Residency · Residency · Vascular Surgery
Arteriovenous Grafts and Central Venous Catheters
Overview
When an autogenous arteriovenous fistula (AVF) is not feasible, prosthetic arteriovenous grafts (AVG) and central venous catheters (CVC) serve as alternative options for hemodialysis access. In the United States, AVGs account for approximately 15-20% of prevalent vascular access. Despite efforts to reduce their use, CVCs remain in use in about 20% of patients, though they are associated with the highest rates of morbidity and mortality among access types. The primary goal in managing hemodialysis access is to minimize dependence on CVCs while ensuring reliable and durable access for dialysis.
Arteriovenous Grafts
Graft Materials
Expanded polytetrafluoroethylene (ePTFE) is the most widely used material for AVGs, with standard wall grafts produced by manufacturers such as Gore and Bard. Early-cannulation PTFE grafts, including Acuseal and Flixene, feature a modified architecture that allows cannulation within 24 to 72 hours after placement. These grafts have a tri-layered or elastomeric design that resists blood leakage from needle punctures, enabling immediate use and thereby avoiding the need for temporary CVC placement. Polyurethane grafts like Vectra possess self-sealing properties, while bovine carotid artery grafts (Artegraft) offer a xenograft alternative with reasonable patency rates. Bioengineered conduits such as the human acellular vessel (Humacyte) have shown promising results in clinical trials. Cryopreserved vein allografts are reserved for use in infected fields or when other options have been exhausted.
Standard Graft Configurations
In the upper extremity, which is the preferred site for AVG placement, the most common configuration is the forearm loop graft. This involves connecting the brachial artery to the antecubital or basilic vein in a U-shaped tunnel with the apex directed distally. Other upper arm configurations include the straight graft from the brachial artery to the axillary vein and the loop graft connecting the brachial artery to the axillary or brachial vein. Less commonly, a forearm straight graft connects the radial artery to the antecubital vein.
In the lower extremity, the thigh loop graft connects the common femoral artery to the common femoral or saphenous vein. However, these grafts have higher infection and thrombosis rates compared to upper extremity grafts and are typically reserved for patients who have exhausted upper extremity options.
Unusual configurations include the necklace graft, which connects the axillary artery to the contralateral axillary or jugular vein, and the axillary-atrial graft designed for patients with bilateral central venous occlusion. The HeRO device (Hemodialysis Reliable Outflow) is a hybrid system combining a graft component with a venous outflow catheter that crosses central venous occlusions. This device is particularly useful for patients with central stenosis preventing standard access and has a lower infection rate than CVCs.
<image>Diagrams of common AVG configurations: forearm loop graft from brachial artery to antecubital vein, upper arm straight graft from brachial artery to axillary vein, and thigh loop graft from femoral artery to femoral vein</image>
Surgical Technique
Preoperative vein mapping and assessment of arterial inflow are essential steps before AVG placement. The procedure is performed under general or regional anesthesia, with brachial plexus block commonly used for upper extremity grafts. Separate incisions expose the inflow artery and outflow vein. A subcutaneous tunnel is created, typically 5 to 6 mm deep from the skin surface. The graft-to-artery anastomosis is performed using 6-0 polypropylene sutures in an end-graft-to-side-artery fashion, with an arteriotomy measuring 5 to 7 mm. The graft-to-vein anastomosis is also done with 6-0 polypropylene sutures, either end-graft-to-side-vein or end-to-end. The graft should lie smoothly without kinks, forming a gentle curve. At the completion of the procedure, a palpable thrill should be confirmed throughout the graft. Standard PTFE grafts require 2 to 4 weeks for full incorporation before cannulation, whereas early-cannulation grafts can be used within 24 to 72 hours.
Graft Outcomes
Primary patency rates for AVGs range from 50-60% at one year and decline to 30-40% at two years. Secondary patency, which includes grafts maintained with interventions, is higher, at 70-80% at one year and 50-60% at two years. Although AVGs have inferior long-term patency and higher complication rates compared to AVFs, they are superior to CVCs in terms of infection rates, mortality, and adequacy of dialysis.
Graft Complications
Thrombosis is the most common complication of AVGs, usually resulting from venous outflow stenosis. Treatment involves thrombectomy, which can be surgical or percutaneous, combined with angioplasty of the underlying stenosis. Surgical thrombectomy is performed via graftotomy using a Fogarty catheter, often accompanied by patch or interposition revision. Percutaneous approaches include pharmacomechanical thrombectomy, aspiration, and balloon angioplasty.
