What is cannulation of grafts in hemodialysis?

Cannulation of Grafts in Hemodialysis: Definition and Techniques

Cannulation of grafts refers to the insertion of specialized needles into an arteriovenous graft (AVG) to access a patient's bloodstream for hemodialysis treatment. This procedure is essential for patients with end-stage renal disease who dialyze using an arteriovenous graft rather than a fistula or catheter.

What is an Arteriovenous Graft?

An arteriovenous graft is a synthetic tube, typically made of polytetrafluoroethylene (PTFE), that connects an artery to a vein to create vascular access for hemodialysis. Unlike arteriovenous fistulas (AVFs) which are created using the patient's own blood vessels, grafts use artificial material.

Cannulation Techniques for Grafts

There are two primary cannulation techniques used for arteriovenous grafts:

1. Rope-Ladder (Step-Ladder) Technique

• Definition: Rotation of needle insertion sites along the length of the graft with each dialysis session 1
• Purpose: To reduce vessel damage and prevent aneurysm formation
• Procedure:
  • New arterial and venous needle sites are selected for each treatment
  • Sites are rotated systematically along the entire length of the graft
  • Previous sites are allowed to heal before being used again

2. Area Cannulation (Not Recommended)

• Definition: Repeated needle insertions in the same general area
• Warning: This poor technique leads to graft aneurysms and damage and should be avoided 1
• Note: Unlike with fistulas, buttonhole technique should NOT be used for synthetic grafts 1

Proper Cannulation Procedure

Pre-Cannulation Assessment

1. Perform complete physical assessment of the graft
2. Locate and palpate the needle cannulation sites prior to skin preparation 1

Skin Preparation

1. Wash access site using antibacterial soap or scrub (e.g., 2% chlorhexidine) and water
2. Cleanse the skin by applying 70% alcohol and/or 10% povidone iodine using a circular rubbing motion 1
   • Alcohol should be applied for 1 minute immediately before cannulation
   • Povidone iodine needs 2-3 minutes to take full effect and must dry before insertion

Cannulation Technique

1. Use clean gloves for the procedure 1
2. Pull skin taut in the opposite direction of needle insertion
3. Use approximately a 45-degree angle of insertion for AVG (compared to 25 degrees for fistulas) 1
4. After penetrating the vessel, there are three common methods:
   • Advance needle slowly with cutting edge facing top of vessel without rotation
   • Immediately rotate needle axis 180 degrees and advance with cutting edge facing bottom
   • Advance needle to desired position, then rotate axis 180 degrees 1
5. Tape the needle at the same angle as insertion
6. NEVER APPLY PRESSURE BEFORE THE NEEDLE IS COMPLETELY OUT when removing 1

Important Timing Considerations

Grafts generally should not be cannulated for at least 2 weeks after placement and not until swelling has subsided so that palpation of the course of the graft can be performed 1. The exception is composite polyurethane grafts, which may be cannulated after 24 hours if swelling has subsided 1.

Complications and Prevention

Common Complications

• Infiltration and hematoma formation
• Infection
• Aneurysm development
• Graft degeneration
• Pseudoaneurysm formation

Prevention Strategies

• Proper aseptic technique for all cannulation procedures 1
• Rotation of cannulation sites to prevent pseudoaneurysm formation 1
• Proper needle angle and insertion technique to minimize trauma 2
• Regular monitoring of the graft for signs of complications 1

Special Considerations

• A steeper needle angle, higher blood flow rates, and deep needle tip can lead to wall stress on the posterior wall up to 10 cm from the cannulation site 2
• Plastic cannulas may provide a viable alternative to metallic needles with potentially lower complications 2
• Newer graft technologies are being developed to be self-sealing and immediately usable post-implant, with more durable cannulation zones 3

By following proper cannulation techniques and protocols, healthcare providers can help extend the lifespan of arteriovenous grafts and reduce complications for patients requiring hemodialysis.