Blood from an artery passes into the dialysis machine and over a thin sheet of membrane that acts as a filter for unwanted substances. The purified blood is then fed back into one of the patient's veins. A variety of machines are available, some of which are small and safe enough to be used by the patient at home. The most modern machine is portable. Many of the problems are associated with maintaining sterility, but most of these have been overcome by the use of machines with disposable parts.
Dialysis is used to treat acute or chronic kidney failure.
In acute renal failure, dialysis continues until the kidneys recover their normal function. In chronic renal failure, dialysis continues either for the rest of the patient's life or until a kidney transplant is performed. Peritoneal dialysis does not require a machine. It is performed by inserting a sterile plastic catheter into the abdominal cavity and irrigating the peritoneum. Metabolic substances are drawn out of the capillaries of the peritoneum and irrigated out of the cavity.