Arteriovenous Graft/Fistula

Radiocephalic Arteriovenous Fistula

The subcutaneous autogenous arteriovenous fistula was initially described by Brescia and coworkers in 1966. Readily accepted by nephrologists and surgeons, the Brescia-Cimino fistula, constructed of the patient's own vessels, largely overcomes the disadvantages of infection and early clotting found with external arteriovenous fistulas. After formation of the fistula, arterial pressure is transmitted directly into the contiguous veins, resulting in dilatation and development of a hypertrophied muscular wall ( Figure 81-1-1 ). This “arterialization” of the veins can take up to 6 weeks before vessels of sufficient size and wall thickness have developed to tolerate repeated venipuncture. During this postoperative period, hemodialysis may be accomplished using peripherally placed central venous catheters.

Before the operation, the superficial arm veins, preferably in the nondominant arm, are distended and examined using a tourniquet applied to the upper arm to produce venous engorgement. All suitably sized veins are marked with an indelible pen. This is done so that if the fistula of choice fails immediately after construction, these markings can aid the surgeon in identifying other possible fistula sites. The ulnar and radial artery pulses are palpated, and if there is any uncertainty about their adequacy, the systolic pressure in each is measured with a Doppler probe. An Allen test, which predicts the ability of the ulnar artery to support adequate circulation of the hand, should be performed to prevent symptomatic steal. The patient makes a fist and the examiner applies digital compression to the wrist, occluding both arteries; this is followed by pallor of the elevated and opened hand. Release of compression over the ulnar artery returns the hand's appearance to normal if the blood supply is sufficient. In addition to visual inspection, many surgeons perform duplex examination of both arms to find the most suitable veins. In fact, the routine use of ultrasound vessel mapping has been recommended. In one study, ultrasound vessel mapping changed the preoperative plan in approximately 23% of patients.

Local infiltration anesthesia using 0.5% to 1% lidocaine is usually satisfactory for construction of autogenous arteriovenous fistulas in the forearm or antecubital fossa. Although general anesthesia may be required in an extremely apprehensive or potentially uncooperative patient, a report on the effect of different types of anesthesia on blood flow during construction of a fistula showed that general anesthesia significantly decreases mean arterial blood pressure compared with local infiltrative anesthesia or regional block. In addition, brachial plexus block (supraclavicular approach) significantly increases brachial artery blood flow compared with local anesthesia. If available, an axillary block is an ideal anesthetic for vascular work in the forearm.

The arm is prepared in standard fashion, abducted at a right angle from the body on an arm board, and aseptically draped. For a Brescia-Cimino fistula, an oblique or longitudinal incision is made midway between the radial artery and the cephalic vein at the wrist. An adjacent 4- to 5-cm length of cephalic vein is dissected free of surrounding subcutaneous tissue. Its tributaries are ligated, freeing it further so that it lies adjacent to the radial artery without kinking or twisting. A 2- to 3-cm length of the radial artery, found under the deep fascia of the forearm, is also isolated from surrounding structures. The distal cephalic vein is divided, and its proximal segment is approximated to the radial artery in an end-to-side fashion using 6-0 monofilament suture.

Four different anastomotic connections of artery and vein have been used ( Figure 81-1-2 ), and each has its advantages and disadvantages:

• 1.

  Side-to-side anastomosis, with a fistula opening approximately 1 cm long, was the first procedure used. Technically, this is an easy anastomosis to construct and produces the highest fistula blood flow. It is also the most likely fistula to be associated with venous hypertension of the hand. This complication is moderated by the presence of venous valves that prevent reversal of venous blood flow in the hand, at least in the early months.

• 2.

  Vein end-to-arterial side anastomosis also decreases turbulence if constructed properly and results in the highest proximal venous flow with minimal distal venous hypertension. It is more technically difficult to construct than the side-to-side fistula, and fistula flow overall is somewhat decreased. If a branch vein is present, opening the inner aspect of the Y creates a generous oval patch to join to the side of the radial artery.

• 3.

  Arterial end-to-vein side anastomosis minimizes turbulence and distal steal of blood but may result in slightly lower fistula flows because it is subject to twisting of the artery during construction.

• 4.

  End-to-end anastomosis produces the least distal arterial steal and venous hypertension but has the lowest fistula flow of the four configurations.

