Interscalene block

9 min read Last updated April 9, 2026

Surgical approach (context: typical operations where interscalene block is used)

  • Shoulder arthroscopy (e.g. rotator cuff repair, subacromial decompression, labral repair)
    • Patient positioning: beach-chair or lateral decubitus, traction may be applied
    • Arthroscopic portals, irrigation fluid, potential for airway/ventilation effects from fluid extravasation (neck/chest swelling)
  • Open shoulder surgery (e.g. arthroplasty, stabilization procedures)
    • More tissue trauma and blood loss than arthroscopy, longer duration
  • Proximal humerus fixation / clavicle surgery (variable coverage)
    • Clavicle often needs additional superficial cervical plexus block or local infiltration (supraclavicular nerves C3–4)

Anaesthetic management (typical plan)

  • Type of anaesthesia: regional (interscalene) + sedation, or GA + interscalene for analgesia
    • GA often preferred for arthroscopy (airway access, immobility, tolerance of irrigation/positioning)
  • Airway: if GA, usually ETT (especially beach-chair, longer cases, aspiration risk), SGA possible for short low-risk cases with good access
    • Beach-chair: secure airway and vigilance for hypotension/cerebral perfusion
  • Duration: commonly 1–3 hours (arthroscopy often 1–2 h, arthroplasty 2–3+ h)
  • Pain: moderate–severe without regional, interscalene provides excellent analgesia for shoulder/proximal humerus
  • Key perioperative risks to plan for: hemidiaphragmatic paresis, local anaesthetic systemic toxicity (LAST), recurrent laryngeal nerve block/hoarseness, Horner’s syndrome, pneumothorax (rare), nerve injury

Indications and dermatomal/myotomal coverage

  • Best for: shoulder surgery (C5–6 predominant), proximal humerus
  • Often incomplete for: ulnar nerve distribution (C8–T1) and medial arm/forearm
    • May need supplementation for distal arm/hand surgery (consider supraclavicular/infraclavicular/axillary approaches instead)
  • Clavicle/AC joint: may require superficial cervical plexus block (supraclavicular nerves C3–4) ± local infiltration

Relevant anatomy (exam core)

  • Target: brachial plexus roots/trunks between anterior and middle scalene muscles at level of cricoid cartilage (approx C6) or slightly caudad
  • Ultrasound landmarks: SCM superficially, interscalene groove, hypoechoic round roots (often C5–C7) lateral to carotid, prevertebral fascia, transverse processes with anterior/posterior tubercles
  • Nearby structures: phrenic nerve on anterior scalene (high incidence of blockade), vertebral artery (medial/deep), dorsal scapular and long thoracic nerves (within/near middle scalene), recurrent laryngeal nerve (medial spread), epidural/subarachnoid space (medial spread)
  • Fascial planes: injection deep to prevertebral fascia around roots, avoid intraneural injection (high opening pressure, pain, swelling)

Contraindications and patient selection

  • Absolute: patient refusal, true LA allergy, infection at site, uncorrected severe coagulopathy (follow regional anaesthesia anticoagulation guidance), inability to cooperate/consent
  • Relative/important: significant respiratory disease (COPD, restrictive disease), contralateral diaphragmatic palsy, severe OSA, morbid obesity, severe pulmonary hypertension
    • Reason: hemidiaphragmatic paresis is common even with ultrasound and low volumes
  • Caution: pre-existing neuropathy, anticoagulation/antiplatelets, difficult airway if planning sedation-only, inability to tolerate supine/semisupine positioning

Technique (ultrasound-guided) and practical steps

  • Preparation: consent (including respiratory effects), IV access, monitoring, resuscitation drugs and intralipid available, asepsis, block performed in area with full monitoring
  • Position: head turned away, semisupine, arm by side, optimize comfort and access
  • Probe: high-frequency linear, scan at level of cricoid (C6) then adjust to best view of C5–C7 roots between scalene muscles
  • Needle: in-plane lateral-to-medial commonly (keeps needle away from carotid/vertebral artery), aim for perineural spread around roots/trunks
    • Incremental injection with frequent aspiration, observe circumferential spread, stop if high resistance or patient reports severe pain/paraesthesia
  • Volumes: aim for lowest effective volume to reduce phrenic palsy risk (often 5–10 mL for analgesia, 10–20 mL for dense surgical block depending on practice and LA choice)
  • LA choices (typical): ropivacaine 0.2–0.5% or levobupivacaine 0.25–0.5%, consider lidocaine for rapid onset (mind total dose)
    • Always calculate maximum safe dose (mg/kg) and account for surgical infiltration and other blocks
  • Adjuncts: perineural dexamethasone may prolong duration (local policy), avoid routine adrenaline if it obscures intravascular injection warning signs (practice varies)
  • Catheter technique: can be used for continuous analgesia after major shoulder surgery, secure well, educate re limb protection and respiratory symptoms

