Introduction
The primary purpose of vascular access is to facilitate hemodialysis for as long as possible at minimal risk of complications. To achieve this goal, vascular surgeons primarily use vascular accesses created from native tissue, but when suitable autogenous components are not available, prosthetic arteriovenous grafts are preferred over tunneled catheter systems.
The creation of hemodialysis fistulas and grafts has become one of the most common types of vascular surgery in the United States, accounting for 40% to 50% of the operative volume in some programs. Because the primary patency of hemodialysis fistulas and long-term patency of hemodialysis grafts is low, interventional therapies now play a prominent role in the health care of hemodialysis patients.
This chapter defines the pathophysiology of hemodialysis access failure, reviews the success rates for endovascular treatments, and uses color figures and videos to illustrate the catheter-based approaches for treating failing and thrombosed fistulas and grafts.
Epidemiology and Prevalence of Stage V Kidney Disease
Survival
More than one in 1000 patients in the United States now has end-stage renal disease (ESRD), and 80% of these individuals undergo hemodialysis. The overall annual mortality rate for patients on hemodialysis exceeds 20%. The mortality rate for elderly patients during the first year after initiation of dialysis is 58%. Almost 40% of patients with ESRD have concomitant coronary artery disease, and the overall annual rate of myocardial infarction for patients on hemodialysis exceeds 10%. In the hemodialysis population, the 1-year mortality rate after myocardial infarction exceeds 50%.
Hemodialysis
The number of patients with ESRD requiring renal replacement therapy (RRT) exceeded 340,000 in 2006, and by the year 2020, the number of patients with ESRD is expected to be 750,000. The United States hemodialysis program now comprises more than 6% of the entire Medicare budget. The growing prevalence of ESRD can be attributed primarily to changing demographics and the under-treatment of hypertension, diabetes, and chronic kidney disease (CKD) in the general population. Functioning hemodialysis access is critical for patients with ESRD.
Vascular Anatomy
Nomenclature
The selection of a surgical site for hemodialysis access is based on evidence favoring the creation of an autogenous hemodialysis access (“fistula”) whenever possible, before resorting to the creation of prosthetic arteriovenous access with polytetrafluoroethylene (PTFE) or other synthetic materials (“graft’), in compliance with the “Fistula First” policy established in the United States and in other countries. The proportion of hemodialysis patients with fistulas has been increasing in the United States. In one report, the proportion of patients on hemodialysis with autogenous fistulas increased from 48 ± 4% to 62 ± 4% between 1999 and 2007.
The identification of a specific site for permanent access creation is based on venous ( Figure 28-1 ) and arterial anatomy ( Figure 28-2 ), according to the practice favoring the nondominant arm before the dominant arm, the forearm before the upper arm, and the upper extremity before the lower extremity.
Autogenous Arteriovenous Accesses
A fistula is surgically created when a native inflow artery is directly anastomosed with a native outflow vein. A common configuration at the wrist involves an end-to-side anastomosis between the radial artery and the cephalic vein, creating the Brescia-Cimino radial-cephalic fistula ( Figure 28-3 ). Another common configuration in the upper arm entails mobilization and tunneling of the basilic vein laterally and superficially for an end-to-side anastomosis with the brachial artery, creating a transposed brachial-basilic fistula.
Prosthetic Arteriovenous Accesses
A prosthetic arteriovenous access is constructed by surgically interposing a segment of PTFE between a native artery and a native vein in either a straight or looped configuration. Loop grafts are favored over straight grafts because they increase the length of the graft amenable to needle entry. The most common graft patterns include the brachial-cephalic configuration in the forearm ( Figure 28-3 ) or the brachial-basilic configuration in the upper arm ( Figure 28-3 ).
In the forearm, the radial-cephalic autogenous access and the brachial-cephalic prosthetic access are the favored configurations ( Figure 28-3 ), with the outflow in both instances carried by the cephalic vein. This follows a medial-to-lateral course, continues along the lateral aspect of the arm, traverses the pectoral groove, and anastomoses with the axillary vein and then becomes the subclavian vein.
In the upper arm, the brachial-basilic autogenous access and the brachial-basilic prosthetic graft are common configurations, with the outflow in both instances carried by the basilic vein. This follows a lateral-to-medial course and continues in a straight line into the axillary vein, subclavian vein, and thence into the central circulation ( Figure 28-3 ). In the thigh, the superficial femoral artery-greater saphenous vein configuration is preferred, with venous outflow following a lateral-to-medial course ( Figure 28-4 ).
