Fresenius Medical Care Completes Acquisition of NxStage Medical
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The timing of interventions, which result in optimal access function and prolong the useful life of a vascular access (VA), is yet to be determined. Both Kidney Disease Outcomes Quality Initiative (KDOQI) and CMS conditions for coverage for ESRD facilities have mandated monitoring by physical examination and surveillance as an integral part of VA care.2,3 Since these mandates were established, there have been remarkable changes in the access landscape. This includes a national proliferation of outpatient vascular access centers, which in one analysis demonstrated significantly fewer vascular access-related infections, fewer septicemia-related hospitalizations, and a lower mortality rate compared to patients treated in hospital outpatient departments.4
Figure 1 | United States AVF Rates by 2014
Since the KDOQI guidelines were first published as the Dialysis Outcomes Quality Initiative (DOQI) recommendations in 1997, access care has changed significantly. For instance, the use of expanded polytetrafluoroethylene (ePTFE) stent grafts, to enhance angioplasty primary patency outcomes, and the use of early stick grafts as a catheter avoidance strategy have emerged. Additionally, dialysis blood pump speed rates rarely exceeded 350cc/min, and guidelines for access intervention recommended waiting until AVF blood flow was less than 400-500 mL/min for AVF and less than 600 mL/min for arteriovenous grafts (AVGs) before referral for diagnosis and intervention.3 Today blood pump flow rates of 450-500 mL/min are expected; waiting until the recommended threshold implies the access may already be dysfunctional.
Although the optimal access flow rate remains unclear, it is known that percutaneous access interventions are effective treatments for failing accesses, and timely interventions will delay episodes of thrombosis and will avoid hospitalizations.6 While the optimal interval of interventions is patient-specific, preemptive interventions as scheduled by monitoring and surveillance techniques have been demonstrated to decrease costly thrombosis episodes.
More sophisticated programs targeting treatment of stenosis at higher flow rates have been shown in some hands to prolong the useful life of an access.1 The goal is to detect and treat clinically relevant stenosis before the patient experiences access failure resulting in missed dialysis treatments and unwanted catheter exposure. Surveillance and monitoring techniques are powerful tools to avoid access complications and are justifications for PTA treatment of stenosis.
Vascular Access Dysfunction
Each of the above is an indication of access dysfunction that is usually caused by an underlying stenosis. Treated preemptively, PTA of the associated stenosis can enhance dialysis efficiency and avoid thrombosis. Stenotic lesions can occur anywhere within the AVF or AVG circuit. Nearly all of these stenoses are treatable with PTA.3
KDOQI states that patients with an AVG or AVF who experience edema of the extremity should undergo an imaging study to evaluate patency of the central veins. If central vein stenosis is found, PTA is the recommended treatment. In the event of acute elastic recoil of the vein (less than 50 percent stenosis) after PTA, or if the stenosis reoccurs within three months, stent placement should be considered.3
KDOQI recommends regular assessment for possible ischemia, as part of the monitoring/surveillance program. Physiological steal syndrome occurs in 73 percent of patients with an AVF and 91 percent of patients with an AVG.7
Although generally well tolerated, this may become symptomatic and result in steal syndrome in up to 20 percent of hemodialysis patients.7-12 Early recognition allows for a timely initiation of treatment to prevent potential tissue loss. If the symptoms are mild, wearing a glove on the involved hand and continuing monitoring via thorough physical exam and assessment are often sufficient.
When symptoms are more severe, endovascular and/or surgical interventions may become necessary. In cases of severe steal, with tissue loss, immediate ligation or physiological restoration of blood flow is imperative.13 When an arterial stenosis is the primary cause, PTA is the preferred route and has been shown to be safe and effective.9,14 Percutaneous treatment of any underlying arterial lesions prior to considering surgery may resolve the symptoms and concurrently avoid compromise of the VA.14-17 Beyond inflow stenosis, steal syndrome is treated with procedures that increase inflow resistance, including distal revascularization and interval ligation (DRIL)18 as inpatients, and MILLER- banding as outpatients.16,17
There have been a number of endovascular techniques used to treat a thrombosed AVF and AVG.19-25 Most of these techniques include treatment of stenosis as an integral part of the thrombectomy process.
Nonmature fistulae generally fail to mature due to an underlying stenosis in the feeding artery, at the arterial anastomosis, in the outflow vein, or a combination of issues. Angioplasty is indicated to treat these stenoses and promote maturation.
An aneurysm of an AVF is an area of bulging dilatation in the body of the AVF that involves all layers of the wall of the vessel. A stable aneurysm can be left alone, as long as it is monitored. Any changes revealed during physical examination of the aneurysm should be evaluated, and any underlying stenosis should be repaired. Treatment of an aneurysm may be surgical, endovascular, or a combination of the two.26 Since this abnormality is so closely associated with venous stenosis, PTA is frequently the first line of therapy.
The following are indicators of potential graft rupture that should be evaluated urgently:
Patients with pseudoaneurysms should be evaluated for outflow stenosis as soon as possible, and if confirmed, the outflow lesion should be treated by PTA or surgery. While the treatment of the pseudoaneurysm per se is handled most effectively by surgical techniques, there are situations where stent grafts may be utilized.27,28
PTA has become the first line therapy for dialysis vascular access dysfunction. By treating a host of conditions, PTA plays a vital role in maintaining optimal dialysis access function in the fragile ESRD population.
Murat Sor, MD
Chief Medical Officer, Azura Vascular Care
FMCNA Corporate Medical Advisory Board Member
A graduate of the University of Pennsylvania, Dr. Murat Sor is certified by the American Board of Radiology, with subspecialty certification in interventional radiology. He is an assistant professor at Georgetown University Hospital’s Interventional Radiology Fellowship program and an adjunct instructor at the George Washington University School of Medicine.
Percutaneous Transluminal Angioplasty Clinical Pathway Summary
by Murat Sor, MD