14.1 Upper Extremity Peripheral Nerve Blocks: Interscalene, Supraclavicular, Axillary

14.1 Upper Extremity Peripheral Nerve Blocks: Interscalene, Supraclavicular, Axillary

Upper extremity peripheral nerve blocks provide surgical anesthesia and postoperative analgesia for procedures ranging from the shoulder girdle to the fingertips. Safe and effective execution requires mastery of brachial plexus 3D functional neuroanatomy, fascial sheath topography, ultrasound sonopathology, and recognition of site-specific procedural complications.

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1. Brachial Plexus Neuroanatomy: Roots to Terminal Branches

The brachial plexus is formed by the anterior (ventral) primary rami of the fifth through eighth cervical nerves (C5, C6, C7, C8) and the first thoracic nerve (T1). Variable contributions can occur from C4 (prefixed plexus) or T2 (postfixed plexus).

+-------------------------------------------------------------------------+
|                    BRACHIAL PLEXUS STRUCTURAL SEQUENCE                  |
+-------------------------------------------------------------------------+
|   Mnemonic: "Really Tired? Drink Cold Beer"                             |
|                                                                         |
|   ROOTS       --> TRUNKS     --> DIVISIONS  --> CORDS       --> BRANCHES|
|   (C5 - T1)       (Sup/Mid/Inf)  (3 Ant / 3 Post)(Lat/Post/Med) (MARMU) |
|   Interscalene    Supraclavicular Retroclavicular Infraclavicular Axilla|
+-------------------------------------------------------------------------+

                  [BRACHIAL PLEXUS SCHEMATIC PROGRESSION]

   ROOTS          TRUNKS         DIVISIONS          CORDS          TERMINAL BRANCHES

   C5 -----\-----> Superior --/-- Anterior -----\---> Lateral -----> Musculocutaneous (C5-C7)
            \                X                  /              \---> Lateral Root of Median
   C6 ------/                 \-- Posterior ---\                  
                                                \---> Posterior ---> Axillary (C5-C6)
   C7 -----------> Middle ----/-- Anterior ----/ \               \---> Radial (C5-T1)
                              \-- Posterior --/   \              
                                                   \---> Medial -----> Medial Root of Median
   C8 -----\-----> Inferior --/-- Posterior ------/              \---> Median (C5-T1)
            /                 \-- Anterior ----------------------> Ulnar (C8-T1)
   T1 ------/                                                    \---> Med. Cutaneous (Arm/FA)

Anatomical Subdivisions & Landmarks

1. Roots (C5-T1): Emerge through the intervertebral foramina and pass into the neck between the Anterior Scalene muscle (originates from anterior tubercles of C3-C6 transverse processes, inserts on 1st rib) and Middle Scalene muscle (originates from posterior tubercles of C2-C7, inserts on 1st rib). The prevertebral fascia splits to envelop both muscles, forming the interscalene space (fascial sheath).
2. Trunks (Superior, Middle, Inferior): Form at the lateral border of the anterior scalene muscle in the supraclavicular triangle:
   • Superior Trunk: Fusion of C5 and C6 roots (gives off the suprascapular nerve and nerve to subclavius).
   • Middle Trunk: Continuation of C7 root.
   • Inferior Trunk: Fusion of C8 and T1 roots.
3. Divisions (3 Anterior / 3 Posterior): Form posterior to the clavicle over the first rib. The three anterior divisions supply the anterior flexor compartments of the limb; the three posterior divisions supply the posterior extensor compartments.
4. Cords (Lateral, Posterior, Medial): Situated in the axilla deep to the pectoralis minor muscle, named according to their anatomical relationship to the second part of the axillary artery:
   • Lateral Cord (C5-C7): Formed by anterior divisions of Superior and Middle trunks.
   • Posterior Cord (C5-T1): Formed by posterior divisions of all three trunks.
   • Medial Cord (C8-T1): Formed by anterior division of Inferior trunk.
5. Terminal Branches:
   • Musculocutaneous Nerve (C5-C7): Terminal branch of lateral cord; innervates coracobrachialis, biceps brachii, and brachialis, terminating as the Lateral Antebrachial Cutaneous nerve.
   • Axillary Nerve (C5-C6): Branch of posterior cord; innervates deltoid, teres minor, and skin over lateral shoulder.
   • Radial Nerve (C5-T1): Largest terminal branch of posterior cord; innervates triceps, wrist extensors, and dorsal aspect of hand/fingers.
   • Median Nerve (C5-T1): Formed by union of lateral root (lateral cord) and medial root (medial cord); innervates forearm flexors and thenar compartment.
   • Ulnar Nerve (C8-T1): Terminal branch of medial cord; innervates flexor carpi ulnaris, medial half of flexor digitorum profundus, hypothenar compartment, and intrinsic hand muscles.

