From the Guidelines
The use of Doppler-enhanced Point-of-Care Ultrasound (POCUS) is recommended for vascular access and interrogation, as it allows clinicians to visualize blood flow in real-time during vascular procedures, improving procedural success rates and patient safety. Recent studies have demonstrated the effectiveness of ultrasound-guided vascular access, including a study published in 2017 1, which found that real-time ultrasound reduced the overall complication rate compared with the landmark technique.
Key Techniques for Vascular Access
- The transverse out-of-plane technique with dynamic needle tip tracking is a preferred approach for central venous catheter placement, reducing complications and improving first-pass success.
- Ultrasound-guided arterial line placement using a short-axis view with the dynamic needle tip positioning technique has shown superior success rates compared to traditional palpation methods.
- For difficult vascular access, near-infrared vein visualization devices and ultrasound-guided midline catheters serve as alternatives to central lines.
Importance of Training and Practice
The implementation of these techniques requires proper training and practice to develop the necessary hand-eye coordination and spatial awareness for successful implementation in clinical settings. A study published in 2012 1 emphasized the importance of training and experience in the successful and safe integration of ultrasound-guided vascular access into clinical practice.
Available Technology and Technique
Higher probe frequencies are most suitable for superficial vessels, while lower probe frequencies are required for imaging target vessels at a greater depth, including obese patients 1. Two-dimensional (2D) imaging is the current clinical standard, although there is clinical interest in three-dimensional (3D) ultrasound for vascular access.
Recommendations for Clinical Practice
The use of real-time ultrasound guidance is recommended for central venous catheter placement, as it reduces the risk of complications such as accidental arterial puncture, pneumothorax, and hematoma formation 1. The supraclavicular approach for subclavian vein catheterization needs to be evaluated in future studies.
From the Research
Recent Novel Techniques for Vascular Access and Interrogation
- The use of Point-of-Care Ultrasound (POCUS) is becoming increasingly popular for vascular access and interrogation, including the evaluation of dialysis vascular access (DVA) 2.
- POCUS can quickly answer yes-no questions, such as whether the vein is too deep, and can also be used to evaluate the depth and diameter of the vessel using brightness-mode ultrasound alone 2.
- With additional training, a limited color Doppler can be added to the standard evaluation to check flow direction and pseudoaneurysms, and spectral Doppler-mode ultrasound can be used to determine access flow volumes 2.
Use of Doppler in POCUS
- Color Doppler sonography is an essential tool for evaluating vascular access, and a good knowledge of theoretical outlines, instrumentation, and operative settings is required for a thorough examination 3.
- Basic concepts on the Doppler shift equation, angle correction, settings on pulse repetition frequency, operative Doppler frequency, and gain are essential for adequate and correct sampling of blood flow velocity 3.
- Doppler aliasing is a common artefact that occurs when the pulse repetition frequency is set too low, and its correction is crucial to analyse the Doppler signals correctly 3.
Advances in Instrumentation and Technology
- Recent advances in instrumentation, such as the use of portable ultrasound machines or top-of-line, high-end, or mid-range ultrasound systems, are expanding the possibilities for vascular access and interrogation 3.
- The introduction of artificial intelligence into routine care is also showing promise, with automation-assisted techniques providing real-time feedback to correct image acquisition for optimal aortic outflow velocity measurement 4.
- These advances have the potential to increase the accuracy and precision of measurements, and to make POCUS more accessible to users with varying levels of experience 4.