Interscalene Brachial Plexus Block

Quick Answer

Interscalene brachial plexus block targets roots (C5-C7) and trunks of brachial plexus between anterior and middle scalene muscles at level of cricoid cartilage (C6). Coverage: Shoulder, proximal arm (C5-C7 dermatomes), NOT hand/forearm (C8-T1 missed - need supplemental ulnar block). Indications: Shoulder surgery (arthroscopy, replacement, rotator cuff), proximal humerus fractures. Technique: Ultrasound-guided (preferred) - visualize plexus lateral to carotid artery, between scalenes, inject 15-20 mL LA (0.5% ropivacaine or 0.375% bupivacaine). Complications: Phrenic nerve palsy (unavoidable, 100%), Horner's syndrome (50-70%), hoarseness (recurrent laryngeal, 10-20%), pneumothorax (1%, higher with nerve stimulator), vascular injection (vertebral, carotid), pneumothorax, epidural/spinal. Contraindications: Contralateral phrenic palsy, severe respiratory disease (COPD, FEV₁ <1L), carotid stenosis (vertebral injection risk), patient refusal. [1-10]

Anatomy

Brachial Plexus at Interscalene Level

Formation:

• Roots: C5, C6, C7, C8, T1 (ventral rami)
• Interscalene location: C5-C7 roots between anterior and middle scalene muscles
• Trunks: Form superior (C5-C6), middle (C7), inferior (C8-T1) trunks
• Interscalene block level: Roots and trunks (most proximal block)

Scalene Muscles:

• Anterior scalene: Origin C3-C6 transverse processes, insertion 1st rib
• Middle scalene: Origin C2-C7 transverse processes, insertion 1st rib
• Interscalene groove: Between anterior and middle scalene muscles
• Contents: Brachial plexus (C5-C7 roots visible), subclavian artery (inferior)

Key Landmarks:

• Cricoid cartilage: C6 level (block performed at this level or slightly cephalad)
• Sternocleidomastoid (SCM): Lateral border at C6 level
• Carotid artery: Medial to anterior scalene
• Transverse process of C6: Chassaignac's tubercle (palpable, large anterior tubercle)

Structures at Risk:

1. Phrenic Nerve (C3-C5):

• Course: Anterior to anterior scalene muscle
• Proximity: 1-2 cm medial to brachial plexus
• Inevitable block: With adequate interscalene block (100% incidence)
• Effect: Hemidiaphragm paralysis (usually well-tolerated in healthy patients)

2. Vertebral Artery:

• Course: Through transverse foramina of C6-C1
• Risk: Injection into artery if needle too deep/medial
• Consequence: Seizures, cardiac arrest (drug directly to brainstem)

3. Carotid Artery:

• Course: Medial to anterior scalene
• Risk: Vascular puncture if needle too medial
• Consequence: Hematoma, LAST

4. Stellate Ganglion:

• Location: C7-T1 level, anterior to 1st rib
• Effect if blocked: Horner's syndrome (ptosis, miosis, anhidrosis, nasal congestion)
• Incidence: 50-70%

5. Recurrent Laryngeal Nerve:

• Course: In tracheoesophageal groove
• Effect if blocked: Hoarseness (unilateral vocal cord paralysis)
• Incidence: 10-20%

6. Pleura/Lung:

• Risk: Pneumothorax if needle too deep/caudal
• Incidence: 1% (higher with landmark/nerve stimulator, lower with ultrasound)

Sensory Distribution

Dermatomes Covered:

• C5: Lateral arm, shoulder
• C6: Lateral forearm, thumb
• C7: Middle finger, posterior arm
• C8-T1: NOT reliably blocked (inferior trunk often spared)

Clinical Implication:

• Shoulder surgery: Excellent coverage
• Forearm/hand surgery: Incomplete (need ulnar nerve supplement at elbow or wrist)

Motor Distribution

Muscles Blocked:

• Deltoid (C5-C6 - axillary nerve)
• Biceps (C5-C6 - musculocutaneous)
• Triceps (C7 - radial)
• Rotator cuff muscles (supraspinatus, infraspinatus, subscapularis, teres minor)

