Delayed Onset of Motor Block in the Hand following Interscalene Block

February 22, 2008

Jack Vander Beek

I’d like to present an interesting case which gives hints to the actions of local anesthetics in regional blocks. It involves a young man about 19 years old who came to surgery for repair of a rotator cuff tear and who received an interscalene block with bupivacaine.

This young man was very calm and even enthusiastic about the block and the interscalene block procedure under ultrasound guidance went well. Bupivacaine 0.375% with epinephrine, 25 mls, was used. The local anesthetic volume was divided as injected; between the brachial plexus sheath and the anterior scalene, within the sheath, and between the sheath and the middle scalene.  The onset of the block was fairly rapid, and within a few minutes he could not raise his arm. He could however still move his fingers and even produce a forceful grip although he reported some numbness in his thumb and forefinger. He was reassured that it was common to be able to still be able to move his hand and fingers.

A few minutes later the patient was rolled back into the operating room where he was given a general anesthetic and the surgical procedure was performed without incident and took a little over an hour. He required very little general anesthetic during the procedure and after transfer to recovery room he awakened very quickly and reported no pain at all in his surgical shoulder and arm and he could still move his hand and fingers. He spent approximately an hour in the recovery room and was transferred back to the outpatient unit to complete preparations for his discharge to home. 

After approximately 2 more hours he noted he could no longer move his hand and fingers and had no grip.  His concerned mother notified the nurse who, in turn, called the anesthesiologist who was still working on scheduled cases in his room. The anesthesiologist reassured the unit nurse that this happened sometimes and that it would “wake up” when the block wore off. The patient was not upset or concerned by this extension of the block, he was in fact happy that his shoulder did not hurt and was anxious to be discharged.

The patient was discharged and the block lasted through the night and completely dissipated the following day with no sequela. 

Okay, big deal, right? Maybe not big deal, but interesting deal. Most conventional wisdom holds that a block, regional or other, caused by local anesthetic is “set” after a given amount of time. For bupivacaine, 40-50 minutes is usually given as the time in which the molecules have found their musical chairs and are comfortably seated for the duration. AND YET, here is a case where the block progressed for at least 4 hours after placement.

Like a Sponge

The direction of onset is not surprising. Proximal to distal progression makes sense since nerves that will distribute to more proximal end organs will exit the brachial plexus nerve bundle earlier and therefore need to be arranged more superficially to make exit easier. Since they are more superficial the local anesthetic solution will come in contact with those early departure axons more quickly because of their exposure. Conversely the nerves in the bundle that will be the last to depart the bundle will be those located most centrally in the nerve bundle. This is the most efficient evolutionary arrangement available. 

When looking at nerve groups (bundles and fascicles) exiting the cord for distribution down an extremity, we would expect to see the following characteristics.

• The closer to the spinal cord, the larger the overall bundle.
• The closer to the cord more axon and glial tissue and the less connective tissue (accounts for more hollow appearance on ultrasound)
• As distance from the cord increases, more axon is leaving the bundle to connect to end organs, less nervous tissue (axon & glial) is present, more organizing and supporting connective tissue is present.
• As distance increases overall diameters will begin to shrink.

Therefore; the closer to the cord the farther it is, in terms of diffusion, from the outside of the nerve group to the inside. So if you are surrounding a bundle, for instance the trunks of the brachial plexus, with local anesthetic, the diffusion of the local from the outside to the inside will result in a stabilization of the axonal membranes in the most proximal distributions to the most distal, in that order. The most distal (most internal) axons will only become blocked when and if the anesthetic molecules reach them. In my opinion the efficiency of the diffusion of the local through the substance of the radius of the bundle will depend upon;

• The beginning concentration of the local anesthetic solution being used. (density of the molecules available, therefore the gradient of the solute at the leading edge of the solution injected)
• Total volume and distribution of volume of the local anesthetic injected for the block. (higher volumes can delay redistribution away from the site by vascular absorption and normal circulation of the interstitial fluid)
• The pH of the nervous tissue and interstices of the area being injected for the block (slight variations in the area toward the more acidic will cause more the local anesthetic molecules to become ionized and thereby unavailable for crossing the lipid membrane and participating in the block. This is usually seen clinically as a delayed onset of a block. Tissue acidosis can be caused by conditions such as trauma, nearby infection, or peripheral micro-vascular disease.)
• The physical size (radius) of the target nerve. 
• The distribution of the local solution around the circumference of the nerve bundle. Local solution which is placed only on one side of the circumference of a nerve will take longer to completely diffuse through a nerve than solution placed in more than one place or even complete around the nerve. (How much this really effects block efficiency in real life is probably negligible.)
• The number and character of barriers that the local molecules must cross on their passage to the center of the nerve. As discussed above, while more distal nerve bundles are smaller in diameter they will contain more connective tissue packaging that resists diffusion.
• Block efficiency is greatly influenced by the proximity of the local solution injection to the target nerve bundle but this only sets up the conditions described above for the passive phase of diffusion into the nerve. 