Venous anastomotic stenosis caused by intimal hyperplasia is the primary cause of graft dysfunction, occurring at the graft-vein junction in over 80% of failing grafts. Balloon angioplasty is the standard treatment, with drug-coated balloons currently under investigation. For recurrent stenosis, stent grafts such as Flair or Viabahn may be employed.
Infection rates range from 5 to 20% per year and are higher than those seen with AVFs. The most common pathogens include Staphylococcus aureus, Staphylococcus epidermidis, and gram-negative bacteria. Localized infections are managed with antibiotics and partial graft excision with interposition grafting, whereas extensive infections require total graft excision, ligation of the artery and vein, and antibiotic therapy. Perigraft fluid collections without systemic signs may represent seromas or early infection and should be monitored closely.
Pseudoaneurysms develop from repeated cannulation at the same sites. Small and stable pseudoaneurysms can be monitored with avoidance of cannulation at the affected site, while expanding pseudoaneurysms or those with skin compromise require surgical revision with interposition graft segments.
Steal syndrome, similar to that seen in AVFs, can occur and is treated with distal revascularization with interval ligation (DRIL), banding, or revision using distal inflow (RUDI). Seromas, which are perigraft fluid collections without infection, are more common in the first few weeks postoperatively and usually resolve spontaneously; persistent seromas may necessitate graft excision.
Central Venous Catheters
Types
Non-tunneled catheters are temporary devices inserted at the bedside for immediate vascular access and are intended for use less than 2 to 3 weeks. Common insertion sites include the internal jugular and femoral veins, while the subclavian vein is avoided due to a high risk of stenosis. Non-tunneled catheters have a high infection rate and are not suitable for chronic use.
Tunneled catheters are designed for long-term use and feature a subcutaneous tunnel from the insertion site to the exit site. A Dacron cuff promotes tissue ingrowth, creating a barrier to infection. Examples include Permcath, Ash Split Cath, Palindrome, and Mahurkar catheters. These devices can remain in place for months to years but are associated with significant complications. They are used when AVF or AVG access is not immediately available, in patients unsuitable for permanent access, or as a bridge to permanent access.
Insertion Technique
The right internal jugular vein is the preferred site for tunneled catheter insertion due to its straight path to the right atrium, which provides optimal flow and the lowest rate of malposition. Ultrasound guidance is mandatory for access, and fluoroscopic guidance is used to position the catheter tip at the cavoatrial junction, where the superior vena cava meets the right atrium. The catheter is tunneled from the access site to an exit site on the anterior chest wall, typically 2 to 3 cm below the clavicle, with the Dacron cuff positioned 1 to 2 cm within the tunnel from the exit site.
The left internal jugular vein is an acceptable alternative but has a longer and more tortuous path through the left innominate vein, leading to higher rates of malposition and flow issues, as well as an increased risk of fibrin sheath formation.
The femoral vein is reserved for temporary access only due to a high infection rate with tunneled femoral catheters, which are used as a last resort when upper body access is exhausted. The catheter tip is positioned at the inferior vena cava/right atrium junction.
The subclavian vein is avoided because of the high risk (30-50%) of subclavian vein stenosis, which can render the ipsilateral arm unusable for future AVF or AVG creation. Subclavian access is only considered when no other options exist.
<image>Illustration of a tunneled dialysis catheter showing insertion via the right internal jugular vein with subcutaneous tunnel, Dacron cuff position, and catheter tip at the cavoatrial junction</image>
Catheter Complications
Catheter-related bloodstream infection (CRBSI) is the most common serious complication of CVCs, with an incidence of 2 to 5 per 1,000 catheter-days. The pathogens involved include Staphylococcus aureus, coagulase-negative staphylococci, enterococci, gram-negative bacteria, and Candida species. Diagnosis relies on paired blood cultures from peripheral veins and the catheter, with differential time to positivity defined as catheter cultures becoming positive at least two hours before peripheral cultures.
Management of uncomplicated CRBSI involves systemic antibiotics and catheter exchange over a guidewire for non-tunneled catheters or catheter removal with placement of a new catheter at a different site, which is preferred. Exit site infections are treated with antibiotics, but if progression occurs, catheter removal is necessary. Tunnel infections mandate catheter removal and antibiotic therapy. Complicated infections such as endocarditis, osteomyelitis, or septic emboli require catheter removal and prolonged intravenous antibiotics for 4 to 6 weeks. In cases of S. aureus CRBSI, echocardiography is always performed to rule out endocarditis. Prevention strategies include chlorhexidine exit site care, antimicrobial catheter locks (such as citrate or taurolidine), maximal sterile barrier precautions during insertion, and catheter care bundles.
