CHAPTER 119 Hemodialysis Fistulas
INTRODUCTION
Hemodialysis, and to a lesser extent peritoneal dialysis, remains the mainstay of treatment of patients with CKD. In acute situations, such as in patients requiring immediate, short-term (less than 6 months) dialysis access, double-lumen catheters are often used. These catheters are inserted in the femoral, internal jugular, or subclavian vein. Long-term hemodialysis requires regular vascular access (e.g., two to five times a week), necessitating the surgical creation of an arteriovenous fistula for more robust vascular access, typically in an upper extremity. This can be performed using the patient’s native artery and vein (arteriovenous fistula or AVF; Fig. 119-1) or with use of prosthetic graft material (arteriovenous graft or AVG; also called a prosthetic AVF; see Fig. 119-1).
FIGURE 119-1The main concern for a dialysis fistula is its patency and duration of patency. In general, a native AVF is believed to have longer problem-free patency rates than a prosthetic AVG and AVF has been the recommended first choice for long-term hemodialysis access by the National Kidney Foundation that was recommended in its 2000 Dialysis Outcomes Quality Initiative Clinical Practical Guidelines for Vascular Access (NKF/DOQI).1 Most often, a hemodialysis fistula is created in the upper extremity by anastomosis of the cephalic vein to the radial artery, close to or in the tabatière anatomique or the anatomical snuffbox, or just proximal to the wrist. This latter type of hemodialysis fistula is also known as the radiocephalic or Brescia-Cimino (BC) fistula or shunt (see Fig. 119-1A). In patients in whom a BC shunt, an AVF, cannot be created, transposition of the basilic vein of the forearm to a ventral position with end-to-side radial-basilic anastomosis is a viable alternative option.2 In patients in whom it is not possible to use autologous arteries and veins, a prosthetic AVG can be placed between an antecubital vein and the brachial artery (see Fig. 119-1B). The AVG is not the hemodialysis fistula of first choice, because the AVGs typically require more frequent (up to five times more frequent) therapeutic intervention compared with native AVFs to maintain their proper function.3 The most common cause of AVG failure is development of stenosis at the arterial and venous anastomoses, which can cause critical flow decline and subsequent thrombosis of the graft. Alternatively, although the AVF fistula has a better patency rate compared to the AVG, an AVF requires much longer period of time to ‘mature,’ typically approximately 6 to 8 weeks. Maturation of the fistula is necessary for enlargement of the draining vein to accommodate its use for hemodialysis. This process of maturation is not successful in all patients and, therefore, AVF fistulas have a higher rate of early failure, sometimes necessitating catheter insertion to provide adequate dialysis. Maturation of AVGs is generally quicker, allowing their earlier use for hemodialysis.
The use of AVF, although greater than that of AVG, for dialysis initiation has been far from universal, a fact that may be attributable to a variety of factors to include practice differences and lack of timely access to specialty care.4 There also remains a lack of sufficient evidence to support the long-held notion of the supremacy of AVF to AVG.5
There are several special roles for imaging in the management of patients with hemodialysis fistulas. First, cross-sectional imaging techniques such as duplex ultrasonography (DUS), computed tomography (CT), and magnetic resonance angiography (MRA) can provide valuable preoperative information on arterial and venous diameters as well as identify stenotic vascular segments and anatomic variants that may influence the choice of hemodialysis fistula type and location. Second, imaging is essential for surveillance of vascular complications, notably stenosis of the hemodialysis fistula. The creation of hemodialysis fistula results in an unnatural or nonphysiologic flow situation in the upper extremity, which combined with a tendency for accelerated development of atherosclerotic stenoses and obstructions in this specific population, increases the likelihood for occlusion in affected segments, which may require endovascular intervention to maintain graft patency.6
A very important consideration when choosing the optimal imaging strategy in patients who are candidates for or who already have a hemodialysis fistula is the presence of residual renal function. Residual renal function is a strong predictor of survival in patients with CKD,7,8 illustrating the important fact that dialysis clearance is not equivalent to renal clearance. Residual function in the native kidneys retains a role in sodium and water removal, and dialysis (both hemodialysis and peritoneal dialysis) remains inefficient for removing larger and protein-bound uremic toxins. Thus, the preservation of even small amounts of residual renal function in patients on HD is of major clinical importance.9 In general, residual kidney function is better preserved in patients who undergo PD versus HD. Care should be taken to avoid further reduction in residual renal function by use of large volumes of iodinated contrast agents. However, whereas MRA would seem a good alternative, the choice between different imaging modalities is becoming increasingly difficult because of the recent discovery of nephrogenic systemic fibrosis (NSF). NSF is a rare but potentially serious condition, almost exclusively seen in patients with severe CKD and renal failure, which has been linked to the administration of gadolinium-based contrast agents (GBCA) for MRA, and will be discussed in more detail in the section on MRI later. NSF has rekindled interest in nonenhanced MRA techniques, but at present these is no published data on the feasibility and accuracy of noncontrast media enhanced MRA in the preoperative workup of patients due to receive a hemodialysis fistula, nor in patients with hemodialysis fistula dysfunction due to suspected arterial or venous stenoses, although studies are underway to investigate these techniques for this purpose.
