Nursing Care for Patients with Synthetic Arteriovenous Grafts.
History of Vascular Access
During the second World War (1943-1945), in the occupied state of Saxony, Germany, WJ. Kolff designed the "artificial kidney." Fabricated from a salvaged car, washing machine parts, orange juice cans, and sausage skins, this was the first hemodialysis machine used in the treatment of kidney failure. Repeated cut downs on veins and arteries were required for each hemodialysis treatment, which caused the vessels to become ligated, and hemodialysis to be limited to treating acute kidney injuries only (Bennion, Williams, & Wilson, 1994). The search continued throughout the next few years for a more long-term hemodialysis vascular access solution.
During the 1960s, access to circulation for patients with ESRD became a reality when Scribner, Dillard, and Quinton introduced the Teflon-Silastic arteriovenous (AV) shunt. Later in the decade, Brescia, Cimino, Appel, and Hurwich (1966) introduced the subcutaneous AV fistula, which replaced the Scribner Shunt due to its improved effectiveness and safety assessments. The hemodialysis graft was then introduced, and in 1972, one new biologic and two new synthetic graft materials were made available. In 1976, L.D. Baker, Jr., presented the first results of a study with expanded polytetrafluoroethylene (ePTFE) grafts in patients on hemodialysis (Konner, 2005). According to May, Tiller, Johnson, Stewart, and Sheila (1969), the development of an access with synthetic materials helped expand the availability of hemodialysis to a larger population.
During a plan of care meeting with the Interdisciplinary Team, the team discussed a patient with exhausted vascular access options. Mrs. M had numerous failed AV fistulas and grafts over the years and was now dependent upon a central venous catheter (CVC) for hemodialysis therapy. The medical director decided to evaluate Mrs. M for placement of a HeRO[R] graft. The hemodialysis team had not previously cared for this type of vascular access. Nurse manager Diane realized quickly that she needed to prepare her team to care for Mrs. M's new vascular access. Diane also discovered that there were several types of synthetic grafts, with which she and her team were unfamiliar.
To ensure her team could provide care guided by the most current information, Diane read several recently published articles. In reading the literature on synthetic grafts, she learned that the core material was generally created from expanded ePTFE or polyurethane. She also found there were differences in the graft material characteristics and related clinical applications based on synthetic graft design (Vachharajani, Wu, Brouwer-Maier, & Asif, 2015).
Merit Medical Synthetic Grafts
Hemodialysis Reliable Outflow (HeRO[R]) and Super HeRO[R] Grafts
The two components of a Hemodialysis Reliable Outflow (HeRO[R]) vascular graft are the arterial graft and the venous outflow section, which are joined by a titanium connector (see Figure 1). The arterial graft portion is composed of ePTFE with an inner diameter of 6 mm. This area connects to an artery and is reserved for AV graft cannulation procedures. The venous outflow segment is designed with radiopaque silicone and braided nitinol to resist kinking and crushing, and is placed in the mid to right atrium. Unlike a CVC, the HeRO graft is entirely subcutaneous, and unlike a typical AV graft, the venous anastomosis is bypassed (Gage et al., 2012; Katzman et al., 2009). The Super HeRO[R] adaptor is engineered to connect to additional standard wall and early cannulation graft options, such as Flixene[R] and Acuseal[R]. When a surgeon chooses to use the Super HeRO (titanium connector and venous outflow component) and attach it to one of the early cannulation grafts (Flixene or Acuseal), patient care staff should follow that manufacturer's instructions for use (IFU) for cannulation (Merit Medical, 2017b). In a retrospective review (n = 164), Gage et al. (2012) found that HeRO grafts outperformed CVCs regarding patency, interventions, and infection rates, and performed comparably to standard AV grafts.
As a result of her review of the research, Diane believed that Mrs. M was a befitting candidate for this type of vascular access. The HeRO graft is an option for those who have exhausted or failing AV fistulas or AV grafts due to central vein stenosis or venous outflow obstruction, are catheter-dependent, or are approaching catheter dependency (Dinwiddie, 2009). Prior to placement of a HeRO graft, patients should be evaluated to confirm central venous stenosis and to ensure the following: 1) no existing allergies to device materials, 2) diameter of brachial or target artery 3 mm or larger, 3) systolic blood pressure greater than 100 mmHg, 4) ejection fraction 20% or higher, 5) blood cultures negative for infection, and 6) medical management for hypercoagulation (Merit Medical, 2016; National Kidney Foundation [NKF], 2012).
