Questions
- 1.
Describe the anatomic structure of the brachial plexus.
- 2.
What are the terminal branches of the brachial plexus, and what do they innervate?
- 3.
- 4.
How does one perform a supraclavicular nerve block?
- 5.
What role does ultrasound have in placement of a brachial plexus nerve block?
- 6.
How is local anesthesia systemic toxicity diagnosed?
- 7.
A 53-year-old, 60-kg woman with a left olecranon fracture presented for open reduction and internal fixation. Her past medical history was significant for hypertension and mild exertional dyspnea. She had a negative nuclear stress test 1 month before surgery, and her estimated ejection fraction was 65%. Placement of a continuous supraclavicular brachial plexus block was performed using an ultrasound-guided technique, with an 18-gauge 50-mm Tuohy needle via an in-plane approach in a medial-to-lateral direction. A 20-gauge catheter was inserted to a distance 5 cm beyond the end of the needle, and 40 mL of 2% lidocaine was injected through the catheter. General anesthesia was induced to provide patient comfort while in the lateral decubitus position, and the airway was secured with a No. 4 laryngeal mask airway. A bolus of 20 mL of 0.375% bupivacaine was administered via the catheter 2 hours into the procedure, and the patient became hemodynamically unstable. Ventricular fibrillation was seen on the electrocardiogram (ECG).
1
Describe the anatomic structure of the brachial plexus.
Ventral rami of C5-T1 form the brachial plexus. The brachial plexus supplies motor and sensory innervation to the upper extremity with the exception of the trapezius muscle and cutaneous innervation to the axilla. These two areas are innervated by the ventral rami of C3 and C4 and the intercostobrachial nerve.
C5-T1 nerve roots pass posterior to the vertebral artery as they exit from the transverse processes. Shortly thereafter, the nerve roots of C5 and C6 combine to form the superior trunk of the brachial plexus. The root of C7 forms the middle trunk, and the roots of C8 and T1 form the inferior trunk. These three trunks pass between the anterior and middle scalene muscles. As the three trunks pass over the first rib, they divide into the anterior and posterior divisions of the brachial plexus, which supply ventral and dorsal innervations to the upper extremity.
After passing the first rib and continuing underneath the clavicle, these divisions merge again to form three cords, which are named relative to their position to the axillary artery: posterior (C5-T1), lateral (C5-C7), and medial (C8-T1). The posterior cord is formed from the union of the posterior divisions of all three trunks and contains innervation from all the nerve roots that compose the brachial plexus. The lateral cord is composed of the anterior divisions of the superior and middle trunks. The medial cord is a continuation of the anterior division from the inferior trunk. These cords divide into various nerve branches that innervate the upper extremity ( Figure 52-1 ).
2
What are the terminal branches of the brachial plexus, and what do they innervate?
The five major terminal branches of the brachial plexus are the musculocutaneous, axillary, radial, median, and ulnar nerves. Nerves that originate from the brachial plexus and their sensory and motor innervations are listed in Table 52-1 .
| Nerve | Brachial Plexus Origin | Motor Innervation | Sensory Innervation |
|---|---|---|---|
| Musculocutaneous | Branch of lateral cord (C5-C7) | Coracobrachialis Biceps brachii Brachialis | Lateral forearm (via lateral antebrachial cutaneous nerve) |
| Axillary | Branch of posterior cord (C5-C6) | Deltoid Teres minor | Posterior upper arm Deltoid |
| Radial | Posterior cord (C5-T1) | Extensors of upper arm, forearm, and hand | Posterior upper arm and forearm (via posterior antebrachial cutaneous nerve) |
| Dorsum of hand (lateral 3½ digits) | |||
| Median | Input from lateral and medial cords (C5-T1) | Flexors of forearm and hand * | Palmar surface of hand (lateral 3½ digits) |
| Thenar eminence | |||
| Ulnar | Branch of medial cord (C8-T1) | Intrinsic hand muscles † Flexor digitorum profundus (medial two muscles) | Medial 1½ digits and corresponding palm Medial 1½ digits and corresponding dorsum of hand |
* The flexor carpi ulnaris on the medial aspect of the forearm is innervated by the ulnar nerve.
3
How does surgical site affect the anatomic approach to the brachial plexus; what are possible and expected effects of each of these blocks?
The brachial plexus comprises C5-T1 nerve roots that are surrounded by prevertebral fascia. Prevertebral fascia extends from the spine into the upper extremity. These nerves divide and exit the plexus at varying points. If a block is performed after a nerve has already exited the plexus, that nerve is spared. Anesthesia of the brachial plexus can be provided by interscalene, supraclavicular, infraclavicular, or axillary approaches. Generally, a block that is placed anatomically distal to the spinal cord provides better distal coverage of the upper extremity at the expense of proximal coverage.
The most proximal block is an interscalene nerve block. It is performed at the level of C6, between the anterior and middle scalene muscles. The interscalene block is best suited for surgery of the shoulder, upper arm, and elbow and for postoperative pain relief of distal clavicle surgery. The interscalene approach often does not cover the C8 and T1 nerve roots, which are crucial for surgical anesthesia of the medial hand (ulnar distribution). Complications of an interscalene nerve block include unilateral phrenic nerve palsy. The incidence of unilateral phrenic nerve palsy reaches almost 100% when the nerve block is performed with a nerve stimulator technique, although this can be reduced under ultrasound guidance. This block also often results in a unilateral Horner syndrome (ptosis, miosis, anhidrosis) and nasal congestion of the ipsilateral nares. Other possible side effects that occur rarely include vertebral artery puncture, subarachnoid puncture, epidural block, and recurrent laryngeal nerve block ( Table 52-2 ).
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