Nội dung

Chapter 13 Upper extremity blocks 13.1 General anatomical considerations The brachial plexus is formed by the ventral rami of the spinal nerves C5–T1. In general, supraclavicular and infraclavicular parts are described. The ventral rami leave the intervertebral foramina posterior to the vertebral artery and after a short distance in the scalenovertebral triangle (bordered by the longus colli muscle medially, the anterior scalenus muscle laterally, and the dome of the pleura inferiorly), they are situated between the anterior and middle scalene muscles (the interscalene space). The first branches are the dorsal scapular and thoracic longus nerves, both of which pierce the middle scalenus muscle to take a dorsolateral course. Subsequently, the roots form a superior (C5/C6), intermediate (C7), and inferior (C8/T1) trunk. The third branch in the lateral cervical region is the supraclavicular nerve which shows a variable level of origin out of the superior trunk. Between the level of the first rib and the clavicle, each trunk bifurcates into an anterior and posterior portion to be rearranged and form the three cords of the brachial plexus. A lateral cord is formed by the anterior portion of the superior and middle trunks, a medial cord by the anterior portion of the inferior trunk, and a posterior cord by the posterior portions of all three trunks. The nomenclature of the three cords (lateral, medial, and posterior) refers to their position around the axillary artery. Note that their respective positions are different in the infraclavicular region (clavipectoral triangle) where they are situated laterally to the artery. The most superficial one is the lateral cord, followed by the posterior and medial cord as the deepest. The brachial plexus is covered by connective tissue from its origin down to the axillary level. Various septae between the cords and nerves of the plexus appear to be responsible for incomplete nerve blockade, particularly at the axillary level when single-injection techniques are used. 102 UPPER EXTREMITY BLOCKS 13.2 Interscalene brachial plexus approach 13.2.1 Anatomy The interscalene groove is bordered by the anterior scalenus muscle medially, the middle scalenus muscle laterally, and the first rib inferiorly (Figure 13.1). Its location is approximately beneath the lateral border of the sternocleidomastoid muscle when the head is rotated to the opposite side. Of note, the interscalene groove is covered more or less by the sternocleidomastoid muscle in the case of a neutral head position. The scalene muscles and the brachial plexus are covered by the prevertebral layer of the cervical fascia. Figure 13.2 illustrates the ultrasound anatomy of the brachial plexus at the level of the interscalene groove. Fig. 13.1 Anatomical cross-sectional image of the nerve roots of the brachial plexus (C5–T1) inside the posterior interscalene groove. SCM: sternocleidomastoid muscle; ASM: anterior scalene muscle; MSM: middle scalene muscle; PN: phrenic nerve; CA: carotic artery; IJV: internal jugular vein; EJA: external jugular vein; left side=medial. INTERSCALENE BRACHIAL PLEXUS APPROACH Fig. 13.2 Ultrasound image of the posterior interscalene groove.The C5–8 nerve roots are located lateral to the sternocleidomastoid muscle (SCM) and between the anterior (ASM) and median scalene muscles (MSM); left side=medial. 13.2.2 Anatomical variations The brachial plexus often receives a communication from the ventral ramus C4. In this case, the plexus is situated more cephalic in relation to the cervical spine and designated as high or prefixed. In prefixed plexuses, C4 provides a large branch and the ventral ramus T1 appears small. When receiving the majority of communications from the ventral ramus C5, the brachial plexus is located more caudally and considered to be low or postfixed. In postfixed plexuses, the ventral ramus of T1 is large with an additional branch to the plexus provided by T2. Variants of the course of the brachial plexus and its components have also been described. In a significant number of cases, the nerve roots are located medial (close to the greater vessels of the neck) or lateral to the lateral border of the sternocleidomastoid muscle. The C5–C7 roots may pierce the anterior scalenus muscle either together or separately (Figure 13.3). In some cases, only C5 pierces the anterior scalenus. These situations were found to occur unilaterally or bilaterally to the same extent. In a smaller number of cases, the C5 root may be found completely anterior to the anterior scalenus muscle (Figure 13.4). A scalenus minimus muscle may be present which is visualized as a small muscle slip running anterior to one or two of the roots. In a significant number of cases, a muscle bridge is located between the C7 and C8 roots (Figure 13.5). In rare cases, the subclavian artery has been found to pierce the anterior scalenus muscle with an accompanying post-stenotic dilatation. The dorsal scapular artery (former transversa colli) may arise from the subclavian artery more medially and take an ascending course between the roots. Muscular tissue interposed between the roots is a frequent finding. 