Dissociation between clearances of small and middle molecules in incremental peritoneal dialysis.

¨ Objective: To evaluate the peritoneal clearance of middle molecules in comparison with the peritoneal clearance of small molecules in incremental peritoneal dialysis (PD). ¨ Study Design: Peritoneal clearances of creatinine and b 2 -microgloblulin (B2M) were compared in 57 continuous ambulatory PD patients on full dose of 4 exchanges, and 54 incremental PD patients with 2 or 3 exchanges over 24 hours. Clearances were also compared when there were changes in the PD regimen, such as in the number of exchanges and the duration of the dwell time. ¨ Setting: Tertiary-care university hospital. ¨ Results: Peritoneal creatinine clearance increased almost linearly with the increase in the number of exchanges. In contrast, peritoneal clearance of B2M was 9.1 ± 3.6 L/week, 8.8 ± 4.4 L/week, and 7.9 ± 2.5 L/week with 2, 3, and 4 exchanges, respectively, per day, amounts that were not different from each other. Peritoneal clearance of B2M did not change when there was an increase in the number of dialysate exchanges from 2 to 3 and from 3 to 4 over a period of 24 hours; whereas the peritoneal clearance of creatinine increased. Peritoneal clearance of B2M almost doubled, from 5.4 ± 2.7 L/week with 2 exchanges over 12 hours per day, to 9.5 ± 4.4 L/week with the same 2 exchanges over 24 hours. The creatinine clearance did not change. ¨ Conclusion: In contrast to peritoneal clearance of small molecules, such as creatinine, which was dependent on the number of dialysate exchanges, peritoneal clearance of middle molecules, such as B2M, depended mainly on the total dwell hours of PD and not on the number of exchanges of peritoneal dialysate in incremental PD. This might be another advantage of incremental PD, since peritoneal clearance of middle molecules in incremental PD over 24 hours can be comparable to that in full dose PD.