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The Supraclavicular Brachial Plexus Block

W-drophen it comes to regional anesthesia/analgesia of the shoulder, arm and hand, the supraclavicular approach to the brachial plexus is the one block that can d it all.

Before ultrasound guidance became common only the brave-of-heart would attempt the supraclavicular approach because of the proximity of the subclavian artery and dome of the lung.  Ultrasound makes this approach not only safe but desirable, because the tight grouping of the target nerves and the presence of the sheath surrounding them, dense blocks of the upper arm are practically assured. 

In addition finding the brachial plexus in the supraclavicular approach is so simple that it is the ideal place to begin when you want to perform a brachial plexus block in the interscalene space.  While this technique is covered in more detail on the interscalene page here (link here) the short explanation of the technique is to locate the brachial plexus in the supraclavicular space and trace the nerves cephalad into the interscalene space.

 

The Block in Brief

The Supraclavicular Brachial Plexus Block

 

Comments

Patient Position

Semi-Fowlers

Head raised will reduce size of veins.

Ultrasound Probe

10 – 14 mHz Linear

 

Needle

1.5 - 2”

 

Needle Approach

In-Plane or Out-of-Plane

There may be an advantage to the In-Plane approach to control the needle.

Local Solution Volume

15 – 30 ml

 

Key Anatomy Landmark

First Rib and Subclavian Artery

Brachial Plexus will be postero-lateral to the artery

Miscellaneous

Brachial Plexus will be in sheath here. Ulnar nerve is frequently lying outside of sheath, at lateral angle formed by artery and rib.

 

Patient Position & Probe Placement

With the patient in semi-sitting position prep the area surrounding the clavicle on the desired side.  Place sterile gel on to the area just posterior to the clavicle.  Place the ultrasound probe just posterior and parallel to the clavicle and aim the probe down into the chest or mediastinum.

Note which side of the survey picture corresponds to the anteromedial side of the patient and which to the posterolateral.

supracclav-est

Locate the bright, horizontal line on the survey screen representing the first rib.  If the 1st rib is not seen, set the survey depth to s deeper setting and look again.  It is helpful to try changing the ultrasound probe angle a few times to locate the rib.

Once the rib is seen locate the subclavian artery as it crosses the rib surface.  The artery will appear as a round, dark, pulsating circle.  If you are having trouble locating the subclavian artery, consider turning on the color or power Doppler feature of the ultrasound machine.  This will show areas of rapid movement which will usually pinpoint or confirm the position of the artery as well as any other vessels in the field.

Image Interpretation

The first rib is the echo-reflective, bright horizontal line at the bottom of the survey display.  The subclavian artery is the round, pulsating, empty-appearing circle lying atop the line representing the first rib.  The brachial plexus lies almost on top of the subclavian artery, extending over the posterolateral side.  The brachial plexus and subclavian artery are bonded on the posterolateral side by the middle/posterior scalene muscle and on the anteromedial side by the anterior scalene. 

The subclavian vein is usually on the anteromedial side of the anterior scalene muscle insertion from the subclavian artery.

Occasionally you will encounter anatomical variations where the subclavian artery and vein are both together between the insertions of both of the scalene muscles. It is important to recognize this when it appears and adjust the technique accordingly, primarily in avoiding additional vascular structures.

The nerves appear as a group of empty-looking small circles lateral and superior to the subclavian artery, much like a cluster of “bubbles”.

Needling

The supraclavicular brachial plexus can be approached In-Plane or Out-of-Plan with the needle but in this case the In-Plane is probably a better plan because it can allow you keep your needle within sight during placement.  This can be an advantage during the first few times you perform the block because of the proximity of the subclavian artery and the dome of the lung. 

Otherwise the Out-of-Plane approach works as well. No matter which needle technique you choose to use, it is important to keep control of the needle to avoid straying to trouble. 

While placing local anesthetic in the vicinity of the brachial plexus will create a block, it is more efficient to place the needle tip within the sheath containing the nerves for the first part of the injection.  To do this aim your needle tip on a track between 2 of the nerves and advance slowly. You may feel a slight release of resistance as the tip enters the sheath. Aspirate to assure that you have not entered a vascular space and inject slowly.  There will be slightly more resistance to the beginning of injection than normally felt outside the sheath, but the resistance will ease quickly. As you inject you will see the the entire nerve group spread and swell slightly, and as you stop and aspirate the nerve group will be seen to contract again.  The pressure caused by the injected solution will cause the sheath to first swell and then as the injection stops the solution will spread axially within the sheath. Because of this the local anesthetic will be distributed cephalad and caudally within the sheath. This means it will reach nerves which leave the sheath proximal to the injection point, many times this will include cervical sympathectomy causing Horner’s syndrome of almost immediate onset. It is sufficient to inject 10 to 15 ml of local solution into sheath.

After injecting local into the sheath containing the brachial plexus it is highly advisable to reposition the needle in the angle formed by the subclavian artery at the 1st rib on the posterolateral side (shown in the illustration below). This is a common “hiding place” for the ulnar nerve.  This spot has been called “the Corner Pocket” and the ulnar nerve in this position “the 8-ball” (which as far as I know was first coined by Macfarlane, Perlas, Chan; & Brull).

Therefore after injecting into the sheath, reposition the needle tip into the corner pocket and, after aspirating, slowly inject 3 – 5 ml of local anesthetic.

Phrenic Block

While the interscalene level brachial plexus block has been associated with inevitable  phrenic involvement and consequent hemidiaphragmatic paresis or paralysis, the supraclavicular level approach is not. By this I’m not saying that you will never see phrenic block only that you can reduce the chances of an inadvertent phrenic block by plotting a more distal approach. 

To ultimately maximize the likelihood of a phrenic block you must know exactly where the phrenic nerve is and for that you must stimulate all of the likely targets on the side you wish to block until you positively identify the phrenic.  Even in this case there will be occasions when you find that the phrenic actually travels some portion of its route along with the nerves of the brachial plexus.  In this case you may be hard pressed to avoid involving it. 

A friend of mine did a survey a few years ago to find the most common locations of the phrenic nerve in the lateral neck and put together a clearcut poster with the results.  This work can be found here : http://www.usra.ca/UIA/GetPublicAbstract.php?UserID=18&AbsID=b3f0860f6ebed0db84cfb2302740f1a7

Still, as detailed elsewhere on this site, the best way to avoid phrenic block without going through the time-consuming drill of localizing the nerve with stimulation is:

Approach at a lower level: At the supraclavicular level the phrenic is usually more physically distant from the brachial plexus.  The phrenic is usually on the anteromedial side of the insertion of the anterior scalene onto the 1st rib at the supraclavicular level.

 Use a smaller volume: Use the smallest volume possible.  Try to perfom the block with 15 mls or less.

Use Ropivacaine instead of Bupivacaine:  Ropivacaine produces less motor block than bupivacaine.

Use a lower concentration of local anesthetic:  By using a lowered concentration, in the neighborhood of 0.2% of bupivacaine or ropivacaine (preferred) you lower the chances of motor block a lot.  You can get a decent sensory block with concentrations below 0.2% which can be used for analgesia.  By using low concentrations you can use larger volumes without compromising your advantage.

 

Ultrasound Artifacts

Shown above is an example of an ultrasound artifact.  While there appears to be 2 arteries, one atop another, this is a reverberation artifact.

It is commonly called the “double-barreled” subclavian artery.  It occurs when there is a very hard surface close to the ultrasound source which can reflect a great deal of the ultrasound energy quickly back to the source allowing it to make the reflect again to the original reflector.  This creates an image identical to the first but twice as far from the ultrasound source, the probe face.

 

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