High‐Flux Dialyzers, Backfiltration, and Dialysis Fluid Quality

Abstract

Currently, high-flux hemodialysis is the most common mode of dialysis therapy worldwide. Its steadily increasing use is largely based on the desire to reduce the excessively high morbidity and mortality of end-stage renal disease patients maintained on conventional dialysis (low-flux, mostly cellulosic membranes) by offering better biocompatibility and enhanced removal of uremic toxins. Two large randomized trials suggest a survival benefit for selected subgroups of high-flux dialysis patients such as diabetics, patients with hypoalbuminemia, or patients who have been on dialysis for a long period (>3.7 years). The major disadvantage of high-flux hemodialysis relates to the use of dialysis fluid, which is commonly not pure and may endanger patients treated with high-flux hemodialysis. Endotoxin fragments and other bacterial substances derived from bacteriologically contaminated dialysis fluid may, even at bacterial counts or endotoxin concentrations within the limits of accepted standards of dialysis fluid purity, enter from the dialysate into the patient's blood either by convective transfer (backfiltration) or by movement down the concentration gradient (backdiffusion). Repeated exposure of high-flux hemodialysis patients to backtransport of dialysate contaminants aggravates the uremia-associated inflammatory response syndrome and contributes to long-term morbidity. At present, the only solution to circumvent the risks of backtransport is the use of dry powder cartridges for bicarbonate concentrate and the use of bacteria- and endotoxin-retentive filters for the online production of ultrapure dialysis fluid. Use of ultrapure dialysis fluid (bacteria <0.1 CFU/ml and endotoxin <0.03 IU/ml) has been found to reduce inflammation and comorbidities in clinical investigations compared to commercial dialysis fluid. The European Renal Association and a number of national societies in Europe or in Japan strongly recommend the use of ultrapure dialysis for high-flux hemodialysis.