6.1 Arteriovenous Fistulas & Arteriovenous Grafts

Arteriovenous Fistulas & Arteriovenous Grafts

Vascular access is universally recognized as the patient's lifeline in maintenance hemodialysis. The adequacy of solute clearance, fluid ultrafiltration, and overall survival depends entirely on the presence of a durable, functional vascular access capable of delivering high blood flow rates ($Q_b$ of 300 to 500 mL/min) repeatedly over months to years. The Kidney Disease Outcomes Quality Initiative (KDOQI) Clinical Practice Guideline for Vascular Access emphasizes a patient-centered "Vascular Access Life-Plan," prioritizing native autogenous vessels whenever anatomically viable to minimize morbidity, hospitalizations, and mortality.

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Principles of Native Arteriovenous Fistulas (AVF)

A native arteriovenous fistula (AVF) is constructed by surgically connecting an artery directly to an adjacent vein (direct end-to-side or side-to-side anastomosis). Under resting physiological conditions, superficial veins carry low-pressure, low-velocity laminar blood flow (~20 to 50 mL/min) with thin, compliant walls. Creating an arteriovenous connection shunts high-pressure, high-velocity arterial blood directly into the venous conduit, producing marked increases in intraluminal wall shear stress.

Biophysical Mechanisms of Arterialization

• Endothelial Nitric Oxide Release: Pulsatile shear stress upregulates endothelial nitric oxide synthase (eNOS), inducing persistent vascular smooth muscle relaxation and progressive outward vessel remodeling.
• Medial Hypertrophy: Over 6 to 12 weeks, the vein wall thickens through smooth muscle hyperplasia and collagen deposition, transforming a delicate, thin-walled vein into a tough, muscular, "arterialized" conduit capable of withstanding repetitive cannulation with large-bore needles (17G to 14G).
• Flow Augmentation: Resistance drops dramatically across the low-resistance vascular bed, increasing access blood flow ($Q_a$) from baseline values to 600–1,500 mL/min.

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Anatomical AVF Configurations & Vessel Selection

Access planning often favors preservation of distal and proximal options, considering vessels, hand dominance, expected treatment course and the patient’s Life-Plan. This is not an inflexible hierarchy, and preserving veins improves options without guaranteeing a later usable access.

1. Radiocephalic Fistula (Brescia-Cimino)

• Anatomy: Direct anastomosis between the radial artery and the cephalic vein at the wrist.
• Clinical Characteristics: Introduced by Brescia, Cimino, and colleagues in 1966, this remains the first-line choice for permanent vascular access. Because it is placed at the most distal point of the extremity, it preserves the entire upper arm and forearm proximal vasculature for future revisions.
• Hemodynamic profile: Upper-arm fistulas may provide higher flow than distal fistulas, but usable flow and maturation must be assessed. High flow can increase cardiac load and distal ischemia risk.
• Clinical trade-offs: A distal fistula preserves proximal options but may fail to mature, particularly with poor vessels or vascular disease. An individualized access plan weighs expected usability, catheter exposure and the patient’s clinical course.

2. Brachiocephalic Fistula

• Anatomy: Surgical anastomosis between the brachial artery and the cephalic vein in the antecubital fossa.
• Clinical Characteristics: The second-line native access choice when wrist vessels are inadequate or have failed. The brachial artery delivers higher inflow volumes, and the upper arm cephalic vein has a larger baseline caliber.
• Flow assessment: A brachiobasilic fistula also needs examination for usable flow, depth and cannulation length after the surgical plan is complete. Its proximal inflow can create important cardiac and distal-perfusion effects.
• Complications: High blood flow increases the risk of Dialysis-Associated Steal Syndrome (DASS) in patients with peripheral arterial calcification. Furthermore, the cephalic vein must navigate the sharp turn through the deltopectoral groove to join the axillary vein, making cephalic arch stenosis a frequent cause of outflow obstruction.