103 104 UPPER EXTREMITY BLOCKS Fig. 13.3 Ultrasound image of the C5 root piercing the anterior scalene muscle (ASM).The C6 and 7 roots are located between the ASM and the median scalene muscles (MSM). SCM: sternocleidomastoid muscle; left side=lateral. Fig. 13.4 Ultrasound image of the C5 root anterior to the anterior scalene muscle (ASM) and completely outside the posterior interscalene groove (white arrows). SCM: sternocleidomastoid muscle; MSM: middle scalene muscle; left side=lateral. Fig. 13.5 Ultrasound image of a typical muscle bridge (white arrow) between the C7 and C8 roots.The C5–7 roots are already surrounded by local anaesthetic. SCM: sternocleidomastoid muscle; ASM: anterior scalene muscle; MSM: middle scalene muscle; left side=medial. INTERSCALENE BRACHIAL PLEXUS APPROACH Fig. 13.6 Ultrasound image of the bifurcations of the nerve roots inside the posterior interscalene groove as the scanning head is slightly laterally moved from the initial position when the nerve roots are visualized as illustrated in Figure 13.2. SCM: sternocleidomastoid muscle; ASM: anterior scalene muscle; MSM: middle scalene muscle; left side=medial. 13.2.3 Ultrasound guidance technique Ultrasound investigation starts at the middle of the neck, at the level where the larynx is most prominent and the greater vessels of the neck are easy visible. Thereafter, the probe is moved slowly in a lateral direction up to the lateral border of the sternocleidomastoid muscle. Once the lateral border of the sternocleidomastoid muscle and the anterior and middle scalene muscles are visible, the position of the probe relative to the skin should be slightly moved from a perpendicular to a caudally oblique direction. The nerve roots appear between the anterior and middle scalene muscles inside the posterior interscalene groove as round or oval hypoechoic structures (Figure 13.2). When scanned more distally, the bifurcations may be visualized (Figure 13.6). 13.2.4 Practical block technique It should be taken into consideration that the external jugular vein is usually visible in the final probe position. The puncture site should therefore be chosen medial or lateral to the external jugular vein. The needle direction relative to the position of the probe should be OOP from cranial (Figure 13.7). Taking a posterior approach using the IP technique can lead to the potential disadvantage of the needle moving perpendicularly to the interscalene groove. As mentioned above, the dorsal scapular and thoracic longus nerves pierce the middle scalenus muscle as the first branches of the brachial plexus (Figure 13.8). They provide motor supply to the shoulder girdle and should be considered at risk if the IP technique is used in a posterior approach through the middle scalenus muscle. Thus, the OOP technique is the anatomically preferential method. Following the positioning of the needle tip between the nerve structures and the anterior and middle scalene muscles, the 105 106 UPPER EXTREMITY BLOCKS Fig. 13.7 OOP position of the needle relative to the ultrasound probe for the interscalene block technique. Fig. 13.8 Ultrasound image of a nerve structure (yellow arrow) inside the middle scalene muscle.The white arrow indicates the nerve roots inside the posterior interscalene groove. SCM: sternocleidomastoid muscle; MSM: middle scalene muscle; ASM: anterior scalene muscle; left side=lateral. Fig. 13.9 Blockade of the nerve roots with a needle position medial (left side of the figure) and lateral (right side of the figure) to the neuronal structures (located between the yellow arrows). The local anaesthetic appears hypoechoic. SCM: sternocleidomastoid muscle; ASM: anterior scalene muscle; left side=medial. INTERSCALENE BRACHIAL PLEXUS APPROACH Fig. 13.10 Typical appearance of connective tissue around nerve roots (between the yellow arrows) after administration of local anaesthetic. The white arrow indicates the tip of the needle. SCM: sternocleidomastoid muscle; ASM: