Cite as: VanderWielen B, Pulos B POCUS spotlight: Ultrasound guided vascular access. ASRA Pain Medicine News 2024;49. https://doi.org/10.52211/asra080124.011.

Introduction

Ultrasound-guided vascular access is useful for anesthesiologists for both central and peripheral venous cannulation and arterial access. We will discuss our approach using the I-AIM framework (Indication, Acquisition, Image Interpretation, and Medical-Decision Making).

Ultrasound Physics

A basic discussion of ultrasound physics can help aid image optimization regardless of whether targets are venous or arterial. A linear array, high-frequency transducer is ideal for all vascular access. Frequency is the number of ultrasound wave peaks per unit of time and is described in hertz. Higher frequency probes have more attenuation or energy loss through a medium than lower frequency probes that allow for deeper tissue penetration. For vascular access, a higher frequency probe is generally selected as this probe will provide improved resolution. While tissue penetration is decreased with higher-frequency probes, most vascular access sites are shallow (less than 6 cm, which is the limit of most high-frequency probes). Decreasing your depth to the most appropriate level will help to allow for a higher frame rate, which can increase spatial and temporal resolution of vascular structures.

Optimizing the gain or brightness of your ultrasound can also assist you in vessel identification. An “overgained” image appears white or washed out, while an “undergained” image appears dark and difficult to decipher. Utilizing the time gain compensation feature for deeper structures allows for specific enhancement of far-field signal intensity to compensate for the attenuation of ultrasound energy with depth. The acoustic impedance, or the resistance of a medium to vibration, of blood is slightly more than surrounding fat or soft tissue, so the needle becomes more visible as it enters a blood vessel. It is helpful to remember that you should see a prominent hyperechoic needle tip once you have accessed the vascular space in either the in-plane or out-of-plane approach.

Color Doppler Mode allows for a two-dimensional cross-section of blood flow that utilizes color markers in coordination with the direction and velocity of flow. By default, positive velocity, or blood moving toward the transducer, is indicated by a red color, while negative velocities represent blood moving away from the transducer and are colored blue (Video 1). No flow will be seen when the ultrasound transducer is perpendicular to the direction of blood flow. In cases of low flow or near perpendicular flow, the power Doppler mode can be utilized. While other Doppler modes can be used to obtain quantitative information on flow velocity, such as pulsed and continuous wave Doppler modes, these modes are not typically utilized for vascular cannulation in the operating room and thus are outside the scope of this article.

Internal Jugular Central Venous Access

Indication: Ultrasound used to assist with central venous access was first described in 1984; however, initial techniques were limited to Doppler studies for vessel location and not to track the needle tip as is common today.¹ Since then, many studies have shown that using real-time ultrasound guidance for central line placement increases procedural success and safety, including decreased attempts and vascular injury.^2-5 Many professional societies, such as the American Society of Anesthesiologists,² Society of Hospital Medicine,⁵ and the Agency for Healthcare Research and Quality⁶ recommend ultrasound use when obtaining central venous access.

Acquisition, Interpretation, and Medical Decision-Making:

Sonoanatomy

Although ultrasound guidance can assist with central access for various locations, the most common central vein used is the internal jugular vein (IJV). The IJV runs lateral to the common carotid artery on the anterolateral side of the neck (Figure 1 and Video 2).

Technique

• Position the patient’s head turned slightly to the contralateral side with the neck extended. Place a high-frequency linear array transducer on the anterolateral neck and pre-scan to assess for patency, approximate depth of the vessel, relationship to the common carotid artery, potential stenosis from prior line placements, and any pertinent anatomic variants. Sterile technique should be used when obtaining central access, including full body drape and sterile ultrasound probe cover. We recommend a transverse (short axis) out-of-plane approach, although some choose to perform the longitudinal (long axis) in-plane approach.
• Position the transducer in a transverse (short axis) view across the base of the neck, ensuring the common carotid artery is not located directly below the IJV as this may make accidental arterial puncture more likely.
• Center the IJV on the ultrasound screen and tilt the transducer toward yourself by a few degrees. The needle insertion site should be close to the transducer and at a 45-60-degree angle.
• Once the needle is through the skin, slowly advance and track the needle tip by tilting the transducer until the tip is seen entering the vessel (Video 3). Note that the IJV is commonly less than 2 cm from the skin. If you can't see the needle tip, do not continue to advance; instead, withdraw the needle until it is seen again and repeat with slow advancement and tracking.
• This is followed by guidewire insertion with ultrasound confirmation (Figure 2, Video 4) and the standard Seldinger technique: make a skin nick, dilate the vessel, pass a central venous catheter over the guidewire and into the vessel with continuous guidewire control, remove the guidewire, and secure the catheter in place.