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2. Interscalene Brachial Plexus Block

The interscalene block is the gold standard regional technique for procedures involving the shoulder, lateral two-thirds of the clavicle, and proximal humerus.

               [INTERSCALENE GROOVE ULTRASOUND ANATOMY (C6 LEVEL)]

                            [ Sternocleidomastoid (SCM) ]
                                         |
                                         v
             [ Anterior Scalene ]   OOO (C5, C6, C7 Roots)   [ Middle Scalene ]
             (Anterior / Medial)     |   "Traffic Light"      (Posterior / Lateral)
                                     v
                       (Phrenic Nerve on surface of ASM)
                                     |
                                     v
                           [ Carotid A. / IJV ]

Clinical Technique & Sonographic Landmarks

• Transducer: High-frequency linear probe ($10 - 15 \text{ MHz}$) placed transversely across the lateral neck at the level of the cricoid cartilage (C6 vertebral level).
• Sonographic Target: The C5, C6, and C7 nerve roots/trunks appear as a vertical column of three round, hypoechoic ("dark") structures stacked between the anterior and middle scalene muscles, colloquially termed the "traffic light" or "snowman" sign.
• Injection Goal: Deposit $10 - 20 \text{ mL}$ of local anesthetic (e.g., $0.25% - 0.5%$ bupivacaine or ropivacaine) into the interscalene groove between the fascial sheath and the nerves.

The Ulnar Sparing Phenomenon

• NCE Board Rule: The interscalene block reliably spares the ulnar nerve (C8-T1 / Inferior Trunk).
• Mechanism: The inferior trunk lies deep and medial within the lower neck, sheltered behind the subclavian artery and cervical pleura. Local anesthetic deposited at the C6 level does not consistently spread caudally to reach C8-T1.
• Clinical Consequence: Interscalene block is inappropriate as a sole anesthetic for surgery at or distal to the elbow, wrist, or hand.

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3. Complications of Interscalene Blockade

+-------------------------------------------------------------------------+
|                    INTERSCALENE BLOCK COMPLICATIONS                     |
+-----------------------+-------------------------------------------------+
| Complication          | Pathophysiology & Clinical Impact               |
+-----------------------+-------------------------------------------------+
| **100% Phrenic Nerve  | Phrenic nerve (C3-C5) crosses anterior scalene  |
|   Paresis**           | 1-2 mm away; causes diaphragmatic hemiparesis;  |
|                       | reduces FEV₁ and FVC by 25-30%                  |
| **Horner Syndrome**   | Stellate ganglion (cervicothoracic sympathetic) |
|   (10-30% incidence)  | block: ptosis, miosis, anhidrosis, enophthalmos |
| **Recurrent Laryngeal | Local diffusion blocks RLN; causes ipsilateral  |
|   Nerve Block**       | vocal cord paresis, hoarseness, stridor         |
| **Vertebral Artery    | Needle enters transverse foramen (C6); tiny     |
|   Injection**         | volume (<1 mL) triggers immediate grand mal sz  |
| **Subarachnoid /      | Medial/posterior needle angle penetrates dural  |
|   Epidural Spread**   | cuff sleeve; causes total spinal anesthesia     |
| **Bezold-Jarisch      | Sitting "beach chair" position + venous pooling |
|   Reflex (BJR)**      | triggers profound bradycardia and hypotension   |
+-----------------------+-------------------------------------------------+

