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Table of Contents  
LETTERS TO EDITOR
Year : 2017  |  Volume : 11  |  Issue : 2  |  Page : 536-537  

Implications of pass-over brachial plexus


1 Department of Anesthesiology and Pain Management, Basavatarakam Indo-American Cancer Hospital and Research Institute, Hyderabad, Telangana, India
2 Department of Anesthesia and Pain Management, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada

Date of Web Publication16-May-2017

Correspondence Address:
Abhijit S Nair
Department of Anesthesiology and Pain Management, Basavatarakam Indo-American Cancer Hospital and Research Institute, Hyderabad - 500 034, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0259-1162.194574

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How to cite this article:
Nair AS, Sahoo RK. Implications of pass-over brachial plexus. Anesth Essays Res 2017;11:536-7

How to cite this URL:
Nair AS, Sahoo RK. Implications of pass-over brachial plexus. Anesth Essays Res [serial online] 2017 [cited 2020 Jul 5];11:536-7. Available from: http://www.aeronline.org/text.asp?2017/11/2/536/194574

Sir,

Successful brachial plexus block requires detailed knowledge of gross anatomy, knowledge of the relevance of muscle twitch when a nerve stimulator is used, and knowledge of sonoanatomy when the block is planned under ultrasound guidance. The groove between the anterior and middle scalene muscle is the landmark where the drug is injected by landmark technique, and the stimulating needle is placed when a nerve stimulator is used to perform an interscalene block. Similarly, when ultrasound is used for performing the block, the two scalene muscles are identified, and the C5–C7 roots are traced in the interscalene groove.[1],[2] However, sometimes the roots do not follow the rule of being placed in the groove. When they deviate from the regular position, the brachial plexus is also known by a different name. It is called a pass-through brachial plexus when the roots of brachial plexus pass through the anterior scalene muscle and a pass-over brachial plexus when the ventral rami of brachial plexus pass over the anterior scalene muscle.[3] Usually, C5 or C5–C6 roots travel this pathway. The possibility of all C5–C7 roots passing over anterior scalene muscle is rare. This anomalous location of the root is the reason for a failed or a patchy interscalene block when landmark technique is used and when the block is performed with a nerve stimulator. The block can fail with the use of ultrasound if the performer fails to recognize a pass-over or a pass-through plexus.

During a random neck scan of a patient who was not scheduled to undergo a surgery of the upper limb, we identified a C5–C6 nerve root passing over the anterior scalene muscle instead of the usual location that is in the interscalene groove [Figure 1]. In such situation, the C5–C6 roots have to be blocked separately in the substance of anterior scalene muscle. However, the problem with this injection in the belly of anterior scalene is that the injected local anesthetic might block the phrenic nerve as well.
Figure 1: The image shows C5–C6 root over the anterior scalene muscle rather than the groove between anterior and middle scalene muscle. The C7 root is seen in the usual location that is the interscalene groove. The interscalene groove is shown with the black line between anterior and middle scalene muscle

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The phrenic nerve arises from C3 to C5 and is usually in proximity to the C5 root at the level of cricoid cartilage. From here, the nerve descends in a caudal direction over the anterior scalene muscle.[4] Therefore, once a pass-over brachial plexus is identified, a meticulous scan should be done to identify the phrenic nerve and a lesser volume of local anesthetic should be injected to avoid complications due to phrenic nerve block.

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   References Top

1.
Franco CD, Williams JM. Ultrasound-guided interscalene block: Reevaluation of the stoplight sign and clinical implications. Reg Anesth Pain Med 2016;41:452-9.  Back to cited text no. 1
[PUBMED]    
2.
Wong GY, Brown DL, Miller GM, Cahill DR. Defining the cross-sectional anatomy important to interscalene brachial plexus block with magnetic resonance imaging. Reg Anesth Pain Med 1998;23:77-80.  Back to cited text no. 2
[PUBMED]    
3.
Miller RD. Miller's Anesthesia. 7th ed. Philadelphia, PA: Churchill Livingstone, Elsevier; 2010. p. 1685. Available from: https://books.google.jo/books?id=HPpgOjIGYtAC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false [Last accessed on 2016 Oct 19].  Back to cited text no. 3
    
4.
Kessler J, Schafhalter-Zoppoth I, Gray AT. An ultrasound study of the phrenic nerve in the posterior cervical triangle: Implications for the interscalene brachial plexus block. Reg Anesth Pain Med 2008;33:545-50.  Back to cited text no. 4
    


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