Weeks or months before hemodialysis begins, a surgeon prepares a vascular access, the place on the body where blood is siphoned and returned. Having a site that allows good blood flow throughout treatment makes hemodialysis work better. There are three kinds of vascular access:

• Arteriovenous (AV) fistula.  A fistula is a connection between two parts of the body where normally there is no opening. The surgeon connects an artery to a vein, usually in the forearm, to allow greater blood flow into the strengthened vein. Often this is an outpatient procedure performed under local anesthesia.

The AV fistula is the preferred type of access for long-term hemodialysis because it lasts for years, allows a high volume of blood flow and has fewer complications, such as infection and clots. The disadvantage of this type of access is that it may take many months for the fistula to develop for use in dialysis.

• Arteriovenous graft. A tube is surgically inserted under the skin in the arm to serve as an artificial vascular access. An arteriovenous graft is usually the alternative option if an AV fistula is not possible (e.g., because the veins are too small). An AV graft often can be used within a few weeks. However, it tends to have greater risk of infection or clotting and to require replacement sooner than a fistula.
  
  A common complication of dialysis grafts is eventual blockage of the blood vessel due to growth of smooth muscle (intimal hyperplasia). Further surgery is needed to reopen the vessel. Researchers are studying use of gene therapy to prevent this obstruction.
  
  
• Venous catheter. A tube with two chambers allowing two-way flow of blood is placed into a vein in the neck, chest or thigh. Unlike the AV fistula and graft, the catheter does not require needles to be inserted into the body during hemodialysis. Because of complications including narrowing of the vein, the venous catheter usually is used as a temporary measure if immediate dialysis is necessary. If AV fistula or graft is not possible, a venous catheter can be used long term and is placed under the skin.

One complication of long-term hemodialysis is that patients may run out of healthy blood vessels that can serve as the vascular access. A potential solution is bioengineering. In late 2005, two hemodialysis patients in Argentina received the world’s first blood vessels grown in a laboratory from small samples of their own skin. Additional research is under way.