In an empty sink basin, put a drop of black ink on a wet sponge, the ink molecules will gradually diffuse to the center of the sponge. Whether the ink color will be noticeable at the center will depend on how big the drop, how dark the ink is, and how thick the sponge is. If you place the sponge in a slow moving stream of water and apply the ink you have a situation closer to the regional nerve block.

The brachial plexus model provides the ideal example for tailoring the placement of the local to the site of the desired effect.

It is really is true that wrist & hand pain is best addressed from a brachial plexus block at the axillary approach (or even below), mid-arm & elbow pain to mid-upper arm is best handled at the supraclavicular level of the brachial plexus, and pain of the shoulder & clavicle to the sternal border can be covered from the interscalene approach.

Sure, a lot of times the hand is numb after an interscalene, but sometimes it’s not and it’s always numb after the axillary level block. So why tempt fate if you don’t have to. Using these 3 approaches to the brachial plexus any of the situations can be handled with confidence and when the unusual need arises, such as a cardiac patient with no neck, and bad bad COPD comes to you for the total shoulder arthroplasty, you will know that a high supraclavicular approach with less than 20 mls stands a good chance of covering the pain while missing the phrenic (possibly) and that an axillary approach is probably not going to get you there.

So, Maybe it’s the Placebo Effect! (WoooOOOoooOOO ← scary other-worldly sound)

So applying the scenario described above to the problem child of blocks; the Sciatic. 

The sciatic is a large caliber nerve and yet many times we make the mistake of expecting it to block like a small nerve bundle. I don’t know about your situation but at our house there is an ongoing “discussion”, especially with a few orthopedic surgeons as to whether a sciatic block is necessary or desirable for pain control after total knee arthroplasties. The logic goes that most people don’t have posterior pain after the operation and you only need to observe patients in recovery to understand this. Okay, well I guess some patients do well with a femoral only but a lot require quite a bit of narcotic for something after femoral-only block. 

The femoral-only viewpoint was bolstered by observations that patients with failed sciatic blocks (quite common at our operating room in the earlier days) were completely comfortable.  The qualification for inclusion to the failed-sciatic club was that the patient could move and feel their feet. We were expecting every sub-gluteal sciatic to diffuse to the center of this large nerve and thereby block the foot. The group lament went like this; “Well, it doesn’t look like your sciatic block worked, but luckily, the patient didn’t need it anyway. Look how comfortable he is!”

Using the model of the above 19 year old guy’s brachial plexus, all of these comfortable post-op total knee patients who could move their feet, actually had very good sciatic blocks even though they could move their feet. It is, in fact, remarkable that so many people with sciatic blocks had blocks that progressed all of the way through to their feet. It is certainly not necessary to block every fiber in the sciatic in order to have a comfortable post-op total knee patient and in fact a numb foot is not appreciated by physical therapy the following morning when they are trying to ambulate the patient.

The Conclusions

The block progression isn’t over ‘til it’s over. While some, maybe most, blocks are “set” after 30-40 minutes, it’s a continuum— some require less time, some require more. 

The block may be therapeutically effective without being complete.  The aim should be comfort. Remember that the majority of the time we want a pain block, we’ll take full sensory, but we need not demand motor.

Disclaimer and Warning

Let’s get this out of the way!
Neuraxiom.com is intended for use by medical professionals, specifically those who perform invasive regional anesthetic procedures. If you’re reading this and don’t know what I mean, you’ve stumbled into the wrong place and you should click here now.

