Indications

Contraindications

Clinical anatomy

The cervical nerves exit from the cervical spine through gutters in the transverse processes that run in an anterolateral direction, immediately posterior to the vertebral artery. The cervical nerves enter a facial space in the posterior triangle of the neck between the anterior and middle scalene muscles called the interscalene compartment (Fig. 15.1). The interscalene block is performed at the level of the cricoid cartilage (C6). Important anatomic relations (Fig. 15.2) include the external jugular vein, which crosses the posterior border of the sternocleidomastoid muscle at this point, the phrenic nerve on the anterior scalene muscle, and the vertebral artery.

Figure 15.1 Coronal T1-weighted MR image showing the anatomy of the cervical region relevant to interscalene block (post contrast). Note relation of anterior and medial scalene muscles on the side contralateral to the injected contrast. 1, Sternocleidomastoid muscle; 2, common carotid artery; 3, middle scalene muscle; 4, clavicle; 5, anterior scalene muscle.

Figure 15.2 Neck dissection of cadaver structures illustrating the brachial plexus. 1, Clavicle; 2, cricoid cartilage; 3, retracted sternocleidomastoid muscle; 4, anterior scalene muscle; 5, middle scalene muscle; 6, brachial plexus; 7, phrenic nerve; 8, internal jugular vein.

Surface anatomy

The main landmarks for the interscalene block (Fig. 15.3) include clavicle; sternal notch; cricoid cartilage; sternal and clavicular heads of the sternocleidomastoid muscle – these can be accentuated by asking the patient to perform a head lift; interscalene groove – both scalene muscles descend to the first rib and can be identified by asking the patient to inhale deeply, because they contract before the sternocleidomastoid muscle; and the external jugular vein –which can be accentuated by asking the patient to perform a Valsalva maneuver. A skin marker should routinely be used to delineate the anatomic structures before performing the block.

Figure 15.3 Landmarks for the interscalene block. Further accentuation of the anatomy can be achieved by asking patients to lift their head up against resistance (with the head turned to the side). Additionally, when palpating the interscalene groove, the groove can be better appreciated by asking the patient to sniff. 1, Clavicle; 2, cricoid cartilage; 3, clavicular head of the sternocleidomastoid muscle; 4, sternal head of the sternocleidomastoid muscle; 5, posterior border of the sternocleidomastoid muscle.

Sonoanatomy

Perform a systematic anatomical survey from medial to lateral and superficial to deep. The carotid artery and internal jugular vein are seen medially. Medial to the vessels, the thyroid and trachea are identified. The ultrasound-guided intrascalene block is performed at the lateral border of the clavicular head of the sternocleidomastoid at the level of the cricoid cartilage. Here the brachial plexus is a superficial structure and a high frequency ultrasound transducer (6 to 13 MHz) is used. A high frequency transducer allows good visualization of structures to a depth of 4–5 cm. The ultrasound transducer is placed in an axial oblique plain (Fig. 15.4) and the most superficial structure consistently encountered is the sternocleidomastoid muscle. This appears as a triangular structure with the apex pointing laterally. Immediately deep to the sternocleidomastoid muscle are the anterior and middle scalene muscles. These can be accentuated by asking the patient to sniff. The roots of the brachial plexus appear between these two muscles in the interscalene groove. At this level it is common to identify between one and five hypoechoic structures (roots or trunks) and, depending on the position of the ultrasound transducer, these may appear oval or round. The brachial plexus at this level lies at a depth of around 1 cm from the skin (Fig. 15.5).

Figure 15.4 The patient is positioned supine with the head turned 45° to the contralateral side. The ultrasound transducer is then positioned in the posterior triangle of the neck at the level of the cricoid cartilage with an axial oblique orientation.

Figure 15.5 Transverse view of the brachial plexus at the lateral border of the sternocleidomastoid muscle, at the level of the cricoid cartilage between the anterior and middle scalene muscles, using a high frequency linear ultrasound transducer. The arrows indicate the roots of the brachial plexus, which are reflected as hypoechoic structures. ASM: anterior scalene muscle; MSM: middle scalene muscle; SCM: sternocleidomastoid muscle.

