Bimodal dialysis: theoretical and computational investigations of adequacy indices for combined use of peritoneal dialysis and hemodialysis.

A theoretically correct method for evaluating the adequacy of bimodal dialysis (BMD), a combination of peritoneal dialysis (PD) and hemodialysis (HD) in the same patient, is lacking. We therefore performed computer simulations using a variable-volume, two-compartment urea kinetic model for 1-week treatments with 1) HD with three sessions, HD3, 2) continuous ambulatory PD, CAPD, 3) 6 days of CAPD and 1 day with HD session, and 4) 5 days of CAPD and 2 days with HD. Four dialysis adequacy indices (KT/V, stdKT/V, fractional solute removal, FSR, and equivalent clearance, EKR) were analyzed using four different reference methods for normalization of urea amount and concentration: 1) peak value, 2) peak average value, 3) time average value, and 4) treatment time average value. The analyses show that a proposed simplified rule of adding one third of weekly FSR for HD3 for each dialysis session and one seventh of weekly FSR for CAPD for each PD day for prediction of weekly FSR for BMD provides a fair prediction, although some corrections may be necessary, depending on the chosen reference method. In particular, KT/V may be added using this rule. We conclude that theoretically correct adequacy indices for BMD may be defined and calculated by using numerical simulations.