Background: Macromolecules, when used as intraperitoneal volume markers, have the disadvantage of leaking into the surrounding tissue. Therefore, Cr-51-labeled erythrocytes were evaluated as markers of intraperitoneal volume and used in combination with I-125-labeled bovine serum albumin to study albumin transport into peritoneal tissues in a rat model of peritoneal dialysis (PD).

Methods: Single dwells of 20 mL of lactate-buffered filter-sterilized PD fluid at glucose concentrations of 0.5%, 2.5%, and 3.9% were performed for 1 or 4 hours. Tissue biopsies from abdominal muscle, diaphragm, liver, and intestine, and blood and dialysate samples, were analyzed for radioactivity.

Results: The dialysate distribution volume of labeled erythrocytes, measured after correction for lymphatic clearance to blood, was strongly correlated with, but constantly 3.3 mL larger than, drained volumes. Erythrocyte activity of rinsed peritoneal tissue biopsies corresponded to only 1 mL of dialysate, supporting our utilization of erythrocytes as markers of intraperitoneal volume. The difference between the distribution volumes of albumin and erythrocytes was analyzed to represent the albumin loss into the peritoneal tissues, which increased rapidly during the first few minutes of the dwell and then leveled out at 2.5 mL. It resumed when osmotic ultrafiltration turned into reabsorption and, at the end of the dwell, it was significantly lower for the highest osmolarity PD fluid (3.9% glucose). Biopsy data showed the lowest albumin accumulation and edema formation in abdominal muscle for the 3.9% fluid.

Conclusion: Labeled erythrocytes are acceptable markers of intraperitoneal volume and, combined with labeled albumin, provided novel kinetic data on albumin transport in peritoneal tissues.