Technique

Landmark-based approach

As for all regional anesthetic procedures, after checking that emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed in the supine position with the head facing away from the side to be blocked. The patient is asked to elevate the head slightly to bring the clavicular head of the sternocleidomastoid muscle into prominence. The palpating finger is placed behind the sternocleidomastoid muscle and the patient is instructed to end the head lift (Fig. 15.6). The finger now lies on the belly of the anterior scalene muscle, and with lateral movement of the finger to the lateral edge of this muscle, the groove between the anterior and middle scalene muscles (interscalene groove) is encountered (Fig. 15.7). The injection site in the interscalene groove lies at the level of the cricoid opposite the transverse process of C6 (Chassaignac tubercle).

Figure 15.6 Locating the interscalene groove. The palpating fingers are placed deep to the sternocleidomastoid muscle.

Figure 15.7 Locating the interscalene groove. The fingers are rolled laterally until a groove behind the posterior border of the sternocleidomastoid is identified.

The needle insertion point is infiltrated with local anesthetic using a 25-G needle. A 35–50-mm 21-G insulated needle is used. The index and middle fingers of the palpating hand should be firmly seated in the interscalene groove. To assure stability of both hands, all fingers not in use should be resting on the neighboring structures. The direction of needle insertion runs inward, slightly dorsally, and 30–40° caudally (backward, inward, and downward; Fig. 15.8). This needle direction takes into account the orientation of the gutter of the transverse processes of the cervical vertebrae, on which the cervical roots lie. It also acts as a safety technique to decrease the risk of intervertebral needle insertion. The stimulating current is set at 1.0 mA, 2 Hz, and 0.1 ms. The needle is advanced slowly until the appropriate muscle response is obtained: shoulder, elbow, index finger, or thumb movement. The needle position is adjusted while decreasing the current to 0.35 mA with maintenance of the muscle response.

Figure 15.8 Interscalene block technique. The needle is inserted into the interscalene groove at the level of the cricoid cartilage and advanced into the groove with an inward, downward, and backward orientation. The index and middle finger of the palpating hand are placed over the interscalene groove and the skin over the groove is stretched.

Muscle responses that indicate a less than optimal final needle location include diaphragmatic contraction. The phrenic nerve lies on the anterior scalene muscle and is thus a needle location that is too anterior to the plexus. Muscle contraction of the posterior compartment muscles of the shoulder indicates suprascapular nerve stimulation, a final needle position that is too posterior. Failure to obtain motor response to nerve stimulation should prompt withdrawal of the needle and reinsertion in a 5–10% angle anterior or posterior to the initial insertion plane.

Incremental injections of local anesthetic (40 mL) are made with repeated aspiration. This volume is sufficient for an adequate block of the brachial plexus and the caudal part of the cervical plexus (Fig. 15.9). Digital pressure is applied proximal to injection (Fig. 15.10) to promote distal spread of local anesthetic; this is to facilitate reaching the lower roots of the plexus. The lower roots of the plexus may not be anesthetized due to the proximal injection site with this technique.

Figure 15.9 Coronal fat-saturated MR image after injection of 30 mL of contrast. Note C4 nerve root joining C5 nerve root, creating a ‘prefixed’ brachial plexus. Spread of contrast reaches the level of the upper border of C4 and caudad to the level of the clavicle. 1, Vertebral artery; 2, C4 root; 3, C5 root; 4, posterior and middle scalene muscles; 5, brachial plexus elements; 6, brachial plexus.

Figure 15.10 Interscalene block technique. Proximal digital pressure promotes distal spread of local anesthetic.

Ultrasound-guided approach

Intravenous access, electrocardiogram (ECG), pulse oximetry and blood pressure monitoring are established. Maximized comfort for the operator and patient is an important step in pre-procedure preparation. For the ultrasound-guided interscalene block, the patient is placed in the supine position with the head turned to the side opposite that to be blocked. The operator stands or sits adjacent to the side to be blocked. The ultrasound screen, transducer, needle, and plane of imaging should all be placed in one view for the operator. For the interscalene block, the ultrasound screen is placed below the shoulder on the side to be blocked (Fig. 15.11). Room lights may be turned down to enhance image viewing. The operating lights can be used to maintain some working lighting in the background. The patient is asked to raise their head to identify the interscalene groove.

