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October 15, 2006

A New Video Entitled

Finding the Brachial Plexus in the Interscalene Space, the Really Easy Way

 

We introduce here a new original content video demonstrating an easy method to identify the brachial plexus in bothe the supraclavicular and subsequently the interscalene space.  This method has been mentioned and described elsewhere on this site in several articles but this is the first video demonstrating the technique.  We believe this method is superior to the method previously described in the Neuraxiom site and represents the best method available at the present time. 

It is based on easily identified landmarks and is useful in performing both supraclavicular and interscalene brachial plexus blocks. 

Please take a moment and watch this video,, we believe that you will understand our enthusiasm with regards to the technique.  The video is in Windows Media Video format (WMV) and runs approximately 4 minutes 20 seconds.

Click Here to Watch the Video

Labeled Anatomical Slice of the

Right Brachial Plexus

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Image Source: Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, Visible Human Web Server
and the Visible Human Project of the National Library of Medicine, National Institute of Health

Interpretation and Labeling by Neuraxiom LLC

August 5, 2006

It isn’t often that one finds a resource which adds so much to the fundamental understanding of a subject as the images produced from the Visible Human dataset created by the National Institute of Health.  I have found that the best application for manipulating the dataset is the Visible Human Server created by the Computer Science Dept. of the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland.  I would encourage anyone interested in anatomy to visit the site and register to gain access to the server and then do a little exploring.  Link to the Visible Human Server here.

In the future I hope to use images generated at this site to illustrate many of the corresponding views on ultrasound.  

Click on the image above to view a 19 frame movie which traces the elements of the brachial plexus from distal to proximal starting at the supraclavicular space.  The nerves of the brachial plexus are colored yellow to make the easy to follow.  The image sequence loops 10 times.  Notice that the C5 nerve root passes through the anterior scalene (as described in the article below “Weird Tales of Variant Anatomy”).  Also note that as the nerve roots are traced retrograde through the dural layer you can see the ventral and dorsal divisions as they come off the spinal cord, Coooool!

 

The Phrenic Sparing Interscalene Block (PSIB) Project Page has now begun.  What is it?   The PSIB study is an “Open Source” study to look at the effectiveness and common problems associated with different techniques of interscalene and supraclavicular blocks.  Along the way, we just might discover something.  Why not come along for the ride?  Click here to go to the page.

The Brachial Plexus, Interscalene Approach

The interscalene brachial plexus block has been performed for years for relief of pain in conditions and surgeries involving the shoulder and upper arm.  In the past landmarks were used for finding the location of the interscalene groove and needle placement there was expected to elicit parasthesias when the target nerves were touched by the needle.  If the correct parasthesias were produced, the needle was assumed to be in the right place and local anesthetic was injected slowly with intermittent aspirations to assure that the local was not being injected into the intravascular space or intrathecally.   All things being equal, the block would then either work or not and would be accompanied by a pseudo-Horner’s Syndrome and a paralyzed hemi-diaphragm on the side of the block, for the duration of the block.

The procedure as it existed prior to ultrasound guidance had several attendant dangers owing to the proximity of the target nerves to other structures such as the vertebral artery, the dome of the pleura, the dura covering the cervical spinal cord, the cervical spinal cord, even the carotid artery and internal jugular vein.  Injection in any of these structures could lead to very unpleasant distractions and even death.

Later in the history of the procedure nerve stimulators replaced needle-induced parasthesias relieving the clinician of the need “touch” the nerves.  Still, as discussed elsewhere on this site , nerve stimulator results are not a reliable indicator of proximity to nerves in many cases.  Neuropathies from diabetes or peripheral vascular disease can render the nerve stimulators useless for even finding the nerves let alone indicating the needle proximity to them.

So what changed with the implementation of ultrasound guidance for injection around the trunks of the brachial plexus, certainly not the nerves’ position in relationship to the important structures mentioned above.  What changed was visualization of the nerves, the important structures, the needle and the injected local.   Since, in most cases, the nerve trunks can be easily identified, placement of the needle to an optimum position next to the nerve trunks can be accomplished in a single needle pass.  Less tissue disruption from repeated needle passes lessens the amount of local anesthetic absorbed during injection.

