3 Interscalene Techniques of Brachial Plexus Block
The brachial plexus is formed by the anterior rami of spinal nerves C5–C8 and T1, and it sometimes receives contributions from C4 and T2. The roots of the spinal nerves exit from the spinal canal behind the vertebral artery and cross the transverse process of the corresponding vertebral body. They then combine to form three trunks and run together toward the most lateral convexity of the body of the first rib (Fig. 3.1).
The upper trunk is formed by the junction of the roots of C5/6, and the suprascapular nerve arises immediately as a lateral branch from the upper trunk.
The middle trunk is formed by root C7.
The lower trunk is formed by roots C8/T1.
The trunks, which here lie on top of one another, cross the (posterior) interscalene groove between the scalenus anterior and scalenus medius muscles. Just above the clavicle, the trunks each split into an anterior and a posterior division (Fig. 3.2).
The three posterior divisions unite to form the posterior cord.
The anterior divisions of the upper trunk and middle trunk form the lateral cord.
The medial cord is the continuation of the anterior division of the lower trunk.
In the interscalene region, we thus first have the trunks, dividing in the immediate supraclavicular and infraclavicular region, and then the cords.
The lower trunk lies deepest and can be reached by an interscalene block only with difficulty (see Fig. 3.1). At the caudal end of the (posterior) interscalene groove just behind and above the clavicle, the subclavian artery, generally located directly in front of the lower trunk, passes with the brachial plexus through the interscalene groove, while the subclavian vein joins them only after they pass through the anterior interscalene groove. Anteriorly, the posterior interscalene groove is crossed by the omohyoid muscle, which can usually be easily palpated.
The phrenic nerve (C3–C5) runs on the belly of the anterior scalene muscle, enclosed in the prevertebral fascia covering the muscle. The cervical and thoracocervical sympathetic ganglia and the recurrent laryngeal nerve are in the immediate vicinity of the brachial plexus, but always medial to the interscalene grooves. The vertebral artery lies anterior to the exit of the cervical spinal nerves through the intervertebral foramina. The cervical epidural and subarachnoid space can be reached or punctured accidentally through the intervertebral foramina. Cervical epidural or high spinal anesthesia can occur (Fig. 3.8).
From where it passes through the interscalene groove as far as the axillary region, the entire brachial plexus is surrounded by a firm connective-tissue sheath (Fig. 3.3 and Fig. 3.4). There is connective-tissue septation within this neurovascular sheath. However, in the majority of people, it does not appear to impede an even spread of local anesthetic.
The posterior border of the sternocleidomastoid muscle is used for orientation. It becomes prominent when the head is elevated (“sniffing position,” Fig. 3.5 and Fig. 3.6). In very thin patients, the posterior interscalene groove can be palpated easily and it sometimes even becomes visible on deep inspiration.
3.2 Meier Approach
The classical technique by Winnie was oriented directly toward the transverse process of C6 (Fig. 3.7) with the risk of puncture near the spinal cord or of the vertebral artery (Fig. 3.8, see also historical overview, p33).
The modification (Meier et al 1997: anterior–lateral) of the “classical” technique (Fig. 3.9) makes it possible to insert an indwelling catheter for a continuous block because of the medial to lateral direction of the needle and the lateral direction of the needle makes it safer (Hofmann-Kiefer et al 2009).
The patient′s head is turned to the opposite side and the needle direction corresponds to the course of the interscalene groove (lateral, caudal, dorsal). The target is the distal end of the interscalene groove lateral to the subclavian artery (Fig. 3.10 and Fig. 3.11). (Note: an oxygen mask prevents the sterile drape from lying on the patient′s mouth and nose!)
The needle normally first reaches the brachial plexus (Fig. 3.12).
Note the phrenic nerve, which runs on the scalenus anterior muscle medial to the brachial plexus (Fig. 3.13). If this is stimulated (response: hiccup), the needle must be corrected in the lateral and dorsal direction. The suprascapular nerve is variable and can leave the upper trunk very far proximally (Fig. 3.13). If there is a motor response (abduction and external rotation in the shoulder region), the needle must be corrected in the medial and anterior direction.
The patient lies supine with the head turned slightly to the opposite side. The posterior border of the sternocleidomastoid muscle serves for orientation. It becomes prominent when the patient elevates the head slightly (“sniffing” position). The scalenus anterior muscle can be palpated behind the sternocleidomastoid and the fingers slide laterally over the scalenus anterior muscle into the posterior interscalene groove, which is formed by the scalenus anterior and medius muscles.
