2. Brachial Plexus

plexus forms in the neck from the anterior primary rami of C5, C6, C7, C8 and T1. five roots merge in the posterior triangle of the neck to form three trunks C5 and C6 form the upper trunk, C7 the middle trunk (above the subclavian artery) and C8 and T1 form the lower trunk (posterior to the subclavian artery). At the lateral border of the first rib the three trunks each divide into anterior and posterior divisions.

Three posterior divisions form the posterior cord described according to its relationship with the axillary artery), from which derives the radial nerve . (also the axillary, thoracodorsal and upper and lower subscapular nerves Anterior divisions of the upper and middle trunks form the lateral cord, from which derive the median nerve (lateral head) and the musculocutaneous nerve (also the lateral pectoral nerve).

Interscalene local anaesthesia blocks the anterior primary rami of the nerves of C5–C8 and T1 before they merge in the posterior triangle to form the trunks of the brachial plexus The cervical nerves leave the intervertebral foramina, and pass caudad and laterally between the scalenus anterior and the scalenus medius muscles. The nerves are enclosed within a fascial compartment which comprises the posterior fascia of the anterior scalene muscle and the anterior fascia of the middle scalene muscle. The patient should lie supine with the head turned slightly away from the side of injection and with the arm by the side (gently pulled down if necessary to depress the shoulder). After standard aseptic preparation, the interscalene groove between scalenus anterior and medius should be identified at the level of the cricoid cartilage (C6). — If the awake patient is asked to lift the head off the pillow (which tenses the sternocleidomastoid muscles) or to give a sniff, the groove becomes more evident. In the anaesthetized patient, identification is helped by the fact that in more than 90% of subjects, the external jugular vein overlies the groove at this level. The groove and the roots beyond are superficial, and in most cases a stimulating needle no longer than 30 mm is needed. The needle should be held perpendicular to the skin in all planes as it is directed medially, posteriorly and caudally (inwards, backwards and downwards) towards the transverse process of C6 (Chassaignac’s tubercle). This is the approach as described by Winnie. An alternative is Meier’s approach, in which the needle is directed caudad down the interscalene groove towards the subclavian artery. Once muscle stimulation is apparent in the required distribution (usually shoulder or biceps movements mediated by C5, 6), 20 ml of solution may be injected after aspiration and with all due precautions. In common with most plexus blocks into fascial compartments, large volumes of appropriately dilute solutions may be needed to obtain adequate analgesia of all the nerves involved. Typically, an interscalene block will last for 12–16 hours. The addition of dexamethasone to the local anaesthetic solution will prolong the duration of analgesia, but the same applies if the drug is given intravenously. This may be a better option in view of the fact that dexamethasone is neurotoxic.

Using ultrasound, the needle can be advanced out-of-plane using the approach as described earlier. This may seem contrary to the abiding principle of ultrasoundassisted nerve blockade, which is the ability to see exactly the position of the needle tip, but it has two advantages. One is the fact that the plexus is very superficial at this point and is frequently located at less than a centimetre from the skin. The second is that it removes the risk of damage to the dorsal scapular (from C5) and long thoracic nerves (C5, 6, 7) which are potentially vulnerable using the in-plane approach and which can be hard to identify on ultrasound. Damage to one or other of these nerves can lead to disabling motor weakness and a winged scapula. This problem can be avoided by using a nerve stimulator with the current set at 0.2–0.3 mA. This will be enough to stimulate movement of the scapula should the needle be too close to one or other of those nerves.

Interscalene block is indicated particularly for shoulder surgery. It can be used to provide analgesia for more distal structures in the upper limb, but it does not provide reliable block of C8 and T1, and so ulnar sparing is frequent (some reports quote 30–40%). It does not block the C4, nerve root and so if lower port sites are used for arthroscopic work then analgesia may not be sufficient. The acromioclavicular joint and the clavicle also have innervation from C4, and so superficial cervical block and/or supplemental infiltration will be necessary

—Successful analgesia is almost invariably associated with block of the phrenic nerve which lies on scalenus anterior. The block therefore should be used cautiously in patients with respiratory disease because it may reduce the functional residual capacity by up to 30%. The accompanying diaphragmatic palsy is usually asymptomatic, but the occasional patient may complain of chest discomfort (rather than dyspnea) as a result. Given the potential respiratory embarrassment, bilateral blocks should not be performed. Complications: these include intravascular injection (particularly into the vertebral artery; central spread via inadvertent dural puncture leading to a total spinal; phrenic nerve palsy [90%]; Horner’s syndrome [cervical sympathetic block, which is usually innocuous (20%)]; vagal and recurrent laryngeal nerve block, which may cause hoarseness [15%] but is usually benign; and pneumothorax [rare]). (There are also the generic complications such as systemic toxicity and neurapraxia.)

This block provides analgesia for most of the upper limb, and has been described as the ‘spinal’ of the arm. It can also be used for shoulder surgery, although the interscalene approach is usually preferred. The three trunks lie on the first rib, between the insertion of the scalenus anterior and scalenus medius muscles, and immediately posterior to the subclavian artery (the pulsations of which can provide a landmark). The trunks cross the rib at about the midpoint of the clavicle before separating into anterior and posterior divisions.

The use of ultrasound has superseded the various landmark techniques (most of which directed the needle down on to the first rib to contact the brachial plexus where it lies cephaloposterior to the subclavian artery). The in-plane approach allows clear identification of the first rib, the underlying pleura and lung, the subclavian artery and the adjacent divisions of the plexus which typically lie superolateral to the vessel. —With accurate localization, 20 ml of appropriate local anaesthetic solution (such as levobupivacaine 0.25–0.5%) may be injected after aspiration and with the usual precautions.

these include pneumothorax with the landmark technique (the incidence may be 0.5–1.0% even in experienced hands, and may take up to 24 hours to develop), although the use of ultrasound is likely, although not yet proven, to reduce this figure; intravascular injection or puncture (subclavian artery or vein), phrenic nerve palsy (in 40–60%); Horner’s syndrome in 70–90% (cervical sympathetic block); neuritis (plus generic complications as discussed previously).

This has fewer complications than other approaches, is generally effective and remains a popular technique with some anaesthetists. The block provides good analgesia for surgery below the elbow. The musculocutaneous nerve may leave the axillary sheath proximal to the site of injection, in which event supplemental analgesia may be needed by blocking the nerve between brachioradialis and the lateral epicondyle at the elbow

The arm is abducted to 90 (hyperabduction may abolish the arterial pulsation). The advancing needle is directed at an angle of about 45 to the skin as far proximally as possible. In practice, this often means injecting at the lateral border of pectoralis major. — Axillary block is now usually performed with ultrasound guidance, with or without the use of a peripheral nerve stimulator. It takes just over 40 ml of solution to fill the axillary sheath as far as the coracoid process in adults, and, in theory, complete block of all three cords will follow circumferential spread round the sheath. Some anaesthetists prefer to identify the major nerves of the upper limb separately, and block each one in turn. This reduces the total dose of local anaesthetic. Axillary brachial plexus block does not provide dense analgesia of the upper arm and does not block the intercostobrachial nerve (which arises from T2 and T3 and supplies the skin of the posterior upper arm). Patients may therefore be unable to tolerate the arterial tourniquet.