3. Brachiobasilic Fistula (Transposition)

• Anatomy: Anastomosis between the brachial artery and the basilic vein in the medial upper arm.
• Surgical Complexity: The basilic vein is anatomically shielded beneath the deep fascia of the arm, adjacent to the median nerve and brachial artery. To be cannulated, the basilic vein must undergo surgical transposition (mobilizing the vein from its deep bed, elevating it superficially, and tunneling it anterolaterally through a subcutaneous pocket away from the median nerve). This is performed either as a single-stage or two-stage procedure.
• Clinical Utility: Third-line native access choice. It yields excellent flow rates (800 to 1,400 mL/min) and durable long-term patency because the basilic vein is rarely damaged by previous peripheral venipunctures due to its deep anatomical position.

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Arteriovenous Grafts (AVG): Biomaterials & Configurations

When native superficial veins are obliterated, sclerosed, or measure $< 2.0\text{ mm}$ on duplex mapping, an arteriovenous graft (AVG) is indicated. An AVG bridges an artery to a deep collecting vein using an interposed biocompatible synthetic conduit.

Biomaterials & Types

• Expanded Polytetrafluoroethylene (ePTFE): The gold-standard prosthetic material. Composed of a porous fluoropolymer fibrillar microstructure that allows perivascular connective tissue ingrowth while resisting structural dilation and infection.
• Polyurethane & Composite Grafts: Flexible synthetic polymers designed with multi-layer, self-sealing inner membranes that prevent blood extravasation after cannulation.
• Early-Cannulation Grafts: Specially engineered multilayer ePTFE or polyurethane grafts that can be cannulated within 24 to 72 hours of implantation. These eliminate the need for temporary central venous catheter starts in urgent-start hemodialysis patients.

Anatomical Configurations

• Forearm Loop Graft: Bridges the brachial artery to the median cubital, basilic, or cephalic vein in the antecubital fossa, creating a wide loop over the volar forearm.
• Upper Arm Straight or Curved Graft: Bridges the brachial artery to the axillary vein, or axillary artery to axillary vein.

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Functional Readiness and the ESKD Life-Plan

KDOQI 2019 emphasizes the patient’s ESKD Life-Plan rather than a universal fistula-first mandate. A native fistula can have low infection risk and good longevity when it matures, but a graft or catheter may be appropriate for particular anatomy, urgency, expected survival or patient goals. Evaluate the whole plan, including future access sites, transplantation and home treatment. Preserving veins remains important regardless of the immediate choice.

The historical rule of 6s referred to approximate flow of 600 mL/min, diameter of 6 mm and depth no greater than 6 mm. It is an educational heuristic, not the current mandatory definition of readiness; six weeks is an assessment interval in older teaching rather than guaranteed maturation. Readiness requires a usable cannulation segment and reliable two-needle treatment at the prescribed flow, assessed by qualified clinicians. Ultrasound helps when examination raises concern. A fistula that looks large but has a short, deep or stenosed segment may be difficult or unsafe to use.

Conventional grafts often require healing before cannulation, whereas early-cannulation products have specific labeling. Follow surgeon and product instructions; no single waiting interval applies to every graft. Before first cannulation, confirm authorization, examine flow and skin, and arrange experienced staff. Repeated blind attempts can turn a potentially usable access into a hematoma and prolong catheter dependence.

Postoperative Education

Teach patients to check for their usual thrill, protect the incision and report redness, drainage, worsening pain, hand weakness or loss of flow promptly. Avoid venipuncture and blood-pressure cuffs on the access arm when feasible and follow the surgeon’s activity instructions. Exercises, if recommended, should be the prescribed type and intensity; patients should not apply improvised constricting tourniquets to force maturation. Maintain realistic expectations: maturation failure requires evaluation, not blame for insufficient squeezing exercises.

Sources checked 2026-10-10: KDOQI 2019 vascular access