Filtration of Dialysate Using An On-Line Dialysate Filter

Abstract

Increased concerns about pyrogenic contamination of dialysate have led to the development of an on-line dialysate filtration system. Bacteriological testing of the system was performed (n=6) by introducing bicarbonate concentrate contaminated with E. coli 026:B 6 (3x10⁹ cfu/ml) into a dialysis machine equipped with a two-stage polysulfone filtration system. The bacterial concentration of the dialysate entering the filtration system was maintained above 10⁶ cfu/ml and endotoxin levels ranged from 30-300 ng/ml during the 3-hour test period. Bacterial and endotoxin levels on the input side of the first-stage filter reached minimum concentrations of 5.4x10⁹ cfu/ml and 30,000 ng/ml respectively. All output samples of filtered dialysate showed no bacterial growth and endotoxin levels were below the sensitivity (0.003 ng/ml) of the LAL assay. A dialysis machine (QD = 500), equipped with a single stage filtration system, was used for 18 months of clinical testing. In order to evaluate the system's reliability with regard to membrane failures and reduced dialysate flow, filter membrane integrity was verified weekly using a pressure holding test and dialysate flow was measured under routine clinical conditions. No membrane failures occurred, and dialysate flow was maintained at 511 ± 17 ml/min (n=70) during the test period. In conclusion: dialysate filtration is an effective and practical method for prevention of pyrogenic reactions due to high levels of bacteria and endotoxins.