Muscles NOT Blocked:

• Hand intrinsics (C8-T1 - ulnar nerve)
• Flexor carpi ulnaris, medial hand (C8 - ulnar nerve)

Indications and Contraindications

Indications:

• Shoulder surgery: Arthroscopy, arthroplasty, rotator cuff repair, stabilization
• Proximal humeral fractures: Reduction, fixation
• Clavicle surgery: ORIF (variable coverage, may need supplemental)
• Chronic pain: Shoulder pain syndromes

Contraindications:

Absolute:

• Contralateral phrenic nerve palsy: Bilateral diaphragm paralysis fatal
• Patient refusal
• Infection at site
• Allergy to local anaesthetics

Relative:

• Severe respiratory disease:
  • COPD with FEV₁ <1L
  • Severe asthma
  • Baseline dyspnea
  • Requires risk-benefit assessment
• Carotid stenosis: Risk of vertebral artery injection
• Previous neck surgery/scarring: Altered anatomy, difficult block
• Contralateral recurrent laryngeal nerve palsy: Bilateral vocal cord paralysis risk
• Anticoagulation: Similar to neuraxial (ASRA guidelines)
• Neurological disease: Pre-existing plexopathy (document first)

Pharmacology

Local Anaesthetic Options:

Single Injection:

• Ropivacaine 0.5%: 15-20 mL
  • Duration: 12-18 hours (sensory), 8-12 hours (motor)
  • Less cardiotoxic than bupivacaine
  • Preferred for day surgery
• Bupivacaine 0.375-0.5%: 15-20 mL
  • Duration: 16-24 hours (sensory), 12-16 hours (motor)
  • Longer duration than ropivacaine
  • Cardiotoxic (avoid IV injection)
• Lidocaine 1.5%: 20-30 mL (short procedures only)
  • Duration: 4-6 hours

Adjuvants:

• Dexamethasone: 4-8 mg IV or perineural (prolongs block 6-12 hours)
  • Controversial: Perineural vs IV equally effective?
• Clonidine: 75-150 μg (prolongs, adds sedation)
• Epinephrine: 1:400,000 (marker of IV injection, reduces bleeding)

Continuous Catheter (Infusion):

• Technique: Insert catheter at interscalene space
• Infusion: Ropivacaine 0.2% 5-10 mL/hour or 0.375% 4-6 mL/hour
• Duration: 2-5 days postoperative
• Benefits: Extended analgesia, reduced opioid use, early mobilization
• Indications: Major shoulder surgery (arthroplasty), severe postoperative pain

Technique

Ultrasound-Guided Approach (Preferred)

Equipment:

• Ultrasound: High-frequency linear probe (10-15 MHz)
• Needle: 50-100 mm, 22G (echogenic if available)
• Local anaesthetic: 15-20 mL (as above)
• Sterile technique: Skin prep, sterile probe cover

Patient Position:

• Supine: Head turned 30-45° away from side to be blocked
• Semi-sitting: Alternative (better comfort, less vascular engorgement)
• Lateral decubitus: Less common

Probe Placement:

• Location: Cricoid level (C6), lateral border of SCM
• Orientation: Transverse (perpendicular to plexus long axis)
• Initial position: Identify carotid artery (medial), then move laterally

Sonographic Anatomy:

1. Carotid artery: Medial, pulsatile, anechoic, non-compressible
2. Internal jugular vein: Lateral or anterior to carotid (compressible)
3. Thyroid: Medial, homogeneous
4. Anterior scalene: Lateral to carotid, hypoechoic muscle
5. Middle scalene: Lateral to anterior scalene
6. Brachial plexus: Between scalenes, hypoechoic structures (roots/trunks)
   • Appear as round/oval hypoechoic structures
   • Honeycomb appearance ( fascicles)
   • "Stoplight sign" at C6: Three roots (C5, C6, C7) aligned vertically

Needle Insertion:

• Approach: In-plane (lateral to medial) or out-of-plane
  • In-plane preferred: Visualize entire needle shaft
  • Direction: From lateral (posterior) to medial (anterior)
• Target: Adjacent to plexus (not intraneural)
• Technique:
  • Advance needle under ultrasound guidance
  • Aim for space between C5 and C6 roots or at level of upper trunk
  • Inject 1-2 mL LA to confirm spread (should see plexus displacement, LA spread)

