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Brachial Plexus Block - Complete Teaching Guide

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1. Anatomy of the Brachial Plexus

• Lateral cord → musculocutaneous nerve + lateral head of median nerve
• Medial cord → ulnar nerve + medial head of median nerve + medial antebrachial/brachial cutaneous nerves
• Posterior cord → axillary nerve + radial nerve

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2. The Four Main Approaches

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3. Interscalene Block (ISB)

Indication

Anatomy target

US-Guided Technique

1. Patient supine, head turned away from operative side
2. High-frequency linear probe placed at supraclavicular fossa, then traced cranially until trunks are visible between scalene muscles
3. Needle advanced in-plane or out-of-plane (out-of-plane avoids the long thoracic and dorsal scapular nerves within the middle scalene belly)
4. Volume: 10-15 mL; as low as 5 mL associated with decreased diaphragmatic paresis
5. For surgical anesthesia: 20-30 mL commonly used

Complications (memorize these - high-yield)

Key rule: Bilateral interscalene blocks are always contraindicated. Phrenic nerve blockade is virtually inevitable with ISB.

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4. Supraclavicular Block

Indication

Ultrasound Technique

1. Patient supine, head turned 30° to contralateral side
2. Linear high-frequency transducer in supraclavicular fossa, angled slightly toward thorax
3. Identify subclavian artery in short-axis; plexus appears as a "cluster of grapes" cephalolateral to the artery, above the first rib
4. Needle advanced in-plane from lateral to medial; avoid directing medially (pneumothorax risk)
5. LA deposited around the plexus cluster; carefully trace cranially and caudally to ensure lower trunk is included (prevents ulnar sparing)

Complications

• Pneumothorax - most feared (risk reduced but not eliminated with ultrasound)
• Phrenic nerve palsy - ~50% of patients; apply same precautions as ISB
• Horner's syndrome
• Subclavian artery puncture

Note: Supraclavicular perineural catheters provide inferior analgesia compared with infraclavicular catheters and are more prone to displacement with movement.

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5. Infraclavicular Block

Indication

Anatomy target

Ultrasound Technique (Lateral Sagittal / Paracoracoid approach)

1. Arm abducted to 90° (externallyrotates humeral head, retracts clavicle, straightens neurovascular bundle)
2. Probe placed below and medial to coracoid process in sagittal orientation
3. Axillary artery visible in short-axis, deep to pec major and minor
4. Target: posterior to the axillary artery - 30-40 mL single injection produces complete block without needing to visualize all three cords
5. Costoclavicular approach alternative: cords clustered lateral to 1st part of axillary artery - faster onset but higher pneumothorax risk

Complications

• Deeper block = decreased needle tip visibility (steep needle angles required)
• Pneumothorax (lower risk than supraclavicular)
• No phrenic nerve block - advantage over interscalene and supraclavicular

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6. Axillary Block

Indication

Critical anatomy - nerves ALREADY diverged at this level:

• Musculocutaneous nerve has already branched off (found between coracobrachialis heads or between coracobrachialis and biceps - must be separately blocked)
• Intercostobrachial nerve (T2) is always spared - causes tourniquet discomfort
• Musculocutaneous nerve = lateral antebrachial cutaneous nerve distally; must be blocked for lateral forearm coverage

Ultrasound Technique

1. Patient supine, arm abducted 90° or hand placed behind head
2. High-frequency linear probe in axilla - identify axillary artery and vein in cross-section
3. Median (anteromedial), ulnar (posteromedial), and radial (posterolateral) nerves surround the artery
4. Multiple injection technique - each nerve must be targeted individually (fascial separations exist between them)
5. 5-10 mL around each nerve; musculocutaneous nerve blocked separately in coracobrachialis muscle

Key Limitations

• Axilla is a poor site for catheters - inferior analgesia vs. infraclavicular, increased infection and dislodgement risk
• Upper arm and shoulder not covered
• Requires more needle passes than other approaches

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7. Lung-Sparing (Phrenic-Sparing) Alternatives for Shoulder

• Superior trunk block - targets the superior trunk (C5+C6) just proximal to the suprascapular nerve branch; noninferior pain scores vs. ISB with less hemidiaphragmatic paralysis
• Anterior suprascapular nerve block - LA deposited deep to omohyoid, shallow to prevertebral fascia; 5-15 mL; volumes >15 mL risk phrenic spread

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8. Local Anesthetics Commonly Used

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9. General Complications (All Approaches)

Persistent neuropathic symptoms are more common after brachial plexus blocks than lower extremity blocks. Mechanisms include local ischemia, vasoconstrictors, neurotoxicity, or direct trauma.