Anatomic Variants
A few anatomic variations are commonly encountered. Alternative patterns for prosthetic grafts include the brachial-basilic graft in the forearm that has a lateral-to-medial course, and the brachial-cephalic graft in the upper arm that has a medial-to-lateral course.
Another configuration in the forearm consists of the proximal radial artery anastomosed in a side-to-side manner with the median antebrachial vein, producing a double-outlet configuration coursing proximally and distally from the arteriovenous anastomosis. Another type of “double-outlet” access is the radial-cephalic fistula that drains into the basilic vein, a desirable variant that reduces the risk of thrombosis when one limb develops an outflow stenosis.
Pathogenesis of Access Failure
Two modes of failure commonly affect fistulas and grafts ( Table 28-1 ), and both types of failure are amenable to interventional treatment. An autogenous fistula has a greater chance for long-term patency than a prosthetic arteriovenous graft, but the primary patency of fistulas remains low because of the lack of suitable anatomy in many cases and the inability to achieve adequate hypertrophy. Fewer than 50% of fistulas mature adequately to allow reliable hemodialysis. When fistulas mature adequately and have been successfully used for hemodialysis, they fail after a median of 3 to 7 years.
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Patients who are not candidates for fistulas can have prosthetic grafts constructed from PTFE. Although the primary patency of such prosthetic grafts exceeds 80% prosthetic accesses fail after a median lifetime of only 12 to 18 months.
Failure to Mature
An anastomotic arteriovenous stenosis in a newly created fistula restricts inflow and prevents fistula hypertrophy. Low primary patency rates may improve slightly after successful angioplasty of the inflow stenosis or surgical revision so that secondary patency rates at 1 year are 10% to 20% higher than primary patency rates.
The failure of autogenous fistulas to mature is a more common problem in diabetic patients and in the elderly. The patency of upper-arm brachial-cephalic and transposed basilic vein fistulas in diabetic patients at 18 months (78%) may be significantly better than that of forearm fistulas (33%).
Stenosis Development in Mature Accesses, with or without Thrombosis
About 50% of failing accesses contain thrombus, but thrombosis is the primary cause of failure in less than 1% of cases. In almost every case, a culprit stenosis restricts flow, produces stasis, and ultimately causes thrombosis. In chronically used fistulas and grafts, high pressures and flow in the thin-walled outflow vein raise shear stress and trigger fibromuscular hyperplasia. When the hyperplasia is exuberant, a severe stenosis appears, reduces flow, and precipitates thrombosis.
The success of catheter-based treatments of access thrombosis requires delineating and treating the culprit stenosis that initiated the pathologic process of stasis and thrombosis. Stenoses can occur anywhere in the dialysis access, but the most common site in 47% to 65% of cases involves the anastomosis between the prosthetic graft and the outflow vein. Other sites for stenosis formation include a nonanastomotic location within a peripheral outflow vein in 37% to 53%, the graft itself in 38% to 50%, central veins in 3% to 20%, and multiple sites in 31% to 59%. Fistulas contain no outflow anastomosis, but like grafts, they are nonetheless susceptible to stenosis formation in the “arterialized” outflow vein.
The bulk of the thrombus that occurs secondarily within a clotted access is typically red thrombus, which is rich in fibrin and red cells and easily extracted with rheolytic methods or pulse-spray thrombolysis. The platelet-rich white clot at the arterial inflow anastomosis is usually resistant to rheolytic or thrombolytic methods and may require mechanical removal with Fogarty thrombectomy.
Primary thrombosis of chronically used hemodialysis accesses occurs rarely. It may occur unpredictably and unavoidably after major surgery, myocardial infarction, or sepsis associated with hypotension or hyperfibrinogenemia. Other causes of primary access thrombosis are excessive postdialysis access compression, hyperviscosity from hemoconcentration, polycythemia, or hypovolemia. When primary thrombosis of an access occurs without an identifiable pathogenic stenosis or if it occurs in the setting of a hypercoagulable state such as Factor V Leiden or the antiphospholipid syndrome, chronic anticoagulation with warfarin is recommended.
No medical therapy has been identified that prevents the development of a venous outflow stenosis or an arterial inflow stenosis. Although several randomized trials of antiplatelet agents have been reported, none has shown clear success in preventing access thrombosis or improving maturation rates. In a randomized trial of 877 patients, clopidogrel was associated with similar maturation rates as placebo (38% vs. 40%). In a separate randomized trial of 649 patients, however, dipyridamole was modestly better than placebo in achieved primary unassisted patency of autogenous arteriovenous fistulas at 1 year (28% vs. 23%).
