PD (like haemodialysis) takes over some of the work that is normally done by the kidneys. It removes the waste products of food and it removes excess water from the body. It can also be used to give people various substances that they are lacking, such as calcium or bicarbonate.
PD and haemodialysis are equivalent techniques in terms of the amount of dialysis they can deliver (about 5% of the function of two normal kidneys). Both relieve the symptoms of kidney failure and both enable patients to go back to work.
How does PD work?
The basic principles of dialysis are the same for PD and haemodialysis. Briefly, both types of dialysis use a special liquid (called the dialysis fluid, dialysis solution or dialysate) and a membrane (called the dialysis membrane) to do some of the work of the kidneys. In PD, the dialysis membrane is the patient’s own peritoneum.
The peritoneum is a natural membrane that lines the inside of the abdominal wall and covers all the abdominal organs (the stomach, bowels, liver etc). The peritoneal membrane resembles a balloon in appearance and texture but has lots of extremely tiny holes in it. These holes allow the peritoneum to be used as a dialysis membrane. As blood flows through the blood vessels in the peritoneum, it flows past the holes. Although the holes are extremely tiny, water and toxins can easily pass through, but blood cells are too large. In this way, the peritoneum in PD works as a “natural filter”, performing the same function as the “artificial filter” used in haemodialysis.
The peritoneum has two layers one lining the inside of the abdominal wall, the other lining the abdominal organs. Between these two layers is a space. This space is called the peritoneal cavity. During PD it is the peritoneal cavity that is used as a reservoir for the dialysis fluid. Normally, the peritoneal cavity contains only about 100 ml of liquid. In fact, it can expand to hold up to five litres of liquid.