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

Objective: To evaluate the peritoneal clearance of middle molecules in comp arison with the peritoneal clearance of small molecules in incremental peri toneal dialysis (PD). Study Design: Peritoneal clearances of creatinine and beta (2)-microgloblul in (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 r egimen, such as in the number of exchanges and the duration of the dwell ti me. 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/w eek with 2 exchanges over 12 hours per day, to 9.5 +/-4.4 L/week with the s ame 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, peri toneal clearance of middle molecules, such as B2M, depended mainly on the t otal dwell hours of PD and not on the number of exchanges of peritoneal dia lysate 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.