A quantitative analysis of sodium transport and removal during peritoneal dialysis

To quantitatively evaluate peritoneal sodium transport, the diffusive mass transport coefficient (KBD) and sieving coefficient (S), as well as the mass of sodium transported by diffusion (DM), by convection (CM) and by fluid absorption (AM) and the total sodium mass removed (RM) were calculated during a series of single dwell studies in CAPD patients. A six-hour dwell study was performed in 68 patients using 2 liter of 1.36% (N = 13), 2.27% (N = 9) or 3.86% (N = 46) glucose dialysis fluid with 131I-albumin as the intraperitoneal volume marker. The patients in whom the 3.86% glucose dialysis fluid was applied were further divided into four transport groups according to a modified peritoneal equilibration test: high (H), high-average (H-A), low-average (L-A), and low (L) transport. There was no significant difference in KBD nor in S for sodium among different solutions. However, the removed sodium mass (RM) was significantly higher in the 3.86% (70.5 +/- 31.5 mmol) and 2.27% (36.0 +/- 21.0 mmol) solutions as compared to that of the 1.36% (-1.8 +/- 26 mmol) solution mainly due to increased both CM and DM. In general, CM was twice as high as DM. AM substantially decreased sodium removal. Among the different transport groups, the KBD and S values for sodium were significantly higher in the H group as compared to the other transport groups (both P < 0.05). However, RM was significantly lower in the H group mainly due to higher AM. Using a 3.86% glucose solution, the D/P for sodium was found to be significantly different (but only after 120 min of the dwell) between all the different transport groups. In conclusion, sodium removal in CAPD is strongly related to the fluid removal. The ultrafiltration induced convective transport (CM) and peritoneal absorption of sodium (AM) were of similar magnitude and were twice as high as the diffusive transport (DM) and both play an important role in the peritoneal sodium balance. A D/P for sodium using the 3.86% glucose solution, especially at the end of the dwell, can be used to discriminate between different transport categories of patients. High transport patients have a poor fluid and sodium removal that are likely to affect their clinical outcome.