Proximal and distal control of the two vessels is gained by the application of small vascular clamps or a fine silicone rubber sling. The inability to pass a 3-mm or larger coronary dilator into the outflow vein has been associated with poor fistula maturation in our experience. The vessels are anastomosed in the desired configuration with 6-0 polypropylene sutures, with knots placed outside the lumen. One must ensure that when approximating the artery and vein, spiral rotation of these vessels does not occur. Before the anastomosis is finally closed, a check is made by gently passing a coronary artery dilator to detect any stenosis. This technique is especially useful to alleviate proximal arterial vasospasm in young patients. Hydrostatic dilatation with heparin-treated saline of a marginally small vein may aid in maintaining early patency. Any bleeding from the anastomotic site should first be controlled by simple pressure with a gauze swab for several minutes. Immediate suture repair can produce further bleeding sites and narrowing of the anastomosis.

Upon conclusion, the artery and vein should lie without twists or kinks. A thrill should be easily felt over the fistula and propagated for a moderate distance along the proximal venous channel. A transmitted pulse without a thrill suggests an outflow obstruction or a clotted fistula. In this case, the proximal vein may be probed and inflated with a Fogarty catheter (avoiding intimal damage by not inflating the balloon during manipulation of the catheter) or carefully dilated with bougies. If these maneuvers do not produce a strong thrill and the fistula is technically satisfactory, construction of the fistula at another, more proximal site should be considered. On occasion, however, the appearance of a bruit and thrill is delayed until the veins dilate and blood flow increases, especially when no outflow obstruction can be demonstrated.

Following discharge, the patient is instructed to keep the arm elevated for 24 hours and to avoid sleeping on the arm. Avoidance of constricting dressings, sphygmomanometer cuffs, and tight clothing is mandatory. Any swelling usually resolves over subsequent weeks. Generally, 4 to 6 weeks allows for adequate venous maturation for use. Puncturing the vessels before they are arterialized is often associated with hematoma formation, because the dilated veins are thin walled during the first few weeks. Although exercise of the forearm by squeezing a rubber ball to increase fistula flow and promote maturation of the arterialized veins has been advocated by some, others have reported that it has no benefit. Once the fistula is ready for cannulation, the buttonhole or constant-site technique should be considered in patients who self-cannulate.

Brachiobasilic and Brachiocephalic Arteriovenous Fistulas

Brachiobasilic (with vein transposition) and brachiocephalic arteriovenous fistulas may be used to achieve upper extremity vascular access after failure of a more distal extremity arteriovenous fistula or if the cephalic vein at the distal forearm or wrist is inadequate. Patency rates of 80% at 3 years have been reported at these sites for chronic hemodialysis vascular access.

Construction of the brachiocephalic fistula ( Figure 81-1-3B ) is preferred before brachiobasilic placement. The cephalic vein lies in a more superficial and accessible anatomic location on the anterolateral aspect of the arm compared with the basilic vein. The use of a transverse incision distal and parallel to the antecubital crease is recommended. Often a median antecubital vein, which drains into the cephalic vein, can be used and adds additional vein length for a tension-free anastomosis. Because more proximal vein diameters tend to be greater, brachiocephalic fistulas have a shorter time to maturity and longer primary patency when compared to radiocephalic fistulas. Attempts at more distal construction (Brescia-Cimino) should be performed whenever possible because upper arm access sites are limited.

The brachiobasilic fistula (see Figure 81-1-3C ) is constructed by identifying the basilic vein just anterior to the medial epicondyle of the humerus. Because of the deeper and more medial location of the basilic vein, this access site is usually avoided during phlebotomy and venipuncture. However, its location usually requires relocation in a subcutaneous tunnel running down the anterior aspect of the arm. If adequate basilic vein diameter (3 mm) is present distal to the elbow crease, the vascular anastomosis should be constructed in this location to maximize vein length for superficialization. This operation can be performed in one stage (vein mobilization, superficialization, and anastomosis) or two stages (anastomosis with delayed superficialization). Advantages of the two-stage approach include the ability to determine fistula maturation prior to vein mobilization, which requires a longitudinal incision in the upper arm, prolonged operative time, and increased postoperative pain. If a short basilic vein is present, length can be added for superficialization with either prosthetic polytetrafluoroethylene (PTFE) or autogenous (e.g., Artegraft, cryopreserved vein) conduits. Care must be taken during mobilization to avoid injuring the cutaneous nerves to the forearm, which lie adjacent to the vein. The proximal end of the vein remains in continuity with the axillary vein. The brachial artery is isolated in the antecubital fossa, and the end of the relocated vein is anastomosed to the anterior aspect of the artery in an end-to-side fashion at this level.