Diagnostic Evaluation
The National Kidney Foundation-Dialysis Outcomes Quality Initiative (NKF-DOQI) document recommends establishing an organized program to identify failing fistulas and grafts.
Monitoring
Access integrity can be assessed with regular bedside examinations and an assessment of dialysis adequacy. The history or physical examination may suggest the presence of an inflow or outflow obstruction. Increased postdialysis bleeding suggests the development of an outflow stenosis.
The presence of a focal and short high-pitched bruit suggests the presence of an obstruction, whereas a continuous medium-pitched bruit similar to the continuous murmur of a patent ductus arteriosus, associated with a prominent thrill along an easily palpable and ballotable course in the subcutaneous tissue, is evidence of normal access function. A soft bruit and inconspicuous thrill over a recently created, slowly maturing, hypoplastic radial-cephalic fistula may indicate the presence of an anastomotic inflow stenosis. On the other hand, prominent access pulsation may signify elevated pressure caused by an outflow stenosis. Multiple aneurysmal segments in the distribution of a large, serpiginous access used for many years may indicate long-standing high pressures within the access. Marked arm edema, sometimes producing peau d’orange, usually indicates dual venous obstruction (cephalic and basilic) or a subclavian vein stenosis or occlusion.
Infected accesses may be difficult to diagnose. Mild isolated erythema without tenderness or edema is usually not a sign of infection, but fever and leukocytosis as signs of infection may be masked in uremic patients. Signs of infection include cellulitis, fluctuance, skin breakdown, or purulent discharge. Access infection is a contraindication to interventional treatment because sepsis may ensue when infected thrombus is agitated.
Surveillance
Surveillance refers to the performance of noninvasive testing of access structure and function. Measurements of intra-access flow and static venous dialysis pressures provide evidence of access adequacy. The finding of rising pressures of more than 150 mm Hg at a constant flow of 200 mL/min on hemodialysis may indicate the presence of an outflow stenosis. Estimating the recirculation fraction using urea concentrations or clinical parameters such as body weight, volume status, or serum potassium concentration may indicate incomplete dialysis. These are probably relatively late predictors of hemodialysis access failure and become abnormal at the time of impending thrombosis.
Repeat ultrasonographic studies may identify early stenosis formation before physical signs are apparent, but the cost of noninvasive methods and the uncertain benefits of pre-emptive graft intervention are tempering enthusiasm for noninvasive surveillance.
Diagnostic Testing
Diagnostic testing refers to the performance of angiographic procedures to define access anatomy and hemodynamics. The generic term “fistulogram” refers to the angiographic study of either an autogenous arteriovenous fistula or a prosthetic arteriovenous graft. A significant stenosis is defined angiographically by the presence of a 50% diameter stenosis and clinically by bleeding or thrombus formation. A successful endovascular intervention is the ability to complete at least one dialysis session via the treated access. The definition of patency duration is the time from intervention to referral for repeat intervention, vascular surgery, or placement of a temporary dialysis catheter because of a failing or thrombosed access.
Hemodynamic measurements made during catheter-based intervention can be important to assess procedural success. The ideal systolic pressure of an access should be less than 50 mm Hg, and the optimal ratio of systolic pressure in the access to systolic systemic pressure should be 0.30 to 0.40. Modest elevations of venous pressures to 60 mm Hg caused by central vein stenoses or occlusions can cause limb edema. If treatment normalizes pressures, edema may improve within one to two days.
Catheter-Based Treatment of Failing Accesses
Indications
A fistulogram is indicated on an emergency, urgent, or semi-elective basis when hemodialysis cannot be successfully carried out or when there is evidence from monitoring or surveillance to suggest that thrombosis is imminent ( Table 28-2 ). Emergency indications for catheter-based treatment include refractory access bleeding, hyperkalemia, volume overload, or refractory hypertension associated with a failing or thrombosed access. An urgent indication within 24 hours of diagnosis and within 48 hours of most recent dialysis session for endovascular treatment is access thrombosis that may avoid the need for temporary catheter placement. A semi-elective indication for angiography is the finding of a malfunctioning but nonthrombosed dialysis access ( Table 28-2 ), which should be referred within 48 hours of discovery because thrombosis may be imminent.
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