Bridge Grafts for Angioaccess

Preoperative Considerations

Construction and maintenance of reliable shunts in renal dialysis patients is challenging, and care must be taken to avoid compromising tissue perfusion. Duration and frequency of previous access use, venipuncture, arterial lines, operations or trauma, local or systemic infections, and comorbid disease processes are important preoperative considerations. Diabetic patients often come to the hospital with disease of the small- to medium-caliber vessels that are commonly used for angioaccess procedures. Detailed vascular system examination includes assessments of chronic arterial insufficiency, venous thrombosis and valvular incompetence, character and location of arterial pulses, digital capillary refill, and performance of an Allen test. Extremity swelling and venous prominence, particularly in the shoulder and proximal extremity, might suggest underlying venous obstructive disease and requires further investigation. Preoperative cardiopulmonary or other subsystem studies are obtained only as indicated by relevant history and physical findings.

The nondominant upper extremity is preferred for initial angioaccess placement to minimize compromise of the patient’s daily activities. Preoperative arteriography and other noninvasive imaging studies are not routinely performed. If there is clinical evidence of venous outflow obstruction, a prior proximal arteriovenous access procedure, recurrent AVG thrombosis, absence of adequate superficial veins, or palpable arterial abnormalities, duplex scanning or contrast radiography is indicated to delineate native vascular anatomy, arterial abnormalities, or proximal venous stenosis.

Many patients who come to the hospital with ESRD need immediate central venous system access, and more than 50% require temporary uncuffed catheters within the first 60 days of hemodialysis. Patients often present with catheters in place or have undergone prior central venous access and might have developed central venous stenoses. The subclavian vein is used for temporary access in two thirds of patients presenting for dialysis. The incidence of subclavian vein stenosis after cannulation is 14% to 50%, and thrombosis is 10% to 30%. The incidence of internal jugular vein thrombosis is substantially less (1% to 2%), although no site is free from this risk. The patient’s future need for reliable vascular access is the main objective when considering temporary catheter sites. Use of the extremity contralateral to the proposed surgical site, use of the internal jugular vein before the subclavian vein, and initial avoidance of the femoral vascular system are principles aimed at preserving subsequent potential permanent access sites.

A cuffed tunneled catheter can serve as a bridge to permanent access in the acutely ill patient. Infection, patency, and flow rates are similar among various catheter types, and differences in placement technique are minimal. They are associated with central venous stenosis. Preoperative noninvasive ultrasound imaging is often justified in patients being considered for construction of an arteriovenous fistula (AVF). Upper extremity physical examination in candidates for an AVF is sometimes inaccurate in identifying suitable veins for anastomosis. Lack of adequate superficial extremity veins on physical examination often precludes peripheral autogenous fistula construction and is a common reason for proceeding to AVG placement. Extremity AVG placement is not deferred on the basis of insufficient superficial veins on physical examination.

The superficial venous system is the preferred outflow channel for initial AVG placement, and the deep venous or more proximal central systems are used secondarily. Preoperative imaging is not routinely obtained in patients presenting for AVG placement unless there is evidence of extensive venous disease. Although technically advantageous, specific identification of venous outflow options is less critical for AVG placement because proximity of the native vessels is not necessary. If there is physical evidence of obstruction to blood flow or valvular incompetence such as edema or venous distention and other sites are not available, construction of the peripheral arteriovenous access is deferred, and the proximal venous system is examined by phlebography or duplex imaging.

Placement of an AVG may be prompted by detection of a jeopardized AVF. Even in the absence of symptoms, AVF revision may be needed if a hemodynamically significant stenosis is found. The KDOQI guidelines suggest a 50% or greater than normal vessel lumen reduction of the venous outflow found on color duplex scanning as a main indication for surgical repair or revision.