Hemodialysis, also called dialysis, is the most common treatment for kidney failure. A dialysis machine is an artificial kidney which cleanses the blood. During dialysis, blood is drawn from the patient into the dialysis machine, circulated through the machine, and then returned to the patient. Two needles are inserted into the patient's bloodstream to allow this process to occur. Hemodialysis is normally performed three times a week and the purpose of vascular access is to provide reliable sites where the bloodstream can be easily accessed each time. There are three major types of vascular access: arteriovenous fistula, arteriovenous graft, and venous catheter. The great majority of vascular accesses are created in the arm, but they can also be created in the leg.