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.
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.
You could do worse than to look at this particular block closely and make it the template for your next interscalene block.
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 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:
M-Mode After the Case in Recovery Room
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.