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Thrombotic Complications of Arteriovenous Access
The achievement and maintenance of sites for hemodialysis is a persistent challenge. A hemodialysis access that remains patent and free of infection and complications is critical to ensuring a high standard of care for the patient with end-stage renal disease (ESRD). The updated Kidney Disease Outcomes Quality Initiative (KDOQI) provides evidence-based clinical practice guidelines for all stages of chronic kidney disease and reports autogenous fistulas (AVFs) to represent the reference standard for primary vascular access because of longevity and low infection rates.
An AVF can be constructed either as a simple fistula (an artery connected to a vein) or as an interposition graft (an artery connected to a vein with prosthetic material [AVG]). The most common prosthetic material used in the construction of interposition grafts is polytetrafluoroethylene (PTFE). The main complications of AVFs and AVGs are stenosis, thrombosis, pseudoaneurysm formation, and infection. The most common of these complications is graft stenosis and subsequent thrombosis. Graft failures are common and contribute to multiple hospital readmissions, complex reinterventions, invasive radiologic studies, and the significant overall morbidity rate associated with chronic hemodialysis.
Risk Factors for Thrombosis of Arteriovenous Access
A variety of factors predispose a patient to thrombosis of arteriovenous access: inflow disease, anastomotic factors, complications with the conduit, systemic factors, and intradialytic factors.
Inflow Disease
Flow-limiting disease in the feeding artery is a cause of early nonmaturation and eventual failure of dialysis access, especially in AVGs. Atherosclerotic disease in the native artery precludes normal flow volumes in the access, leading to primary nonmaturation of AVFs. Progressive disease in the native vessels leads to early failure and thrombosis of prosthetic AVGs.
Anastomotic Factors
The major predisposing factor for thrombosis of PTFE grafts has been stenosis of the graft–venous anastomosis in up to 60% (range, 35%–60%) of events documented in case series caused by myointimal hyperplasia, especially in prosthetic grafts. These stenotic lesions are located at or near the site of a venous anastomosis. Myointimal fibromuscular hyperplasia of the venous anastomosis has been described as steadily progressive proliferative responses induced by material, humoral, hemodynamic, and cellular factors
Complications with the Type of Conduit
Patients with PTFE AVGs are more likely to experience access thrombosis when compared to those with native AVFs. Relative risk is estimated to be 1.98 over 1 year. Estimates of graft failure have found to be between 33% and 67% over 12 months in different series.
Systemic Factors
A few authors have described a significant amount of recurrent spontaneous thrombosis occurring without an obvious anatomic cause ranging from 37% to 44%, where hypercoagulability has been elucidated as a cause. This is even more suspicious as a cause in patients with recurrent graft thrombosis. Various diseases causing hypercoagulability and their inherent complications have been characterized thoroughly, and they include the antiphospholipid syndrome, antithrombin III deficiency, protein-S deficiency, protein-C deficiency, and activated protein-C resistance caused by the heritable genetic abnormality factor V Leiden. The presence of antiphospholipid antibodies in patients maintained on chronic hemodialysis has been correlated with an increased risk of thrombosis. The presence of central venous stenosis adds to venous hypertension of the extremity in which the access is present, thereby increasing outflow resistance and promoting stasis.
Intradialytic Factors
One case series has reported that frequent episodes of intradialytic hypotension and lower predialysis systolic blood pressure is associated with increased peridialysis thromboses.
Clinical Presentation
It is important to determine when the access was created, what kind of access is in place, and when the clotting occurred. It is also important to ask if the access site has been warm or erythematous and if the patient has had fevers or chills. A history of prior interventions is essential, because an access requiring more than two interventions in a period of less than 1 month might indicate a high likelihood of failure of intervention and/or a need for a hypercoagulable workup to diagnose a nonanatomic cause of failure.
Regardless of the access, the extremity arterial pulses should be documented. Additional clues on the clinical examination that point to adjunct but not direct factors affecting access malfunction include presence of dilated chest and neck veins suggesting central venous stenosis. In addition, cardiac and pulmonary examination is important, and patients with evidence of significant fluid overload might require catheter-based dialysis before thrombectomy. A targeted neurologic examination pertinent to the sensorimotor function in the affected extremity is also needed to document preexisting and rule out new-onset neuropathy, the latter pointing toward acute ischemia of the extremity.
For AVG, several parameters need to be assessed. Warmth or erythema at the AVG site can indicate graft infection or cellulitis. An active graft infection is an absolute contraindication to percutaneous intervention. Assessing the type of access, inflow and outflow, sites of graft degeneration, and location of anastomotic sites help to plan access sites for interventions and avoids multiple punctures. Presence or absence of a thrill or bruit is another factor. Infrequently, a patient is referred with a presumed clotted access that is actually not clotted but has an arterial inflow issue with low-volume flows and might just need augmentation of the inflow by percutaneous or open techniques.
For AVF, a similar routine is followed, except that a thrombosed fistula might have erythema and tenderness caused by the phlebitis provoked by the clot, which, in contrast to grafts, is not a contraindication for intervention. A clinical examination may be supplemented with an ultrasound if needed. This helps confirm the diagnosis and plan the site of access.
Management
Patient Selection
Arteriovenous access thromboses are often identified during attendance for routine dialysis sessions. Therefore, it is of the utmost importance that factors such as hyperkalemia and fluid overload be considered before referral for further management. As a result, a number of patients need to undergo placement of a temporary dialysis line for immediate hemodialysis before proceeding to a thrombectomy procedure.
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