Continuous ambulatory peritoneal dialysis, or CAPD, is a technique used to filter waste from the blood when the kidneys, which normally perform this function, are not working properly. It is an alternative to the procedure known as hemodialysis, where patients are connected to a machine which filters blood through an artificial membrane. This type of peritoneal dialysis allows more freedom because the filtering process takes place inside the body, using the peritoneum, a layer of tissue lining the abdominal cavity, as the dialysis membrane. This removes the need for attachment to a machine while dialysis is taking place and allows the person to carry out normal, daily activities.
In order for continuous ambulatory peritoneal dialysis to take place, minor surgery is required to insert a tube, called a peritoneal dialysis, or PD, catheter, into the space inside the abdomen, known as the peritoneal cavity. The operation site then has to heal fully before dialysis can begin. All the equipment needed for continuous peritoneal dialysis is stored in the patient's home, and the technique involves carrying out a simple, painless procedure about four times each day.
Part of the PD catheter, which is made of a soft material, protrudes from an opening in the skin of the abdomen, where it is taped in place and normally covered with a dressing. Inside the body, the catheter tube is anchored by special cuffs, which become fused with body tissues. The continuous ambulatory peritoneal dialysis procedure involves connecting a pair of bags to the end of the PD catheter, using a system of tubes and clamps. One bag contains fresh dialysis solution and the other is used to collect old solution which has been in the body for several hours.
The fresh dialysis solution contains glucose, which acts, by a force known as osmotic pressure, to draw water out of blood vessels through the peritoneum and into the solution in the peritoneal cavity. Waste products from the blood, which would normally be filtered out by a functioning kidney, also pass through the peritoneum into the dialysis solution. Normally, fresh dialysis fluid is left in the peritoneal cavity for between four and six hours before being drained into a waste bag. New solution is then added so the dialysis process is continuous.
It is important that strict hygiene practices are followed during continuous ambulatory peritoneal dialysis, because there is a risk of infection spreading from the catheter site into the peritoneal cavity. This causes a potentially serious illness known as peritonitis, which needs urgent treatment. Symptoms of peritonitis include pain in the abdomen, fever, and the waste dialysis fluid appearing cloudy. In most cases, treatment with antibiotics resolves the condition.