Bidirectional peritoneal transport of albumin in continuous ambulatory peritoneal dialysis.

The present study was undertaken in order to assess bidirectional peritoneal 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 continuous ambulatory peritoneal dialysis (CAPD). The plasma volume, intravascular albumin mass (IVM), and overall extravasation rate of albumin were not significantly different from that found in healthy controls. Albumin flux from the plasma into the peritoneal cavity was 3.71 +/- 0.82 (SD) mumol/h, which was only 3% of the overall extravasation rate (137 +/- 52 mumol/h). Albumin flux from the peritoneal cavity into the plasma was substantially lower (0.22 +/- 0.07 mumol/h, P < 0.01). The net peritoneal accumulation of the albumin from plasma over 4 h was 14 +/- 3.2 mumol, which was significantly lower than the intraperitoneal albumin mass at the end of the dialysis (54 +/- 19 mumol, P < 0.01). This indicates that only about 25% of the albumin loss during CAPD occurs directly from the plasma. The initial osmotic net filtration was 508 +/- 302 ml. The volume flow equivalent to the albumin flux was 6.3 +/- 1.5 ml/h into the peritoneal cavity and 7.8 +/- 1.9 ml/h back into the plasma. Although minor, as compared to the osmotic net filtration (508 ml), the albumin flux equivalent volume (31.2 ml) exceeded the steady state filtration (25.2 ml) significantly (P < 0.01) during the 4 h investigation. In conclusion, albumin flux into the peritoneal cavity is small compared to the overall extravasation rate, but our results suggest that CAPD loss of albumin predominantly occurs from the subperitoneal interstitial space and only to a minor degree directly from the plasma. Albumin flux equivalent volume flow is relatively small and most probably represents peritoneal lymph drainage.