AIUM Practice Parameter for the Performance of Vascular Ultrasound for Postoperative Assessment of Hemodialysis Access, 2024 Revision

The American Institute of Ultrasound in Medicine (AIUM) is a multidisciplinary association dedicated to advancing the safe and effective use of ultrasound in medicine through professional and public education, research, development of clinical practice parameters, and accreditation of practices performing ultrasound examinations.

The AIUM Practice Parameter for the Performance of Vascular Ultrasound for Postoperative Assessment of Hemodialysis Access was revised by the American Institute of Ultrasound in Medicine (AIUM) in collaboration with other organizations whose members use ultrasound for performing this examination(s) (see “Acknowledgments”). Recommendations for personnel requirements, the request for the examination, documentation, quality assurance, and safety may vary among the organizations and may be addressed by each separately.

This Practice Parameter is intended to provide the medical ultrasound community with recommendations for the performance and recording of high-quality ultrasound examinations. The parameter reflects what the AIUM considers the appropriate criteria for this type of ultrasound examination but is not intended to establish a legal standard of care. Examinations performed in this specialty area are expected to follow the Parameter with the recognition that deviations may occur depending on the clinical situation.

As the number of patients with kidney failure requiring hemodialysis each year exceeds 660,000 patients, the initial creation and maintenance of functional hemodialysis access is an increasingly critical healthcare concern.¹ To improve the care of hemodialysis patients, the National Kidney Foundation established the Kidney Disease Outcomes Quality Initiative (KDOQI) in 2000 and updated it in 2006 and 2019.^2-4 The project set recommendations for placement and monitoring of hemodialysis access. Overall, there has been a movement toward earlier and more frequent hemodialysis in patients with chronic kidney disease, which in turn has resulted in more complications, requiring an estimated 68% increase in interventions to repair accesses.⁵

The failure rate of hemodialysis access in the first year is high.⁶ In 5.1% of patients, early thrombosis occurs within 18 days of arteriovenous fistula (AVF) creation and is associated with small arterial diameter, forearm location, small draining vein diameter, protamine use, female sex, surgeon frustration/concern during access creation procedure, and reduced or absent thrill at surgery.⁷ After fistula maturation and use, subsequent failure is frequently associated with thrombosis secondary to underlying focal stenosis, most commonly at the anastomosis. Clinical monitoring of AVF function is recommended to detect deterioration in function before thrombosis occurs.^8-10 However, in arteriovenous grafts (AVGs), occult stenosis may be present in a significant number of patients with normal findings on clinical evaluation.^{11, 12} The reported sensitivity of clinical examination for stenosis in AVGs is only 36–57%.^{13, 14} In patients who have abnormal flow volumes, salvage procedures or surgical revision may lengthen the life of the access, but there are conflicting data in the literature.^15-18 In a data analysis of 40,132 CMS beneficiaries, the benefits of percutaneous intervention were greatest in patients with new-access or low-access flow rates.⁶ Differences in flow parameters within an AVF versus an AVG must be considered because different diagnostic Doppler criteria for stenosis are associated with these two access types. This practice parameter is intended to help physicians in the performance of hemodialysis access evaluation by ultrasound, ensure a high-quality diagnostic examination, and promote further understanding of potential salvage options.

The practice parameter will address primarily upper-extremity hemodialysis access. Although lower-extremity hemodialysis grafts have a significant role in patients without usable upper extremity access, the diagnostic Doppler criteria for lower-extremity hemodialysis graft evaluation are less well-defined.

There are no absolute contraindications to the performance of this examination, but there may be physical limitations that prevent a complete duplex Doppler examination, such as the presence of indwelling catheters, open wounds, recent surgery, pain, scar tissue, or calcification especially in the regions of multiple puncture sites, severe edema, contractures, or other reasons for immobility.

Physicians interpreting or performing this type of ultrasound examination should meet the specified AIUM Training Guidelines¹⁹ in accordance with AIUM accreditation policies.²⁰

Sonographers performing the ultrasound examination should be appropriately credentialed²¹ in the specialty area in accordance with AIUM accreditation policies.²⁰

Physicians not personally performing the examination must provide supervision, as defined by the Centers for Medicare and Medicaid Services Code of Federal Regulations 42 CFR §410.32,²² which is available from the U.S. Government Publishing Office.

The written or electronic request for an ultrasound examination must originate from a physician or other appropriately licensed healthcare provider or under the provider's direction. The clinical information provided should allow for the performance and interpretation of the appropriate ultrasound examination and should be consistent with relevant legal and local healthcare facility requirements.

The ultrasound examination is designed to detect abnormalities that may cause access thrombosis, poor function, inability to access dialysis, or undesirable upper-extremity symptoms and to assess for causes of AVF nonmaturation.

