Effects of Hemodialyzer Reuse on Clearances of Urea and β2-Microglobulin

Although dialyzer reuse in chronic hemodialysis pa- tients is commonly practiced in the United States, performance of reused dialyzers has not been extensively and critically evaluated. The present study analyzes data extracted from a multicenter clinical trial (the HEMO Study) and examines the effect of reuse on urea and b2-microglobulin (b2M) clearance by low-flux and high-flux dialyzers reprocessed with various germicides. The dialyzers evaluated contained either modified cellulosic or polysulfone membranes, whereas the germicides examined included peroxyacetic acid/acetic acid/hydrogen per- oxide combination (Renalin ® ), bleach in conjunction with formaldehyde, glutaraldehyde or Renalin, and heated citric acid. Clearance of b2M decreased, remained unchanged, or increased substantially with reuse, depending on both the membrane material and the reprocessing technique. In contrast, urea clearance decreased only slightly (approximately 1 to 2% per 10 reuses), albeit statistically significantly with reuse, regardless of the porosity of the membrane and reprocessing method. Inasmuch as patient survival in the chronic hemodi- alysis population is influenced by clearances of small solutes and middle molecules, precise knowledge of the membrane material and reprocessing technique is important for the pre- scription of hemodialysis in centers practicing reuse. High-flux hemodialyzers and reuse of dialyzers have been widely used for decades, yet the effects of these practices on solute clearances have not been fully evaluated. Although the beneficial effect of increasing urea clearance on clinical outcome has been established, at least up to a single-pool Kt/V value of 1.2 (1), there are also accumulating data suggesting that the removal of middle molecules (using vitamin B12 as marker) influences patient survival (2,3). Thus, maintenance of the clearance of both small and large solutes for reused dialyzers is important. Reuse can affect dialyzer performance in at least two different ways. The first is the result of deposition of blood elements inside the lumen of the blood compartment and onto the dialyzer mem- brane. The second is the result of the reprocessing procedure. At present, the popular germicides used in reprocessing in the United States are Renalin (made up of peroxyacetic acid, acetic acid, and hydrogen peroxide, Minntech, Minneapolis, MN), formaldehyde, and glutaraldehyde (4). To enhance the aesthetic appearance of the dialyzers during reuse, sodium hypochlorite (bleach) is often used in conjunction with formaldehyde or glutaraldehyde to re- move residual blood proteins. More recently, heated citric acid has also been introduced to clean and disinfect dialyzers for reuse. Because the chemical composition and mechanical structure are vastly different among various types of dialysis membranes, their interactions with the blood elements and reprocessing agents are likely to differ as well. The HEMO Study is a prospective randomized multicenter trial sponsored by the U.S. National Institutes of Health designed to examine the effects of urea Kt/V and the type of dialysis mem- brane on clinical outcome of chronic hemodialysis patients (5). Various models of dialyzers and reprocessing methods are used among the 15 clinical centers (more than 45 dialysis units) in the trial. Using this large database, we have prospectively examined the effects of various combinations of dialyzers and reprocessing agents on the clearance of urea and b2-microglobulin (b2M). The data show that the effects of reuse on b2M are far more drastic than those on urea clearance. Furthermore, the effects vary greatly depending on the dialysis membrane material and reprocessing reagents. These observations confirm and extend our fundamental understanding of alterations in dialyzer performance during reuse.