The first use of ultrasound to guide regional block was for brachial plexus block above the clavicle.¹ These pioneers used an offline Doppler technique to mark the position of the subclavian artery as a surrogate landmark of the brachial plexus. Although today there may be many criticisms of this technique, their results were impressive: a 98% success rate with no complications.

Ultrasound imaging blurs the distinction between interscalene and supraclavicular blocks. If the brachial plexus is seen stacked between the anterior and middle scalene muscles, the block is generally referred to as an interscalene block. If the brachial plexus is seen as a compact group of nerves lying superior and lateral to the subclavian artery, the approach is generally referred to as a supraclavicular block. Because this distinction can be subtle, both blocks will be treated together.

Variations in brachial plexus anatomy with respect to the scalene muscles are common. The cephalad components of the plexus (in particular, the C5 and C6 ventral rami) often pass over or through the anterior scalene muscle. This may pose a problem for nerve stimulation–based approaches to brachial plexus blocks above the clavicle. The incidence of scalene muscle anomalies is similar for sonography of volunteers and in cadaveric dissections, suggesting that ultrasound can accurately detect these anomalies.²

Cervical ribs are relatively uncommon, occurring in about 0.5% of the population.^3,4 Most cervical ribs are partial (incomplete) and therefore do not pose a problem. However, if the cervical rib is sufficiently large, transducer manipulation can be difficult, and acoustic shadowing by the bone obscures imaging of the brachial plexus.

Suggested Technique

The monofascicular ventral rami of the brachial plexus are hypoechoic and therefore can be difficult to identify between the scalene muscles. The ventral rami can be similar to blood vessels in their ultrasound appearance. The brachial plexus lies deep to the tapering posterolateral edge of the sternocleidomastoid in the neck.

The best nerve visibility is usually near the first rib because the brachial plexus is compact and lateral to the subclavian artery. The plexus contains more connective tissue moving from interscalene to supraclavicular views, resulting in more hyperechoic echotexture. To obtain a good supraclavicular view with the subclavian artery in true short axis, the imaging plane must face caudally at the brachial plexus (not posteriorly). Brachial plexus imaging in the supraclavicular region is most consistent and can be used to trace the plexus back to the interscalene groove. Perform the block where the imaging is most reliable.

The semisitting (beach-chair) position helps comfort the patient, lowers the arm by gravity, and brings the plane of imaging closer to the plane of the display. The head-of-bed elevation should be about 45 degrees. The patient’s head turns to the opposite side from the block. The operator stands either at the head of the bed or at the side of the bed, depending on the side of the block and the handedness of the operator.

Working room is limited above the clavicle, and therefore a compact transducer is favored. A small curved or small linear (20- to 25-mm footprint) transducer is preferred. The compact transducer can be rocked back to improve needle visibility. Broad linear probes are more difficult to rock than narrow linear or curved transducers for this procedure. The ulnar aspects of both hands of the operator are placed on the patient for the best control of the needle and transducer.

A short (50 mm), broad (21 gauge) echogenic needle is used for optimal control and visibility. Hand-on-needle hub (not hand on syringe) is recommended for better needle control. A medial to lateral in-plane needle path heads away from pleura.

Most authors recommend a multiple injection technique to ensure complete plexus anesthesia. With this approach the initial aim of the needle is deep (under the more caudal elements of the plexus) so that the brachial plexus rises closer to the skin surface with the injection of local anesthetic. This makes the subsequent needle passes easier to perform. The needle tip should be positioned adjacent to the components of the brachial plexus for injection within the interscalene groove.⁵ Inferior trunk sparing occurs less often with this multiple injection ultrasound technique compared with nerve stimulation–based approaches to interscalene block.⁶

The anatomy of the posterior triangle of the neck is complex. Nerves close to the brachial plexus, and therefore potentially in the needle path, include the phrenic nerve, dorsal scapular nerve, and spinal accessory nerve. The phrenic nerve lies medial to the brachial plexus and travels over the anterior scalene muscle toward the midline as it descends into the chest. The dorsal scapular nerve is a branch of the brachial plexus that is often observed lateral to the brachial plexus within the middle scalene muscle. The spinal accessory nerve is difficult to image but lies lateral to the brachial plexus within the posterior triangle of the neck.⁷

The number of visualized components of the brachial plexus (five ventral rami, three trunks, and six divisions) vary with the angle of the transducer and its position in the neck. A mixture of these elements is possible within a given field of view. Sparing of the superficial cervical plexus and intercostobrachial nerves can occur.