Injection:

• Aspiration: Before each increment (watch for blood, CSF)
• Test dose: 3-5 mL (watch for signs of IV injection - tinnitus, metallic taste, seizures)
• Total volume: 15-20 mL
• Spread: Should see LA surrounding plexus, spreading caudad and cephalad
• End point: Adequate spread around C5-C6 roots

Confirmation:

• Sensory: Check C5-C6 dermatomes (lateral arm, thumb)
• Motor: Deltoad/biceps weakness
• Time: 10-20 minutes for full effect

Landmark/Nerve Stimulator Technique (Historical)

Landmarks:

• Cricoid cartilage: C6 level
• Sternocleidomastoid: Lateral border
• Interscalene groove: Felt between SCM and anterior scalene (patient lifting head against resistance tenses SCM)

Needle Insertion:

• Location: 2-3 cm lateral to cricoid cartilage, posterior border SCM
• Direction: Slightly caudad, medial, posterior (towards C7 transverse process)
• Depth: 2-3 cm
• End point: Paresthesia to shoulder/arm or nerve stimulator response (deltoid/biceps/triceps contraction at 0.3-0.5 mA)

Disadvantages:

• Higher complication rate: Pneumothorax, vascular puncture
• Less reliable: No visualization of anatomy
• Contraindicated: Anticoagulated patients (higher hematoma risk)
• Not recommended: Use ultrasound instead

Complications and Management

Phrenic Nerve Palsy:

• Incidence: 100% with adequate block (unavoidable)
• Mechanism: C3-C5 roots (phrenic) blocked by LA spread
• Effect: Hemidiaphragm paralysis
• Clinical:
  • FVC reduced 25-30%
  • Usually asymptomatic in healthy patients
  • Dyspnea in supine position (more significant)
• Prevention: Cannot prevent (inevitable)
• Contraindication: Bilateral blocks (never do bilateral interscalene), contralateral phrenic palsy, severe respiratory disease
• Management: O₂, sitting position, reassurance, avoid opioids (depress respiratory drive further)

Pneumothorax:

• Incidence: 1% (landmark), <0.5% (ultrasound)
• Mechanism: Pleural puncture (needle too deep/caudal)
• Signs: Cough, chest pain, dyspnea, desaturation, reduced breath sounds
• Prevention: Ultrasound guidance (visualize pleura), careful needle depth
• Management:
  • Small (<20%): Observation, O₂
  • Large or symptomatic: Chest drain
  • Postpone surgery if significant

Epidural/Subarachnoid Injection:

• Incidence: Rare (<0.1%)
• Mechanism: Needle through intervertebral foramen into spinal canal
• Signs:
  • Epidural: Bilateral block, lower extremity block, hypotension
  • Subarachnoid: Rapid total spinal (apnoea, hypotension, unconsciousness)
• Prevention: Ultrasound (visualize plexus, avoid medial/deep advancement), careful technique
• Management:
  • Supportive: Airway, ventilation, fluids, vasopressors
  • Cardiac arrest: ACLS

Vertebral Artery Injection:

• Incidence: Rare (<0.5%)
• Mechanism: Needle in transverse foramen or directly into artery
• Signs: Seizures (immediate), loss of consciousness, cardiac arrest (drug to brainstem/cardiac centers)
• Prevention: Ultrasound (avoid medial/deep), aspiration, incremental injection
• Management:
  • Supportive: Airway protection, control seizures (benzodiazepines), CPR if arrest
  • LAST protocol: Intralipid emulsion 20%

Local Anaesthetic Systemic Toxicity (LAST):

• Incidence: 0.1-1%
• Signs: Tinnitus, metallic taste, perioral numbness, agitation, seizures, cardiac arrhythmias, arrest
• Prevention: Aspiration, incremental injection, ultrasound (avoid intravascular)
• Management:
  • Stop injection
  • Intralipid emulsion 20% 1.5 mL/kg bolus then infusion
  • Supportive: Airway, seizures (benzodiazepines), cardiac (standard ACLS avoid vasopressin/calcium channel blockers)