 By now you should be aware that not everything you hear and read is true, real or appropriate to real life. So the following disclaimer is there for the obvious reasons. The short form is: IF IT DOESN'T MAKE SENSE OR SEEM RIGHT TO YOU, DON'T DO IT. Having said all of this we hope that information found in this site is helpful to you in making decisions regarding you practice. Most of the techniques described here are either new and non-invasive (like ultrasound surveys) or invasive things you already do (like sticking needles into people). 
So then:
Neuraxiom.com and those people associated with it make no warranties as to the correctness, safety or appropriateness of any therapies, medications, dosages, techniques or any other aspects of medical practice or patient care and safety. Nothing in this site should be interpreted to imply that anything but YOUR BEST MEDICAL JUDGMENT is appropriate for making safe medical decisions and implementing therapies for your patients. 

 

Phrenic Sparing Interscalene Block -PSIB Study Database Summary

Neuraxiom/USinRA PSIB Database Summary
as of August 27, 2008, 23:39:00 h EDT

PSIB - the Phrenic Sparing Interscalene Block Study Project Underway

We’ve been collecting Interscalene Block Case Data from you since October 2006. Thanks to all of those that have contributed. Follow this link --> PSIB to go to the data entry page. Read the article below to find out what the PSIB study is about. Go to the PSIB Project Page to learn more. View the data that’s been collected so far by either going to the PSIB Project Page or by going directly to the PSIB Database Listing and Summary Page.

 Read the Full Introduction to the Project Here.

What’s New in the Neuraxiom site?

• March 30, 2008 - Proposal for Preventing Patient Falls following Leg Block
• February 22, 2008 - Neuraxiom Notebook - Prolonged Block Progression
• July 1, 2007 - The Axon - Part 1
• April 24, 2007 - Additional Security Measure Installed in Neuraxiom Forum to Reduce Spam
• April 21, 2007 - Changed to Flash Animations to speed up Popliteal & Sciatic Training Pages
• April 19, 2007 - Added RSS News Feed from the Neuraxiom Site - See Left hand columns
• April 15, 2007 - New Sciatic Ultrasound Training Aid Trial
• April 13, 2007 - Newly Re-Written Popliteal Sciatic Block Page
• April 8, 2007 - Newly Re-Written Sciatic Page - Plan A & Plan B Methods
• March 4, 2007 - Animated Scan of Popliteal Space with Labels
• March 4, 2007 - Article - Thoughts on the Sciatic Block (Front Page)
• December 2, 2006 - Low Volume Interscalene Block Page Opened
• October 15, 2006 - New Video Demonstrating Easy Way to Identify Interscalene Brachial Plexus
• October 12, 2006 - PSIB Database Summary Toteboard placed on Front Page
• October 7, 2006 - PSIB Database Summary and Listing Implemented - View Database Contents
• October 7, 2006 - PSIB Data Entry Page Implemented. Enter your Interscalene Case Data
• September 25, 2006 - New Page - PSIB Project Page, Phrenic Sparing Interscalene Block Project
• September 25, 2006 - Introduction to the Phrenic Sparing Interscalene Block Study
• September 8, 2006 - A Description of an Exemplary Interscalene Block with Great Results
• August 5, 2006 - Brachial Plexus Anatomical Slice Image - Labeled & Short Brachial Plexus Animation
• August 1, 2006 - Fixed the Axillary Block Hi-Resolution Video Download Problem, Sorry for the inconvenience!
• July 23, 2006 - Illustration of Lumbar Plexus - Lumbar Plexus Page
• July 17, 2006 - Table of Contents Page - Link on Every Page
• July 16, 2006 - Saphenous Nerve Page Content Started.
• July 15, 2006 - Update to Femoral Nerve Block Page,
• July 9, 2006 - Plan B - Another Method of Localizing the Sciatic
• July 7, 2006 - Change in Site Style
• June 17,2006 - New Method of Locating Interscalene Brachial Plexus - Interscalene Page
• June 10, 2006 - Page Layout Border Change
• June 3, 2006 - Epidural Title Picture - Epidural Page
• May 27, 2006 - Simple Diagram and Description of Supraclavicular Space Added - Supraclavicular Page
• May 27, 2006 - Supraclavicular Scan Illustration added to Front Page
• May 25, 2006 - Article on Variant Brachial Plexus Anatomy and Scalenes
• May 10, 2006 - Supraclavicular Brachial Plexus Block Page Added.
• March 31, 2006 - Added Femoral Nerve Target Practice Page- Femoral Page
• March 21, 2006 - Revised section on finding the sciatic nerve.
• March 1, 2006 - Links to Related Internet Articles - Links Page
• February 26, 2006 - Privacy Policy published. - Privacy Policy Page
• February 19, 2006 - New Opening Picture Sequence, Ultrasound View Right Axilla - Home Page
• February 18, 2006 - User Forum Instituted - Link from All Pages (icon upper left page)
• February 13, 2006 - Narrated Video of Ultrasound Guided Axillary Block - Axillary Brachial Plexus Page
• January 29, 2006 - Illustration Cross Section Leg Anatomy - Popliteal Page
• January 21, 2006 - Axillary Block Cross Section - Axillary Brachial Plexus Page
• December 31, 2005 - Approaches to the Tibial Nerve - Popliteal Block Page
• December 31, 2005 - Modes of Failure in Ultrasound Guided Nerve Block - Ultrasound Page
• December 29, 2005 - Find the Sciatic in 3 Steps - Sciatic Page
• December 11, 2005 - Popliteal Anatomy Illustration Added - Popliteal Page
• December 9, 2005 - General tips for Recognizing Nerves on Ultrasound - Ultrasound Page
• December 8, 2005 - Published Radial Nerve Block Section - Axillary Brachial Plexus Page
• December 5, 2005 - Published median nerve block section.- Axillary Brachial Plexus Page
• November 20, 2005 - Illustration of Sciatic Nerve anatomy published.
• November 10, 2005 - Illustration of Femoral Nerve anatomy published.
• November 5, 2005 - Brachial Plexus Diagram published.
• October 20, 2005 - New site format introduced.