It is important to understand the anatomic configuration of the hemodialysis access to enable accurate and complete evaluation. A review of clinical records can be useful if there is a history of documented variant anatomy or surgery, such as failed fistulas or jump grafts. Although previous guidelines have emphasized a “Fistula-First” approach, newer data suggests a patient-centered approach to customize access to the individual patient according to the End-Stage Kidney Disease Life Plan.⁴

AVFs are most commonly placed in the upper extremity, either in the forearm or upper arm. A forearm AVF directly connects an artery (usually radial) to a vein (usually cephalic) at the wrist or distal forearm to increase flow in the draining vein (forearm cephalic vein AVF). This results in dilatation and wall thickening of the vein, allowing for frequent cannulation for hemodialysis. An upper arm AVF is typically created at the antecubital fossa and connects the brachial artery to the cephalic vein or at the basilic vein, which is usually transposed more anterolaterally for easier access and is called a basilic vein transposition fistula. Percutaneous techniques have been introduced in some centers for minimally invasive creation of AVFs through radiofrequency or thermal energy. Following creation, these systems would be assessed for dysfunction and/or maturity in a similar fashion as typical surgical AVFs,²³ although their use is not widespread.

If AVF creation is not possible or not preferred, a prosthetic graft may be placed to create an AVG. A graft is a tube, typically using polytetrafluoroethylene (PTFE) material, connecting an artery and vein that is used to provide a conduit for needle access during hemodialysis. Graft configurations may include a forearm loop graft anastomosed between the brachial artery and an antecubital vein at the antecubital fossa, an upper arm straight graft from the brachial artery at the antecubital fossa to the axillary or proximal basilic vein, or an upper arm loop graft anastomosed to the axillary artery and axillary vein.

Whether an examination is requested for failure to mature or dysfunction, the components of the sonographic study of both AVFs and grafts are similar.^{24, 25} Copious amounts of ultrasound gel and careful attention to applying only limited pressure from the transducer will minimize deformity of the vein, which may affect measurements of the vein diameter. Evaluation of arterial inflow, venous outflow, turbulent or stenotic flow, anterior AVF vein wall depth from the skin, and identification of PSAs, large or numerous accessory veins, or an area of significant diameter narrowing are basic components of the hemodialysis access examination. Characterization of any collection/mass near the access should be performed.

Note: For anatomic localization of an abnormality in the upper-extremity venous structures, the words “cranial” and “caudal” are preferred because there is inconsistency in the use of the terms “proximal” and “distal” with regards to the veins. Alternatively, the location of a draining vein stenosis may be described by its distance from the anastomosis. The longitudinal, or long, axis is parallel to or along the length of the vessel. Transverse, or short, axis is perpendicular to the long axis of the vessel. When measuring the velocity in the feeding artery or draining vein to be used as the denominator in the peak velocity ratio of a stenosis, the location may be described as “2 cm upstream,” indicating the distance from the anastomosis. The artery supplying the anastomosis is commonly described as the “feeding artery” or “arterial inflow.”

The written or electronic request for postoperative hemodialysis access ultrasound should provide sufficient information to demonstrate the medical necessity of the examination and allow for its proper performance and interpretation.

Documentation that satisfies medical necessity includes 1) signs and symptoms and/or 2) relevant history (including known diagnoses). The provision of additional information regarding the specific reason for the examination or a provisional diagnosis would be helpful and may at times be needed to allow for the proper performance and interpretation of the examination.

The request for the examination must be originated by a physician or other appropriately licensed health care provider. The accompanying clinical information should be provided by a physician or other appropriately licensed health care provider familiar with the patient's clinical problem or question and consistent with the state's scope of practice requirements.

Accurate and complete documentation is essential for high-quality patient care. Written reports and ultrasound images/video clips that contain diagnostic information should be obtained and archived, with recommendations for follow-up studies if clinically applicable, in accordance with the AIUM Practice Parameter for Documentation of an Ultrasound Examination.⁷³

Equipment performance monitoring should be in accordance with the AIUM Routine Quality Assurance of Clinical Ultrasound Equipment.⁷⁴

The sonographic evaluation of the peripheral veins and arteries should include both real-time imaging of the vessels and their contents and evaluation of the flow signals originating from within the lumen using grayscale as well as color and spectral Doppler with careful attention to the anastomoses and any area of perceived narrowing/stenosis or intraluminal echoes/thrombus. Grayscale imaging of the anastomosis is critical as color Doppler may obscure thrombus synechiae or overwrite focal narrowing, resulting in either overestimation or underestimation of stenosis. Real-time imaging should be conducted at the highest clinically appropriate frequency, realizing that there is a trade-off between resolution and beam penetration. This should usually be at a frequency of 7 MHz or greater, with the occasional need for a lower frequency transducer, such as during insonation of the central veins. To determine flow rates, higher resolution transducers are needed, preferably 9–15 MHz. In most cases, a linear transducer is preferable to obtain optimal images. The flow signals originating from within the lumen of the vessels should be evaluated with a Doppler frequency of 2.5 MHz or above. A display of the relative amplitude and direction of moving blood should be available.

Imaging and flow analysis are currently performed with duplex sonography using range gating in the center of the vessel and angle correction with a Doppler angle <60°. Color Doppler is used to detect aliasing that is indicative of stenosis and to facilitate the examination. Color and spectral Doppler are also useful for the evaluation of PSA or nonocclusive thrombus. Appropriate gain and scale settings should be used. The wall filter should be chosen as appropriate for the vessel interrogated.

Policies and procedures related to quality assurance and improvement, safety, infection control, and equipment-performance monitoring should be developed and implemented in accordance with the AIUM Standards and Guidelines for the Accreditation of Ultrasound Practices.²⁰