Horner's Syndrome:

• Incidence: 50-70%
• Mechanism: Stellate ganglion block (spread to C7-T1)
• Signs: Ptosis (drooping eyelid), miosis (constricted pupil), anhidrosis (dry face), nasal congestion, flushing (warm, red face on affected side)
• Duration: Until block resolves (12-24 hours)
• Reassurance: Benign, explain to patient preoperatively

Recurrent Laryngeal Nerve Block:

• Incidence: 10-20%
• Mechanism: Spread to vagus nerve or direct LA effect
• Signs: Hoarseness, weak voice, aspiration risk (cord paralysis)
• Duration: Until block resolves
• Risk: Bilateral blocks (if doing bilateral procedures, wait for first side to recover)

Neural Injury:

• Incidence: 0.1-0.5% (temporary), <0.1% permanent
• Mechanism: Needle trauma, intraneural injection, compression (hematoma)
• Signs: Prolonged sensory/motor deficit beyond block duration
• Prevention: Ultrasound (avoid intraneural injection), gentle technique, avoid patient sedation (warn if paresthesia)
• Management: Follow-up, nerve conduction studies if prolonged (>6 weeks), rehabilitation

Other:

• Hematoma: Vascular puncture (carotid, vertebral, jugular)
• Infection: Rare with sterile technique

Clinical Management

Preoperative

Assessment:

• Respiratory: FEV₁, exercise tolerance, baseline SpO₂
• Neurological: Baseline limb function (document)
• Anatomy: Previous neck surgery, radiation
• Coagulation: Per ASRA guidelines

Informed Consent:

• Expected effects: Arm numbness, weakness (immobile arm), Horner's syndrome, hoarseness, dyspnea (usually mild)
• Complications: Phrenic palsy (expected), pneumothorax, LAST, nerve injury
• Duration: 12-24 hours (explain block will last into postoperative period)

Premedication:

• Anxiolytic: Midazolam 1-2 mg (careful - respiratory depression with phrenic palsy)
• Opioid: Minimal or avoid (respiratory depression)

Intraoperative

Sedation:

• Light: Midazolam 1-2 mg, fentanyl 50-100 μg
• Caution: Avoid heavy sedation (respiratory depression + phrenic palsy)
• Monitoring: SpO₂, EtCO₂ (if deeply sedated), airway equipment ready

Positioning:

• Beach chair: Common for shoulder surgery
• Lateral decubitus: Alternative
• Airway access: Ensure accessible (sedated patient, potential respiratory compromise)

General Anaesthesia Supplement:

• Many surgeons prefer GA + block (patient comfort, airway control)
• Block provides analgesia, reduces GA requirements
• LMA or ETT acceptable

Postoperative

Monitoring:

• Sensory: C5-C6 dermatomes (block success)
• Motor: Deltoid, biceps (expect weakness)
• Respiratory: SpO₂, RR, dyspnea
  • Auscultate chest (pneumothorax)
  • Sitting position if dyspneic
• Voice: Hoarseness expected (recurrent laryngeal)
• Eye: Ptosis, miosis (Horner's)

Analgesia:

• Block: Primary analgesic
• Supplemental:
  • Paracetamol 1 g q6h
  • NSAIDs (if appropriate): Celecoxib, ibuprofen
  • Opioids (cautiously): Oxycodone 5-10 mg 4-6 hourly PRN (start low, respiratory depression risk)

Arm Care:

• Sling: Protect insensate, immobile arm
• Pressure areas: Elbow, wrist (check regularly, no sensation)
• Position: Elevated to reduce swelling

Discharge Criteria (Day Surgery):

• Block resolving: Some sensation returning, motor function beginning to recover
• Pain controlled: With oral analgesics
• No complications: No respiratory distress, no pneumothorax symptoms
• Instructions: Care of insensate arm, when to return (block may last 12-24 hours)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Access Issues:

• Geographic: Regional centers may lack ultrasound or trained regional anaesthetists
• Cultural factors: Fear of needles, unfamiliar with regional techniques
• Communication: Explain block thoroughly, interpreter if needed

