The present invention relates to methods and apparatus for subcutaneously positioning a graft and catheter for access to the vascular system of a patient.  In particular, this invention relates to an arteriovenous (AV) shunt for use in conjunction with hemodialysis. 
Hemodialysis is the purification of blood by removing toxic substances and restoring chemical balance using an extracorporeal dialysis machine.  The process is used as a substitute for proper kidney function in those with renal failure.  Despite the benefits, a persistent drawback of hemodialysis devices is patient morbidity and mortality caused by failure of and infection from the hemodialysis access site.  In particular, nearly 80% of access failure in arteriovenous grafts is caused by blood returning from the hemodialysis machine into the patient with sufficient high pressure to damage vein walls.  Morbidity and Mortality of Dialysis, NIH Consens.  Statement 1993; 11:1-33. 
Hemodialysis access sites include arteriovenous grafts, arteriovenous fistulas and hemodialysis catheters.  An arteriovenous graft is a tube surgically placed under the skin, which is connected to an arterial source on one end and a venous source on the other.  The graft is accessed by the cannulas of the dialysis machine, so the blood is removed from the body, cleansed in the dialysis filter and then returned to the patient.  An AV fistula is a direct connection of an artery to a vein where a graft is not used.  The vein is used for dialysis access.  A hemodialysis catheter is a percutaneous tube placed through the skin and directly into the subclavian vein, internal jugular vein or femoral vein.  The extracutaneous portion is used for dialysis access. 
These access methods are problematic because they cause vein damage and leave the patient susceptible to infection and clotting.  Furthermore, the weak veins of renal failure patients may not accommodate certain access methods. 
In AV grafts, neointimal hyperplasia is caused when the cells of the inner layer of the vein hypertrophy and multiply in response to the high blood flow and pressure of the arteries.  This multiplication along with turbulent flow causes frequent venous outflow obstruction and resultant clotting and failure of the AV graft. ( Paulson, W. D.; Ram, S. J.; Zibari, G. B., “Vascular Access: Anatomy, Examination, Management”, Semin.  Nephrol.,  Vol.  22, No.  3, May 2002, pp.  183-194).  In AV fistulas, the common cause of failure is formation of venous aneurysms and clotting on the venous portion of the graft.  Venous aneurysms are caused because of the flow pressure differential between the high pressure grafted artery and the vein.  High pressure arterial flow through the thin walls of the veins causes damage because veins lack the prominent arterial layers of elastic and muscular tissue.  These aneurysms then form clots because of the turbulent, irregular blood flow and subsequently the AV fistula completely clots off and fails. [ U.S. Pat.  Nos.  6,102,884; 6,086,553; 5,556,426; 4,822,341; 4,654,033; 4,479,798; 3,998,222; 3,826,257; 3,818,257; and 3,818,511—incorporated by reference.]  Hemodialysis catheters are the least preferred in the surgical community.  The large bore catheters can last from two months to one year and are frequently complicated by infection and clotting because the limbs of the catheters are outside of the skin. 
It would be desirable to have an arteriovenous device placed subcutaneously that does not require anastomisis to a vein, eliminates exposure of the vein to high pressure blood returning to the patient from the dialysis apparatus and utilizes a single lumen venous outflow catheter.  It would also be desirable to have an arteriovenous device that provides long term patency, prevents clotting and minimizes infection.