Mid-dilution on-line haemodiafiltration in a standard dialyser configuration

Background. Mid-dilution haemodiafiltration (HDF) results in an improved middle molecule removal compared with standard HDF. The OLpūr™ MD 190 haemodiafilter represents a new dialyser design exclusively for mid-dilution on-line HDF. Compared with standard haemodialysers, structural changes in the headers allow the infusion of high replacement fluid volumes after a first post-dilution and before a second pre-dilution stage. Methods. We compared in vitro the new device [blood flow (QB) 400 ml/min, substitution flow (QS) 100 and 200 ml/min, dialysate flow (QD) 800 ml/min] with a conventional high-flux dialyser of the same surface area in haemodialysis (HD) (QD 500 ml/min) and post-dilution HDF (at QS 60, QD = 500 ml/min and at QS 100, QD = 800 ml/min) modes. Subsequently, we performed an initial clinical application of the new device in six mid-dilution HDF treatments of five end-stage renal disease patients (QB 400 ml/min, QS 200 ml/min, QD 800 ml/min, treatment duration 205±23 min). Results.In vitro urea and β2-microglobulin clearances in mid-dilution HDF were, respectively, 309.2±5.5 and 144.4±15.2 ml/min (QS 100) and 321.6±4.1 and 204.9±4.1 ml/min (QS 200), compared with 278.6± 17.2 and 94.0±7.6 ml/min in HD, and 310.8±10.2 and 123.0±6.5 ml/min (QS 60) and 323.6±11.2 and 158.0±10.3 ml/min (QS 100) in post-dilution HDF. The in vivo trials showed the clinical utility of the device and confirmed the in vitro data: urea and β2-microglobulin clearances were, respectively, 324.6± 10.9 and 207.9±29.3 ml/min, while reduction ratios were 75.0±5.5 and 83.6±4.7%. Conclusion. Our preliminary results need confirmation in a prospective cross-over study. However, the Nephros MD 190 haemodiafilter promises to be a true technological step ahead in terms of improved β2-microglobulin removal.