The Importance of a Screen With Doppler Ultrasound for Vascular Access Surveillance
Doppler ultrasound (DUS) plays an important role in monitoring vascular access (VA). It provides information that physical exams cannot and is helpful from the planning stage of surgery through long-term follow-up after a kidney transplant. DUS is especially valuable because it can detect changes in blood flow and structural problems early, which helps prevent serious complications.
- Pre-operative Planning and Maturation
DUS is crucial for creating an arteriovenous fistula (AVF) and ensuring it works well in the early stages.
- Vessel Mapping:
DUS is used before surgery to check if an AVF is possible by examining the arteries and veins. Mapping during surgery can also help determine the best type of access and improve results for the patient. - Early Maturity Assessment:
A duplex ultrasound two weeks after creating an AVF is recommended to identify any that are not developing well. This allows early intervention and helps the AVF mature before dialysis is needed.
- Detecting Stenosis and Reducing Thrombosis Risk
When a VA is being used, DUS measures blood flow (Qa) to detect narrowing (stenosis) before it causes a complete blockage (thrombosis).
- Supplementing Clinical Exams:
Physical exams come first, but DUS provides additional details about blood flow problems. - Thrombosis Prevention:
Studies show that using Doppler flow to guide early treatment of new narrowing can lower the risk of thrombosis, even if it does not always extend how long the access lasts. - Evaluation for Immediate Reconstruction:
An AV fistula can be assessed with Doppler ultrasound immediately after thrombosis. This can reveal the likelihood of immediate revision; therefore, the access can be used immediately without the need for a central catheter. This is also possible for AV grafts.
- Post-Transplant Surveillance Protocol
DUS is an important tool for managing a “buzzing” fistula after a kidney transplant, when the focus becomes protecting the patient’s heart and blood vessels.
- Proposed Algorithm:
The recommended protocol is to perform a Reference DUS in the first two months after transplant, a Comparison DUS at 12 months, and then a Revaluation DUS every two years. - Flow Thresholds:
- If DUS shows blood flow of 1 L/min or more, a heart evaluation (echocardiography) is needed to check for early signs of heart failure.
- Flow rates above 1.5–2.0 L/min are considered high and may harm the heart. If the flow exceeds 1.5 L/min, repeat evaluations at least every two years.
- Aneurysm Tracking:
DUS helps monitor venous and brachial artery aneurysms. High blood flow, as measured by Doppler (over 1,500 mL/min), increases the risk of brachial artery aneurysm by 4.5 times.
- Managing Risks From Immunosuppression
For transplant patients, DUS is important because antirejection drugs can change arteries and veins, making them more likely to develop aneurysms or rare cancers like angiosarcoma. DUS allows specialists to track changes in the brachial artery and veins, helping them decide when to perform ligation to prevent rupture.
- Identifying Candidates for Reconstruction
DUS helps specialists determine whether a VA can be reconstructed. By assessing the condition and length of the matured vein, DUS helps the team decide whether the access can be rebuilt, which can help avoid the need for a high-risk central venous catheter (CVC).
