Direct Arteriovenous Communication Angioaccess

Preoperative Evaluation

One determinant, possibly the most important, of a successful vascular access surgery is the preoperative planning. With the availability of imaging modalities, a patient should never be subjected to exploration of various vessels at the time of surgery to determine an appropriate location. A preoperative ultrasound evaluation of the upper extremity yields important data that are used in procedural planning. Information obtained includes size and patency of the radial, ulnar, and brachial arteries; presence of calcium or shadowing in the artery; diameter, depth, and patency of the cephalic and basilic veins; and presence or absence of central vein stenosis.

Vein diameter is a major predictor of the maturation process of a fistula. In many instances a fistula can be technically constructed, but it will not mature because of the size of the vessels involved. Data from our institution demonstrate that fistulas established using a vein less than 2 mm in diameter portends a poor outcome.

Some researchers feel that the primary failure rate in the fistula-first era is a result of artery size rather than vein size. Of equal importance is the condition of the artery. Severe calcification, as identified by ultrasound, can indicate difficulties in performing the anastomosis, thus adversely affecting patency.

In patients who have had any type of central venous catheter for longer than 6 weeks or who have had multiple catheters, there is a risk of central venous stenosis. These central veins cannot always be assessed with ultrasound; therefore, a central venogram should be obtained to verify the absence of ipsilateral obstruction.

Failure to adequately assess both the arterial and venous systems before forming the fistula can lead to prolonged or failed maturation, decreased patency rates, and increased catheter use.

Location of the Fistula

In the upper extremity a fistula may be constructed using the radial artery at the wrist, proximal radial artery, ulnar artery, or brachial artery. Upper extremity veins commonly include the cephalic vein at various locations, the basilic vein with transposition, and the brachial vein with transposition.

It is important to select the appropriate vascular access based on careful preoperative planning and not only to consider the first procedure but also to have a long-term, stepwise plan for possible multiple access procedures. Some authors recommend starting as distally as possible in the extremity, thus allowing the construction of a more proximal fistula in case of failure. In general, the nondominant arm should be employed in case any untoward events such as hand ischemia occur.

The radial artery is often used as the initial site for an arteriovenous fistula, including a snuffbox fistula, a wrist radiocephalic fistula, or a forearm radiocephalic fistula. Also, an anastomosis between the ulnar artery and the basilic vein below the antecubital fossa may be used on occasion.

Basilic vein transposition has been used successfully in many cases. This is a more difficult operation because complete mobilization of the basilic vein is generally required. Basilic vein transposition in one or two stages is based on superficializing the basilic vein, which may be done at the time the initial fistula is created or as a second-stage procedure. However, patency rates are good and this may be a successful way of salvaging a fistula in a patient in whom a more proximal construction has failed.

Brachial artery AVFs have a better patency rate than those constructed in the more distal radial artery. More creative ways can be used to establish a fistula, such as a transposed femoral vein anastomosed to the femoral artery.

Technique

Meticulous technique in constructing the arteriovenous fistula is of extreme importance for long-term patency. Local infiltration anesthesia is a good option for wrist fistulas, and a regional block, such as a brachial plexus block, is an alternative option and is especially useful for fistulas in the upper arm. The surgeon should be seated comfortably with adequate lighting. Surgical magnification glasses are useful for performing the anastomoses.

Various techniques have been developed for wrist, forearm, and upper arm fistulas. For example, the proximal radial artery inflow can work extremely well. In addition, antebrachial fistulas with bidirectional flow are useful in some instances. Jennings and colleagues have an excellent monograph, including pictures that show alternative access options with arteriovenous hemodialysis.

Four different anastomotic connections of artery and vein have been described, each with its associated advantages and disadvantages: side to side, end of vein to side of artery, end of artery to side of vein, and end to end. Most surgeons prefer the technique of end of vein to side of artery, which results in the highest proximal venous flow, with minimal distal venous hypertension. Examples of different methods of constructing an arteriovenous access include the proximal radial artery, antebrachial AVF with bidirectional flow, antegrade AVF, and retrograde venous outflow AVF. In the retrograde venous outflow AVF, a valvulotome may be required to disrupt venous valves.