA (r=0.67), (P<0.05) for SF. Dialytic clearance ranged from 20+/-5 to 179+/-20 ml/min for LF and from 24+/-6 to 191+/-24 ml/min for SF; being higher with SF for UA, HA, IS and IAA (SF vs LF, P<0.05). KoA was higher for most compounds with SF-HD. Albumin loss per SF session was 3.4+/-1.3 g. The retrieved amount of uraemic solutes in dialysate with LF and SF was comparable. In conventional HD, SF-CTA was superior to LF-CTA for removal of most protein-bound compounds, especially IS. Reduction rate, dialytic clearance and KoA were higher with SF. The SF-CTA membrane is albumin-leaking; however, this property could not completely explain the amount of retrieved protein-bound compounds in dialysate.
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                Author and article information

                Journal
                Clin Kidney J
                Clin Kidney J
                ckj
                ndtplus
                Clinical Kidney Journal
                Oxford University Press
                2048-8505
                2048-8513
                May 2010
                : 3
                : Suppl 1 , Dialysis for High Quality of Life - Complications and Prognosis
                : i36-i39
                Affiliations
                Division of Nephrology, Dialysis and Hypertension, Azienda Ospedaliero–Universitaria di Bologna, Policlinico S. Orsola–Malpighi, Via Palagio Palagi 9, 40138, Bologna, Italy
                Author notes
                Antonio Santoro; E-mail: antonio.santoro@ 123456aosp.bo.it
                Article
                sfq035
                10.1093/ndtplus/sfq035
                4392133
                52351ec5-776d-4474-982e-4d0d9c7fdc4e
                © The Author 2010. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

                History
                : 7 December 2009
                : 22 February 2010
                Categories
                Original Article

                Nephrology
                adsorption,convection,dialysis membranes,diffusion
                Nephrology
                adsorption, convection, dialysis membranes, diffusion

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