Dialysis is a treatment for kidney failure that removes waste and extra fluid from the blood, using a filter. In hemodialysis (HD), the filter is a plastic tube filled with millions of hollow fibers, called a dialyzer.
The following is an edited reprint of information compiled and created by the National Kidney and Urologic Diseases Information Clearinghouse, a service of the National Institute of Health.
Hemodialysis uses a special filter called a dialyzer that functions as an artificial kidney to clean your blood. The dialyzer is a canister connected to the hemodialysis machine.
During treatment, your blood travels through tubes into the dialyzer, which filters out wastes, extra salt, and extra water.Then the cleaned blood flows through another set of tubes back into your body. The hemodialysis machine monitors blood flow and removes wastes from the dialyzer.
Several months before your first hemodialysis treatment, an access to your bloodstream will need to be created. You may need to stay overnight in the hospital, but many patients have their access created on an outpatient basis. This access provides an efficient way for blood to be carried from your body to the dialyzer and back without causing discomfort. The two main types of access are a dialysis fistula and a graft.
- A surgeon makes a fistula by using your own blood vessels; an artery is connected directly to a vein, usually in your forearm. The increased blood flow makes the vein grow larger and stronger so it can be used for repeated needle insertions. This kind of access is the preferred type. It may take several weeks to be ready for use.
- A graft connects an artery to a vein by using a synthetic tube. It doesn’t need to develop as a fistula does, so it can be used sooner after placement. But a graft is more likely to have problems with infection and clotting.
Before dialysis, needles are placed into the access to draw out the blood.
If your kidney disease has progressed quickly, you may not have time to get a permanent vascular access before you start hemodialysis treatments. You may need to use a catheter—a small, soft tube inserted into a vein in your neck, chest, or leg near the groin—as a temporary access. Some people use a catheter for long-term access as well. Catheters that will be needed for more than about 3 weeks are designed to be placed under the skin to increase comfort and reduce complications.