It is critically important that the guidewire is confirmed to be in the IJV and not the common carotid or subclavian artery prior to dilation and catheter insertion. Note the proximity of the subclavian artery directly below the proximal IJV, visualized near the end of Video 4, part A. Relying solely upon wire visualization (Video 5) with ultrasound before dilation can be misleading as the wire may traverse the back wall of the IJV causing the catheter to be malpositioned into the subclavian artery. Another method to avoid this complication is to confirm the wire position via manometry before vessel dilation. This requires the insertion of an angiocatheter over the wire, wire removal, and attaching a 30 cm tubing line, held vertically. If the meniscus formed by the column of blood slowly backfills the tubing, then plateaus and is non-pulsatile, this confirms venous placement, and the wire is reinserted through the angiocatheter. However, manometry may also give false reassurance in a shock state. Transesophageal echocardiography (Video 5) and/or transducing the central venous pressure with waveform confirmation are the most reliable confirmatory tests of wire location before vessel dilatation.

Peripheral Venous Access

Indication: Real-time ultrasound guidance can also be helpful for effectively and efficiently obtaining peripheral IV (PIV) access. Depending on the surgery, ultrasound-guided peripheral venous access may help avoid the need for central venous access. This technique may be beneficial for patients with obesity, those who require large bore IV access such as rapid infusion catheter (RIC) placement, cannulation of veins that are small, or otherwise difficult to visualize, or for patients who have been in the hospital for a prolonged period with multiple prior attempts.

It is critically important that the guidewire is confirmed to be in the IJV and not the common carotid or subclavian artery prior to dilation and catheter insertion.

Acquisition, Interpretation, and Medical-Decision Making:

Sonoanatomy

Although this technique can also be used for venous access of the lower extremity, we will focus on the upper extremity here. The most common places for ultrasound-guided PIV access are the anterior forearm, antecubital fossa, and more medial upper arm. To increase the rate of successful cannulation, straight veins should be chosen and neither too superficial nor too deep from the skin, with an ideal vessel depth of 0.3- 1.5 cm. The key to image interpretation is differentiating between veins and arteries. In general, veins will be non-pulsatile and elliptical with thin walls and easily compressible with light pressure from the transducer. In contrast, nearby arteries will be round and pulsatile (with gentle pressure from the transducer) with thicker walls (Video 6).

Technique

• Place a tourniquet above the area to be scanned and thoroughly clean the area.
• With the patient supine, position the arm comfortably with the palm upwards and the ultrasound in the direct line of vision.
• Using a high-frequency linear probe, scan the arm in a transverse (short axis) manner using very light pressure to avoid collapsing the target veins. A small footprint linear array transducer or “hockey stick probe” may also be used.
• Once a target vessel has been identified, select an appropriately sized IV catheter depending on vein diameter and depth, ensuring enough catheter length to reach the target vessel. If the patient is awake before surgery, local anesthetic can increase the patient’s comfort.
• Holding the probe in the non-dominant hand transverse, center the target vein in the middle of the ultrasound screen.
• Insert the needle in the middle of the probe at a 45-degree angle or less relative to the skin, depending on the depth of the target vessel.
• Advance the needle slowly and slightly tilt the transducer to keep the needle tip in view as it enters the vein (Video 7). Once a “flash” of blood is seen in the IV catheter, the insertion angle should be decreased, and the needle should be advanced just slightly further before threading off the catheter.
• RIC lines are commonly inserted in the cephalic or basilic veins due to their large size. Typically, this cannulation occurs proximal to the antecubital fossa. First, an 18-20g IV is placed, followed by a wire placement into the vessel.
• Once the wire is in place, the angiocatheter is removed, and a generous skin nick is made, followed by dilation and cannulation of the RIC catheter, which is commonly either 7Fr or 8.5F, depending on the manufacturer. Given that these catheters are utilized in situations with a high likelihood of rapid volume loss requiring rapid repletion, extravasation of these lines can be devastating and rapidly progress to compartment syndrome of the upper extremity.

Once the RIC line is placed into the large peripheral vein, a rapid fluid bolus of 200 mL of volume is often administered via a rapid infuser, and pressure within the line and catheter is monitored and expected to be maintained at <300 mmHg. To help ensure correct placement, an ultrasound examination during this rapid infusion process is often helpful to ensure the fluid is not extravasating into nearby tissues (Video 8).

Arterial access

Indication: A palpation and landmark-based technique have traditionally achieved arterial access in the perioperative period. However, ultrasound-guided access can help increase first-pass success rates and decrease complication rates. Arterial lines can be complicated by hematoma, vessel dissection, and vasospasm; these complications can increase with multiple attempts at cannulation of the same vessel. Real-time ultrasound guidance for arterial access may benefit patients with obesity, edema, anatomical differences or otherwise altered landmarks, low blood pressure/low-flow states that may make palpation challenging, or when only one arm is available for access. A similar technique can be used for arterial access in different locations such as the radial, ulnar, brachial, femoral, or dorsalis pedis arteries. Here, we will focus on access to the radial and brachial arteries.