Figure 15.11 Global view of the block field for the ultrasound-guided interscalene block. If the needle is to approach from the medial aspect of the transducer, then the ultrasound screen is placed on the side to be blocked below the patient’s shoulder.

The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The brachial plexus at the interscalene level is scanned in the axial oblique plain. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the right side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

Developing and maintaining a predetermined basic scanning routine is of enormous help in improving operator confidence and success. The trachea, common carotid and internal jugular veins and sternocleidomastoid muscle are identified. The ultrasound transducer is moved laterally to identify the lateral edge of the sternocleidomastoid muscle. Beneath this muscle edge, the anterior and middle scalene muscles lie with the roots of the brachial plexus between (Fig. 15.5). The patient can be asked to sniff to identify the scalene muscles. Moving the transducer down the neck facilitates identification of the brachial plexus roots. The roots will appear as large hypoechoic (dark) structures.

A skin wheal of local anesthetic is raised at the lateral aspect of the ultrasound transducer. The needle bevel should face the active face of the transducer to improve visibility of the needle tip. A free-hand technique rather than the use of a needle guide is preferred. A 21-GA × 50-mm insulated needle (Pajunk, Geisingen, Germany; or B. Braun, Bethlehem PA) is inserted parallel to the axis of the beam of the ultrasound transducer (Fig. 15.12). The needle is attached to sterile extension tubing, which is connected to a 20-mL syringe and flushed with local anesthetic solution to remove all air from the system. The operator can slide and tilt the transducer to maintain the needle tip within the plane of imaging as much as possible. The needle tip is slowly advanced under ‘real-time’ imaging until the needle reaches the side of the target neural structures (Fig. 15.13). The operator can slide and tilt the transducer to maintain the needle tip within the plane of imaging as much as possible. Manipulation of the transducer or redirection of the block needle may be necessary to bring the needle tip into the plane of imaging.

Figure 15.12 Ultrasound transducer and needle positioning during ultrasound-guided interscalene block. Note the needle orientation in the same plane as the ultrasound beam.

Figure 15.13 Real time imaging of needle insertion for the interscalene block. Needle insertion is on the lateral aspect of the transducer. Notice the needle shaft marked with arrows and the needle tip (N) in close proximity to the nerve roots. N: needle tip; SCM: sternocleidomastoid; ASM: anterior scalene muscle; MSM: middle scalene muscle.

The final needle position can be further confirmed with the use of a nerve stimulator (Stimplex; B. Braun, Bethlehem, PA). Characteristic motor activity in the forearm and hand is seen. An alternate method of needle insertion for the interscalene block can be from the medial aspect of the ultrasound transducer (Fig. 15.14). During the slow serial injection of the local anesthetic solution, the spread of the solution can be indirectly confirmed by interscalene space distention and enhanced nerve borders (Fig. 15.15). However, if appropriate local anesthetic is not visualized after a small volume of solution (0.5 to 2 mL) has been injected, the needle tip should be repositioned. Typically, smaller volumes of local anesthetic solution are required for ultrasound-guided interscalene blocks compared to non-guided techniques. The volume of solution injected is determined by the spread pattern observed. The needle is readjusted to allow complete encirclement of the nerve roots with local anesthetic. Typically in adults, 20 mL of local anesthetic solution is used. Local anesthetic appears as a hypoechoic image.

Figure 15.14 Real time imaging of needle insertion for the interscalene block. Needle insertion is on the medial aspect of the transducer. Notice the needle shaft marked with arrows and the needle tip (N) in close proximity to the nerve roots. N: needle tip; SCM: sternocleidomastoid; ASM: anterior scalene muscle; MSM: middle scalene muscle.

Figure 15.15 View of the interscalene space after administration of 20 mL of local anesthetic solution, using a high frequency linear transducer. The arrows indicate the nerve roots of the brachial plexus surrounded by local anesthetic. LA: local anesthetic; ASM: anterior scalene muscle; MSM: middle scalene muscle; SCM: sternocleidomastoid muscle.

Adverse effects

Figure 15.16 The final needle location on the C6 vertebra and the foramen that contains the vertebral artery. The cervical roots are posterior to the vertebral artery.