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10. Quick Reference: "Which Block for Which Surgery?"

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Key High-Yield Points to Remember

1. The brachial plexus lies in a fascial sheath derived from prevertebral fascia - this is why a single injection at the right level can block the entire plexus
2. Phrenic nerve palsy is inevitable with ISB and occurs in ~50% with supraclavicular block; it is absent with infraclavicular and axillary blocks
3. The inferior trunk (C8-T1 / ulnar distribution) is the most commonly missed segment - check coverage explicitly
4. Supraclavicular = most compact point of plexus = fastest onset, densest block
5. Infraclavicular = best for catheters; axillary = safest (no pleural or phrenic risk)
6. The intercostobrachial nerve (T2) is never blocked by any brachial plexus approach - it must be separately blocked for tourniquet tolerance

• Miller's Anesthesia 10e, Chapter 42 - Regional Anesthesia of the Upper Extremity
• Morgan & Mikhail's Clinical Anesthesiology 7e, Chapter 46 - Peripheral Nerve Blocks

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Adductor Canal Block (ACB) - Doubt Killer

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The Core Concept in One Line

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1. Anatomy - What is the Adductor Canal?

• Superficial femoral artery (SFA) - main landmark
• Superficial femoral vein (SFV)
• Saphenous nerve - lies anterior/anterolateral to the SFA
• Nerve to vastus medialis - lies outside the canal in its own fascial sheath (clinically important - see below)
• Posterior division of the obturator nerve (inconsistently)

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2. The Big Clinical Question: ACB vs. Femoral Nerve Block (FNB)

Key fact (Morgan & Mikhail): Patients with continuous adductor canal catheters ambulate further on day 1 following TKA than patients with either femoral block (limited by weakness) or no block (limited by pain).

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3. The "True ACB" Controversy - High-Yield Exam Trap

• "True" adductor canal block - identified by sartorius medial border converging with adductor longus medial border; deeper in the canal
• Problem: The nerve to the vastus medialis (major contributor to knee pain after TKA) often lies outside the true adductor canal in its own fascial sheath - a block too far distal misses it
• Recommended technique (Jaeger et al.): Periarterial injection lateral to the femoral artery, deep to the sartorius, deep to the vastoadductor membrane, at the midpoint between the ASIS and patella - this position captures both the saphenous nerve AND the nerve to vastus medialis
• "High" ACB = injection under the sartorius lateral to the SFA, at the level where vastus medialis and saphenous nerves co-exist in the same fascial plane; essentially a transarterial perifemoral injection

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4. Ultrasound-Guided Technique

• SFA = large pulsatile round structure (compressible with pressure = vein; non-compressible = artery)
• SFV = adjacent, compressible
• Saphenous nerve (SN) = small hypoechoic oval, anterolateral to SFA
• Sartorius = superficial, roof of canal
• Vastoadductor membrane = echogenic double contour defining canal floor

• In-plane approach, needle 2-3 cm lateral to probe, advanced anteromedially
• Target: deep to sartorius, anterior and lateral to the artery
• Inject after negative aspiration (highly vascular area)
• Volume: 10-15 mL (Miller's) / 15-20 mL (Morgan & Mikhail)

Warning: Higher volumes risk spread to the femoral triangle proximally → quadriceps weakness (defeats the purpose of the motor-sparing block).

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5. Indications - Where ACB Fits

• Posterior knee (add IPACK block for this)
• Lateral leg (peroneal territory)
• Tourniquet discomfort (needs femoral or sciatic coverage)
• Hip or thigh surgery

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6. IPACK Block - The Perfect ACB Complement

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7. Complications

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8. Continuous ACB Catheter

• Catheter at the adductor canal provides superior postoperative analgesia for TKA
• Technically stable, catheter well-secured under sartorius muscle
• Allows ambulation-friendly analgesia for early physiotherapy
• Preferred over continuous femoral catheter when ambulation is a rehabilitation priority

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Quick Memory Card

ACB = Saphenous nerve block (+ nerve to VM)
      ↓ at mid-thigh, under sartorius, lateral to SFA
      ↓ 10-15 mL, in-plane US technique
      ↓ Motor sparing → safe ambulation
      ↓ For TKA/ACL/knee arthroscopy
      ↓ Add IPACK for posterior knee coverage
      ↓ Falls still possible → patient education mandatory

• Miller's Anesthesia 10e, pp. 6270-6272 (Chapter 42)
• Morgan & Mikhail's Clinical Anesthesiology 7e, pp. 1926-1927 (Chapter 46)
• Barash Clinical Anesthesia 9e, Chapter 36 & 45