Acquisition, Interpretation, and Medical-Decision Making:

Sonoanatomy

The most common location for arterial access is the radial artery. Although complications are generally low, the ulnar artery's dual blood supply to the hand decreases the risk of ischemic complications. At the level of the wrist, the radial artery (RA) is located on the lateral (thumb) side between the brachioradialis tendon and the flexor carpi radialis tendon. It is quite superficial and can often be felt by careful palpation.

The brachial artery (BA) is found on the medial side of the antecubital fossa between the biceps brachii muscle and the pronator teres muscle. Of important note, the median nerve lies just medial to the artery at this location and is at risk of injury during attempts at arterial access (Video 9).

Technique

• A high-frequency linear probe should be used to see the relatively superficial arteries and nerves more easily. Again, the ultrasound screen should be placed in a direct line of sight to minimize the need for head-turning during the procedure. Sterile techniques, including sterile ultrasound sheath and gel, should be used to decrease the risk of infection.
• Identify the artery to be cannulated based on landmarks and ultrasound characteristics, including a round shape with thicker, more echogenic walls and non-compressibility with pressure from the transducer. If it is difficult to determine whether the vessel is an artery or a nerve, color or power Doppler (as described above) may help differentiate the two.
• For the RA, placing a small rolled-up towel under the patient’s wrist is often helpful to achieve slight wrist extension and to secure the patient’s hand to the armboard to maintain the position.
• A transverse approach scans more proximally from the chosen insertion site to assess the vessel's path.

Center the target artery in the middle of the ultrasound screen and enter the skin proximal to the probe at a 45-degree angle (Figure 3). A shallower insertion angle will likely be necessary if the RA is superficial. Fujii and Jones (2017) describe the technique of tilting the transducer away from the operator until the needle tip disappears from the screen and then slowly advancing the needle until the tip reappears slightly deeper, repeating this maneuver until a slight “pop” is felt. The needle tip enters the artery.⁷ This will appear as a “bullseye.”

• Once the needle is in the center of the artery, a wire is advanced into the artery, and the catheter can be threaded into the vessel. Several devices for arterial line placement include solitary angiocatheters (which can be threaded directly off the needle into the artery or with the assistance of an independent wire), combination systems (which include a wire within the catheter chamber), or needle/catheter packages.

It is important to focus on the ultrasound screen rather than on the catheter, and it may be helpful to have another person watching for the “flash” of blood once the artery is entered. If the artery is entered off-center, this may result in an inability to thread the catheter. If multiple prior attempts have been made, it is best to move more proximally to avoid any hematoma from forming. Other potential complications include thrombosis, arterial dissection, pseudoaneurysm formation, nerve damage, or infection. If the patient already has a compromised collateral ulnar arterial flow, hand ischemia can result from injury or occlusion of the RA. Injury or occlusion of the BA can result in limb ischemia. In addition, the median nerve is near the BA, and transection can result in permanent nerve injury.

Conclusion

Ultrasound guidance can be useful for central or peripheral venous and arterial cannulation. Hands-on practice utilizing the techniques described above will help to decrease the number of attempts, limit complications, and improve overall success and confidence.

References

1. Legler D, Nugent M. Doppler localization of the internal jugular vein facilitates central venous cannulation. Anesthesiology. 1984;60(5):481-2. https://doi.org/10.1097/00000542-198405000-00016
2. Practice guidelines for central venous access 2020: an updated report by the American Society of Anesthesiologists task force on central venous access. Anesthesiology 2020;132(1):8-43. https://doi.org/10.1097/ALN.0000000000002864
3. Shekelle PG, Dallas P. Use of real-time ultrasound guidance during central line insertion: brief update review. In: Making Health Care Safer II: An Updated Critical Analysis of the Evidence for Patient Safety Practice Rockville, MD: Agency for Healthcare Research and Quality, 2013. Available from: https://www.ncbi.nlm.nih.gov/books/NBK133405
4. Martin AK, Renew JR, Ramakrishna H. Practice guidelines for central venous access: latest report from the American Society of Anesthesiologists. J Cardiothorac Vasc Anesth 2020;34(8):2012-14. https://doi.org/10.1053/j.jvca.2020.03.022
5. Franco-Sadud R, Schnobrich D, Mathews BK, et al. Point-of-care ultrasound task force; Soni NJ. Recommendations on the use of ultrasound guidance for central and peripheral vascular access in adults: a position statement of the Society of Hospital Medicine. J Hosp Med 2019;14(9):E1-E22.https://doi.org/10.12788/jhm.3287
6. Shojania KG, Duncan BW, McDonald KM, et al. Making health care safer: a critical analysis of patient safety practices. Evidence report/technology assessment (summary). Evid Rep Technol Assess (Summ) 2001;(43):i-x, 1-668.
7. Fujii S, Jones PM. A technique for optimizing ultrasonography-guided radial arterial catheter insertion. Can J Anaesth 2017;64(6):683-4. https://doi.org/10.1007/s12630-017-0850-z