Assessment of block and intraoperative management

  • Expected sensory: C5–C6 (lateral shoulder/upper arm) most reliable, motor: deltoid weakness (axillary nerve), biceps weakness (musculocutaneous)
  • If inadequate: allow time, top-up if safe, supplement with local infiltration, suprascapular/axillary nerve blocks, or convert to GA
  • Sedation-only cases: maintain verbal contact, capnography, be ready to manage airway (block does not guarantee immobility or complete analgesia)

Complications (FRCA viva list) and management

  • Hemidiaphragmatic paresis (phrenic nerve block): very common, may cause dyspnoea, reduced FVC/FEV1, usually resolves as block wears off
    • Management: reassure, sit upright, oxygen, consider NIV if needed, avoid/choose alternative block in high-risk respiratory patients
  • Horner’s syndrome (stellate ganglion spread): ptosis, miosis, anhidrosis, benign and self-limiting
  • Recurrent laryngeal nerve block: hoarseness, risk of airway compromise if contralateral vocal cord palsy
    • If stridor/airway concern: urgent airway assessment, consider ENT history, avoid in known contralateral palsy
  • LAST (intravascular injection/overdose): tinnitus, metallic taste, agitation, seizures, arrhythmias, cardiovascular collapse
    • Immediate actions: stop injection, call for help, airway/100% O2, treat seizures (benzodiazepine), follow lipid rescue protocol, manage arrhythmias (avoid large doses of propofol if unstable, avoid vasopressin, use reduced-dose adrenaline)
  • High spinal/epidural spread (rare): hypotension, bradycardia, respiratory insufficiency, loss of consciousness
    • Management: airway/ventilation, vasopressors, fluids, treat bradycardia, ICU support until resolution
  • Nerve injury: intraneural injection, needle trauma, ischaemia, haematoma, persistent sensory/motor deficit
    • Prevention: ultrasound visualization, avoid paraesthesia/pain, low-pressure injection, incremental dosing, document neuro exam if concerns
  • Pneumothorax: rare with interscalene (more with supraclavicular) but possible if very caudad/deep approach
    • Management: oxygen, assess (US/CXR), treat tension pneumothorax immediately, chest drain if indicated
  • Vascular puncture/haematoma: carotid/IJV/vertebral artery (rare with US but serious)

Alternatives and modifications (to reduce phrenic palsy / tailor analgesia)

  • Low-volume interscalene: reduces but does not eliminate phrenic palsy
  • Suprascapular + axillary nerve blocks: good shoulder analgesia with less diaphragmatic involvement, may be preferred in respiratory compromise
  • Superior trunk block: targets convergence of C5–6, may spare phrenic nerve more than classic interscalene (evidence evolving, still possible paresis)
  • Local infiltration / surgeon-delivered periarticular infiltration: adjunct only, usually inferior to regional for severe pain
  • Benefits: superior analgesia, reduced opioids/PONV, improved early rehab, potential day-case facilitation
  • Common/expected: numb arm/weakness, Horner’s, hoarseness, shortness of breath from hemidiaphragm paresis
  • Serious/rare: LAST, nerve damage, pneumothorax, infection/bleeding, high neuraxial block
  • Aftercare: limb protection (burns/trauma), sling use, when to seek help (progressive dyspnoea, chest pain, persistent deficit)

Test yourself…

Describe how you would perform an ultrasound-guided interscalene block.

Structure your answer: preparation → anatomy/sonoanatomy → needle approach → LA dosing → safety checks → confirmation.

