How does a kidney dialysis machine work?


A dialysis machine mimics some of the functions of a human kidney. A primary job of kidneys is to remove urea and certain salts from blood so they can exit the body in urine.

A dialysis machine removes blood from the patient and runs it through tubes made of a semi-porous membrane. On the outside of the tubes is a sterile solution made of water, sugars and other components. Certain substances including red blood cells, white blood cells and other important blood components cannot fit through the pores in the membranes because those components are too large. The urea and salt, however, flow through membranes easily and are removed through the sterile solution.

During dialysis, a patient's blood is passed through an external filter (a hemodialyzer) that performs some of the functions of the kidney: removing wastes, excess fluids, and salts from the blood and correcting levels of specific chemicals. Patients on dialysis have their blood filtered several times a week; to make this process easier, doctors create a window to the bloodstream that allows blood to be removed and returned quickly, efficiently, and safely. The window is usually in the arm and completely beneath the skin.

Doctors use one of two procedures to create a dialysis access, a fistula or a graft. In both cases, an artery is connected to a vein to increase the blood flow through the vein. Over time the vein enlarges, carrying more blood and making it easier for dialysis technicians and nurses to gain access to the bloodstream.

To create a fistula, the surgeon joins an artery to a large, nearby vein. Over the following weeks and months, the vein increases in size. If the vein is blocked or too small to use, doctors will create a graft, an artery-to-vein connection using a synthetic tube instead of the patient's own blood vessels. Because fistulas are constructed using the patient's own blood vessels, they are generally more durable and resistant to infection than grafts.

Continue Learning about Dialysis


Healthy kidneys remove waste from your blood and produce hormones your body needs. If your kidneys fail, you either need a kidney transplant or dialysis. Dialysis is a procedure that uses a machine to perform many of the functions ...

of the kidney. Dialysis can help prevent problems resulting from kidney failure and it allows people with kidney failure to live productive lives. Dialysis filters your blood, and like a health kidney, removes waste from your blood. Patients using dialysis are also required to follow a strict diet in order to stay healthy. There are two types of dialysis: hemodialysis and peritoneal dialysis. There are different advantages and disadvantages with both hemodialysis and peritoneal dialysis. Talk to your doctor about which type of dialysis would work better for you.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.