Visualization of the structures during injection of the local means that the needle can be repositioned if necessary (and most of the time it is beneficial to do this) to insure that local surrounds the target nerve mass.  Watching while you inject also means that if you see the local solution accumulating around the nerve, you are reassured that the solution is not going into the vascular space or intra-thecally. 

A single needle pass to a positively identified position avoids any interaction with the dome of the pleura, or any of the other common areas of trouble.

In conclusion by learning the techniques involved in interscalene placement of the block needle under ultrasound guidance can relieve the clinician of the guess-work surrounding what could be a fairly challenging procedure for many. 

A Convenient Pocket-Sized Map of the Neck as Seen with Ultrasound

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Forget the Scalenes, Focus on the Nerves

June 17, 2006

An Example of the Unique Benefits of Using Ultrasound to Identify Nerve Targets --

A New Take on Localizing the Trunks of the Brachial Plexus in the Interscalene Space

Up until now finding the nerves of the brachial plexus for an interscalene block has involved finding the landmarks that identify the scalene muscles then placing the needle between them.

In the standard (non-ultrasound) method, palpation of the lateral insertion of the sternocleidomastoid on the clavicle provides the key reference point for the anterior scalene muscle's likely location as it inserts onto the first rib.

If you're using ultrasound in the method described elsewhere in this site, we start in the anterior midline at the level of the thyroid gland and move laterally, identifying the carotid, internal jugular and then the anterior scalene and middle scalene, triangulating against the sternocleidomastoid muscle in the scan. By localizing the scalenes, we can then infer the interscalene space and focus our attentions there for pinpointing the trunk nerves of the brachial plexus.

While both of the methods are usable in many, if not most, cases, there are a good number of block candidates that, for one reason or another, challenge the efficiency of these methods. People with excessive subcutaneous tissue around their necks, previous surgery such as carotid endarterectomy, can present anatomical challenges that obscure the usual landmarks used for finding the scalenes.

What if we could skip the step of localizing the scalene muscles, and simply find the nerves themselves? The routine described below presents a schema for doing just about that. In brief, the you identify the nerve bundle comprising the brachial plexus in the supraclavicular space and trace them retrograde to a spot most convenient for approach with a needle.

Acquiring the Target

By far the most favorable place to find the nerves of the brachial plexus is in the space of the supraclavicular triangle. The majority of the nerves that make up the trunks of the brachial plexus are grouped tightly together surrounded by a connective tissue wrapper and sitting just above and slightly behind an easily identifiable structure, the subclavian artery. The subclavian artery sits atop the first rib and is bounded in front by the insertion of the anterior scalene onto the first rib, and behind by the insertion of the middle and posterior scalene muscles to the first rib. An ultrasound view which best shows the subclavian artery in the supraclavicular space will be the one which also best shows the target nerve group of the brachial plexus. (A more complete discussion of locating the brachial plexus in the supraclavicular space can be found at this site on the Supraclavicular Page.)

The nerve bundle as a group will appear more dense (brighter) in the ultrasound image, while the individual nerves in the bundle will still have a hollow appearance characteristic of the nerves of the brachial plexus. Once you have the subclavian artery in view, focus on the area slightly above and behind the artery. If you don't immediately recognize the nerve bundle there, slowly adjust the angle of the ultrasound probe first in a clockwise-counterclockwise orientation, then the angle of incidence to the skin surface, back and forth slowly, watching the area of interest on the ultrasound screen until you see the round hollow-looking structures characteristic of the brachial plexus trunk nerves.

Moving the ultrasound back and forth along long axis of the artery may help you find the nerve bundle. With the movement the structures seen in the ultrasound display will change while the bundle will remain more echo-dense (brighter) than the surrounding structures.

Following the Trail

Whatever method you use to identify the nerve bundle, once found, keep your eye focused on the bundle and slowly move the probe retrograde, back towards the neck. Keep your focus on the nerve bundle as you move. The orientation the probe to the skin surface should stay at nearly 90 degrees as you turn the corner to go up the side of the neck.

The goal of this should be to find the most ideal proximal location for placing a needle next to and among the nerve bundle rather than finding the “interscalene” orientation of the brachial plexus nerves.

