Urea and water balance during peritoneal dialysis of patients with renal failure

The total body water and its equilibration with dialysis liquid during peritoneal dialysis of 3 patients with renal failure was determined by means of isotope dilution analysis with 2H2O. Under the conditions of the therapeutic treatment, water exchange between the two compartments was 30 to 40 percent; decrease of the body weight of the patients corresponded to their loss of water. From the isotope dilution of 15N-urea, the total amount of urea in the body of 2 patients was calculated; the volume, in which it was dissolved, proved to be identical with the total body water. The decrease of the specific activity of the urea during dialysis yielded the de novo-synthesis of this metabolite; the equilibration rate of urea between body water and dialysis liquid was about half of that of water. The results can be described by a kinetic model based on gradient elution and diffusion; the experiments aim toward improvement of the efficiency of peritoneal dialysis