The posterior interscalene groove can usually be palpated easily; it runs posterolaterally from the sternocleidomastoid muscle in a slightly lateral direction. The subclavian artery is palpable directly above the clavicle and marks the caudal end of the interscalene groove. The artery can also be imaged using a vascular Doppler probe. The posterior interscalene groove feels like the gap between two fingers lying lightly next to one another. On deep inspiration, it sometimes becomes more visible.
In the caudal region, the posterior interscalene groove is crossed by the omohyoid muscle, which is usually easy to palpate. If the interscalene groove cannot be palpated, a horizontal line 3 cm long can be drawn at the level of the annular cartilage (C6) from the middle of the sternocleidomastoid muscle laterally (Fig. 3.14 and Fig. 3.15). The end of this line marks the interscalene groove (Meier et al 2001).
The intersection of a horizontal line about 2 cm above the annular cartilage marks the needle insertion site, and this is therefore further cranial than the classical insertion site with the Winnie technique (Winnie 1970).
3.2.2 Needle Approach
The interscalene groove is palpated: the upper finger of the palpating hand slides cranially in the posterior interscalene groove until it disappears under the sternocleidomastoid (Fig. 3.10). The posterior border of the sternocleidomastoid is pushed slightly cranially, while the lower finger lies further caudally in the interscalene groove.
The insertion site is as far cranial as possible, usually directly beneath the cranially palpating finger. The needle approach is performed along the plexus in the direction of the interscalene groove, that is, in the direction of the medial border of the “Mohrenheim fossa” (Fig. 3.15). Depending on the angle of needle insertion (approx. 30° to the skin) the brachial plexus is reached after about 2.5 cm to a maximum of 5 cm. A pronounced click is often felt on penetration of the prevertebral fascia (Fig. 3.16, Fig. 3.17, Fig. 3.18, Fig. 3.19).
The use of a nerve stimulator and/or ultrasound (Chapter 3.2.3) is mandatory while performing this technique.
If there is a motor response of the phrenic nerve (twitching of the diaphragm, “hiccup”) the needle is too far medially and forward, and it must be corrected laterally and backward.
If there is a motor response of the suprascapular nerve (supraspinatus and infraspinatus: external rotation and abduction of the shoulder), the needle is at the outer border of the brachial plexus and correction in the medial and anterior direction may be necessary. A motor response in the hand region should not be striven for.
This technique can be performed as a “single-shot” or as a continuous technique (Fig. 3.20).
Single injection: needle 5 to 6 cm
Continuous technique: 6-cm needle with “pencil-point” tip and lateral opening
Tips and Tricks
Orientation is made much easier in obese patients using an adhesive dressing to pull the muscle and fat tissue downward (Fig. 3.21).
The technique should always be performed with a nerve stimulator and/or ultrasound.
The motor response usually occurs due to stimulation of the upper trunk (deltoid, biceps brachii, or triceps). This response is sufficient and should be striven for (Silverstein et al 2000, Urmey 2000).
If there is a motor response of the phrenic nerve (twitching of the diaphragm, “hiccup”), the needle is too far medially and forward and must be corrected laterally and backward.
If there is a motor response of the suprascapular nerve (supraspinatus and infraspinatus: external rotation and abduction in the shoulder), the needle is at the outer border of the brachial plexus and correction medially and forward may be necessary.
A motor response in the region of the hand does not have to be striven for.
If performed correctly, the risk of injuring the pleura (pneumothorax) is slight.
Orientation aid for finding the posterior interscalene groove (see Fig. 3.14 and Fig. 3.15). At the level of the cricoid cartilage, a 3-cm long horizontal line is drawn laterally from the middle of the belly of the sternocleidomastoid; the end of the line marks the interscalene groove. The injection site is approximately 2 cm further cranially at the intersection of the posterior interscalene groove and the posterior border of the sternocleidomastoid.
The needle is advanced under stimulation to the medial border of the “Mohrenheim fossa” until a response in the region of the upper trunk is produced. An adequate response is contraction of the biceps brachii, deltoid, or triceps. Depending on the puncture angle and patient′s constitution, the plexus is reached after 2.5 to 5 cm.
Under ultrasound guidance, the nerve structures can be readily visualized (Chapter 3.2.3). With sufficient experience in this technique, ultrasound can be very helpful for difficult anatomical conditions.
When the needle is in the correct position, a volume of 20 to 30 mL is injected.
In slender patients, a triangular swelling in the prevertebral fascia is visible in the region of the interscalene groove (Fig. 3.20).