The performance evaluation of endotoxin retentive filters in haemodialysis.

BACKGROUND Hemodialysis is a method for removing uremic toxins and water directly from the blood into a dialysis fluid through an artificial semipermeable membrane called a dialyzer. The ability of the dialyzer to remove uremic toxins has steadily improved, but the likelihood has also increased that bioactive substances, such as bacterial endotoxin (ET) fragments, can be transferred from the dialysis fluid into the patient's blood through the phenomena of back-diffusion and back-filtration in the dialyzer. Therefore, further efforts to improve the quality of water are required. In 2008, the Committee of Scientific Academy of the Japanese Society for Dialysis Therapy presented its new recommendations for the quality standards of dialysis fluid, but achieving and maintaining these standard values would seem difficult without installing an ET-retentive filter (ETRF). In the present study, we evaluated whether the standards for ultrapure dialysis fluid of the Japanese Society for Dialysis Therapy can be achieved and maintained by installing 3 types of ETRF for a period of 12 months. METHODS To evaluate the quality of dialysis fluid, ET values were measured with nephelometry, and viable cell counts were determined with the membrane filter method. Changes in the basic performance of the ETRFs were evaluated by measuring their water permeability, ET-retentive capacity, and hollow-fiber membrane intensity. Moreover, the hollow-fiber membrane surfaces of the ETRFs were observed with scanning electron microscopy, and the elements of the adherent substances were identified by means of energy dispersive X-ray spectrometry. RESULTS The ET concentrations were less than the limit of detection during the evaluation period for samples obtained at post-ETRF sites. The viable cell counts for pre-ETRF sites were approximately 10 colony-forming units/mL. However, colonies had not formed in samples obtained from the post-ETRF sites. The substances adhering to hollow fibers included the silicon from the dialysate powder, the iron from the fluid path, and the elements derived from stainless steel. Scanning electron microscopy of the ETRF hollow fibers showed no substances except the hollow fibers and the elements derived from the dialysis fluid. CONCLUSION Installation of an ETRF is useful for achieving and maintaining the quality standards for ultrapure dialysis fluid and for preventing the entry into the blood of ETs, viable cells, and such substances as silicon and metals.