Fluid Kinetics in CAPD Patients during Dialysis with a Bicarbonate-Based Hypoosmolar Solution

Abstract

The magnitude of transcapillary backfïltration by the colloid-osmotic pressure within the peritoneal capillaries compared to the effective lymphatic absorption was investigated in continuous ambulatory peritoneal dialysis patients. This was done during a 4-hour dwell period, using a hypoosmolar dialysis fluid (280 mosm/kg H₂O) in 8 patients and compared to 5 of these patients using a 1.36% glucose (GS; 324 mosm/kg H₂O). The low molecular weight solute transport did not differ between the two solutions. The intraperitoneal dextran 70 concentration increased during the dwell with the hypoosmolar dialysis fluid (from 770 to 945 mg/l; p = 0.000002) and decreased with the GS (from 859 to 719 mg/l; p = 0.007). With the GS the transcapillary ultrafiltration was directed towards the abdominal cavity during the dwell period. With the hypoosmolar fluid, the transcapillary ultrafiltration was continuously directed towards the circulation. In this solution, the magnitude of transcapillary backfiltration due to colloid-osmotic pressure within the peritoneal capillaries was 0.4 ± 0.1 ml/min. In conclusion, intraperitoneal markers can be used in continuous ambulatory peritoneal dialysis patients for determination of effective lymphatic absorption and transcapillary fluid passage in both transport directions.

Measuring Peritoneal Absorption with the Prolonged Peritoneal Equilibration Test from 4 to 8 Hours Using Various Glucose Concentrations

“…The correlations between the 4-and 8-hour peritoneal absorption measurements and the solute transport parameters were stronger than those with peritoneal UF (Table 2). That finding accords with results of previous studies on peritoneal absorption, which suggested that back-filtration is the main component of absorption (9,(30)(31)(32); for other authors, lymphatic uptake prevailed (2,14,17). However, the relationship between peritoneal absorption and small-solute transport was not found in other studies (25,33,34).…”

“…The use of macromolecular markers in PD is based on dilution measures to calculate the peritoneal volume and on the clearance rate of the (2,6,14,17). The finding that the fluid absorption rate from the 4th to the 6th hour and the clearance rate of the marker, RISA, were similar, with a positive correlation, suggests that K E and the fluid absorption rate reflect lymphatic absorption (13).…”

The Effective Lymphatic Absorption Rate is an Accurate and Useful Concept in the Physiology of Peritoneal Dialysis

“…For instance, in the study by Daugirdas et al , 24% of the administered fluid volume, but only 17% of IP administered RISA, had disappeared at the end of the dialysis dwell (1). Also, the effluent dextran 70 concentration increased progressively during a 4-hour dwell when dialysate without an osmotic agent was employed, illustrating transcapillary back filtration of water but not of macromolecules (15). An average value of 0.4 mL/min could be calculated for back filtration.…”

The contribution of free water transport and small pore transport to the total fluid removal in peritoneal dialysis

“…The changes in the in situ intraperitoneal volume during the dwell were calculated by means of dextran dilution after correction for incomplete recovery [11,19,20]. Net ultrafiltration is the difference between the in situ intraperitoneal volume and the initial intraperitoneal volume.…”