anterior scalene muscle; left side=medial. local anaesthetic is administered (Figure 13.9). Depending on the spread of the anaesthetic, redirection of the needle to a position between the nerve structures and the anterior scalene muscle may be necessary. If a muscle bridge is detected between the C7 and C8 root or if blockade of the T1 root is required, it is necessary to adjust the depth of the needle. In these cases, care should be taken to avoid an inadvertent neuraxial position of the needle tip. After administration of the local anaesthetic by the described multi-injection technique, the nerve roots are much better presentable on ultrasound (a general rule for most of regional anaesthetic techniques). In addition, connective tissue can be identified, which could influence onset times (Figure 13.10). The quantity of connective tissue between the local anaesthetic and the neuronal structures do not influence the success rates of individual blocks. 13.2.5 Essentials Block characteristic Basic technique Patient position Supine, arm adducted, elbow slightly flexed Ultrasound equipment Linear probe, 38mm Specific ultrasound setting Maximum frequency of the probe Important anatomical structures Sternocleidomastoid muscle, anterior and middle scalene muscles Ultrasound appearance of the neuronal structures Round or oval, hypoechoic Expected Vienna score 1–2 Needle equipment 50mm, Facette tip Technique OOP Estimated local anaesthetic volume 8–12mL 107 108 UPPER EXTREMITY BLOCKS 13.3 Supraclavicular approach 13.3.1 Anatomy In the supraclavicular region, between the first rib and the clavicle, the brachial plexus becomes rearranged as described in Section 13.1 (Figure 13.11). The plexus is located laterally to the subclavian artery which is situated close to the pleura and the first rib (Figure 13.12). If present, the dorsal scapular artery (former transverse colli) arises from the subclavian artery and traverses the brachial plexus regularly (Figure 13.13). Fig. 13.11 Anatomical cross-sectional image of the brachial plexus in the supraclavicular region. ASM: anterior scalene muscle; MSM: middle scalene muscle; SCA: subclavian artery; SCV: subclavian vein; left side=lateral. SUPRACLAVICULAR APPROACH Fig. 13.12 Ultrasound illustration of the brachial plexus in the supraclavicular region lateral to the subclavian artery and above the 1st rib. The grey arrows indicate the cervical pleura. The nerve structures appear as hypoechoic, round and oval structures and are labelled between the yellow arrows. SA: subclavian artery; left side=medial. Fig. 13.13 A dorsal suprascapular artery may arise from the subclavian artery and traverses the brachial plexus in the supraclavicular region. The yellow arrows mark parts of the brachial plexus. DSA: dorsal suprascapular artery; SA: subclavian artery; left side=lateral. 109 110 UPPER EXTREMITY BLOCKS 13.3.2 Anatomical variations If the dorsal scapular artery has a more prominent appearance than expected, an infraclavicular approach should be considered (see Section 13.4). It should also be noted that the suprascapular nerve has a variable level of origin from the superior trunk (see Section 13.6). 13.3.3 Ultrasound guidance technique Ultrasound investigation should start as described for the interscalene approach (see Section 13.2). Once the brachial plexus is adequately identified within the interscalene space, a further caudal movement of the probe allows the identification of the neural structures as multiple, round and oval hypoechoic structures lateral to the subclavian artery (Figure 13.12). The anterior and middle scalene muscles can be traced distally to their insertion on the first rib. 13.3.4 Practical block technique Once the nerve structures of the brachial plexus and all the relevant adjacent anatomical structures (subclavian artery, cervical pleura, and first rib) are identified, an IP technique should be used with a needle insertion site from the posterior (Figures 13.14 and 13.15). After careful aspiration and initial administration of a small volume of local anaesthetic, an intermediate analysis of the spread of fluid is mandatory. If the spread is regular, the needle position can be maintained and local anaesthetic should be administered until all nerve structures are surrounded. If the initial needle position does not give a regular spread, the needle should be repositioned. Sometimes, a number of needle positions are necessary. Fig. 13.14 IP needle guidance technique for the supraclavicular brachial plexus block technique with a posterior–medial needle direction.