Indications: Anesthesia and analgesia for shoulder, upper arm, and clavicle sugeries

Goal: Local anesthetic spread around superior and middle trunks of the brachial plexus, between the anterior and middle scalene muscles

Transducer: Linear, high frequency

Needle: 23-22 gauge, 5 cm short bevel

Local anesthetic volume: 7-15 mL

Functional anatomy

The Brachial Plexus is formed by the ventral rami of the roots C5 to T1 (Fig-1).

These roots join to form the superior (C5, C6), middle (C7), and inferior trunks (C8, T1) above the clavicle.

The trunks then branch into anterior and posterior divisions.

At the interscalene level, the brachial plexus is visualized (Fig-2):

• Lateral to the carotid artery and internal jugular vein.
• Between the anterior and middle scalene muscles.
• Deep to the prevertebral fascia, superficial cervical plexus, and sternocleidomastoid muscle (SCM).

The interscalene brachial plexus block results in anesthesia of the shoulder, upper arm, and lateral two-thirds of the clavicle (Fig-1).

The proximal spread of the local anesthetic outside of the interscalene space commonly blocks the supraclavicular branches of the cervical plexus that supply the skin over the acromion and clavicle.

The inferior trunk (C8-T1) is usually spared with an interscalane approach to the brachial plexus.

When nerve stimulation is used, a number of motor responses of the upper, middle, and inferior trunks of the brachial plexus can be evoked (Fig-2).

Common responses to nerve stimulation in clinical practice are:

• Flexion of the elbow (C5-C6), a biceps branchii motor response.
• Extension of the elbow joint (C7), a triceps brachii motor response.
• Pronation of the forearm, wrist twitches, and flexion of the fingers (C8-T1), most commonly.

Fig-2. Functional innervation of the upper extremity muscles (myotomes).

Patient position: Supine with a semi-sitting position and the head facing away from the side to be blocked.

External landmarks: Clavicle, sternocleidomastoid muscle, and external jugular vein (EJV), when visible.

Transducer position

• Place the transducer in a transverse orientation over the neck, approximately 2-3 cm superior to the clavicle and over the external jugular vein when visible.

Scanning

Different scanning techniques can be used:

A. Identify the carotid artery deep to the sternocleidomastoid muscle, and move the transducer posteriorly to visualize the anterior and middle scalene muscles. The brachial plexus is typically visualized at a depth of 1–3 cm.

B. Traceback technique:

• Start scanning at the supraclavicular fossa.

• Identify the brachial plexus.

• Trace the supraclavicular brachial plexus to the level of the interscalene space.

Depending on the depth of the field selected and the level at which scanning is performed, the first rib and/or the apex of the lung may be seen.

Needle insertion 

• Insert the needle in-plane towards the brachial plexus in a lateral-to-medial direction. The exit of the needle from the middle scalene muscle into the interscalene space is often accompanied by a perceptible click.

• Aspirate to rule out intravascular needle placement and inject 1-2 mL of local anesthetic to verify proper needle position.

• A proper spread, inside the sheath, will result in the displacement of the brachial plexus by the local anesthetic.
• Complete the block with 10-15 mL.
• Scan proximally and distally along the neck to verify spread within the interscalene space covering the brachial plexus roots.

Let's review the block:  

Interscalene block; Reverse Ultrasound Anatomy with needle insertion in-plane. SCM, sternocleidomastoid; ASM, anterior scalene muscle; LCa, longus capitis muscle; VA, vertebral artery; MSM, middle scalene muscle; LTN, long thoracic nerve; DSN, dorsal scapular nerve; C7-TP, transverse process of C7.

Interscalene catheter

Important: Avoid LONG-acting local anesthetics in patients who cannot tolerate a decrease in lung function by 20% (phrenic nerve paralysis).

• Start from the clavicle: Many trainees find it easier to trace the plexus from the supraclavicular fossa to identify the plexus and scan proximally to the interscalene space.
• Intramuscular C5: C5 root often courses through the anterior scalene muscle. Trace the root distally until it enters the interscalene space.
• Routine nerve stimulation: May alert the operator when the dorsal scapular and/or long thoracic nerves are in the needle path in the middle scalene muscle.
• Unexpected distal motor response during nerve stimulation (0.5 mA; 0.1 msec) indicates that the needle is on or in the nerve and should prompt cessation of needle advancement and re-evaluation to decrease the risk of injury to these nerves.
• Color Doppler: The neck is a highly vascular area; use Color Doppler before performing a block to identify and avoid any major vessel in the path.
• Whenever possible avoid medial-to-lateral needle insertion to decrease the risk of injury to the phrenic nerve. Rationale: The phrenic nerve is typically located medially (anteriorly) to the anterior scalene muscle.
• C5-C6: It is prudent to avoid injecting between the nerves coming from a single root, as this may result in an intraneural injection.
• High pressure: Never inject against high resistance (high opening injection pressure; >15 psi) because such resistance may indicate needle–nerve contact or an intrafascicular injection.
• Successful injection: An injection inside the brachial plexus “sheath” a) displaces the brachial plexus away for local anesthetic b) the spread can be seen proximal and distal to the site of injection on both sides of the plexus.
• Multiple injections: May result in a somewhat faster onset of the block, but are not necessary and may carry a higher risk of nerve injury.