Catheter dysfunction is defined as blood flow less than 300 mL/min during dialysis. Thrombotic causes include intraluminal thrombus, which is treated with tissue plasminogen activator (tPA) locks (2 mg per lumen with a dwell time of 30 to 60 minutes), fibrin sheath formation that encases the catheter and impairs flow, and mural thrombus. Fibrin sheaths are managed by catheter exchange over a guidewire with fibrin sheath disruption or tPA infusion, while mural thrombi may require anticoagulation and possibly catheter removal.
Non-thrombotic causes of dysfunction include catheter malposition or migration, which can be corrected by fluoroscopic repositioning or catheter exchange, catheter kinking requiring exchange or repositioning, and mechanical obstruction such as suture entrapment of the lumen.
Central venous stenosis results from catheter-induced endothelial injury and is most problematic with subclavian catheters, which have a stenosis rate of 30-50%. Internal jugular catheters have a lower stenosis rate of 5-15%. Stenosis can prevent ipsilateral AVF or AVG creation or cause failure of existing access. Treatment involves balloon angioplasty, though recurrence rates are high; stenting is reserved as a last resort due to risks of stent fracture and in-stent stenosis. Prevention focuses on avoiding subclavian catheters, minimizing catheter dwell time, and early transition to AVF or AVG.
Other complications include air embolism during the procedure, which should be recognized and managed with Trendelenburg positioning and left lateral decubitus. Pneumothorax can occur with subclavian or misdirected jugular access and is evaluated by chest X-ray post-insertion. Arterial injury is typically managed with compression and rarely requires surgical repair. Cardiac perforation and tamponade, though rare, are fatal complications caused by catheter tips positioned too deep in the right atrium. Catheter fracture and embolization may require percutaneous snare retrieval.
<image>Fluoroscopic images showing proper tunneled dialysis catheter tip position at the cavoatrial junction, catheter malposition with tip against the SVC wall, and fibrin sheath demonstrated on contrast injection around the catheter</image>
Catheter Lock Solutions
Heparin locks, typically at concentrations of 1,000 to 5,000 units per milliliter, are standard but carry risks of heparin-induced thrombocytopenia and bleeding. Citrate locks at 4% concentration have antimicrobial properties without bleeding risk and are increasingly adopted. Taurolidine-citrate locks have demonstrated reduced CRBSI rates compared to heparin in randomized controlled trials. Antibiotic locks, such as gentamicin or cefazolin, are used prophylactically in high-risk patients but raise concerns about antibiotic resistance. Tissue plasminogen activator locks are used therapeutically for catheter thrombosis but are not routine prophylaxis.
Catheter-to-Access Transition
Every CVC placement should be accompanied by a plan for permanent access. Simultaneous AVF creation and CVC placement may be performed when the AVF requires time to mature. "Same-day" conversion involves coordinated permanent access creation and CVC removal. Early cannulation grafts can eliminate the need for CVCs entirely. Institutional protocols that facilitate timely transition from CVCs to permanent access reduce catheter dwell time and associated complications.
Clinical Pearls
An AVG that thromboses can almost always be salvaged if intervention occurs promptly, ideally within 24 to 48 hours. The most common cause of graft thrombosis is venous outflow stenosis due to intimal hyperplasia; therefore, it is critical to identify and treat the underlying stenosis during thrombectomy to prevent rethrombosis. Early-cannulation grafts represent a significant advancement for patients requiring urgent dialysis as they can eliminate the need for CVCs entirely. Staphylococcus aureus catheter infections mandate echocardiography because endocarditis is common and often occult in dialysis patients. The subclavian vein should never be used for dialysis catheter placement if there is any possibility that the patient will require ipsilateral arm access in the future. Catheter locks between dialysis sessions, using heparin, citrate, or taurolidine, are essential to maintain catheter patency and reduce infection risk. The HeRO device is a valuable option for patients with central venous occlusion who have exhausted conventional access sites, providing better outcomes than chronic CVC use.
References
- Lok CE, et al. KDOQI clinical practice guideline for vascular access: 2019 update. Am J Kidney Dis. 2020;75(4 Suppl 2):S1-S164.
- Vachharajani TJ, et al. Dialysis catheter infection: current perspectives. Hemodial Int. 2019;23(3):259-266.
- Ravani P, et al. Associations between hemodialysis access type and clinical outcomes: a systematic review. J Am Soc Nephrol. 2013;24(3):465-473.
- Weijmer MC, et al. Randomized, clinical trial comparison of trisodium citrate 30% and heparin as catheter-locking solution in hemodialysis patients. J Am Soc Nephrol. 2005;16(9):2769-2777.
- Al-Jaishi AA, et al. Complications of the arteriovenous fistula: a systematic review. J Am Soc Nephrol. 2017;28(10):2868-2878.