Sciatic Block Solved

Follow the link below to the Sciatic Page and read about Plan A, and Plan B; 2 methods that will lead to to ANY sciatic nerve!

Step by Step Instructions

 Read the details here.   Sciatic Practice Aid found here!

April 13th, 2007 -- Re-Written Popliteal Sciatic Block Page

Revision: October 8, 2006             Interscalene Brachial Plexus Nerve Block

An Open Study by UsinRA and Neuraxiom

“Phrenic Sparing Interscalene Brachial Plexus Block” -PSIB   An Open Study to Make a Good Block Better

Searching for the Interscalene Brachial Plexus Block that has the Least Incidence of Ipsilateral Hemidiaphragm Paralysis

The Phrenic Sparing Interscalene Block (PSIB) Study is an innovative approach to solving problems and moving the area of ultrasound guided brachial plexus blocks ahead. You are invited to enter data on cases into the project database anonymously and are able to view the data as it is collected. You may interpret the data and draw your own conclusions then submit your interpretations and conclusions (if you like) to the forum for open discussion. We're hoping to apply this method to other areas of concern is the future. A lot depends on your participation. We'll keep it short and sweet. Let's start from the beginning and tell how this came to be.The PSIB Project page can be found on a page by following this link or by choosing it from the menu bar branching from the Interscalene Block page titled the PSIB Project Page.

Find the Entire Introduction Article Here

December 2, 2006

A Low Volume Interscalene Brachial Plexus Block

Anyone who has performed blocks under ultrasound guidance has noted that some nerve targets can be completely surrounded with local anesthetic solution with volumes far below those previously thought necessary to complete a solid block. Some of the people who have used ultrasound guidance to perform blocks have actually stopped the injection when the nerve was seemingly adequately surrounded with the local anesthetic solution and then noted that the resulting the nerve block is completely effective and appears identical in every way to the block as performed with a much larger volume.

So, is it a good idea to do the same block was less volume? Is there any real benefit in modifying the block technique to base it on a smaller volume of local anesthetic?

In most cases the goal of of modifying a block technique by lowering the volume of local anesthetic injected may seem equivocal, change for change sake. But it could be argued that any time you can create the same therapeutic effect with lower doses of a drug, the proposed change would be applaudable. Less drug would theoretically lead to less side effects, the actual results would have to wait for a large study.

But in some nerve blocks the goal of lowering the volume of the anesthetic used would have a more immediate and therapeutically beneficial consequence. The interscalene block of the brachial plexus represents just such a block. According to the current results of the PSIB project study carried out by Neuraxiom.com and USINRA.EU and published here on Neuraxiom.com, approximately 70% of the unintended blocks of the phrenic nerve which occur as a side effect of the interscalene block are volume related. Specifically too much volume.

So if you think the paralyzed hemidiaphragm is a bad thing, or at least undesirable in some cases, then modifying the block procedure to lower the volume used for the block would be a good thing.

