Effects of Bleach Reprocessing on Hemodialysis Membranes
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AA14.3.1
Effects of Bleach Reprocessing on Hemodialysis Membranes Susanne H. Wolff and Andrew L. Zydney The Pennsylvania State University Department of Chemical Engineering University Park, PA 16802
ABSTRACT Hemodialysis membranes are exposed to bleach during standard reprocessing methods, but there is little quantitative understanding of the effects of bleach on the mass transfer characteristics or surface properties of these membranes. A battery of experiments was used to evaluate the effects of bleach on the properties of Fresenius F80A, F80B, and Optiflux 180A dialyzers. Bleach caused a significant increase in the membrane hydraulic permeability. The clearance of urea (MW=60 Da) increased by only 3% after a 1-hour exposure to bleach at 50 °C compared to more than a 10-fold increase in the clearance of a 15 kD MW dextran. The solute clearance data were used to determine the effective membrane pore size using available hydrodynamic models. Bleach caused a significant increase in the effective pore size, which was attributed to the leaching of the polyvinylpyrrolidone (PVP) out of the polysulfone membrane. Bleach also caused a significant increase in the magnitude of the negative charge on the membrane surface; the zeta potential varied from –4.1 mV for the new membrane to –13.0 mV after a 14-hour exposure to bleach. These changes in pore size and surface properties provide important insights into the effects of bleach on hemodialysis membranes.
INTRODUCTION Currently more than 240,000 Americans require hemodialysis to treat chronic renal failure, with this patient population increasing at a rate of nearly 10% each year [1]. Hemodialysis is performed with semipermeable membranes that are designed to remove both small wastes (e.g. urea) and important middle molecules like β 2-microglobulin. To help control the cost of this treatment, hemodialyzers are often reprocessed and reused multiple times by the same patient. Currently, about 80% of hemodialysis performed in the United States is conducted with reprocessed dialyzers [2]. Reprocessing involves cleaning the dialyzer with a chemical agent, e.g. bleach, peracetic acid, or hot citric acid, followed by thorough rinsing and disinfection. Several clinical studies have suggested that reprocessing may reduce the effectiveness of hemodialysis. In particular, Ikizler et al. [3] and Kaplan et al. [4] have reported an increase in membrane permeability leading to undesired protein losses after bleach reprocessing of polysulfone dialyzers. The objective of this study was to develop an improved understanding of the effects of bleach exposure on both the mass transfer characteristics and surface properties of Fresenius hemodialysis membranes, which are made from a co-polymer of polysulfone and polyvinylpyrrolidone (PVP).
AA14.3.2
EXPERIMENTAL DETAILS Phosphate buffered saline (PBS, 0.14 M) was made by dissolving 8.04 g Na2HPO4•7H20, 4.08 g KH2PO4 and 0.67 g NaOH in 1 liter of de-ionized water. The pH of the buffer solution was adjusted to 7.4 by the addition of either H3PO
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