DISEASE
Definition
CKD is defined as either kidney damage or decreased kidney function for 3 or more months. The level of kidney function, regardless of diagnosis, determines the stage of CKD according to the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (K/DOQI) CKD classification into five stages (Table 119-1). It is important to realize that the prevalence of earlier stages of disease is more than 100 times greater than the prevalence of kidney failure. Kidney failure, also known as CKD stage 5, is defined as a patient with glomerular filtration rate (GFR) of less than 15 mL/kg/1.73 m2, or in practical terms, a patient requiring renal dialysis therapy. It is important to note that kidney failure is not actually synonymous with the term “end-stage renal disease (ESRD).” End-stage renal disease is an administrative term used in the United States to indicate that a patient is undergoing renal dialysis in anticipation of renal transplantation, and is a condition for payment by the Medicare ESRD program.10
| Stage | Description | GFR (mL/min per 1.73 m 2) |
|---|---|---|
| 1 | Kidney damage with normal or increased GFR | ≥90 |
| 2 | Kidney damage with mild decreased GFR | 60-89 |
| 3 | Moderately decreased GFR | 30-59 |
| 4 | Severely decreased GFR | 15-29 |
| 5 | Kidney failure | <15 or dialysis |
GFR, glomerular filtration rate.
Prevalence and Epidemiology
CKD is highly prevalent and affects approximately 8.5% of the United States adult population (26 million adults in 2008). The number of persons with kidney failure in the United States who are treated with HD and transplantation is rising rapidly and projected to increase from 340,000 in 1999 to 651,000 in 2010.10 Worldwide, an estimated 1.22 million patients were on HD in 2004, representing a 20% increase over 2001.11,12 Because of a shortage in kidney donors, the majority of CKD patients are treated by renal dialysis therapy. With the steady growth of the aging population, the number of CKD patients continues to increase, especially in patients older than 65 years of age. The fraction of patients receiving a renal transplant decreases with age. Conversely, the percentage of patients being treated by HD increases with age. Over the next few years, the number of CKD patients in need of dialysis is expected to increase by approximately 5% per year, reaching over 3 million worldwide by 2010. Because of the chronic nature of the disease, CKD is accompanied by a large increase in healthcare-related costs. In 2008, the annual costs of the Medicare ESRD program were $20 billion, and $42 billion was the amount spent on treating patients with CKD.13
Etiology and Pathophysiology
Up to 10% to 20% of all newly created hemodialysis fistulas thrombose within the first week after creation due to insufficient flow.14 Nonmaturation is defined as a hemodialysis fistula being inadequate for hemodialysis due to insufficient flow or insufficient venous distention within 6 weeks after creation. Causes of hemodialysis fistula nonmaturation are thought to include the use of small-diameter vessels (<1.6 mm in diameter),15 and presence of stenoses or occlusions in arterial inflow and/or venous outflow segments.16 The presence of large caliber side branches may also jeopardize hemodialysis fistula maturation due to altered flow distribution. Hemodialysis fistula nonmaturation rates within the first months after creation range from 5% up to 54%.17
Manifestations of Disease
Clinical Presentation
Patients in need of a hemodialysis fistula usually have a long medical history of renal disease. In fact, because almost all patients with stage 5 CKD are known to have this condition, the creation of a hemodialysis fistula can be anticipated, and sufficient time can be taken to allow for DAG maturation. The K/DOQI guidelines recommend that patients be referred for surgical evaluation when the creatinine clearance falls below 25 mL/min, or a serum creatinine >4 mg/dL (354 micromoles/L), or when creation of a hemodialysis fistula is anticipated within 1 year.18
Patients with functioning hemodialysis fistula should be under continuous surveillance for failure (i.e., stenosis or thrombosis). The K/DOQI guidelines recommend monthly flow measurements using an ultrasound-based dilution technique in every patient on HD. If absolute hemodialysis fistula flow at any time falls below 600 mL/min, or if the patient exhibits a decline >25% between two consecutive measurements in combination with an absolute flow of less than 1000 mL/min, the hemodialysis fistula is considered at risk for thrombosis.18 If this is the case, imaging is indicated to investigate the presence of inflow and/or outflow stenoses.
Imaging Indications and Algorithm
Any presurgical workup should start with a thorough history and physical examination. Women, elderly patients, and patients suffering from diabetes mellitus, obesity, cardiovascular morbidity, and patients with a history of previous vascular access procedures as well as previous limb and thoracic surgery or radiation therapy are at increased risk for hemodialysis fistula nonmaturation.19 Physical examination is an important and valuable tool in the workup of patients awaiting access surgery. Skin lesions, local infections, generalized dermatological problems and scars may indicate poor chance of successful hemodialysis fistula creation at standard locations and should be addressed. All patients should undergo bilateral blood pressure measurements of the upper extremity. A difference of more than 20 mm Hg or an arm-to-arm index of <0.9 are indicative for the presence of arterial pathology.
