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Ambulatory Treatment of Dialysis Access Stenosis
Dialysis access management was traditionally performed in the hospital setting. Now, newly developed percutaneous techniques have allowed some of these procedures to be transitioned to the outpatient office setting.
The increased prevalence of diabetes and hypertension in an aging population has resulted in a steady rise of patients with chronic kidney disease (CKD) in need of hemodialysis. The autogenous arteriovenous fistula (AVF) is preferred over synthetic grafts as a result of their superior long-term patency; however, the cost of this choice is inferior maturation of autologous arteriovenous access and the subsequent need for several interventions before the access can be used. The increase in the total number of AVFs has increased the number of procedures and interventions required to maintain them. The scheduling of an increased number of cases in the operating room, outside of the block time, can be difficult and often results in a prolonged waiting time for patients with a failing dialysis access. Moving these procedures to the office setting can shorten the waiting time and improve overall patient satisfaction.
Inherent in this practice is the early identification of a failing dialysis access in order to prevent thrombosis, because thrombosis can result in a poor outcome. Stenosis results from the development of neointimal hyperplasia in the anastomosis, outflow tract, and central veins. The easiest way to monitor the access is by routine history and physical examination of the fistula.
If a suspicion exists that the AVF is failing, a duplex ultrasound (US) of the fistula is routinely performed to exclude or confirm the diagnosis of a hemodynamically significant stenosis.
An established protocol is used for scanning the fistula. The protocol routinely starts with color imaging. A brief scan helps depict distinct color patterns in stenotic areas (e.g., aliasing, mosaicking, turbulence). B-mode imaging of the entire fistula provides information regarding the nature of these stenoses, such as the presence of intraluminal venous webs and/or frozen valves. A severe stenosis is one greater than 70% in the inflow artery, the anastomosis, along the access conduit, or in the outflow vein based on duplex criteria of direct vessel diameter reduction measured on color images after optimization of the pulse frequency repetition (PRF) to avert errors caused by bleeding effect and peak systolic velocity (PSV) ratio of 3 or more. We also measure the size of the AV fistula in different segments and the volume flow. Knowledge of the size of the fistula can allow preparing appropriate equipment the day before intervention, which helps to keep inventory in the office at the bare minimum.
After the diagnosis has been established and stenosis has been visualized with duplex US, the patient is scheduled for an outpatient office-based intervention. Once the failing fistula is identified, it can be managed in the office with two main techniques: fluoroscopic and/or US guidance. At present, the author uses only US guidance in the office for managing stenosis of the fistula.
Technique of Ultrasound-Guided Fistula Treatment
An HDI 5000 scanner with a SonoCT feature (Philips Medical Systems, Bothell, WA) is used for all imaging. The most advantageous position of the ultrasound machine in the room is on the side of intervention, close to the patient’s arm. This helps provide adequate visualization for the surgeon and vascular technologist. After the patient is positioned on the examination table, the ipsilateral upper extremity is prepped and draped in the usual sterile manner. A compact linear 15-7-MHz transducer gives superb images of the entire fistula length owing to its superficial localization. The vascular technologist assisting with duplex scan imaging is scrubbed, gowned, and gloved in the same manner as the operating interventionalist. All patients are connected to the monitor for continuous recording of vital signs, including the patient’s oxygen saturation.
All AVFs are cannulated under ultrasound guidance, using local anesthesia, with the puncture site being at least 4 cm away from the most proximal stenosis. We use either a micropuncture or an 18-gauge hollow-bore needle for initial cannulation. We perform most of the procedures through small 4-Fr or 5-Fr sheaths. The stenosis is addressed with balloon angioplasty in a retrograde or antegrade fashion. A 0.018-inch curved-tip guidewire (Terumo Medical Corporation, Somerset, NJ) is inserted and then gently threaded through the stenosis and parked in the proximal artery (during retrograde cannulation) or distal vein (during antegrade cannulation). Occasionally, the distal artery is selected for cannulation. If this wire encounters resistance because of intraluminal web, we attempt to cross it with the soft end of a 0.035-inch curved tip guidewire, supported by a 4-Fr Bern directional catheter (Boston Scientific Corporation, Natick, MA).
The safety of these maneuvers is enabled by a real-time visualization of the wire tip in the lumen by way of the duplex scan. Balloon insertion, positioning, and inflation are performed under duplex scan guidance as well. Angioplasty balloons are chosen based on precise duplex scan measurements of the venous or arterial lumen diameter adjacent to the stenosis. Sterling (Boston Scientific) ultra-low-profile balloons of various sizes (3–10 mm) are inflated several times up to 20 atmospheres of pressure until the stenosis has resolved. We monitor balloon inflation carefully under US guidance.
Cutting balloons may be used for lesions that recoil following standard balloon angioplasty. We define recoiling stenosis as a 40% diameter reduction on color-flow imaging, creating an increased PSV ratio greater than 2. We routinely use completion duplex scans to evaluate for adequacy of treatment. Mean AVF volume flows and the highest PSV at the area of former stenoses are registered and recorded. Patients stay in the office, on average, for 20 minutes, and are released to home after a nursing check of the puncture wound dressing and the patient’s vital signs.
Limitations of this technique include inability to visualize more central lesions in the veins of the chest. For those lesions, conventional fluoroscopy is advantageous. These procedures require cooperation from the patient because it is important to precisely localize and treat the lesion without any motion interference from the patient. Uncooperative or anxious patients might not be able to tolerate a procedure in the office setting without sedation. In that case, the procedure should be terminated and rescheduled for in-hospital treatment with moderate sedation.
There are several benefits to ultrasound-guided fistula management. First, it does not require the use of contrast material and thus can be used in patients not currently on hemodialysis and in patients with intravenous contrast allergies. Second, it eliminates radiation exposure to the patient and operative personnel. Third, it is less expensive than fluoroscopic management because of lesser equipment requirements.
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