What is Peritoneal Dialysis?
Peritoneal dialysis (PD) is an alternative treatment to haemo-dialysis. A special sterile fluid is introduced into the abdomen through a permanent tube that is placed in the peritoneal cavity. The fluid circulates through abdomen to draw impurities from surrounding blood vessels in the peritoneum, which is then drained from the body.
PD can be carried out at home, at work, or on trips, but requires careful supervision. PD gives patients more control. However, they need to work closely with the health care team including the nephrologist, dialysis nurse, dialysis technician, dietitian and social worker. The role of the PD patient and his/her family are very important. By learning more about the treatment, patients can work with the health care team to achieve the best possible results and lead an active life.
How does it work?The walls of the abdominal cavity are lined with a membrane called the peritoneum, which allows waste products and extra fluid to pass from your blood into the dialysis solution. In PD, a soft tube called a catheter is used to fill the abdomen with a cleansing liquid called dialysis solution. The solution contains a type of sugar called dextrose that will pull waste and extra fluid into the abdominal cavity, will be exuded out of the body when the dialysis solution is drained. The used solution will be thrown away.
The process of draining and filling is called an exchange and takes about 30 to 40 minutes. The period when the dialysis solution is in the abdomen is called the dwell time. A typical schedule calls for four exchanges a day, each with a dwell time of 4 to 6 hours. Different types of PD have different schedules of daily exchanges.
Types of PDThere are two types of Peritoneal Dialysis:
Continuous Ambulatory Peritoneal Dialysis (CAPD)
Unlike Haemodialysis, patients do not need a machine for CAPD. They need gravity to fill and empty their abdomen. The doctor will prescribe the number of exchanges a patient needs, typically three or four exchanges during the day and one evening exchange with a long overnight dwell time while one sleeps. As the word "ambulatory" suggests, the patient can walk around with the dialysis solution in the abdomen.
Automated Peritoneal Dialysis (APD)
An alternative to CAPD is Automated Peritoneal Dialysis (APD) where a machine called a cycler will change the dialysate solution during the night, usually while patients are asleep. This means that patients have to be attached to the machine for 8-10 hours.
Benefits of APDAPD is suggested to offer a number of unproven psychosocial benefits over CAPD. It relates directly to fewer connections and allows patient to lead a normal lifestyle during the day, particularly for workers, school pupils and those taking care of the elderly or debilitated patients. Additional benefits include the absence of fluid during the day, which possibly reduces back pain and body image difficulties. Performing APD at night in the supine position also results in reduced intra-abdominal pressures as compared with the upright position in CAPD.
APD is designed to be simple and is often performed in the bedroom. The machines are user-friendly. Before going to sleep, the machine needs to be loaded with fluid. It will then perform a number of cycles throughout the night. The fluid is drained away into a large drainage bag for disposal. Often, the machine will provide a last fill of fluid, which stays inside the tummy until the following night when it is drained away.
Peritoneal dialysis units worldwide are increasingly adopting APD. It is estimated that one quarter of the world's peritoneal dialysis patients are now on APD. The use of cyclers in North America has increased from 10% in 1990 to 43% in 1997. 60% of patients treated with APD in North America also receive at least one exchange during the day. APD is more expensive than CAPD, but is usually cheaper than a transfer to in-centre Haemodialysis.
PD Effectiveness TestingTo see if the exchanges are removing enough waste products such as urea, several tests must be performed regularly. These tests are especially important during the first weeks of dialysis to determine whether the patient is receiving an adequate amount or dose of dialysis.
The peritoneal equilibration test measures how much sugar has been absorbed from a bag of infused dialysis solution and how much urea and creatinine have entered into the solution during the 4-hour exchange.
In the clearance test, samples of used solution drained over a 24-hour period are collected, and a blood sample is obtained during the day when the used solution is collected. The amount of urea in the used solution is compared with the amount in the blood to see how effective the PD schedule is in removing urea from the blood.
From the used solution, urine and blood measurements, the health care team can compute a urea clearance rate called Kt/V and a creatinine clearance rate. The residual clearance of the kidneys is also considered. These measurements will show whether the PD prescription is adequate. If the laboratory results show that the dialysis schedule is not removing enough urea and creatinine, the doctor can change the prescription.