A sterile transparent dressing (Tegaderm; 3M Health Care, St. Paul, Minn) can be used to cover the hockey-stick transducer for better external visualization of the probe position and therefore easier line-ups.⁸ For this technique the adhesive dressing is applied directly to the transducer without acoustic coupling gel. Sterile gel is used between the covered probe and the skin. Not all sterile adhesive dressings have favorable acoustic properties for this purpose.

The subclavian artery and the transverse cervical artery are the primary vascular puncture risks of this procedure. Transverse cervical arteries are frequently observed running over or through the brachial plexus in the neck.⁹

Clinical Pearls

• The needle tip should be positioned adjacent to the ventral rami of C5, C6, and C7 to ensure complete plexus anesthesia with a multiple-injection technique.⁶

• Arteries that traverse the interscalene brachial plexus can divide it into separate compartments. The deep cervical artery (the dorsal scapular artery) usually runs between the seventh and eighth cervical roots. This artery continues between the middle and the lower trunks of the brachial plexus. Multiple injections may be necessary to obtain complete plexus anesthesia when this anatomy is present.

• The seventh cervical ventral ramus is usually the largest, with progressively smaller cephalad and caudad ventral rami. These size differences tend to equalize the size of the three trunks that form the brachial plexus.

• Both the medial to lateral and lateral to medial approaches to supraclavicular block have similar efficacy and safety profiles.¹⁰

FIGURE 27-1 External photograph showing the transducer position for interscalene imaging (A) and corresponding sonogram (B). In this location, the components of the brachial plexus are stacked between the anterior and middle scalene muscles underneath the tapering anterolateral edge of the sternocleidomastoid muscle.

FIGURE 27-2 Supraclavicular imaging. If the probe is moved toward the clavicle and angled caudally, the brachial plexus is seen to bundle compactly in the superior and lateral positions with respect to the subclavian artery.

FIGURE 27-3 Interscalene imaging reveals a large artery passing through the middle scalene muscle in this subject. The deep cervical artery (the dorsal scapular artery) usually runs between the seventh and eighth cervical roots and can sometimes be identified dividing the middle and the lower trunks of the brachial plexus.

FIGURE 27-4 B-mode sonogram (A) and duplex power Doppler (B) identify a superficial cervical artery. The interscalene region is highly vascular. When these vessels are identified, the probe position for interscalene block is moved slightly cephalad or caudad.

FIGURE 27-5 External photographs showing in-plane approaches to interscalene block. The medial to lateral approach (A) and the lateral to medial approach (B) are shown.

FIGURE 27-6 Short-axis view of the interscalene plexus during medial to lateral in-plane approach. Local anesthetic is seen to distribute around nerves of the brachial plexus.

FIGURE 27-7 Image sequence showing interscalene block. A medial to lateral in-plane approach is demonstrated where the needle tip is carefully placed adjacent to the components of the plexus (A and B). After injection, local anesthetic is distributed around both sides of the brachial plexus (C).

FIGURE 27-8 Image sequence showing interscalene block. A lateral to medial in-plane approach is demonstrated (A). After injection, local anesthetic is distributed around both sides of the brachial plexus (B).

FIGURE 27-9 Pass-through brachial plexus. In this sonogram, cephalad elements of the brachial plexus are seen to pass through the anterior scalene muscle. This anatomic variation potentially divides the brachial plexus, with the potential for incomplete blocks.

FIGURE 27-10 Pass-over brachial plexus. In this sonogram, three ventral rami (C5, C6, and C7) are seen to pass over the anterior scalene muscle. It is uncommon for three ventral rami to pass over the anterior scalene, although more commonly, C5 or both C5 and C6 can travel in this pathway.