Sites for Arteriovenous Prosthetic Grafts

Bridge arteriovenous grafts can be constructed at almost any location where suitably sized arteries and veins are surgically accessible. For patient comfort, ease of handling during hemodialysis, and safety, however, the majority are constructed in the upper extremity or occasionally in the thigh.

In the upper extremity, bridge arteriovenous grafts can be satisfactorily constructed between the radial artery and an antecubital fossa vein, between the brachial artery (in the antecubital fossa before its branching) and either the adjacent cephalic or basilic vein (U configuration loop), and between the brachial artery and the axillary vein ( Figure 81-1-4 ). Construction of an upper-extremity bridge fistula is often more technically demanding than the creation of a femoral fistula, and its long-term patency is not as high. This is generally attributed to the larger vessels and greater blood flow in the thigh. The risk of infection and distal limb ischemia is less in fistulas constructed in the upper extremity, however, and this is the preferred site. Patients with claudication or an ankle arterial pressure less than 80% of that at the wrist might not be suitable for thigh fistulas, because the proximal steal of blood through the fistula is likely to increase ischemia in the leg. Therefore upper extremity fistulas are particularly well suited for elderly patients with significant atherosclerosis in the lower extremities. Obese patients in whom perspiration or dermatitis involving the groin skinfolds may increase the likelihood of infection should have an arm fistula. Incontinence is a relative contraindication for implantation of the graft in the upper thigh.

The arterial anastomosis in the lower extremity should be to the superficial femoral artery, immediately proximal to either the adductor canal or its more cephalad portion ( Figure 81-1-5A ). If the superficial femoral artery is occluded, the common femoral artery may be used (see Figure 81-1-5B ), with the understanding that if it becomes infected and ligation is subsequently necessary, leg ischemia may ensue. At times, patency of a short segment, including the origin of the superficial femoral artery, can be re-established and used for the arterial anastomosis. The venous anastomosis is made to the proximal saphenous, common, or superficial femoral vein.

Historically, the site selected for the initial placement of an arteriovenous graft was in the forearm, from the distal radial artery to the cephalic or basilic vein in the antecubital fossa. The graft was anastomosed in an end-to-side fashion to the distal radial artery, tunneled along the lateral aspect of the forearm, and then anastomosed end-to-side to the largest vein in the antecubital fossa. In positioning the graft, one had to ensure that the patient's arm would rest comfortably when receiving hemodialysis.

Currently, more common vascular access sites in the upper extremity include brachiocephalic or brachiobasilic loop fistulas in the forearm and brachioaxillary fistulas in the upper arm. Loop fistulas placed in the forearm allow a large area of graft to be available for needle puncture, whereas the brachioaxillary fistula, which curves over the lateral aspect of the upper arm, has several sites for venous anastomosis on the axillosubclavian segment. Upper extremity loop grafts have also been found to have significantly higher patency rates at all time intervals than do straight upper extremity grafts. Upper-extremity procedures can be performed using an axillary nerve block or local infiltration anesthesia with sedation.

Arteriovenous grafts in the thigh are usually constructed with the patient under a spinal or general anesthetic, although in cooperative patients, a local infiltration technique can be used. Placing the arterial origin of the conduit just proximal to the adductor canal portion of the superficial femoral artery is often advisable so that if a vascular complication should cause occlusion of the artery, adequate collateral channels will provide filling of the popliteal segment. The end-to-side arterial anastomosis should be oblique, and the graft should leave the artery at an angle to minimize turbulence. The venous anastomosis is also performed in an end-to-side fashion and as obliquely as possible. This method is used to counteract any purse-string effect of the suture, as well as buildup of fibrin and fibrous tissue at the venous anastomosis, which commonly causes late graft thrombosis. A vascular steal phenomenon, with reversal of flow in the distal superficial femoral artery, is common in bridge fistulas in the lower extremity and can lead to symptoms of limb ischemia. Fortunately, most patients with steal do not have symptoms, because dialysis patients are often fairly inactive.

