Once the access is made and healed, two needles are inserted in the fistula or graft, one on the artery side and one on the vein side. Blood drains into the dialysis machine to be cleaned. The machine has two parts, one side for blood and one for a fluid called dialysate. A thin, semipermeable membrane separates the two parts. As dialysate passes on one side of the membrane, and blood on the other, particles of waste from the blood pass through microscopic holes in the membrane and are washed away in the dialysate.
Blood cells are too large to go through the membrane and are returned to the body.
The benefits of hemodialysis are that the patient requires no special training, and he or she is monitored regularly by someone trained in providing dialysis. The other type of treatment, peritoneal dialysis, uses the patient's own peritoneal membrane as a filter. The peritoneal membrane is a sac around the abdominal organs. Waste particles can get through it, but larger blood cells cannot. The patient has a plastic tube called a peritoneal catheter surgically implanted into the belly.