Focus On: Ultrasound-Guided Interscalene Approach To the Brachial Plexus Nerve Block

By Daniel  Mantuani, M.D.; Caitlin  Bailey, M.D.; Mike Stone,  M.D.; and Arun Nagdev, M.D.

 Contributors

Dr. Mantuani is an Ultrasound Fellow and Attending Physician at Alameda County Medical Center Department of Emergency Medicine and Highland General Hospital in Oakland, Calif. Dr. Bailey is an Ultrasound Fellow and Attending Physician at Alameda County Medical Center Department of Emergency Medicine and Highland General Hospital in Oakland, Calif. Dr. Stone is an attending physician and Associate Research Director at Alameda County Medical Center, Highland General Hospital in Oakland, Calif. Dr. Nagdev is an attending physician, Director of Emergency Ultrasound, and the Ultrasound Fellowship Director at Alameda County Medical Center, Highland General Hospital in Oakland, Calif.

Disclosures
In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, all individuals in control of content must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.

Dr. Mantuani, Dr. Bailey, Dr. Stone, Dr. Nagdev, and Dr. Solomon have disclosed that they have no significant relationships with or financial interests in any commercial companies that pertain to this article.

This activity has been planned and implemented in accordance with the Essential Areas and Policies of the Accreditation Council for Continuing Medical Education (ACCME). The American College of Emergency Physicians is accredited by the ACCME to provide continuing medical education for physicians.

The American College of Emergency Physicians designates this enduring material for a maximum of 1 AMA PRA Category 1 Credit^TM. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

"Focus On: Ultrasound-Guided Interscalene Approach To the Brachial Plexus Nerve Block" is approved by the American College of Emergency Physicians for one ACEP Category I credit.

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Use of regional anesthesia is be­ coming more prevalent in the emergency department as more data emerge about its safety, efficacy, and, in many cases, associated de­creased length of stay. Procedural seda­tion requires intravenous access, dedicated personnel for both the sedation and procedure, and a room within the emergency department equipped to provide airway management and resuscitation in the event of complications from IV anesthesia. Complications include hypoventila­tion/apnea, aspiration, laryngospasm, and hypoten­sion. Often, the required painful procedure is brief, but the discomfort associat­ed with the illness is long- lasting; procedural sedation provides anesthesia for a brief period of time, but does not control pain after the sedation is over. Region­al anesthesia provides pain relief lasting for hours, allowing intervention in the patient's acute illness without sub­jecting him or her to the risks of seda­tion. For patients whose injuries require transfer to a center with broad­er expertise, regional anesthesia can provide critical pain control without a change in respiratory pattern or men­tal status that could become dangerous during transit.

In the emergency department, ultra­ sound-guided brachial plexus block can provide rapid and definitive pain relief from traumatic injuries to the upper extremity. Emergency physicians have published data on using two approaches (interscalene and supraclavicular) for the ultrasound-guided brachial plexus block.^1,2 Either can be used as a primary or supplementary method to provide analgesia for traumatic injuries and infections, including humeral fractures, upper-extremity joint reduction, abscess drainage, and burns. The interscalene and supraclavicular brachial plexus blocks are considered ultrasound-guided procedures with intermediate difficulty. However, the interscalene approach allows for identification of the brachial plexus while maintaining a greater dis­tance from vascular structures and pleu­ra than the supraclavicular approach. A simplified method to locate and perform the block will allow for integration of this useful procedure into the practice of emergency medicine. Both blocks are performed with ultrasound guidance in the emergency department setting. While anesthesiologists may use nerve stimulators to achieve these blocks, this technique is not typically employed in the emergency depart­ment. Moreover, there is evidence sug­gesting that ultrasound provides superior efficacy compared with nerve stimulator block of the brachial plexus at the interscalene level.³

Clinical Indications 
The ultrasound-guided interscalene brachial plexus block provides regional anesthesia to the entire upper extremi­ty including the shoulder. Anesthesiol­ogists routinely utilize the interscalene brachial plexus block during orthope­dic surgery to provide anesthesia to the lateral clavicle, acromioclavicular joint, proximal humerus, and elbow. In the emergency department, current indications for the interscalene block in­clude pain control for upper-extremity fractures (proximal humerus, midshaft humerus, etc.) and facilitation of manip­ulations and reductions of upper-extremity injuries. Also, the interscalene brachial plexus block may bean ideal alternative in the setting of large abscess incision and drainage, deep wound exploration, and complex lacer­ation repair when procedural sedation  is not feasible.