According to the manufacturer's information for use in hemodialysis (Merit Medical, 2016, 2017a), nursing staff should follow KDOQI guidelines for graft assessment, preparation, and cannulation.
* Allow 2 to 4 weeks for graft incorporation and healing post-implant (unless using an early cannulation graft with a HeRO adapter).
* Resolve edema prior to cannulation.
* Assess the graft by looking, listening, and feeling.
* Use aseptic technique for all cannulation.
* Understand that a light tourniquet is allowed to dilate the graft before cannulation because the absence of a venous anastomosis may produce a softer bruit and thrill than a traditional ePTFE graft.
* Never cannulate the venous outflow component.
* Cannulate at least 3 inches away from the connector incision site to avoid injury to graft rings.
* Stay within fistula needle length from the arterial anastomosis.
* Rotate needles sites to avoid pseudoaneurysm formation.
* Apply moderate digital pressure post-needle removal. Do not use mechanical clamps or straps because occlusion may occur.
Bard Synthetic Grafts
Venaflo[R] II Vascular Grafts
Venaflo[R] II vascular grafts are made of ePTFE material with carbon impregnated into the inner portions of the graft wall (see Figure 2). These grafts, modified with a proprietary cuff with trim lines at the venous end, are recommended only for use as subcutaneous AV conduits for blood access. Through advanced flow and carbon surface, they are designed to improve patency and lessen the severity of venous stenosis (Bard Peripheral Vascular, 2015b).
In one research study, a prospectively randomized group (n = 48) was followed for up to 24 months after placement of either a cuffed or a standard ePTFE graft. The overall incidence of graft failure was significantly lower in the cuffed ePTFE graft group; graft patency rates in the cuffed versus standard groups were 64% vs. 32% at 12 months and 58% vs. 21% at 24 months (Sorom et al., 2002). In another study, patency rates after 6 weeks were 25% for straight grafts and 62% for Venaflo-type grafts (Heise et al., 2011).
Carboflo[R] Vascular Grafts
Carboflo[R] vascular grafts contain carbon that has been impregnated into the inner portions of the graft walls (see Figure 3). They are designed to reduce early graft failure due to thrombosis. In addition, the grafts are intended for use as subcutaneous AV conduits for blood access, bypass, or reconstruction of peripheral arterial blood vessels, as well as use for decreasing platelet adhesions (Bard Peripheral Vascular, 2012).
In a prospective, randomized multicenter research study, researchers examined the comparison of patients with a 6 mm carbon-coated Bard Carboflo vascular graft or an uncoated Bard ePTFE vascular graft for a femoral-anterior tibial artery bypass. At a 3-year follow up, there were no significant differences between the two groups regarding patency or limb salvage (Kapfera, Meichelboeck, & Groegler, 2006).
Impra[R] Vascular Grafts
Impra[R] vascular grafts are synthetic grafts constructed of ePTFE material, indicated for the use as a vascular access prosthesis (see Figure 4). These grafts have better patency results when compared to wrapped grafts. They are also designed for fewer interventions and promote better tissue incorporation (Bard Peripheral Vascular, 2015a).
In one study, Hurlbert et al. (1998) examined whether there were differences in patency rates, complications, and costs between two manufacturers of ePTFE grafts: Gore-Tex[R] and Impra vascular grafts. Results from the study did not find any difference in the performance of 6 mm standard ePTFE grafts.
While nurses perform care for the Venaflo II, Carboflo, and Impra vascular grafts, manufacturers advocate not cannulating prior to 2 weeks post-access placement. The immediate use of these grafts may increase the risk of a hematoma formation. Upon cannulating, the blood access needle must be inserted with the bevel upward at an angle of 20[degrees] to 45[degrees], carefully avoiding the possibility of cannulating the cuffed portion of the graft. Once cannulated, the access needle should be advanced parallel to the graft, and adhering to recommendations, shall not be flipped. Upon removing the needles, apply moderate digital pressure. Finally, needle sites must be rotated to avoid development of hematomas and pseudoaneurysms.
