title: Removal of water-soluble and protein-bound solutes with reversed mid-dilution versus post-dilution haemodiafiltration.
abstract: BACKGROUND
  Convective dialysis strategies are superior in the removal of protein-bound uraemic retention solutes. Mid-dilution and mixed-dilution haemodiafiltration (HDF), both combining pre-dilution and post-dilution, are promising options to further improve removal capacity and have been shown of additional benefit for large middle molecules. In this study, we compared the removal of small water-soluble and protein-bound solutes in post-dilution versus mid-dilution HDF.
  
  
  METHODS
  Fourteen chronic haemodialysis (HD) patients were included in this crossover study. Patients were kept for 4 weeks on high-flux HD. On the mid-week session of Weeks 3 and 4, either post-dilution or reversed mid-dilution HDF were applied, in random order. Blood and dialysate flows were maintained at 300 and 800 mL/min, while the substitution flow was 75 mL/min in post-dilution and 150 mL/min in mid-dilution HDF. Based on the data collected during the sessions under study, extraction ratio (ER) and reduction ratio (RR) of small water-soluble and protein-bound solutes were calculated, as well as total solute removal (TSR) based on spent dialysate.
  
  
  RESULTS
  No differences were observed for TSR, ER and RR for protein-bound solutes. For small water-soluble solutes, ER in post-dilution HDF was significantly higher than in mid-dilution HDF: 0.92 ± 0.02 versus 0.87 ± 0.04 for urea (P < 0.001), 0.92 ± 0.02 versus 0.88 ± 0.02 for creatinine (P < 0.001) and 0.84 ± 0.02 versus 0.82 ± 0.03 for uric acid (P = 0.009). TSR and RR were, however, not different due to the lower inlet concentrations with post-dilution HDF.
  
  
  CONCLUSIONS
  TSR of mid-dilution and post-dilution HDF was not different for both small water-soluble and protein-bound compounds. Both strategies in the setting as applied in this study are as adequate for the removal of these solutes.
authors.affiliation: Nephrology Section, Department of Internal Medicine, Ghent University Hospital, Gent, Belgium.61sunny.eloot@ugent.be
authors.forename: Sunny
authors.initials: S
authors.lastname: Eloot
authors.forename: Annemieke
authors.initials: A
authors.lastname: Dhondt
authors.forename: Mieke
authors.initials: M
authors.lastname: Van Landschoot
authors.forename: Marie-Anne
authors.initials: MA
authors.lastname: Waterloos
authors.forename: Raymond
authors.initials: R
authors.lastname: Vanholder
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D018592:Cross-Over Studies; D005260:Female; D017583:Hemodiafiltration / Q000379:methods*; D015312:Hemodialysis Solutions; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011485:Protein Binding; D012995:Solubility; D014118:Toxins, Biological / Q000302:isolation & purification; D014511:Uremia / Q000378:metabolism / Q000628:therapy*; D014867:Water
chemical_list: D015312:Hemodialysis Solutions; D014118:Toxins, Biological; C026865:uremia middle molecule toxins; D014867:Water