Although the interscalene approach has a lower risk of iatrogenic pneumothorax than the supraclavicular ap­proach secondary to the higher approach on the neck, it is more likely to cause phrenic nerve paralysis due to tracking of local anesthetic around the anterior scalene muscle. Traditional high volumes injections of local anes­thetic (greater than 30 mL) will reliably affect the phrenic nerve and cause paralysis of the ipsilateral hemidi­aphragm for the duration of the block.⁴ While clinically insignificant in healthy patients, the risk of phrenic nerve paralysis may potentially be decreased by using small-volume intraplexus in­jections under real-time ultrasound guidance.⁵ However, since currently there is no clear evidence suggesting that phrenic nerve paralysis can be reli­ably avoided, this block is not recommended for pa­tients with known low pul­monary reserve such as those with chronic obstruc­tive pulmonary disease.

Furthermore, it is not recommended that the block be used in patients who are intoxicated, demented, or otherwise with­out normal mental status, as the patient's report of paresthesias, worsening pain, or other symptoms during the procedure helps avoid complications from misdirected anesthetic (intravascular or intraneural injection). Also, post-block evaluation for peripheral nerve injury (PNI) will not be possible if a consistent neuro­logic exam cannot be performed be­fore the procedure is started.

Anatomy
The brachial plexus originates from the anterior rami of the C5-T1 spinal nerves and divides into the roots, trunks, divisions, and cords that ultimately contribute to the axillary, radial, median, and ulnar nerves that provide cutaneous and motor innervation for the entire upper limb. After exiting the neural foramina, the brachial plexus travels through the interscalene groove between the anterior and middle scalene muscles and joins the subclavian artery anterior to the first rib and posterior to the clavicle. This neurovascular bundle travels to the axilla and supplies both motor and sensory inner­vation to the entire upper extremity via the axillary, musculocutaneous, radial, median and ulnar nerves. When successfully performed, the interscalene block may also affect the distal branches of the divisions and cords that give rise to the suprascapular, lateral and medial pectoral, thoracodorsal, and subscapular nerves.

The interscalene approach targets the brachial plexus at the level of the roots or trunks as they pass lateral to the great vessels and through the interscalene groove between the anterior and medial scalene muscles. The interscalene groove is located deep to the clavicular head of the sternocleidomastoid muscle and is bordered medially by the anterior scalene muscle and laterally by the middle scalene. Important landmarks that lie medial to the anterior scalene muscle include the carotid artery, internal jugular vein, and phrenic nerve. The dome of the pleura is located caudad and should not be considered at risk if the block is performed correctly at the level of the larynx. Occasionally, the interscalene block will fail to anesthetize the C8 dermatome that provides sensation to the fifth digit and distal medial forearm. This is because of a described anatomic variation in which the C8 nerve root lies deep to the C5-7 plexus and is separated by an additional fascial layer or muscle bridge that may limit the spread of local anesthetic.⁶ For emergency physicians who are using this block for proximal upper-extremity in­ juries, the lack of complete anesthesia of the C8 root is not clinically significant. For patients who require complete anesthesia below the elbow, a supraclavicular or infraclavicular approach may be more desirable.

The Procedure: Ultrasound-Guided Interscalene Brachial Plexus Nerve Blocks

Patient Positioning and Probe Selection
The patient is placed on a cardiac monitor and positioned supine in a semi-reclining position with the head rotated 30 degrees away from the side of the injury. The ultrasound screen and cardiac monitor should be directly opposite the patient so that the physician can easily view the display screen while performing the block, permitting the visualization of the neck and ultra­sound screen in the same visual axis (Fig. 1). A high-frequency linear transducer probe (10-5 MHz) with a large footprint is ideal for the procedure. Al­ ways clean the ultrasound probe in a standard fashion and place a clear adherent dressing over the probe (Fig. 2), using sterile surgical lubricant as a coupling agent.