W.L. Gore Synthetic Grafts
Hybrid[R] vascular grafts are designed to reduce intimal hyperplasia and improve outflow dynamics (see Figure 5). Davidson, Ross, Gallichio, and Slakey (2014) found that intimal hyperplasia causes 90% of access dysfunction. The material in Hybrid vascular grafts has a nitinol reinforced section (nickel titanium), as well as a continuous lumen bonded with Carmeda BioActive Surface (CBAS), a stable reduced molecular weight heparin. With a combination of Stretch graft and CBAS, this graft expands options for patients with challenging site locations and deep vessels. A study by Davidson et al. (2014) reported a 70% patency rate after 12 months. Care considerations and complications are standard for any graft used for hemodialysis and can include infection and pseudoaneurysm formation due to excessive, large needle punctures.
Propaten[R] vascular grafts are made of the same ePTFE material, but they have heparin bonded to the luminal surface (see Figure 6). This is intended to help prevent blood from clotting and aid in prolonging the use of the graft. The long-term patency is similar to the Stretch graft (see below), leading to the belief that in both graft types, neointimal hyperplasia occurs at the vein-graft anastomosis and in the graft wall due to repeated needle punctures for hemodialysis and endothelial dysfunction caused by uremia (Davidson et al., 2014). Use of this type of graft is contraindicated particularly for patients with known heparin sensitivity and those who have had previous incidence of heparin-induced thrombocytopenia (HIT) type II.
Intering[R] vascular grafts, also known as Stretch grafts, are made of reinforced ePTFE with an integrated radial support (see Figure 7). It easily conforms to native vessels and has a smooth, luminal surface. The graft is soft, yet strong, and its 2-layer principle provides protection against aneurysm formation. It has been used successfully for difficult hemodialysis accesses, such as the necklace graft. (Morsy, Khan, & Chemla, 2008). One-year patency has been reported at 73% (Thibodeaux & Reyes, 2005). When using this, care must be taken to adequately separate puncture sites, and to avoid repeated localized clamping or excessive clamping on any section of the graft.
Acuseal[R] vascular grafts incorporate three layers of materials designed to optimize early cannulation within 24 hours of implantation (see Figure 8). Although the outer layer is consistent with the majority of ePTFE synthetic graft composition, the middle layer is composed of an elastomer membrane, which is intended to reduce suture line and puncture site bleeding, while also potentially decreasing the risk of seroma formation. The inner layer, which is similar to the Hybrid vascular graft, contains an end-point bonded heparin, and this CBAS is affixed to the ePTFE lumen to support resistance to thrombosis. Due to the intraluminal surface of the CBAS, Acuseal vascular grafts are contraindicated in patients with HIT (Maytham, Sran, & Chemla, 2015; W.L. Gore & Associates, Inc., 2011, 2017).
Early cannulation guidelines were developed to prevent infection, bleeding, and damage to the new vascular access. Aseptic technique is essential for all cannulation procedures; clinicians should wear sterile gloves for the first 3 hemodialysis sessions as surgical incisions are healing. Manufacturer instructions for early cannulation also recommend the following for a minimum of 3 consecutive treatments: cannulate with 17-gauge needles, reduce the blood flow to 200 to 250 mL/minute, administer low dose heparin, and hold digital pressure for 10 to 15 minutes post-needle removal (W.L. Gore & Associates, Inc., 2016).
Vascular Flow Technologies
This type of vascular graft is an ePTFE, with chronoflex polyurethane injected molded components consisting of the Spiral Flow[TM] inducer, an inducer ring, and a pre-cut distal anastomotic cuff (see Figure 9). The patented Spiral Luminal Flow[TM] technology was designed to prevent neointimal hyperplasia by decreasing turbulence and creating a spiral flow that mimics the blood flow of a native AV fistula into the venous system (Vascular Flow Technologies, 2017b). Results of a study by Hoffman and Feldkirch (2015) showed a 22-month primary patency rate of 72% and a secondary rate of 85.5%.
Specific guidelines apply in the care and assessment of this unique vascular access. To preserve its lifespan, the area from the inducer ring to the venous anastomosis must not be cannulated. The inducer ring is easily palpated over the skin, but the thrill and bruit may be softer than a traditional graft because there is little to no turbulence across the venous anastomosis. Standard manufacturer guidelines include adhere to strict aseptic technique, cannulate at a 35[degrees] to 45[degrees] angle, rotate needle sites, and use 2finger compression post-needle removal to achieve hemostasis (Vascular Flow Technologies, 2017 a).