If you lose track of the nerves as you move the probe, just go back to the supraclavicular space, locate them and start back-tracking again. Slight adjustments might need to be made in the orientation of the probe as it is moved back along the track of the nerve.

In many cases as you move the probe and focus on the nerve you will gain a rough 3-dimensional view of the nerves and see their positions rotate as you move proximally. After performing this maneuver a few times it will become easier  and you will be able to better sense the correct orientation of the probe to the nerve for the best view and the entire procedure will go more quickly.

Bundle Morphology

Note that the nerves of the plexus are loosely held together by a thin walled sheath of tissues and when they are passing through a space with few encroaching structures (like the supraclavicular space) they orient in a rounded group, whereas as you follow them retrograde and find the segment where they are passing between the scalenes, the pressure from the scalenes on either side of the bundle causes them to be squeezed into a “line abreast” stack (one atop another) which is typical of their undisturbed appearance in the interscalene space. I included the adjective “undisturbed” in the previous sentence because, once local anesthetic is injected in the interscalene space expanding it and therefore taking the direct pressure of the nerve bundle, the nerves will once again assume their circular bundle orientation while the scalene are held apart by the anesthetic fluid bolus. This appearance should be taken as a positive sign that the bundle is indeed surrounded by local and that a solid block is very likely. Be aware that this appearance is similar to that seen after mistakenly injecting the local solution into the belly of the anterior scalene muscle. This condition results in block failure via the adjacent compartment mode of failure. This reinforces the point that it is important to have a positive identification of the target before much volume is committed to the block. Injecting volume while focused on the target should clearly show the surrounding dividing or membrane structures being pushed away from the nerves.

Where to Stop

For a classical “interscalene” height block, a good place to end your search is where the nerves are lined up vertically (perpendicular to the probe) and the most lateral trunk (the superior trunk) is at it's most superficial position. This is many times in kind of a “low” interscalene or “high” supraclavicular position from an external perspective. Remember we're heading for the nerves and not the muscles so a clear nerve target is better than a clear set of muscular landmarks.

Dealing with Stragglers

Keep in the back of your mind that you may notice a hollow “nerve”-looking structure on the other side of the anterior scalene at about 1 o'clock (if you're looking at the left neck from the foot, or 11 o'clock if on the left from the foot). It occurs in some percentage of the necks you look at, depends on the study you look at.  It is likely the c5 nerve root aberrantly passing anterior to the anterior scalene and is one of your targets. (looking for a scan of this to post) It is not necessary to address this variant directly with a separate injection of local anesthetic. The relatively “pressurized” bolus (it's more than 20 mls isn't it?) of local you place between the scalenes to surround the nerve bundle will flow out over the top of the anterior scalene into the space between the anterior scalene and the carotid and internal jugular vein and block this wayward nerve as well as the phrenic nerve which hangs out on that side of the anterior scalene too.

The other variation you will see occasionally will be the nerve (c5 or c6 or both) aberrantly passing through the belly of the anterior scalene. This appears as a round void or hole a few millimeters in diameter within the substance of the anterior scalene muscle. It looks like a vessel but focusing the color doppler on this spot will show no flow present. If you see this you may want to direct you needle to it and inject a few mls of local around it. Because of it's position inside the muscle sheath there is no other way for local anesthetic to reach it.

 

September 6, 2006

Interscalene Brachial Plexus Block

The Perfect Block

It started out as a normal summer day in Olympia Washington. Sunny, supposed to get to about 80' F, nice breeze. I was assigned to the Nerve Block squad down at the four-one-three, Main OR division. Big commuter mug of hot java had gotten me ready for my day and I thought I could handle anything. I never suspected that the next couple hours turn the whole OR topsy-turvy and change my life forever. OK, maybe that's a bit overly dramatic but, you could do worse than to look at this block closely and make it the template for your next interscalene brachial plexus block.

You could do worse than to look at this particular block closely and make it the template for your next interscalene block.

The patient was a lady in her 50's in for a Total Shoulder Arthroplasty, she was about 160 cm tall and weighed about 105 kg. The anesthesiologist interviewed her and got her agreement on a plan consisting of an single-shot interscalene brachial plexus nerve block in the pre-op unit followed by a general anesthetic for the surgery. The plan was for her to be discharged home later that day.

