P1082COMPARISON OF THE REMOVAL OF PROTEIN-BOUND TOXINS AND LARGE MIDDLE MOLECULES WITH HIGH-FLUX PMMA AND MEDIUM CUT-OFF DIALYZERS
Authors: Molina Pablo , Peiró Julio , Martínez-Gómez María Amparo , Vizcaíno Belén , Gonzã¡lez Moya Mercedes , Esteller Cristina , Beltrán Sandra , Kanter Julia , Pérez-Zafra Erika , Alcover Silvia , Pantoja Jonay , Sancho Calabuig Asunción , Estañ Nuria , Climente Mónica , Pallardó Luis M 
Published: June 2020

Abstract

Background and Aims
Dialytic clearance of protein-bound toxins and large middle molecules is poor by diffusive treatment and limited by high-flux hemodialysis (HD) and on-line hemodiafiltration (OL-HDF), and only a few studies have examined how to improve their removal by other extracorporeal strategies. Since 2017, there is a new generation of polymethyl methacrylate (PMMA) membranes that suppress platelet adhesion on the membrane surface improving hemocompatibility and permeability, while also maintaining adsorption properties related to conventional PMMA membranes. Expanded HD (HDx) with medium cut-off (MCO) membranes has also recently been incorporated into clinical practice and may improve the removal of uremic toxins in HD treatments. The aim of this pilot study was to compare the efficacy of a new high-flux PMMA dialyzer (Filtryzer® NF-2.1H) in a post-dilution OL-HDF session with a new MCO membrane (Theranova® 400) in a HDx session.

Method
In an open, cross-over, single-center, controlled, prospective clinical study, 40 adult stable HD patients were assigned to be treated by post-dilution OL-HDF with the NF-2.1H dialyzer or by HDx with the Theranova 400 dialyzer. All other dialysis parameters, including blood and dialysate flow rates, length of dialysis session, and ultrafiltration rate remained unchanged during both sessions. P-cresyl sulfate (PCS), indoxyl sulfate (IS), and kappa (κ) and lambda( λ) free light chains (FLC) reduction rates were intraindividually compared for the two dialyzer types (primary outcomes). Secondary outcomes included the kt and the reduction ratio of blood urea nitrogen, phosphate and β2 -microglobulin (β 2-m).

Results
The reduction ratio of protein-bound toxins ranges from 60% to 67%, with no differences between membranes (Figure). PMMA membrane achieved greater FLC reduction ratios than MCO membrane, reaching significance for λFLC (56.6% vs. 77.4%; p &lt; 0.001). Conversely, β2M reduction ratio was slightly but significantly higher with MCO membrane (68.5 vs. 72.1%; p = 0.002). Small molecules removal including urea and phosphate were similar in both groups, achieving an optimal Kt with no differences between groups (61.3±9.2 Vs. 59.7±9.3; p=0.16). Albumin reduction ratio tended to be higher with PMMA membrane without reaching significance (10.1±5.9% Vs. 7.8±12.3%; p=0.17). The mean convective volume achieved with PMMA was 23.5±4.4 L.

Conclusion
This study suggested that new high-flux PMMA dialyzer in post-dilution OL-HDF mode might achieve better FLC reduction ratios than MCO dyalizer in HDx mode, whereas both techniques may equally remove protein-bound toxins. OL-HDF with new PMMA membranes could be a good dialysis strategy for adding convective transport to the well-known mechanisms of diffusion and absorption previously described with conventional PMMA membranes, enabling an adequate substitution volume.