Synthetic Graft Complications
A substantial number of patients on chronic hemodialysis require prosthetic AVGs. Early reports describing hemodialysis access using ePTFE explained how surgical results with these materials have remained suboptimal and noted graft thrombosis as the most common dialysis graft dysfunction (Scher & Katzman, 2004). In 90% of thrombosed grafts, the underlying pathology leading to thrombosis is neointimal hyperplasia at the venous anastomosis associated with turbulent flow. However, there have been recent modifications in ePTFE grafts, as well as alternative graft materials that have yielded encouraging results in the effort to improve both patency and clinical outcomes.
The most prominent vascular access-related complications for patients on hemodialysis are thrombosis or stenosis, infection, and formation of an aneurysm. To successfully care for a client with an AV graft, Diane and the patient care team would need to follow the following guidelines.
* Palpate for a thrill and auscultate for a bruit prior to cannulation.
* Do not take blood pressure readings on an extremity in which the vascular access is placed.
* Do not start an intravenous (IV) line or perform a venipuncture in the extremity in which vascular access is placed.
* Assess the patient's distal pulses and circulation in the extremity with the vascular access.
* Assess for manifestations of infection, such as fever, tachycardia, redness, and drainage at the needle site.
* Check for bleeding at needle insertion sites (Ignatavicius & Workman, 2015).
Vascular accesses have improved significantly over the years, affording patients better outcomes for long-term hemodialysis therapy. However, patients are still at risk for graft failure and issues with patency. The ideal vascular graft for patients on hemodialysis needs to be easy to handle, should closely mimic native vessels in the body, and be resistant to infection to retain strength and patency.
Through her initiative and literature review, Diane has gained practical knowledge about many types of synthetic grafts. She is now better equipped to share her knowledge and prepare her team in caring for Mrs. M's newly placed HeRO vascular access graft. Because of the variety of AVGs and the unique features of each that make one or another particularly amenable to a specific patients' needs, Diane decided to provide an overview of the features of one AVG type each week during team meetings. With the information she gleaned from the literature reviews, she has the information necessary to present to her team on the use, contraindications, implications, and care considerations for diverse synthetic grafts.
Statement of Disclosure: The authors reported no actual or potential conflict of interest in relation to this continuing nursing education activity.
Note: The Learning Outcome, additional statements of disclosure, and instructions for CNE evaluation can be found on page 399.
Please Note: Illustration(s) are not available due to copyright restrictions.
Bard Peripheral Vascular. (2012). ePTFE grafts. Retrieved from http://www. bardpv.com/wp-content/uploads/ 2013/07/S120181_R0_ePTFE_Peri pheral2.pdf
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Michelle Gilliland MSN, RN, CNN, is Principal, Clinical Innovation Initiatives, the Medical Office of Fresenius Medical Care, Bennington, NE; a member of ANNA's Administrative SPN Group; and a member of ANNA's Nebraska Platte River Chapter.
Jami S. Brown, DHEd, RN, CNN, is an Assistant Professor, the University of Tennessee Health Science Center, the College of Nursing, Memphis, TN; is Leader of ANNA's Educator SPN Group; and is a member of ANNA's Memphis Blues Chapter.
Lillian Pryor, MSN, RN, CNN, is Principal, Clinical Innovation Initiatives, the Medical Office of Fresenius Medical Care Lawrenceville, GA; and is the ANNA National Director and Health Policy Representative for ANNA's Dogwood Chapter.
Statement of Disclosure: The authors reported no actual or potential conflict of interest in relation to this continuing nursing education activity.
Caption: Figure 1 HeRO[R] Vascular Graft
Caption: Figure 2 Venaflo[R] II Vascular Graft
Caption: Figure 3 Carboflo[R] Vascular Graft
Caption: Figure 4 Impra[R] Vascular Graft
Caption: Figure 5 Gore Hybrid[R] Vascular Graft
Caption: Figure 6 Gore Propaten[R] Vascular Graft
Caption: Figure 7 Gore-Tex[R] Stretch Vascular Graft
Caption: Figure 8 Gore Acuseal[R] Vascular Graft
Caption: Figure 9 Spiral Flow[TM] Vascular Graft
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|Author:||Gilliland, Michelle; Brown, Jami S.; Pryor, Lillian|
|Publication:||Nephrology Nursing Journal|
|Date:||Sep 1, 2017|
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