2.1 Vascular Access Management

AV Fistula Creation and Maturation

An arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis because of its longevity and lower complication rates. AVF creation involves a surgical anastomosis linking a native artery directly to a vein. Common configurations include the radiocephalic fistula (Brescia-Cimino) at the wrist and the brachiocephalic fistula at the elbow. In cases where the cephalic vein is unavailable, a basilic vein transposition may be performed, relocating the deeper basilic vein closer to the skin surface to facilitate access.

Post-operative assessment is critical to ensure proper arterialization of the vein. The vessel must withstand repetitive large-bore needle cannulations. Standard clinical monitoring includes verifying the presence of a palpable thrill (a continuous rushing vibration) and an audible bruit (a low-pitched swooshing sound) over the access site. The absence of these indicators suggests access stenosis or thrombosis, requiring urgent vascular evaluation.

The Rule of 6s and Cannulation Techniques

To determine if an AVF is mature enough for routine clinical cannulation, nephrology nurses apply the Rule of 6s. Under these guidelines, the access should be evaluated at six weeks post-operation. The fistula must meet specific physical and physiological metrics:

• A blood flow rate of at least 600 mL/min through the access.
• A vessel diameter of at least 6 mm, measured using ultrasonography.
• A depth of no more than 6 mm from the skin surface.
• Clear margins for cannulation, showing at least a 6-inch straight segment of vessel.

If the AVF does not meet these criteria, a nephrologist may order vessel mapping or fistulogram to identify barriers to maturation, such as accessory veins or stenosis.

Cannulation techniques are vital to preserving access integrity. Needle sizes range from 17-gauge (for initial use at blood flows of 200–250 mL/min) to 14-gauge (for mature accesses at blood flows exceeding 400 mL/min). The arterial needle is inserted at a 25 to 35-degree angle, pointing either retrograde or anterograde. The venous needle must always be inserted anterograde (with the flow) to prevent vascular wall trauma and recirculation. Needles must be spaced at least 2 inches apart.

To extend the life of an AVF, nurses use either the rope ladder or buttonhole technique. The rope ladder technique utilizes new sites for each treatment, rotating along the entire length of the vessel to prevent localized weakening and aneurysm formation.

In contrast, the buttonhole technique involves cannulating the exact same site, angle, and depth every session with blunt-tipped needles once a scar tissue track is established. While useful for home hemodialysis, buttonhole cannulation carries a higher risk of infection than rope ladder rotation.

Arteriovenous Grafts and Catheter Care

An arteriovenous graft (AVG) uses a synthetic conduit, typically polytetrafluoroethylene (PTFE), to connect an artery and a vein. AVGs are indicated for patients with poor vascular anatomy unsuitable for an AVF. While AVGs can be used sooner than fistulas (typically within two to three weeks), they have a higher rate of complications, particularly stenosis and thrombosis, due to neointimal hyperplasia at the venous anastomosis.

For patients requiring immediate hemodialysis or those who have exhausted permanent access sites, a central venous catheter (CVC) is utilized. CVCs are typically placed in the internal jugular vein. They may be tunneled (with a cuff underneath the skin to prevent bacterial migration) or non-tunneled. Aseptic technique is mandatory during CVC dressing changes and connection procedures to prevent catheter-associated bloodstream infections (CLABSI). Prior to treatment, the heparin or citrate lock must be aspirated and discarded to prevent accidental systemic anticoagulation.

Hub disinfection should utilize a friction scrub with chlorhexidine gluconate.

Clinical Access Complications

Nephrology nurses must recognize and manage access-related complications:

1. Stenosis: Pathological narrowing of the vessel lumen, most common at the venous anastomosis in AVGs. Clinically detected by a high-pitched bruit or high venous pressure alarms.
2. Thrombosis: Complete occlusion of the access by a thrombus, leading to loss of the thrill and bruit. This requires immediate thrombectomy or thrombolytic therapy.
3. Dialysis access-associated steal syndrome (DASS): Shunting of blood away from the distal extremity. This leads to coldness, pain, paresthesias, and tissue necrosis in the hand.
4. Recirculation: Already dialyzed blood returning to the patient re-entering the arterial needle. This decreases dialysis efficiency and is caused by poor needle placement or stenotic outflow.
5. Infection: Indicated by localized erythema, warmth, purulent drainage, or systemic fever. Infection requires blood cultures, antibiotics, and potentially access removal.

Troubleshooting Venous Pressure Alarms

During hemodialysis, the machine monitors pressure in the venous return line. A high venous pressure alarm indicates resistance downstream from the venous needle. Causes include venous anastomosis stenosis, kinking of the blood lines, clotting in the drip chamber, or venous needle infiltration. Nurses must inspect the circuit from the patient connection to the dialyzer, palpate the access, and reduce blood flow rates if necessary. Correcting the underlying resistance prevents needle displacement, hematoma formation, or access rupture.