Bidirectional peritoneal transport of albumin in continuous ambulatory peritoneal dialysis

The present study was undertaken in order to assess bidirectionalperitoneal kinetics of albumin after simultaneous i.v. and i.p.injection of radioiodinated albumin tracers (¹²⁵I-RISA and ¹³¹I-RISA)in eight clinically stable uraemic patients undergoing continuousambulatory peritoneal dialysis (CAPD). The plasma volume, intravascularalbumin mass (IVM), and overall extravasation rate of albuminwere not significantly different from that found in healthycontrols. Albumin flux from the plasma into the peritoneal cavitywas 3.71 ± 0.82 (SD) µmol/h, which was only 3%of the overall extravasation rate (137 ± 52 µmol/h).Albumin flux from the peritoneal cavity into the plasma wassubstantially lower (0.22 ± 0.07 µmol/h, P<0.01).The net peritoneal accumulation of the albumin from plasma over4 h was 14 ± 3.2 µmol, which was significantlylower than the intraperitoneal albumin mass at the end of thedialysis (54 ± 19 µmol, P<0.01). This indicatesthat only about 25% of the albumin loss during CAPD occurs directlyfrom the plasma. The initial osmotic net filtration was 508± 302 ml. The volume flow equivalent to the albumin fluxwas 6.3 ± 1.5ml/h into the peritoneal cavity and 7.8± 1.9ml/h back into the plasma. Although minor, as comparedto the osmotic net filtration (508 ml), the albumin flux equivalentvolume (31.2 ml) exceeded the steady state filtration (25.2ml) significantly (P<0.01) during the 4 h investigation. In conclusion, albumin flux into the peritoneal cavity is smallcompared to the overall extravasation rate, but our resultssuggest that CAPD loss of albumin predominantly occurs fromthe subperitoneal interstitial space and only to a minor degreedirectly from the plasma. Albumin flux equivalent volume flowis relatively small and most probably represents peritoneallymph drainage.