What is good about PD + HD combined therapy.

It is known that β(2) -microglobulin (β(2) -MG) concentration in peritoneal dialysis (PD) patients is inversely correlated to the residual renal function (RRF). With decreasing RRF, some PD patients may necessarily be treated with hemodialysis (HD) once a week, not only for removing excess water and small solutes, but also for removing much larger solutes such as β(2) -MG. In this study, a kinetic model allowed us to show what is good about PD + HD combined therapy in long-term PD patients. A mathematical model was established based on a classic compartment theory for clinical use. Model validations were made by comparing calculated results with clinical data in order to specify what was good about PD + HD combined therapy (5-day PD + 1-HD/week). Time-averaged concentration (TAC) for urea and creatinine decreased by 20% on the average by introducing PD+HD combined therapy no matter which dialyzers were used. TAC for β(2) -MG in PD+HD combined therapy, however, was strongly dependent upon the dialyzer clearance, and when a low flux dialyzer (clearance for β(2) -MG = 10 mL/min under Q(B)  = 200, Q(D)  = 500 mL/min) was used, pre-dialysis β(2) -MG concentration may increase. Use of super high-flux dialyzers (clearance for β(2) -MG = 60 mL/min under the same conditions) should greatly reduce the β(2) -MG concentration from 30 to 8 mg/L in 4-hr treatment. Then, when PD+HD combined therapy is introduced to a PD patient with diminishing RRF, use of super high-flux dialyzers may be strongly recommended in order not to increase concentrations of pre-dialysis β(2) -MG and/or even greater solutes. Use of super high-flux dialyzers is a key to the success of PD+HD combined therapy that could prevent concentrations of large solutes from increasing.