Figure 55

Polytetrafluoroethylene (PTFE) vein graft. The most common synthetic material used for dialysis access construction is the PTFE conduit. This material replaced bovine heterografts; alternative materials such as the umbilical vein graft have not yet made much headway. Because of the infection risk, Dacron bypass grafts have never functioned well for dialysis. PTFE is an inert material that is formed into a pliable conduit. Its ultramicroscopic structure is a series of nodes connected by tiny filaments, leaving pores whose size can be varied during manufacture. The process of healing after implantation involves ingrowth of fibroblasts into the pore structure, giving a final graft-tissue amalgam that is "incorporated" when encountered by the surgeon for revision. There is virtually no neovascularization through the pores, which are too small for capillary ingrowth. In humans, neointima grow along the graft for no more than 3 cm from the anastomosis. In animal models, neointima can be much more robust, growing along most of the length of the graft and providing it with greater resistance to thrombosis. Typical layouts for the construction of a PTFE access site are A, the forearm loop, and B, linear forearm graft, respectively. Alternative sites include upper arm loop grafts, groin grafts, axillary artery-to-vein grafts, and a variety of other constructions. The sites of choice are limited by the requirements of hemodialysis: delivery of a high rate of blood flow and accessibility to the dialysis staff for cannulation with an adequate length of graft to keep the needles sufficiently separated and allow rotation of cannulation sites.

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