Choice of Local Anesthetic
Lidocaine 1%-2% drawn into a 20-30 mL syringe is recommended. All providers using nerve blocks should be familiar with the standard recommended dosages and clinical signs of toxicity, and have established protocols for treatment of local anesthetic toxicity that incorporate use of lipid infusions. For novice users, lidocaine rather than bupivacaine is recommended be­cause of its better safe­ty profile in cases of inadvertent vascular injection. Using epinephine-containing anesthetics can prolong the duration of the block, and also provides an additional safety benefit: sudden tachycardia, hypertension, and characteristic electrocardio­graphic T-wave morphology changes indicate accidental intravascular injection, alerting providers before large volumes of local anesthetics have been injected. A standard 21- to 23-gauge, 1.5-inch needle provides adequate visu­alization without significant tissue trauma but may not have sufficient length to reach the interscalene groove. For this reason, a 3.5-inch spinal needle is recommended in cases in which the depth of the relevant structures appears significantly deep to the skin surface as it interfaces with the ultrasound probe (Fig. 3)

.

Injection Technique
Place a high-frequency linear transducer in a transverse orientation (probe mark­er facing the right of the patient) at the level of the larynx, identifying the inter­nal jugular vein (IJV) and carotid artery. Clinicians comfortable with ultrasound-guided cannulation of the IJV should be able to locate the vascular anatomy of the neck at this level. From this posi­tion, slowly move the probe laterally past the great vessels until the border of the clavicular head of the sternocleido­mastoid muscle (SCM) comes into view midscreen(Fig. 4).At this level, the anterior and middle scalene muscles lie just deep to the SCM, with the interscalene groove lo­cated between the two prominent muscles. The nerve roots of the brachial plexus will be visualized as oval or round hypoechoic structures located in the groove between the anterior and middle scalene muscles, where they are tightly clustered within their own fascial sheath. Here the C5-7 roots of the brachial plexus appear as three vertically aligned, round, hypoe­choic structures, sometimes referred to as the "traffic light" sign (Fig. 5).

The C8 root may be located within this fascial plane or may be deeper as previously mentioned. Lateral to the brachial plexus is the middle scalene muscle, comprising the lateral border of the interscalene groove. The transverse cervical and suprascapular arteries typi­cally run laterally and caudad to the brachial plexus at this level. After locat­ing the brachial plexus, color Doppler is recommended to confirm that vascula­ture structures will not be present in the path of the needle and/or mistaken for hypoechoic nerve roots.

An alternative approach to finding the brachial plexus (if the provider is having difficulty locating the structures at the level of the larynx) involves identifying the brachial plexus distally at the level of the supraclavicular fossa and following the nerve trunks proximally into the interscalene groove. Here, the transducer is placed transversely in the supraclavicular fossa and aimed caudally until the subclavian artery is visual­ized. The brachial plexus lies just posterolateral to the artery at this level and will appear as a tight group, a hy­poechoic "cluster of grapes." Follow these hypoechoic structures cephalad until they form the traffic light sign within the interscalene groove at the level of the larynx (Fig. 6).

Needle Insertion and Injection 
Two distinct injection techniques have been described: 

• The classic periplexus approach tar­gets the potential space between the middle scalene muscle and the brachial plexus sheath. This approach reduces the risk of intraneural injection but requires higher volumes of local anesthet­ic to achieve a complete block. Unfortunately, large volumes of anesthetic are thought to be more likely to track around the anterior scalene muscle to the phrenic nerve, causing paraly­sis of the ipsilateral hemidiaphragm.
• The intraplexus approach targets the space between the nerve roots within the brachial plexus sheath and requires smaller volumes of local anesthesia to achieve an adequate block. Lower vol­umes of injected anesthetic limits spread to the phrenic nerve but may also result in anesthetic tracking supe­riorly within the plexus sheath, affect­ ing the recurrent laryngeal nerve and/or sympathetic chain, causing temporary hoarseness or Horner's syn­drome, respectively.

The authors recommend performing the interscalene brachial plexus with an in-plane technique so that the nee­dle is visualized in its entirety. After cleaning the skin with a sterilizing solution such as chlorhexidine, and cov­ering the cleaned ultrasound probe with a sterile adhesive dressing, place 2-3 mL of lidocaine (with or without epinephrine) about 0.5-1 cm lateral to the ultrasound probe. This will be the location of entry for the block needle, and adequate local anesthesia will allow for patient comfort during the block.

