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.