In peritoneal dialysis a part of the peritoneum is used as a dialyser. Water and solutes are able to move from the blood side to the dialysate side through the peritoneal membrane, which is a very thin layer of skin that covers the intestines and the liver. About two litres of dialysis fluid are slowly infused into the abdominal cavity via a flexible silicone tube, called a catheter.
The catheter stays in place the entire time a patient is on peritoneal dialysis therapy. When dialysate is present in the peritoneal cavity, removal of waste products and excess water takes place until the concentrations of solutes on the blood side and the dialysate side are equilibrated. This movement of water and waste products takes place during the dwell time. After a certain dwell time, the infused dialysate is drained out again via the catheter. Peritoneal dialysis continues as the drained PD fluid is replaced with fresh PD fluid. This process of replacing the used PD fluid with fresh PD fluid is called an exchange. An exchange is repeated several times a day, usually 4-5 times.