Impact of increasing haemodialysis frequency versus haemodialysis duration on removal of urea and guanidino compounds: a kinetic analysis

Methods. This study was based on two-compartmental kinetic data obtained in stable haemodialysis patients (n = 7) for urea, creatinine (CREA), guanidinosuccinic acid (GSA) and methylguanidine (MG). For each individual patient, mathematical simulations were performed for different dialysis schedules, varying in frequency, duration and intensity. For each dialysis schedule, plasmatic and extraplasmatic weekly time-averaged concentrations (TAC) were calculated, as well as their %difference to weekly TAC of the reference dialysis schedule (three times weekly 4 h). Results. Increasing dialysis duration was most beneficial for CREA and MG, which are distributed in a larger volume (54.0 +/- 5.9 L and 102.6 +/- 33.9 L) than urea (42.7 +/- 6.0 L) [plasmatic weekly TAC decrease of 31.5 +/- 3.2% and 31.8 +/- 3.8% for CREA and MG with Q(B) of 200 mL/min, compared to 25.7 +/- 3.2% for urea (P = 0.001 and P < 0.001)]. Increasing dialysis frequency resulted only in a limited increase in efficiency, most pronounced for solutes distributed in a small volume like GSA (30.6 +/- 4.2 L). Increasing both duration and frequency results in weekly TAC decreases of > 65% for all solutes. Comparable results were found in the extraplasmatic compartment. Conclusion. Prolonged dialysis significantly reduces solute concentration levels, especially for those solutes that are distributed in a larger volume. Increasing both dialysis frequency and duration is the superior dialysis schedule.