Overview
Definition:
An arteriovenous (AV) graft is a synthetic tube surgically implanted to create vascular access for hemodialysis
It connects an artery to a vein, typically in the arm, allowing for adequate blood flow for dialysis
The graft acts as a conduit for the needles used to draw blood and return it to the body during treatment.
Epidemiology:
End-stage renal disease (ESRD) affects millions worldwide, with a growing prevalence due to aging populations and increased incidence of diabetes and hypertension
AV grafts are a common form of vascular access, often used when native AV fistulas are not feasible or have failed
Approximately 20-30% of hemodialysis patients utilize AV grafts.
Clinical Significance:
Adequate and durable vascular access is paramount for effective hemodialysis and patient survival in ESRD
AV grafts offer a viable alternative when native fistulas are not an option, providing reliable access for treatment
Understanding AV graft placement, management, and complications is crucial for surgeons managing patients with kidney failure, impacting patient outcomes and quality of life.
Indications
Indications For Placement:
Primary indication is the need for chronic hemodialysis access in patients with ESRD
Specific scenarios include: inadequate vein diameter for AV fistula creation
failure or maturation delay of a previously created AV fistula
patients requiring immediate or urgent dialysis access when other methods are not suitable
absence of suitable peripheral veins for fistula formation.
Patient Selection Criteria:
Appropriate patient selection involves assessing the likelihood of fistula maturation and the patient's overall health status
Factors considered include peripheral vascular disease, previous surgeries in the limb, and patient preference
Pre-operative assessment of the anatomy of the arm vessels is essential.
Contraindications:
Absolute contraindications are rare but may include active infection at the proposed access site, severe peripheral arterial disease compromising blood flow to the limb, or inability of the patient to tolerate surgery
Relative contraindications might include severe comorbidities that significantly increase surgical risk.
Preoperative Preparation
Patient Assessment:
Thorough pre-operative evaluation includes a detailed medical history, physical examination focusing on the vascular system of the upper extremities, and review of prior imaging or surgical reports
Assessment of limb viability and presence of collateral circulation is important.
Imaging Studies:
Pre-operative imaging, such as duplex ultrasonography, is essential to map the anatomy of the arteries and veins, assess their diameter, and identify any stenotic lesions or occlusions
This helps in planning the optimal graft configuration and placement.
Consent And Counseling:
Informed consent must be obtained from the patient, discussing the procedure, potential risks (infection, thrombosis, bleeding, limb ischemia, steal syndrome), benefits, and alternatives
Patients should be counseled on post-operative care and the importance of limb care.
Procedure Steps
Anesthesia And Positioning:
The procedure is typically performed under local anesthesia with sedation, or general anesthesia for more complex cases
The patient is positioned supine with the arm abducted and prepared aseptically
A sterile tourniquet may be used.
Graft Selection:
Synthetic grafts, commonly made of polytetrafluoroethylene (PTFE), are used
Grafts come in various diameters (typically 6-8 mm) and lengths, and the choice depends on the patient's anatomy and surgeon preference
The graft material should be biocompatible and promote tissue ingrowth.
Arterial Anastomosis:
The graft is typically tunneled subcutaneously to connect a suitable artery (e.g., brachial artery) to a suitable vein (e.g., cephalic vein)
The arterial anastomosis is usually end-to-side, connecting the proximal end of the graft to the artery
Meticulous dissection and secure, watertight sutures are crucial to prevent bleeding.
Venous Anastomosis:
The venous anastomosis is also typically end-to-side, connecting the distal end of the graft to a suitable vein, usually cephalic vein or basilic vein
The graft segment between the anastomoses should be straight and free from tension to minimize kinking and thrombosis.
Graft Positioning And Closure:
The graft is then tunneled subcutaneously, ensuring adequate coverage with soft tissue
The skin incision is closed in layers, and a sterile dressing is applied
Hemostasis is meticulously achieved throughout the procedure.
Postoperative Care
Immediate Postoperative Monitoring:
Close monitoring of the graft for patency is critical in the immediate post-operative period
This includes assessment of palpable thrill and audible bruit over the graft, limb color, temperature, and distal pulses
Hemodynamic stability and fluid balance are also monitored.
Wound Care:
The surgical site should be kept clean and dry
Dressing changes are performed as per protocol
Patients are instructed to avoid strenuous activity with the operated arm and to monitor for signs of infection.
Anticoagulation And Antibiotics:
Prophylactic antibiotics are usually administered peri-operatively
Anticoagulation is generally not required unless there is a specific indication, such as during cannulation for dialysis
Heparin may be used during the procedure to prevent graft thrombosis.
Timing Of First Cannulation:
AV grafts typically mature faster than AV fistulas
The first cannulation for hemodialysis is usually performed 2-3 weeks post-operatively, allowing time for the graft to heal and for surrounding tissue to mature, reducing the risk of bleeding or graft complications.
Complications
Early Complications:
Early complications can occur within the first few weeks
These include: Hemorrhage from the anastomosis sites
Graft thrombosis (clotting within the graft)
Infection of the graft or surrounding tissues
Arterial steal syndrome (insufficient blood flow to the distal limb).
Late Complications:
Late complications can arise months or years after implantation
These include: Graft stenosis leading to outflow obstruction and poor dialysis efficiency
Graft pseudoaneurysm formation
Graft rupture
Graft infection
Distal embolization
Infection of the graft with systemic spread (endocarditis).
Prevention And Management:
Prevention involves meticulous surgical technique, appropriate graft selection, and careful post-operative monitoring
Management of complications depends on the specific issue: thrombosis may require thrombectomy and revision
stenosis is treated with angioplasty or surgical revision
infection requires systemic antibiotics and often graft excision.
Key Points
Exam Focus:
Understand the indications for AV graft placement vs
AV fistula
Know the common synthetic graft materials (PTFE) and their properties
Be familiar with the arterial and venous anastomosis techniques
Crucial complications to remember are thrombosis, infection, stenosis, and steal syndrome.
Clinical Pearls:
Always assess the entire limb for vascular access options before planning surgery
The straightest course for the graft between the artery and vein minimizes tension and risk of kinking
Post-operative monitoring for thrill and bruit is paramount for early detection of thrombosis
Recognize signs of steal syndrome early and consider surgical revision.
Common Mistakes:
Failure to adequately assess pre-operative vascular anatomy leading to suboptimal graft placement
Inadequate hemostasis at anastomosis sites leading to post-operative bleeding
Implantation of a graft under tension, increasing risk of thrombosis
Neglecting to monitor for early signs of infection or thrombosis.