The brachial plexus derives from nerve roots from C5 to T1 with minor or absent contribution from C4 and T2. These roots emerge from their intervertbral foramina and travel between the anterior and middle scalene muscles where they form 3 trunks (upper, middle and lower). As the trunks pass over the first rib and dive under the clavicle each trunk forms anterior and posterior divisions. As the plexus emerges from under the clavicle divisions yield the 3 cords (lateral, posterior and medial) named for their proximity to the axillary artery. At about the lateral border of the pectoralis minor muscle, each cord gives off a branch before becoming a terminal nerve. Areas of the anterior shoulder are innervated by the superficial cervical plexus (C1-4). The medial brachial cutaneous (C8- T1) and intercostobrachial (T2) nerves must be blocked separately, as they emerge too low from the plexus to be reliably blocked with an interscalene technique, and too early for the supraclavicular, infraclavicular, or axillary techniques to be reliable. The brachial plexus is invested with fascia derived from the prevertebral and scalene fascia. The intercostobrachial nerve doesn’t travel in this sheath. A pneumonic for remembering the anatomy of the brachial plexus is: Robert Taylor Drinks Cold Beer (roots, trunks, divisions, cords, branches).
Generally performed at the level of the cricoid cartilage in the interscalene groove. If using a nerve stimulator, activity of the phrenic suggests the needle is too anterior and activity of the trapezius too posterior. Activity of the arm, wrist, or hand should be illicited. Best for shoulder and upper arm surgery. The interscalene approach blocks the plexus at the level of roots/trunks. Complications include stellate ganglion block (results in Horner’s syndrome—ptosis, miosis and anhidrosis), phrenic nerve paralysis (as high as 100% of the time-well tolerated in healthy individuals, but problematic in patients with limited pulmonary reserve), recurrent laryngeal nerve paralysis (results in hoarseness, only problematic in patients with pre-existing contralateral vocal cord paralysis where it can result in airway obstruction), intra-arterial injection (into vertebral artery—even small amounts of local anesthetic can cause seizure, as it travels directly to the brain) and epdidural/subdural/subarachnoid injection are possible given close proximity to neural foramina.
Performed at the level of the trunks, which are tightly bundled vertically on top of the first rib and just posterior to the subclavian artery as it prepares to dive under the clavicle. Provides excellent anesthesia for the entire arm and hand because of this tight bundling—it is difficult for structures to “escape” local anesthestic. With nerve stimulator, seek activity of the forearm or hand. Complications include pneumothorax (1-6% without ultrasound) and hemothorax (uncommon). Horner’s Syndrome and diaphragmatic paralysis occur often, but less frequently than the interscalene approach.
Performed at the level of the cords as the plexus emerges from beneath the clavicle and enters the axilla. Like the supraclavicular, this block provides good homogeneous anesthesia to the hand, forearm elbow and upper arm. It has the added benefit of being conducive to placing indwelling catheters. Chylothorax is a possible complication with left-sided blocks and pneumothorax/hemothorax occur more frequently than with the supraclavicular approach.
Performed at the level of the branches. Best used for procedures distal to the elbow. The axillary pulse is the key landmark, and the block should be performed at the highest level that the pulse is palpable. The classical transarterial technique involves directing a needle at the point of maximal pulse until blood is aspirated. The needle is then advanced and/ or withdrawn until blood cannot be aspirated and a relatively large volume of anesthetic is distributed (typically 40 or more milliliters) anterior and/or posterior to the axillary artery. Distal pressure may encourage proximal spread of anesthetic to the plexus. Axillary blockade can also be performed with nerve stimulator or ultrasound. Of note, the musculocutaneous nerve usually leaves the fascia of the plexus and enters the substance of the coracobrachialis muscle proximal to where this block is performed. Therefore, the musculocutaneous nerve must be blocked separately for forearm/wrist surgery (to block the lateral antebrachial cutaneous nerve). The axillary artery can be thought of as the hub of a wheel with 4 spokes: 1) ulnar nerve inferiorly 2) radial nerve inferior-posteriorly 3) median nerve superiorly and 4) the musculocutaneous superior-posteriorly in the coracobrachialis (see diagram below). Complication profile is the best of any approach to the plexus. Compressive hematoma and infection are rare. Intravascular injection may be more common than other blocks, as with the transarterial technique the goal is to penetrate the artery.
Provides intense anesthesia for short cases (45-60 minutes) on the forearm or hand. A double pneumatic tourniquet is placed on the arm after an IV is started in the hand. The arm is elevated and exsanguinated, the proximal tourniquet is inflated and typically 25-50 ml of 0.5% lidocaine is injected over 2-3 minutes. Anesthesia is achieved after 5-10 minutes. After 20-30 minutes tourniquet pain develops, at which point the distal tourniquet (which is over anesthetized skin) is inflated and the proximal cuff is deflated.
Digital block Isolated finger surgery can be performed with a digital block. Each digit is supplied by 4 small digital nerves that enter the digit at its base in each of the four corners.
Remember that all 4 major nerves to the upper extremity can be blocked individually at multiple places along their course to supplement a patchy block as the primary block.