We brought the ultrasound machine up to bedside and had prepared a skin wheal of lidocaine 1% and a block solution of 25 ml of mepivacaine 0.8% + bupivacaine 0.3% with epinephrine 1:333,000. An IV was already in place, monitors were placed on the patient, oxygen started by nasal cannula at a couple liters per minute, and midazolam 1mg + fentanyl 50mcg were given IV.

Acquiring the Brachial Plexus

Locating and isolating the brachial plexus was accomplished using the method discussed in the article above entitled “Forget the Scalenes, Focus on the Nerves”, please refer to that piece for more (and some of the same) discussion of the method.   The neck was scanned with the shallow ultrasound probe (5-10 mHz) starting at the supraclavicular space (image below). Move your mouse cursor over the image and you will see labels over the major landmarks.

We started at the supraclavicular space because the anatomy is so easily identified. (this technique is described a couple other places in this website, the supraclavicular page and another article on the interscalene page) The view as above should be behind the clavicle and the subclavian vein that lies just behind it. The scan must be set deep enough to see a white (echo reflective) horizontal line at the bottom of the screen created by the top surface of the first rib. Pause at this point and look for the pulsatile dark circle on the screen that is the subclavian artery. There is a space between the subclavian vein and the smaller subclavian artery, this space is occupied by the insertion of the anterior scalene onto the top surface of the first rib.

Having identified the subclavian artery focus your attention just above and behind (superior and posterior) the artery for a bundle of lighter color objects the same size or lighter larger than the artery. If you been around this site (the supraclavicular page) or some others already, you probably have guessed that the “bundle” is the brachial plexus. Don't worry too much if the bundle doesn't jump out at you visually, next we'll talk about how to make IT come to you.

Focusing on the Brachial Plexus Bundle – The Gestalt Method

We then visually isolated the bundle by moving the probe back and forth, proximally and distally, along the suspected track of the brachial plexus bundle, keeping the probe at a right angle to the body surface. When you focus your attention on the area above and behind the artery while moving the probe your eye's attention will be drawn to the bundle. The background elements of the image will all change, structures will come and go, changing most of the image brighter and darker, ALL EXCEPT FOR THE BRACHIAL PLEXUS! The bundle is surrounded and held loosely together by a thin connective tissue sheath. We'll talk again later about this sheath.

The brachial plexus bundle will hang together while everything else changes. If you don't see it immediately, don't give up, “Un-Focus” on the the picture a little, move the probe a little faster back and forth, let your eyes do the work. The bundle will hold together and you will soon see it. Once you see it, you won't lose it again AND you will never have trouble finding the bundle on other scans.

Once you identify the brachial plexus bundle, watch it change its arrangement of elements as it courses up and down the neck. You will sometimes see one trunk spiral around the others, or see 2 trunks change places. You will many times get a fairly clear 3-dimensional picture of the brachial plexus' arrangement. They are not all the same.

Moving up to the Interscalene Space

With the brachial plexus bundle in your sights, focus on the bundle and move the probe proximally up the neck. As you move up you will see the trunks change formation from a roughly circular bundle to a stack (one atop another). They are doing this because the anterior and middle scalene muscles are pushing on either side of them forcing them to line up. This is the interscalene space. Anywhere along here is an alright place to inject the local to create the right height block. (See the image below, move the mouse cursor over the image to see labels)

The Planned Order of Injection

The plan is to inject 10 mls of local anesthetic on each side (anterior and posterior) of the brachial plexus nerve bundle while keep the local outside the fascial borders of the 2 abutting scalene muscles, staying well below the superficial layers which define the compartment.  There should be little or no extravasation of local over the tops of the scalene muscles.  The labels on the image above show the planned needle paths. (move mouse cursor over image to see labels).

First Placement of the Needle

A skin wheal is placed over the insertion point which is in the center of the broad side of the ultrasound probe.  The needle used was a 22G insulated needle made for nerve stimulation but no nerve stimulation  was planned for this block, it was chosen for it's “feel” as it passes through tissue AND it left the possibility open for stimulation of a nerve for identification if a nerve is seen in the substance of the anterior scalene (to rule out its identity as the phrenic).

