Abstract: Objective To observe the effect of mixed predilution and postdilution hemodiafiltration (mixed-HDF) on solute removal in maintenance hemodialysis (MHD) patients.  Methods  Ten MHD patients who met the inclusion and exclusion criteria were selected in this self-cross-control study. They were treated with conventional hemodialysis (HD) three times a week and HDF once a month. Each hemodialysis lasted 4 hours. HDF was performed in the order of predilution hemodiafiltration (pre-HDF), postdilution hemodiafiltration (post-HDF), and mixed-HDF. According to the distribution of pre-displacement fluid volume and post-displacement fluid volume, the mixed-HDF was divided into 2:1 mixed-HDF group, 1.5:1 mixed-HDF group and 1:1 mixed-HDF group. Blood samples before and after the treatment were collected to observe the changes of blood routine, blood urea nitrogen (BUN), serum creatinine (Scr), phosphorus (Phos), β2-microglobulin       (β2-MG) and parathyroid hormone (PTH) before and after the hemodialysis. Adverse reactions during treatment including blood pressure change, muscle spasm, and coagulation in dialyzer and extracorporeal circulation circuit were observed.  Results  The 10 MHD patients completed the 5 different modalities of HDF treatment. The BUN clearance rates of 2:1, 1.5:1, and 1:1 mixed-HDF had no significant differences with the BUN clearance rates of pre-HDF (t=-0.576, 1.150 and 0.215 respectively; P=0.290, 0.140 and 0.417 respectively) and post-HDF (t=-1.054, 0.243 and -1.168 respectively; P=0.161, 0.407 and 0.136 respectively). The Scr clearance rate was higher in 1:1 mixed-HDF than in 2:1 mixed-HDF (t=1.893, P=0.047). The clearance rate of Phos was significantly higher in 1:1 mixed-HDF than in pre-HDF (t=2.171, P=0.029), but had no significant differences as compared with the rates of 2:1 and 1.5:1 mixed-HDF with the rates of pre-HDF (t=1.677 and 1.734; P=0.064 and 0.058) and post-HDF (t=0.735 and 0.545; P=0.240 and 0.300). The clearance rate of β2-MG was significantly higher in 1.5:1 mixed-HDF than in post-HDF (t=3.314, P=0.005), but had no significant differences as compared the rates of 2:1 and 1:1 mixed-HDF with the rates of pre-HDF (t=1.218 and 0.879; P=0.127 and 0.201) and post-HDF (t=1.235 and 0.837; P=0.124 and 0.212). The clearance rate of PTH was higher in 1.5:1 mixed-HDF than in post-HDF (t=1.870, P=0.047), but had no significant differences as compared the rates of 2:1 and 1:1 mixed-HDF with the rates of pre-HDF (t=-0.672 and -0.833; P=0.259 and 0.213) and post-HDF (t=1.479 and 0.974; P=0.087 and 0.178).  Conclusion  Mixed-HDF has the ability of efficient clearance of small molecule solutes as well as medium and large molecule solutes. For clearance of small molecule solutes, mixed-HDF has the similar efficiency as pre-HDF and post-HDF; for clearance of medium and large molecule solutes, mixed-HDF has the efficiencies higher than pre-HDF and post-HDF.

Key words: Hemodiafiltration, Pre-dilution, Post-dilution, Mixed dilution