What is a graft in a fistula?

What is a Graft in a Fistula?

A graft in a fistula context refers to an arteriovenous graft (AVG), which is a synthetic tube made of materials like polytetrafluoroethylene (PTFE) that connects an artery to a vein to provide vascular access for hemodialysis when native vessels are not suitable for creating a direct arteriovenous fistula. 1

Types of Vascular Access for Hemodialysis

Vascular access options for hemodialysis can be categorized in order of preference:

1. Native Arteriovenous Fistula (AVF) - Direct connection between an artery and vein

   • Radiocephalic (wrist) fistula - first choice
   • Brachiocephalic (elbow) fistula - second choice
   • Transposed basilic vein fistula - third choice

2. Arteriovenous Graft (AVG) - Synthetic bridge between artery and vein

   • Used when native vessels aren't suitable for direct fistula creation
   • Common materials include PTFE (polytetrafluoroethylene)
   • Various configurations: forearm loop, upper-arm straight/curved, upper-arm loop

3. Catheters - Least preferred option due to infection risk

Advantages of Arteriovenous Grafts

AVGs offer several benefits when native fistulae aren't feasible:

• Large surface area available for immediate cannulation
• Technically easier to cannulate than some fistulae
• Shorter maturation time (14 days minimum, ideally 3-6 weeks)
• Multiple insertion sites available
• Variety of shapes and configurations for placement flexibility
• Easier for surgeons to handle and implant
• Relatively easy to repair surgically or endovascularly 1

Disadvantages of Arteriovenous Grafts

Despite their advantages, grafts have important limitations:

• Higher thrombosis rates than native fistulae
• Require more frequent interventions (3-7 times more "access events")
• Higher infection rates than native fistulae
• Lower long-term patency rates
• Higher overall maintenance costs 1

Types of Graft Materials

Several materials are used for vascular grafts:

• PTFE (Polytetrafluoroethylene) - Most common synthetic material
• Composite/PU grafts - Self-sealing properties allow earlier cannulation
• Biological grafts - Including bovine heterografts (higher complication rates)
• Cryopreserved grafts - Used in specific infection scenarios 1

Role of Grafts in Vistula Planning

In the "fistula first" approach, grafts can serve important roles:

• As a "planned bridge" to a future fistula
• When failing forearm grafts can be converted to upper-arm fistulae
• When lower-level fistulae can be converted to more proximal fistulae 1

Cannulation of Grafts

Special considerations for cannulating grafts include:

• Waiting at least 14 days after placement (ideally 3-6 weeks) for tissue incorporation
• Using rotation of cannulation sites to prevent complications
• Recognizing that biografts may become more aneurysmal than PTFE grafts
• Following manufacturer guidelines for specific graft types 1

Complications and Management

Common complications with grafts include:

• Thrombosis (more common than with native fistulae)
• Infection (higher risk than native fistulae)
• Stenosis (particularly at venous anastomosis)
• Aneurysm formation (especially with biografts)

Early detection and intervention for these complications can significantly extend graft lifespan and functionality.

Conclusion

While native arteriovenous fistulae remain the gold standard for hemodialysis access due to their superior patency and lower complication rates, arteriovenous grafts play a crucial role when native vessels aren't suitable. Understanding the characteristics, advantages, and limitations of grafts helps optimize vascular access planning and management for patients requiring long-term hemodialysis.