Use of the Disappearance Rate for the Estimation of Lymphatic Absorption during CAPD

Abstract

Several studies are discussed which investigated the usefulness of the disappearance rate of macromolecules from the peritoneal cavity for estimating convective fluid loss from the peritoneal cavity into the peritoneal lymphatic system. It is shown that dextrans are removed from the peritoneal cavity by a size-independent process at a mean rate of 1.37 ± 0.15 ml/min, whereas the clearance from blood to dialysate of dextrans is size-dependent. The fluid removal rate estimated by the difference in bidirectional transport of inulin (1.79 ± 0.38 ml/min; p < 0.0005) was of the same order of magnitude as has been found using the removal rate of macromolecules from the peritoneal cavity. Also, the role of local accumulation of macromolecules was studied during continuous administration of dextrans. No differences were found in the dextran disappearance rate before and after saturation of the peritoneal interstitium with dextran (1.1 ± 0.6 vs. 1.0 ± 0.4 ml/min). During a study using a hypoosmotic solution we calculated a net transcapillary backfiltration of fluid, whereas the dextran removal rate was in the same order of magnitude as found using commercially available dialysate. In our opinion, the disappearance rate of macromolecules is an estimate of convective fluid loss from the peritoneal cavity into the peritoneal lymphatic system.

Lymphatic Absorption in CAPD Patients with Loss of Ultrafiltration Capacity

“…The relative contribution of these two components of peritoneal absorptive flow (which both are considered to be bulk flows [19,27]) is controversial [6,7,[18][19][20]36], However, the simultaneous estimation of the peritoneal bulk absorptive flow (as estimated by Ke) and the direct lymphatic absorption (as estimated by KPP) may yield an approxi mate estimate of the order of magnitude of absorption into adjacent tissues (as absorp tion into tissue approximately should equal the difference between KP and KPP).…”

“…Thus, the interstitial adjacent tissues may serve as a reservoir for RISA from which it is slowly absorbed into local lymphatic ves sels [13,14,19,36]. A few investigators have claimed that this RISA absorption into local lymphatics should be included in the lym phatic term [6,7] and thus that the lymphatic flow should be equal to the tracer disappear ance rate [6,7]. This would assume that there is no tracer accumulation in the adjacent tis sues.…”

“…In additon, increased peritoneal absorp tion of fluid (together with macromolecular volume markers), sometimes interpreted as increased lymphatic absorption [1,4], has been observed in patients with loss of UFC [ 1,4], In fact, the disappearance rate of a macromolecular marker has commonly been as sumed to provide an estimate of the lymphat ic absorption rate in peritoneal dialysis pa tients [5][6][7]. However, several studies have shown that the plasma appearance rate of a macromolecular marker is on average only about 10-20% of its disappearance rate from the peritoneal dialysate (in clinically stable CAPD patients [8][9][10] as well as in animals [11][12][13][14][15]).…”

Standard Peritoneal Permeability Analysis in Children

“…Transcapillary ultrafiltration rate (TCUFR), effective lymphatic absorption rate (ELAR), and net ultrafiltration rate (NUFR) were calculated as described previously (4). Briefly, the ELAR can be calculated as the dextran disappearance rate in which all pathways of uptake into the lymphatic system, both subdiaphragmatic and interstitial, are included (19,20):…”