The anatomy of the venous system is also important to determine because it can be highly variable. The presence of small caliber veins, venous obstructions, low compliance segments, and large accessory veins is associated with higher hemodialysis fistula nonmaturation rates.18 Physical examination is useful to identify factors influencing hemodialysis fistula maturation, but it is typically not sufficient to rely on by itself. For instance, Malovrh and colleagues examined 116 patients due to undergo access creation and found that physical examination failed to identify suitable vessels for hemodialysis fistula creation in more than half of the patients.20 Venous imaging is critical for preprocedural planning for hemodialysis fistula placement.
Imaging Techniques and Findings
Ultrasound
Duplex ultrasonography (DUS) is the imaging modality of first choice in patients due to undergo graft creation as well as in patients with a failing DAG. DUS enables assessment of vessel patency, diameter, flow volume and velocities. The application of DUS enables proper depiction and determination of suitable vessels for hemodialysis fistula creation that may not be detected by physical examination, especially in obese patients.21–24
Preoperative DUS examination should include assessment of the arteries and veins from the subclavian artery down to the radial and ulnar vessels at the wrist. The exact course and continuity as well as the presence of stenoses should be addressed because patients with arterial stenosis are thought to be at increased risk for developing hand and finger ischemia after AVF creation due to steal phenomena. For detection of relevant stenoses (defined as >50% luminal reduction) in the upper extremity arterial system, DUS has a sensitivity and specificity of 90.9% and 100% for the subclavian artery, 93.3% and 100% for upper arm arteries, 88.6% and 98.7% for forearm arteries, and for the arteries of the hand 70% and 100%, respectively.25,26
Another important morphologic parameter apart from the presence of arterial stenosis is arterial diameter. Arteries with diameters smaller than 1.5 to 3.0 mm have been associated with increased AVF nonmaturation rates.14 Additional parameters such as radial artery flow volume and peak systolic velocities before or during reactive hyperemia have also been reported to be predictors of AVF maturation. In Figure 119-2 radial artery flow velocity changes due to fist clenching and reactive hyperemia are shown. Lockhart and associates, in contrast, found that arterial diameters, resistance indices, and peak systolic velocities had little if any predictive value for AVF outcome.16
FIGURE 119-2The superficial venous system of the upper extremity is also easily assessable by DUS and—not surprisingly—results in detection of more veins compared to physical examination alone. DUS also allows for assessment of local hemodynamics, such as the determination of subclavian venous flow. A typical example of Doppler signal changes of the subclavian vein during deep inspiration in a healthy volunteer is shown in Figure 119-3. The absence of changes in venous Doppler signal due to deep inspiration or loss of venous compressibility suggests the presence of a local venous stenosis or occlusion. Preoperative detection of stenoses and obstructions is important to avoid unsuccessful hemodialysis access surgeries. Nack and colleagues reported a DUS sensitivity, specificity, positive predictive value, and negative predictive value of 81%, 90%, 90%, and 78%, respectively, for detection of venous stenosis, thrombi, and occlusions when compared to DSA.27 The clinical value of upper extremity DUS for detection of venous abnormalities is lower for proximal compared to distal veins. Nack and colleagues also reported progressively decreasing DUS sensitivities for detection of abnormalities in the subclavian vein (79%), innominate vein (75%), and superior vena cava (33%), when compared to DSA.27 This can be explained by the fact that these veins course beneath bony structures such as the clavicle and ribs over a substantial length and/or are relatively distant from the skin surface and inaccessible by DUS.
FIGURE 119-3As is the case for arteries, DUS-derived venous diameter is an important parameter for prediction of vascular access outcome. For assessment of venous diameter, a proximally applied cuff should be used to induce venous dilation for better appreciation of maximum or true venous diameter.28 Reported venous cut-off diameters for successful hemodialysis fistula creation range from 1.6 to 2.6 mm.6,28 This range may be partially explained by differences in vein mapping protocols because only few authors reported the measurement conditions and methods to achieve venous dilation. DUS venous diameter measurements, furthermore, are observer-dependent with an interobserver variation reported to be 0.5 mm.29 Recently, Planken and associates have demonstrated that superficial forearm vein diameter measurements vary over time with a coefficient of variation of 27%.28 Forearm superficial venous diameter measurement reproducibility also depends on the applied venous congestion pressure and best reproducibility is achieved at venous congestion pressures >40 mm Hg.30
The preoperative length of nondiseased contiguous vein >10 cm used for AVF in addition to venous diameter was predictive for the success of AVF creation.31,32 Apart from venous diameter, some authors have found an association between the presence and size of venous side branches and AVF nonmaturation. Wong and colleagues suggested that a side branch <5 cm away from the planned anastomosis may impair AVF function, whereas Beathard and associates have stressed the importance of the size of the venous side branches. In the aforementioned studies nonmaturation was more likely in the event of a large venous side branch.33