The needle is attached to the syringe containing the local solution via an integral tubing of about 16”.  The needle is introduced through the skin wheal and advanced through the fascia layer overlying the interscalene line under direct ultrasound control.  A “pop” is felt as the tissue layer gives way and the needle tips enters the division between the scalene muscles.  The position of the needle tip is located in the ultrasound image by watching the tissue deform as the needle tip makes its way through it. 

The needle is angled slightly anteriorly to pass along the anterior side of the brachial plexus bundle and it is advance past the outermost nerve trunk to a position even with the 2nd nerve trunk on the anterior side of the bundle.  The syringe is aspirated gently to assure there is no intravascular placement and then gentle pressure is placed on the plunger while the ultrasound image is observed.  Many times there is a slightly increased pressure necessary to begin an injection as a potential space is opened up, then injection pressure should become easy (like blowing up a new balloon). 

Excessive injection pressure could mean the needle is within the substance of the nerve and intraneural injection must be avoided.  The right amount of pressure necessary to inject the local is difficult to describe, the feeling becomes second nature after a couple blocks.  Until then think of the right amount of force as being like that necessary to perform a slow intramuscular injection.  If excessive pressure needed to start an injection, the needle should repositioned and the aspiration/injection sequence should begin again.  Once the injection has begun it should continue slowly, about 1 ml every 2-3 seconds, this will provide the best spread of the solution.  Pause, periodically and aspirate to assure no vessels are receiving the drug.  Keep in touch with the patient, ask them if they are feeling anything unpleasant, complaints of pressure at the injection site are common..  Stop and re-evaluate things if there is any complaint burning pain extended from the site.  see Modes or Failure for tips about injecting around nerves

So anyway 10 mls of the local are injecte slowly along the anterior side of the bundle. (see the image below, move mouse cursor over the image to see labels)

Second Placement of the Needle

The needle is withdrawn to a point just below the outer fascial layer overlying the interscalene space and then it's re-directed slightly posteriorly and advanced downward along the posterior side of the brachial plexus nerve bundle past the level of the outermost visible nerve trunk until the needle tip is about even with the second nerve trunk.  Again, the needle is aspirated and 10 mls of the local solution is slowly injected as described above for the front side.  (see the image below, move mouse cursor over the image to see labels)

Stand Back and Admire the Handiwork

Notice on the image showing the block in place, that the solution is sequestered along both sides (anterior and posterior) of the nerve bundle.  The nerve bundle itself has not been entered by the needle (you could and you might get a parasthesia and patient report of immediately feeling the effects of the block).  The local forms a “sandwich” in which the meat is the nerve bundle. The scalene borders are both pushed back from the nerve bundle reassuring us that none of the local was inadvertently injected into the muscle bellies and thus wasted (in terms of the block).   The nerve group floats alone in the center of the picture.  Obviously the image shows a “slice” of a 3-dimensional arrangement here, you cannot see where the local is spreading to above and below the image slice but chances are fair that no other tissue planes will be crossed to the extent of the volumes injected here.

The Results

The block became effective slowly, over about 10 minutes.  The patient awakened pain-free in the recovery room.  An M-Mode ultrasound scan with a 2-4 mHz curved array before and after surgery showed no inadvertent phrenic nerve block as evidenced by good diaphragmatic movement on deep breaths and forceful sniffing.   In addition, there were no signs of Horner’s Syndrome.

M-Mode Before the block:

07.14.54 hrs Image__[0001821]

07.15.05 hrs Image__[0001822]

 

M-Mode After the Case in Recovery Room

10.09.27 hrs Image__[0001834]

 

10.09.38 hrs Image__[0001835]

 

The Rear View Mirror

It should be noted that this particular block technique, while it looks very hopeful for the ideal combination of volume, needle placement, and speed of injection for avoiding side effects, an almost identical block performed a couple days later, while it was equally effective and had no Horner’s sign, produced an ipsilateral hemidiaphragm paralysis.  Anatomical variations such as the moving target of the path of the phrenic may keep any technique from being 100% successful in avoiding side effects but further refinements will undoubtedly improve the odds.

 

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