Interscalene

The interscalene block is one of the most familiar and desired procedures to perform with ultrasound guidance among anesthesia providers.  However, it can be challenging to master for the anesthetist new to UGRA because of the lack of readily identifiable landmarks.  Additionally, this block has the potential for significant complications such as inadvertent vascular puncture and local anesthetic toxicity.

Indications: Shoulder and upper arm surgery

Patient Position: Supine, with the patient’s head turned in a contralateral position

Transducer: High frequency transducer (>7 MHz)

Transducer Position: lateral neck, at or below the level of the cricoid cartilage

Needle: 5cm, 22 gauge stimulating needle

Local Anesthetic: 20 -30mls of local anesthetic

Keys To A Successful Block: circumferential spread around all three nerve roots

interscalene anatomyThe interscalene block is directed at cervical roots 5-7 of the brachial plexus.  They are generally found at the level of the cricoid cartilage (C6) in the neck, located beneath the Sternocleidomastoid muscle (SCM) between the anterior scalene (ASM) and middle scalene (MSM) muscles. The US image for this block is best obtained with the patient in the supine position, arms relaxed by the side, and the head turned to the non-operative side.   Since the brachial plexus is usually shallow (< 4cm) at this level, a high frequency transducer (>7MHz) should be used.  Two separate approaches can be used for identifying the interscalene nerve roots.  The first uses the major anatomical landmarks in the medial neck at level of C6, such as the carotid artery and internal jugular (IJ) vein.   Moving laterally and slightly posterior should bring the ASM and MSM into view.  At the root level, nerves appear as dark circular or oval hypoechoic structures, and can be confused as being small blood vessels.  Doppler ultrasound can be used to determine the nerve roots by verifying the absence of blood flow.  After quickly scanning the neck and the optimal level to perform the procedure is identified, the depth and gain can be further adjusted to bring the plexus into the best possible focus.

Identifying the nerve roots of the brachial plexus can be difficult because there are no easily discernible landmarks with ultrasound.  Using conventional descriptions to find the plexus often is not helpful as it tends to lie more inferior than at the level of the cricoid cartilage.  When using ultrasound, it is best to start at a location that has distinctive landmarks such as the supraclavicular fossa, or the carotid or internal jugular in the medial neck.

This video shows identification of nerve roots C5-7 beginning from the the supraclavicular fossa.  once obtaining the supraclavicular image, the trunks and divisions are identified.  The transducer is then moved cephalad following the nerves until the roots become visible between the anterior scalene and middle scalene muscles.

The video below shows identification of nerve roots C5-7 from the medial neck.  The transducer is initially placed on the medial neck at the level of C6 (cricoid cartilage).  the trachea, thyroid gland, internal jugular vein and carotid artery are visible.  The transducer is then moved laterally where the anterior scalene muscle is identified.  The transducer is then moved slightly caudal until all three roots are seen.

Confirming the root level of your ultrasound image can be aided by using the anterior and posterior tubercles on the transverse process of the cervical spine as landmarks.  The absence of the anterior tubercle at C7 (indicated by pen) serves as a landmark to ensure all three roots are identified.  The visualization of these landmarks alerts the anesthetist to the close proximity of the C5 root, where an intraneural injection can lead to an unintended epidural or spinal injection.

The video below begins with identification of the C5 root in the lower middle left of the screen.  Shadowing from the anterior and posterior tubercles appears to “cup” nerve.  The transducer is moved cephalad until the C6 root appears with a similar shadow.  Continuing cephalad, the C7 root appears, with only posterior shadowing noted below and to the right of the root.  The three roots of the plexus are then seen together in the middle of the screen.  The video ends with the transducer moved slightly caudal until the posterior shadowing is again visible in the middle of the screen.

 

While traditional regional techniques advocate the needle being placed perpendicular to the skin, ultrasound-guided interscalene placement favors in-plane needle insertion. This allows for better visualization of the block needle. Out-of-plane perpendicular approaches and medial in-plane approaches have also been described in the literature. While these approaches have their merits, the lateral in-plane approach offers the new practitioner a high level of success without the technical difficulty of visualizing only the needle tip in the out-of-plane approach, or the increased risk of vascular puncture with the medial approach. Once satisfied that the US image is at the appropriate anatomic location, a small amount of local anesthetic is infiltrated under the skin prior to inserting the block needle. Advancing the block needle along the long axis of the transducer in an in-plane approach allows the provider to observe its movement toward the targeted nerves in real-time. Confirmation of correct needle placement can be accomplished with the use of a nerve stimulator, and is often recommended for the new practitioner. As proficiency improves, visualization of proper needle placement is sufficient to achieve an adequate block, and the use of nerve stimulation may actually decrease block proficiency. Once proper needle placement is confirmed, 20-30 mls of local anesthetic is injected.

This video shows an in-plane interscalene single-shot injection.  A 5cm block needle is passed lateral to medial in-plane through the connective tissue of the brachial plexus.  After negative aspiration, incremental injections of local anesthetic is accomplished until circumferential spread is achieved.

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References

Mulroy MF, Bernards CM, McDonald SB, Salinas FV. A Practical Approach to Regional Anesthesia. 4th. Ed. Baltimore, MD: Lippincott Williams and Wilkins; 2009:172-183.

Pollard BA, Chan VW. An introductory curriculum for ultrasound-guided regional anesthesia: a learner’s guide. Toronto. University of Toronto Press Inc.; 2009:56-59.

Gray AT. Atlas of ultrasound-guided regional anesthesia. Philadelphia, PA. Saunders, Elsevier; 2010:74-84.

Bigeleisen PE, ed, Orebaugh SL, Moayeri N, et al. Ultrasound-guided regional anesthesia ad pain medicine. Baltimore, MD. Lippincott Williams & Wilkins; 2010:45-52.

Morgan GE, Mikhail MS, Murray MJ. Clinical Anesthesiology. 4th ed. New York, NY: Lange Medical Books/McGraw-Hill; 2006:329-332.

 

 

 

 

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