1. Phrenic Nerve Paresis (Diaphragmatic Hemiparesis)

• Incidence: Approaching $100%$ with standard volumes ($>15 - 20 \text{ mL}$) due to anterior fascial diffusion over the anterior scalene muscle.
• Respiratory Impact: Loss of ipsilateral hemidiaphragmatic excursion causes paradoxical upward diaphragmatic movement during inspiration, reducing Forced Expiratory Volume in 1 second ($FEV_1$) and Forced Vital Capacity ($FVC$) by $25 - 30%$.
• Absolute / Relative Contraindications: Severe COPD, emphysema, severe restrictive lung disease, baseline contralateral diaphragmatic paralysis (e.g., prior phrenic injury), or severe baseline home oxygen dependence.

2. Horner Syndrome

• Mechanism: Cephalad or medial diffusion of local anesthetic blocks the cervical sympathetic chain / stellate ganglion situated anterior to the C6-C7 transverse processes.
• Classic Clinical Pentad:
  1. Ptosis: Drooping of the upper eyelid (paralysis of superior tarsal / Müller's muscle).
  2. Miosis: Pupillary constriction (unopposed parasympathetic sphincter pupillae).
  3. Anhidrosis: Loss of sweating over the ipsilateral face and neck.
  4. Enophthalmos: Apparent sunken eyeball appearance.
  5. Nasal Congestion: Vasodilation of nasal mucosa.
• Reassure the patient that this is a benign, transient side effect that resolves with block dissipation.

3. Bezold-Jarisch Reflex (BJR) in the Beach Chair Position

During shoulder arthroscopy in the upright "beach chair" position under interscalene block:

• Pathophysiologic Trigger: Venous pooling in the lower extremities reduces venous return and left ventricular end-diastolic volume. In the setting of elevated sympathetic tone or exogenous epinephrine, the underfilled, hypercontractile ventricle stimulates unmyelinated intramyocardial vagal C-fibers.
• Clinical Presentation: Paradoxical inhibitory vagal triad: profound bradycardia, severe hypotension, and peripheral vasodilation.
• Prophylaxis & Management: Minimize sitting time before fluid loading; pre-treat with IV crystalloids ($500 - 1000 \text{ mL}$); administer Atropine ($0.5 - 1.0 \text{ mg}$ IV) or Glycopyrrolate ($0.2 - 0.4 \text{ mg}$ IV); support vascular tone with Ephedrine ($5 - 10 \text{ mg}$) or Phenylephrine ($50 - 100 \text{ mcg}$); consider prophylactic beta-blockade (e.g., Metoprolol) to blunt hyperdynamic ventricular contraction.

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4. Supraclavicular Brachial Plexus Block: "The Spinal of the Arm"

The supraclavicular block targets the brachial plexus at the level of the trunks and divisions as they cross the first rib in close proximity to the subclavian artery.

                 [SUPRACLAVICULAR ULTRASOUND ANATOMY (FIRST RIB)]

                                  Skin / Platysma
                                         |
                                         v
             [ Subclavian Artery ]   OOOOO (Trunks / Divisions)
             (Round, Anechoic,       (Lateral / Superior: "Pack of Grapes")
              Pulsatile Medial)          |
                     \                   v
                      \---->  ====================  <--- [ FIRST RIB ] (Hyperechoic bony line
                              (Dark Acoustic Shadow)                   with shadow beneath)
                                         |
                              --------------------  <--- [ PLEURAL LINE ] (Lung sliding / Comet tails)

