Replication of fouling in vitro in hollow fiber dialyzers by albumin immobilization

On the total albumin losses during haemocatharsis

Excessive albumin losses during HC (haemocatharsis) are considered a potential cause of hypoalbuminemia-a key risk factor for mortality. This review on total albumin losses considers albumin "leaking" into the dialysate and losses due to protein/membrane interactions (i.e. adsorption, "secondary membrane formation" and denaturation). The former are fairly easy to determine, usually varying at the level of ~ 2 g to ~ 7 g albumin loss per session. Such values, commonly accepted as representative of the total albumin losses, are often quoted as limits/standards of permissible albumin loss per session. On albumin mass lost due to adsorption/deposition, which is the result of complicated interactions and rather difficult to determine, scant in vivo data exist and there is great uncertainty and confusion regarding their magnitude; this is possibly responsible for neglecting their contribution to the total losses at present. Yet, many relevant in vitro studies suggest that losses of albumin due to protein/membrane interactions are likely comparable to (or even greater than) those due to leaking, particularly in the currently favoured high-convection HDF (haemodiafiltration) treatment. Therefore, it is emphasised that top research priority should be given to resolve these issues, primarily by developing appropriate/facile in vivo test-methods and related analytical techniques.

Effect of Membrane Surface Area on Solute Removal Performance of Dialyzers with Fouling

In a clinical situation, since membrane fouling often causes the reduction of solute removal performance of the dialyzer, it is necessary to evaluate the performance of the dialyzer, considering the effects of fouling even in aqueous in vitro experiments that are useful for the better design of dialyzers. We replicated the membrane fouling by immobilizing albumin on the membrane in a dialyzer using glutaraldehyde as a stabilizer. The modules of various membrane surface areas with and without replication of the fouling were used for performance evaluation of solute (creatinine, vitamin B12, and inulin) removal in dialysis experiments in vitro. Clearances for these solutes in the modules with fouling were lower than those without fouling. Furthermore, the smaller the surface area, the larger the fouling effect was observed in all solutes. Calculated pressure distribution in a module by using a mathematical model showed that the solute removal performance might be greatly affected by the rate of internal filtration that enhances the solute removal, especially for larger solutes. The increase in the rate of internal filtration should contribute to improving the solute removal performance of the dialyzer, with a higher effect in modules with a larger membrane surface area.

Semi-Quantitative Evaluation of Asymmetricity of Dialysis Membrane Using Forward and Backward Ultrafiltration

Performance of the dialysis membrane is strongly dependent upon the physicochemical structure of the membrane. The objective of this study is to devise a new in vitro evaluation technique to quantify the physicochemical structures of the membrane. Three commercial dialyzers with cellulose triacetate (CTA), asymmetric CTA (termed ATA^®), and polyether sulfone (PES) membranes (Nipro Co., Osaka, Japan) were employed for investigation. Forward and backward ultrafiltration experiments were performed separately with aqueous vitamin B₁₂ (MW 1355), α-chymotrypsin (MW 25,000), albumin (MW 66,000) and dextran solutions, introducing the test solution inside or outside the hollow fiber (HF), respectively. Sieving coefficients (s.c.) for these solutes were measured under the test solution flow rate of 200 mL/min and the ultrafiltration rate of 10 mL/min at 310 K, according to the guidelines provided by Japanese academic societies. We defined the ratio of s.c. in the backward ultrafiltration to that in the forward ultrafiltration and termed it the index for asymmetricity (IA). The IA values were unity for vitamin B₁₂ and α-chymotrypsin in all three of the dialyzers. The IA values for albumin, however, were 1.0 in CTA, 1.9 in ATA^®, and 3.9 in PES membranes, respectively, which corresponded well with the fact that CTA is homogeneous, whereas ATA^® and PES are asymmetrical in structure. Moreover, the asymmetricity of ATA^® and PES may be different by twofold. This fact was verified in continuous basis by employing dextran solution before and after being fouled with albumin. These findings may contribute to the development of a novel membrane for improved success of dialysis therapy.