The femorosaphenous bridge fistula is curved subcutaneously over the lateral aspect of the thigh and anastomosed to the proximal saphenous vein. The caudal portion of the saphenous vein may be ligated to prevent retrograde venous flow, although venous hypertension in the lower extremity is not a problem with a patent iliofemoral system. Another lower-extremity access configuration is the loop fistula placed in the groin from the common femoral or very proximal superficial femoral artery to the femoral vein. The high blood flow rate (>1000 mL/min) can lead to a significant increase in cardiac output. The possibility of limb loss in the event of infectious complications and the increased risk of infection make this site less desirable.

With the longer survival of chronic hemodialysis patients, the surgeon may be asked to evaluate a patient who requires vascular access but whose extremity access sites have all been expended. In this circumstance, a more central location, such as a bridge arteriovenous fistula placed between the axillary artery on one side and the axillary vein on the other side, has been used successfully. The grafts are of fairly large diameter, so they are easy to cannulate; flow is reported to be excellent, and despite the location of the access site on the anterior chest wall, patients adapt promptly. The major drawback of central access sites is that when complications occur, they are serious and more difficult to manage.

Materials for Prosthetic Arteriovenous Bridge Grafts

Both biological and prosthetic materials have been used in the creation of arteriovenous bridge fistulas for hemodialysis since this modality was introduced in 1969. Although saphenous vein, bovine heterografts, human umbilical vein, cryopreserved homografts, and Dacron velour grafts have all been tried during the last 4 decades, only expanded PTFE grafts have had an extended period of observation. Although one report on the use of autologous tissue-engineered vascular grafts in high-risk patients demonstrated primary patency in 78% of patients 1 month after implantation and 60% of patients 6 months after implantation, larger trials are needed to better determine the safety and efficacy of these grafts.

Since its initial introduction as an alternative material for the creation of arteriovenous bridge fistulas in 1976, expanded PTFE has become the most commonly used material. Much of its popularity stems from the fact that it is easy to handle, requires no preclotting, is widely available, has a long shelf life, and has relatively high patency rates with secondary revisions. PTFE bridge fistulas are consistently reported to have 12-month secondary patency rates of more than 70%. In a large comparative clinical study comprising 187 graft placements, 36-month patency rates of PTFE grafts were significantly greater than those of bovine heterografts (62% vs. 24%). Forty-eight–month patency rates of 43% to 60% have been reported. However, multiple procedures for revision are usually required to maintain patency, with one study reporting an average of one operation for revision required every 1.1 years (range, 1 to 16 revisions per graft).

Thrombosis of the conduit is a relatively common event in PTFE bridge fistulas, with figures ranging from 7% to 55%. Endovascular techniques such as thrombolysis, percutaneous mechanical thrombectomy, and angioplasty allow for re-establishment of graft flow and function. Surgical revision with Fogarty thrombectomy and patch angioplasty of the stenotic outflow vein is also effective. Infection of PTFE is not uncommon, with one report of 80 AV grafts monitored for 30 months showing an overall incidence of infection of 19%, with 67% of these infections occurring during the initial 4 months of use. Of the infected grafts, 73% required excision, and the remainder were treated successfully with antibiotics. The most common type of graft infection today occurs at needle puncture sites. Pseudoaneurysm at needle puncture sites develops in approximately 5% of fistulas.

Recently, heparin-bonded ePTFE grafts have been introduced in reports of increased patency compared with conventional ePTFE grafts. The long-term advantages and complications of heparin-bonded ePTFE grafts are not yet known.

History and Physical Examination

A thorough patient history should document the patient's dominant extremity; any recent history of peripheral intravenous lines; sites of indwelling or previous central lines, including pacemakers and defibrillators; all previous access procedures; any history of trauma or previous nonaccess surgery to the extremity; and all co-morbid conditions. On physical examination, the brachial, radial, and ulnar arteries should be evaluated for compressibility and equality bilaterally. An Allen test should be performed to evaluate palmar arch patency. The superficial venous system should be evaluated with and without a venous pressure tourniquet in place, examining for distensibility and interruptions. The arm should be examined for prominent venous collaterals and edema, which are signs of central venous stenosis.