As it happens, in the case of the interscalene block, nature has provided us with some anatomical assistance; a sheath fitted around the proximal portion of the brachial plexus. This tubular containment is not new. It has been available to us for most of mankind's existence it is not even newly recognized. I'm sure it was identified from nearly the earliest anatomical dissections of the human body. I'm also sure that we share this feature with many other mammalian species. What is new, is that this sheath is finally accessible, on a routine and accurate basis, by any practitioner with an ultrasound machine.

This is the basis of the Low Volume Interscalene Brachial Plexus Nerve Block. Please follow this link to the Low Volume Interscalene Block page on the Neuraxiom site to find out more about what we’re doing about it.
 

Variant Anatomy of Brachial Plexus

vs.

 Anterior and Middle Scalene Muscles

While viewing a great number of necks by ultrasound I ,time and again, noted "holes" in the anterior scalene muscles of some patients. By "holes" I mean dark (hypoechoic) circles about 3-5 mms in diameter. The spots were usually near the centers of the anterior scalenes when viewed in their short axis. When I first saw them I assumed they were blood vessels, having no visible pulse, veins then. But when I turned on the color doppler there was no flow in them. Looking through the anatomy books I could find no reference to structures passing through the anterior scalene. Asking some local ENT surgeons about these observations brought me no new information or possibilities.

Then during my work on the illustration of the scans of the supraclavicular space for the supraclavicular brachial plexus block page of this site, I noted holes in the middle scalene muscle on the scan. This was too much. I began a search in earnest. Finally a google search of "scalene variations" brought me the lead I was looking for. A neurosurgery journal article on findings of the long thoracic nerve passing through the middle scalene, and the related article on the dorsal scapular nerve passing through the middle scalene as well. This answered my second question.  Then onto the first question. What are the "holes" in the anterior scalene?

The answer is obvious, they're nerves. The nerves of the brachial plexus, taking a detour to their ultimate destinations. Turns out the standard picture of the brachial plexus tells only part of the story.  It's possible that only a slight majority of people have the standard anatomical structure described in most anatomy books.

Consider. 

A study from the University of Texas, Medical Branch at Galveston published in Clinical Anatomy, (1997; 10(4):250-2) examined dissections of 51 cadavers showed that the standard description of the brachial plexus routed between the anterior and middle scalenes in the interscalene approach occurred in only 60% of instances, and ;

• Scalenus minimus occurred in 46% (bilateral in 14/51)
• C5 + C6 (fused together) passed through the anterior scalene in 15% (bilateral in 4/51)
• C5 root passed through the anterior scalene in 13% (bilateral in 3/51)
• C5 & C6 (separately) passed through the anterior scalene in 6% (bilateral in 1/51)
• C5 root traveling anterior of the anterior scalene in 3%

A Brazilian study published in Acta Cirurgica Brasileira (Vol 18, Suppl. 5, Sao Paulo, 2003) regarding 27 cadaver dissections reported that ;

• the phrenic had it's complete origin from the brachial plexus in 20% of sides dissected (73% = Right, 27% = Left)
• there was an accessory phrenic nerve in 12 of the cadavers
• the long thoracic nerve pierced the middle scalene in 63 %
• the dorsal scapular nerve traveled through the middle scalene in 73% of sides

"The American Surgeon", (Vol. 72, Number 2, Feb 2006, pp 188-192 (5)) article concerning dissection of 93 cadavers, 186 sides found variant anatomy in the relationship between the brachial plexus and the anterior scalene.

• C5 root anterior to the anterior scalene in 12 sides
• the anterior scalene was doubled in 1 cadaver and the upper trunk of the brachial plexus passed between them
• the upper trunk of the brachial plexus passed anterior to the anterior scalene in 4 cases and passed through the anterior scalene in 12 cases
• C5 passed anterior and C6 passed through the anterior scalene 1 cadaver

OK, enough considering, what does this mean to us (or to just me). Well 2 things,

1. It explains the "holes" we (I) see in the scalenes sometimes. 
2. It may account for the occasional, inexplicable block failure. A nerve lying inside the muscle belly and sequestered from the local anesthetic will remain unblocked and subsequently main account for 100% of the pain experienced by the patient.

How does it change the approach? The intramuscular passage of a root or trunk of the brachial plexus is relatively easy to spot with ultrasound and if you are aware of what it signifies, it seems prudent to place some local around it.

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