Dialysis removes from the blood waste products and excess water, which are retained in people with kidney failure. It can be a temporary treatment for acute kidney failure or a long-term measure used in end-stage kidney failure. There are two forms: peritoneal dialysis, in which the peritoneal membrane in the abdomen is used as a filter; and haemodialysis, in which a kidney machine filters the blood.
How dialysis works
During dialysis, excess water and waste products from the blood pass across a membrane into a solution (the dialysate), which is then discarded.
In peritoneal dialysis, the peritoneum, the membrane that surrounds the abdominal organs, is used instead of the kidneys to filter the blood. A procedure called an exchange is carried out four times a day at home. During an exchange, dialysis fluid that was infused into the abdomen 4–6 hours earlier is drained out of the peritoneum through a catheter in the abdominal wall. The fluid is replaced with fresh solution, then the equipment is disconnected and you can carry out normal activities. Between exchanges, wastes and excess water pass from the peritoneal blood vessels into the dialysis fluid.
Using the peritoneum as a filter
The abdominal organs are covered by the peritoneal membrane, which is rich in blood vessels. In peritoneal dialysis, waste products and water pass from the blood across the membrane and into dialysate fluid in the abdomen.
Undergoing peritoneal dialysis
In peritoneal dialysis, dialysis fluid is changed at regular intervals and is continually present in the abdomen. Once a fluid exchange has taken place, the bags and tubing are detached, and you can move freely.
In haemodialysis, blood is pumped by a kidney machine through a filter attached to the side of the machine. Inside the filter, blood flows on one side of a membrane and dialysis fluid flows on the other. Waste products and water pass from the blood across the membrane and into the dialysate fluid, and the filtered blood returns to the body. Each treatment takes 3–4 hours and is usually repeated three times a week.
During haemodialysis, you are attached to the kidney machine for several hours while waste products and water are removed from your blood. Haemodialysis is usually carried out in outpatient dialysis centres, but some people are able to treat themselves at home.
Access to the bloodstream
Dialysis requires fast blood flow. A vein and an artery near the skin surface are surgically joined so that the vein carries blood at high pressure. This vein can then be used for access to the circulatory system.
From the 2010 revision of the Complete Home Medical Guide ©