Procedural Characteristics & Indications

• Coverage: Provides dense, rapid-onset anesthesia for the entire upper extremity distal to the shoulder (mid-humerus, elbow, forearm, wrist, and hand).
• Sonographic Landmarks: Place high-frequency linear probe coronal-obliquely in the supraclavicular fossa posterior to the mid-clavicle. Locate the round, pulsatile Subclavian Artery resting on the hyperechoic first rib. The brachial plexus appears as a compact, hypoechoic "pack of grapes" or "honeycomb" cluster sitting posterosuperior and lateral to the artery.

Clinical Risks & Safety Rules

1. Pneumothorax: The dome of the cervical pleura (cupola) lies immediately deep and medial to the first rib. The needle must be continuously tracked in-plane, aiming toward the "corner pocket" (junction of subclavian artery and first rib) while never crossing below the hyperechoic first rib surface. Incidence with ultrasound is $<0.1%$ (compared to $\approx 1 - 5%$ with blind landmark techniques).
2. Phrenic Nerve Blockade: Occurs in approximately $50%$ of patients (reduced compared to interscalene, but still carries respiratory risk in severe baseline pulmonary compromise).
3. Subclavian Artery Hematoma: Avoid multiple arterial punctures; hold prolonged direct pressure if punctured.

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5. Infraclavicular & Axillary Brachial Plexus Blocks

+-------------------------------------------------------------------------+
|                INFRACLAVICULAR vs AXILLARY BLOCK COMPARISON             |
+--------------------+------------------------+---------------------------+
| Feature            | Infraclavicular Block  | Axillary Block            |
+--------------------+------------------------+---------------------------+
| **Anatomical Level**| Cords (Lat, Post, Med) | Terminal Branches (M, R, U)|
| **Location**       | Deep to Pectoralis Min | Axillary neurovasc sheath |
| **Ultrasound View**| Cords surround Axillary| Nerves surround Axillary  |
|                    | Artery (deep 3-5 cm)   | Artery (superficial 1-2cm)|
| **Musculocutaneous**| Blocked with Lat Cord  | **EXITS SHEATH SEPARATELY**|
|                    | (in single sheath)     | **in Coracobrachialis M.**|
| **Catheter Utility**| **Gold standard for    | Prone to dislodgement and |
|                    | continuous catheters** | axillary hygiene issues   |
| **Phrenic Block**  | Rare (0 - 3%)          | **0% (Zero)**             |
| **Pneumothorax**   | Very low (<0.1%)       | **0% (Zero)**             |
| **Indications**    | Forearm, wrist, hand   | Forearm, wrist, hand      |
+--------------------+------------------------+---------------------------+

Axillary Block Technique & The Musculocutaneous Nerve Rule

• Positioning: Patient supine with arm abducted $90^\circ$ and elbow flexed $90^\circ$.
• Sonographic Anatomy: Probe placed transversely across the axillary crease. Identify the pulsatile Axillary Artery and adjacent axillary veins:
  • Median Nerve: Located anteromedial / superficial to the artery.
  • Ulnar Nerve: Located superficial and medial/inferior to the artery.
  • Radial Nerve: Located posterior / deep to the artery (often exhibits acoustic enhancement).
• The Musculocutaneous Nerve Rule:
  • Crucial Board Concept: The Musculocutaneous Nerve departs the brachial plexus sheath proximally in the high axilla and travels independently within the muscular fascial substance of the Coracobrachialis muscle (between biceps and coracobrachialis).
  • Required Action: The CRNA must scan laterally and superiorly to identify the oval, hyperechoic musculocutaneous nerve within the coracobrachialis muscle belly and inject $3 - 5 \text{ mL}$ of local anesthetic directly around it. Failure to perform this separate injection results in sensory sparing over the lateral forearm (Lateral Antebrachial Cutaneous nerve distribution) and weakness of elbow flexion.