Health Disparities:

• Higher rates: Diabetes (neuropathy risk, check baseline), renal disease (LA toxicity risk, reduce dose)
• Shoulder disease: May present late with advanced arthritis

Cultural Safety:

• Family involvement: Explain procedure to family/support
• Pain expression: May be stoic, ensure adequate analgesia
• Follow-up: Challenges with remote monitoring if complications

Māori Health Considerations

Cultural Considerations:

• Whānau involvement: Family understanding of regional anaesthesia
• Communication: Clear explanation of what to expect (numb arm, Horner's syndrome)
• Pain management: Ensure culturally appropriate analgesia planning
• Follow-up: Coordination with primary care for any complications

ANZCA Final Exam Focus

SAQ Patterns

Common Questions:

• "Describe the ultrasound anatomy for an interscalene brachial plexus block."
• "What are the complications of interscalene block and how would you manage them?"
• "Why is phrenic nerve palsy inevitable with interscalene block?"
• "What are the contraindications to interscalene block?"

Marking Scheme Priorities:

• Anatomy (C5-C7 roots between scalenes)
• Distribution (shoulder, lateral arm, NOT ulnar/medial hand)
• Complications (phrenic palsy 100%, Horner's 50-70%, pneumothorax 1%, vascular injection)
• Contraindications (contralateral phrenic palsy, severe respiratory disease)
• Technique (ultrasound approach, LA volume, catheter option)

Viva Scenarios

Scenario 1: Respiratory Distress Post-Block

• Patient dyspneic after interscalene block
• Cause: Phrenic palsy (expected) ± pneumothorax (complication)
• Management: SpO₂, sitting position, CXR to exclude pneumothorax, reassure

Scenario 2: Seizures During Block

• LA injection, immediate seizure
• Vertebral artery injection or LAST
• Management: Stop injection, intralipid emulsion, airway, seizure control

Scenario 3: Contraindication Assessment

• COPD patient with FEV₁ 0.8 L for shoulder replacement
• Interscalene relatively contraindicated
• Alternative: Suprascapular + axillary nerve blocks (spare phrenic), GA with opioids

Key Points for Examination Success

1. Coverage: C5-C7 (shoulder, lateral arm), C8-T1 missed (ulnar spared)
2. Phrenic palsy: 100% incidence, unavoidable, hemidiaphragm paralysis
3. Contraindications: Contralateral phrenic palsy (absolute), severe COPD (relative), never bilateral
4. Horner's syndrome: 50-70% (ptosis, miosis, anhidrosis, nasal congestion)
5. Pneumothorax: 1% risk, ultrasound reduces risk
6. Vertebral artery: Medial/deep, injection causes immediate seizures/cardiac arrest
7. Technique: Ultrasound at C6 (cricoid), between anterior and middle scalene, 15-20 mL LA
8. Continuous: Ropivacaine 0.2% infusion for 2-5 days postoperative
9. Adjuvants: Dexamethasone IV or perineural prolongs block
10. Safety: Aspiration, incremental injection, intralipid available

References

1. ANZCA. PS22. Guidelines for Perioperative Management of Regional Anaesthesia. 2020.
2. Neal JM et al. Upper extremity regional anesthesia. Reg Anesth Pain Med. 2020;45(11):911-935.
3. Riazi S et al. Phrenic nerve palsy and regional anesthesia. Reg Anesth Pain Med. 2018;43(3):260-267.
4. Urmey WF et al. Pulmonary function changes during interscalene brachial plexus block. Anesthesiology. 1991;74(6):1085-1090.
5. Tran DQ et al. A comparison of ultrasound-guided vs landmark-based techniques. Reg Anesth Pain Med. 2009;34(4):335-339.
6. Mariano ER et al. Continuous interscalene brachial plexus block. Anesth Analg. 2009;109(3):779-782.
7. Barrington MJ et al. Ultrasound-guided interscalene block. Reg Anesth Pain Med. 2014;39(6):508-521.
8. ASRA. Checklist for Treatment of Local Anesthetic Systemic Toxicity. 2020.