Peritoneal transport characteristics with glycerol-based dialysate in peritoneal dialysis

* Background: Glycerol is a low molecular weight solute (MW 92 D) that can be used as an osmotic agent in continuous ambulatory peritoneal dialysis (C APD). Due to its low molecular weight, the osmotic gradient disappears rapi dly. Despite the higher osmolality at the beginning of a dwell, ultrafiltra tion has been found to be lower for glycerol compared to glucose (MW 180 D) when equimolar concentrations are used. Previous studies have shown glycer ol to be safe for long-term use, but some discrepancies have been reported in small solute transport and protein loss. * Objective: To assess permeability characteristics for a 1.4% glycerol dia lysis solution compared to 1.36% glucose. * Design: Two standardized peritoneal permeability analyses (SPA), one usin g 1.4% glycerol and the other using 1.36% glucose, in random order, were pe rformed within a span of 2 weeks in 10 stable CAPD patients. The length of the study dwell was 4 hours. Fluid kinetics and solute transport were calcu lated and signs of cell damage were compared for the two solutions. * Setting: Peritoneal dialysis unit in the Academic Medical Center, Amsterd am. * Results: Median values for the 1.4% glycerol SPA were as follows: net ult rafiltration 251 mt, which was higher than that for 1.36% glucose (12 mt, p < 0.01); transcapillary ultrafiltration rate 2.12 mt/min, which was higher than that for glucose (1.52 mL/min, p = 0.01); and effective lymphatic abs orption rate 1.01 mt/min, which was not different from the glucose-based so lution. Calculation of peritoneal reflection coefficients for glycerol and glucose showed lower values for glycerol compared to glucose (0.03 vs 0.04, calculated with both the convection and the diffusion models). A marked di p in dialysate-to-plasma ratio for sodium was seen in the 1.4% glycerol exc hange, suggesting uncoupled water transport through water channels. Mass tr ansfer area coefficients for urea, creatinine, and urate were similar for b oth solutions. Also, clearances of the macromolecules <beta>(2)-microglobul in, albumin, IgG, and alpha (2)-macroglobulin were not different for the tw o osmotic agents. The median absorption was higher for glycerol, 71% compar ed to 49% for glucose (p < 0.01), as could be expected from the lower molec ular weight. The use of a 1.4% glycerol solution during a 4-hour dwell caus ed a small but significant median rise in plasma glycerol, from 0.22 mmol/L to 0.45 mmol/L (p = 0.02). Dialysate cancer antigen 125 and lactate dehydr ogenase (LDH) concentrations during the dwell were not different for both s olutions. * Conclusions: These findings show that glycerol is an effective osmotic ag ent that can replace glucose in short dwells and show no acute mesothelial damage. The higher net ultrafiltration obtained with 1.4% glycerol can be e xplained by the higher initial net osmotic pressure gradient. This was seen especially in the first hour of the dwell. Thereafter, the osmotic gradien t diminished as a result of absorption. The dip in dialysate-to-plasma rati o for sodium seen in the glycerol dwell can also be explained by this high initial osmotic pressure gradient, implying that the effect of glycerol as an osmotic agent is more dependent on intact water channels than is glucose .