Enter the skin at the site of the local skin wheal in a lateral to medial in-plane approach. Flatter needle angles will allow for better needle visualiza­tion, which will depend on the depth and location of the brachial plexus. Advance the needle in 1- to 2-cm incre­ments, maintaining clear visualization of the needle tip at all times. This block may be performed with either an in-plane or out-of-plane approach.

In many cases, the authors prefer an in-plane approach because the needle tip can be better visualized, allowing for more precise intraplexus injections. The needle is inserted lateral to the lateral aspect of the transducer. For a periplexus injection, the needle tip is advanced through the middle scalene muscle to the lateral border of the deepest nerve root. Local anesthetic (15-20 mL) is delivered into the poten­tial space between the middle scalene muscle and the brachial plexus sheath (Fig. 7).

For an intraplexus injection, the nee­dle is advanced into the brachial plexus sheath between the two most superficial nerve roots, and a low-volume in­jection of 5-10 mL may be used. For all ultrasound-guided nerve blocks, fre­quent aspiration to confirm lack of vasculature puncture and visualization of the needle (including needle tip) are recommended before injection.

Finally, if anechoic fluid is not seen on the ultrasound screen (or if high in­jection pressures or parethesias are en­countered) when injecting anesthetic, the procedure should be halted, and the visualization of the needle tip should be confirmed. Local anesthetic will track around the brachial plexus bundle, pro­ducing the classic "donut" sign.

Evaluating Block Efficacy
Successful blocks are associated with direct visualization of  hypoechoic anesthetic adjacent to the brachial plexus in the interscalene groove, as well as fluid tracking in the fascial plane. Waiting at least 20 minutes before performing the motor and sensory exam of the upper extremity is recom­mended. Block duration should be ap­proximately 1-3 hours, but a block occasionally lasts as long as 6 hours.

Aftercare
After the block is performed, the time and date of the block should be marked on the patient's skin with a sterile marking pen (if they are being admitted) or not­ed in discharge paperwork. Patients should be reminded that they are at risk of injuring the affected extremi­ty because of the anesthesia. A sling should be provided to support the arm even if not otherwise warranted by the injury. Patients should be given strict verbal and written instructions to re­turn for persistent paresthesias, weak­ness,or severe pain that lasts more than 48-72 hours.

Summary
The interscalene approach to the brachial plexus block provides effec­tive anesthesia for painful traumatic and infectious conditions of the upper extremity. Ultrasound guidance allows the emergency physician to perform this block safely. The interscalene brachial plexus is identified between the scalene muscles at the level of the larynx, or followed up from the supra­ clavicular location, where the plexus is more unified. Local anestheticis de­livered via the periplexus or in­traplexus approach, with the needle visualized in-plane. The patient's neurologic exam should be recorded before and after the block, and appro­priate aftercare and return precautions given.

References

1. Blaivas M, Adhikari S, Lander L. A prospective comparison of procedural sedation and ultrasound-guided inter­scalene nerve block for shoulder reduc­tion in the emergency department. Acad. Emerg. Med. 2011;18(9):922-7.

2. Stone MB, Wang R, Price DD. Ultra­ sound-guided supraclavicular brachial plexus nerve block vs procedural seda­tion for the treatment of upper ex­tremity emergencies. Am.J. Emerg. Med. 2008;26(6):706-10.

3. Kapral S, Greher M, Huber G, et al. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg. Anesth. Pain Med.2008;33(3):253-8.

4. Urmey WF, Talts KH, Sharrock NE. One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anes­thesia as diagnosed by ultrasonogra­phy. Anesth. Analg. 1991;72(4):498-503.

5. Riazi S, Carmichael N, Awad I, Holt­ by RM, McCartney CJL.Effect of local anaesthetic volume (20 vs 5 ml) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br. J. Anaesth. 2008;101(4):549-56.

6. Marhofer P, Harrop-Griffiths W, Willschke H, Kirchmair L.Fifteen years of ultrasound guidance in re­gional anaesthesia, Part 2: Recent developments in block techniques. Br.J. Anaesth. 2010;104(6):673-83.