For these patients, kidney function may be replaced by one of two methods of treatment - either peritoneal dialysis or hemodialysis. Both peritoneal dialysis and hemodialysis are based on the same principles. The first principle, osmosis, is the tendency of water to move from a low concentration of particulates to a higher concentration. And the second is diffusion - the tendency of particles to distribute themselves evenly throughout a solution. Together, osmosis and diffusion comprise dialysis.
Blood cells are too large to pass across the semipermeable membrane used in dialysis.
However water, naturally occurring body chemicals, and certain impurities will be transported, depending on the composition of the solution on the side of the membrane opposite the blood. This solution is known as dialysate. For some ESRD patients, the treatment of choice is peritoneal dialysis, which uses as the dialyzing membrane the lining of the person's abdomen. In peritoneal dialysis, dialysate enters the body through a special tube inserted into the abdomen. Excess water, wastes and chemicals pass from very small blood vessels, across the peritoneal membrane and into the dialysate.