PERITONEAL TRANSPORT CHARACTERISTICS WITH GLUCOSE POLYMER-BASED DIALYSATE

Dialysate fluids containing glucose polymers as osmotic agent are diff erent from the conventional solutions, because they are iso-osmotic to plasma and produce transcapillary ultrafiltration (TCUF) by colloid o smosis. To investigate the effects on fluid and solute kinetics, a com parison was made between a 7.5% glucose polymer based dialysate (icode xtrin) and 1.36% and 3.86% glucose based dialysate in 10 stable CAPD p atients. In each patient three standard peritoneal permeability analys es (SPA) were done with the osmotic agents and concentrations mentione d above. Dextran 70 was added to the glucose solutions to calculate fl uid kinetics. In the glucose polymer SPAs fluid kinetics were calculat ed from the dilution and disappearance of dextrin. The TCUF rate with icodextrin was closer to that obtained with 3.86% glucose than to 1.36 % glucose. Extrapolation of the fluid profiles revealed sustained ultr afiltration with icodextrin. TCUF increased linearly in time in the ic odextrin tests, whereas a hyperbola best described the glucose profile s. The effective lymphatic absorption rate with icodextrin was similar to the glucose based solutions. Mass transfer area coefficients of lo w molecular weight solutes with icodextrin were also similar to the va lues obtained with glucose, as was D/P creatinine. A positive correlat ion was present between the MTAC creatinine and the TCUF rate with ico dextrin (r = 0.66, P = 0.05), which was absent in the glucose SPAs. Th is suggests that in patients with a larger effective peritoneal surfac e area, more ultrafiltration can be achieved by glucose polymer soluti ons. Clearances of beta 2-microglobulin (beta(2)m) were higher with ic odextrin than with 3.86% glucose and 1.36% glucose dialysate (P < 0.05 ). No differences were found for the larger serum proteins albumin, Ig G and alpha 2-macroglobulin. Initial D/P-Na(+) was higher (0.96) with icodextrin than with the glucose based solutions (0.92), due to the hi gher Na+ concentration of icodextrin, and it remained unchanged during the dwell. In contrast, D/P-Na(+) of 1.36% glucose increased during t he dwell, whereas D/P-Na(+) decreased with 3.86% glucose until 60 minu tes, followed by a subsequent increase. The ultrafiltration coefficien t (UFC) of the total peritoneal membrane was assessed using 3.86% gluc ose (0.18 +/- 0.04 ml/min/mm Hg), and the UFC of the small pores was a ssessed using icodextrin (0.06 + 0.008 ml/min/mm Hg). The difference b etween these represented the UFC through the transcellular pores, whic h averaged 50.5% of the total UFC, but with a very wide range (0 to 85 %). An inverse relation existed between the duration of CAPD treatment and the total ultrafiltration coefficient (r = -0.68, P < 0.04), whic h could be attributed to a lower UFC of the transcellular pores in lon g-term patients (r = -0.66, P < 0.05), but not to the UFC of the small pores (r = -0.48, NS). The TCUFR(0-60 min) through the transcellular pores correlated with the sodium gradient, corrected for diffusion, in the first hour of the dwell (r = 0.69, P < 0.04), indicating that bot h parameters indeed measure transcellular water transport. It can be c oncluded that the glucose polymer solution induced sustained ultrafilt ration and had no effect on peritoneal membrane characteristics. In ad dition, the results of the present study support the hypothesis that t he glucose polymer solutions exerts its osmotic pressure across interc ellular pores with radii of about 40 Angstrom. This leads to increased clearances of low molecular weight proteins such as beta(2)m that are transported through these pores without sieving of Na+. The latter, a s found during 3.86% glucose dialysate, is probably caused by transcel lular water transport. The transcellular water transport accounted for 50% of the total ultrafiltration with glucose based dialysis solution s. It was lower in long-term CAPD patients.