  • Preparation: consent (include dyspnoea/hoarseness), IV access, standard monitoring, full resus equipment + lipid available, asepsis, time-out
  • Position: semisupine, head turned away, scan lateral neck at C6 (cricoid level) to identify scalene muscles and roots
  • Sonoanatomy: C5–C7 roots/trunks between anterior and middle scalene, avoid vascular structures, identify prevertebral fascia
  • Needle: in-plane lateral-to-medial, aim for perineural spread around roots, avoid intraneural injection (pain/high resistance)
  • Injection: aspirate frequently, incremental dosing, observe spread, use lowest effective volume (often 5–10 mL for analgesia, more for surgical anaesthesia depending on policy)
  • Post-block: monitor for LAST/respiratory symptoms, document block, drug/dose, complications, provide limb safety advice
What are the complications of an interscalene block and how would you manage them?

Give common first, then serious/rare, include immediate management steps.

  • Hemidiaphragmatic paresis: reassure, sit up, oxygen, avoid in high-risk respiratory patients, consider alternative blocks
  • Horner’s syndrome: explain benign/self-limiting
  • Hoarseness (recurrent laryngeal nerve): assess airway, high risk if contralateral vocal cord palsy
  • LAST: stop injection, call help, airway/100% O2, treat seizures, lipid emulsion protocol, ALS modifications
  • High neuraxial block: ventilate, vasopressors, ICU support
  • Nerve injury: prevention (US, low-pressure injection), if persistent deficit follow local nerve injury pathway and document
  • Pneumothorax/vascular puncture: recognize and treat, escalate early
Why does an interscalene block cause breathlessness and how common is it?

Mechanism + physiology + who is at risk + mitigation.

  • Mechanism: phrenic nerve (C3–5) lies on anterior scalene, local anaesthetic spread commonly blocks it → ipsilateral hemidiaphragm paresis
  • Incidence: high with classic volumes, ultrasound and low-volume techniques reduce but do not abolish
  • Effect: reduced FVC/FEV1, most healthy patients tolerate, symptomatic dyspnoea more likely with COPD/restrictive disease/obesity/OSA
  • Mitigation: consider alternative blocks (suprascapular+axillary, superior trunk), reduce volume, avoid bilateral blocks
A patient develops tinnitus and perioral tingling during injection. What do you do?

Treat as evolving LAST until proven otherwise.

  • Stop injecting immediately, keep needle still or withdraw safely, call for help
  • Airway and breathing: 100% oxygen, maintain ventilation (avoid hypercarbia/acidosis which worsen toxicity)
  • Circulation: monitor ECG/BP, establish/confirm IV access, prepare lipid emulsion
  • If seizure: benzodiazepine first-line, consider small doses of propofol only if haemodynamically stable
  • If cardiovascular instability: follow lipid rescue and ALS modifications (reduced-dose adrenaline, avoid vasopressin, avoid lidocaine as antiarrhythmic)
  • Post-event: critical care observation, document, report via governance, counsel patient
How would you consent a patient for an interscalene block?

Benefits, common effects, serious risks, alternatives, and aftercare.

  • Benefits: excellent shoulder analgesia, less opioid/PONV, improved early mobilisation, may facilitate day-case surgery
  • Expected: numb/weak arm for hours, need sling/limb protection
  • Common side effects: breathlessness (hemidiaphragm), hoarseness, Horner’s syndrome
  • Serious/rare: seizures/cardiac arrest from LA toxicity, nerve damage, bleeding/infection, pneumothorax, high spinal/epidural spread
  • Alternatives: GA with systemic analgesia, other shoulder blocks (suprascapular/axillary) if respiratory risk
In which patients would you avoid an interscalene block and what would you do instead for shoulder analgesia?

Focus on respiratory compromise and contralateral nerve issues.

  • Avoid/strong caution: severe COPD/restrictive disease, contralateral diaphragmatic palsy, severe OSA/morbid obesity, severe pulmonary hypertension
  • Also caution: known contralateral vocal cord palsy (risk if RLN blocked), significant anticoagulation, inability to cooperate
  • Alternatives: suprascapular + axillary nerve blocks, superior trunk block, multimodal analgesia + infiltration, consider catheter techniques where appropriate
Why might an interscalene block be inadequate for surgery below the elbow?

Explain plexus anatomy and distribution.

  • Interscalene primarily blocks upper roots/trunks (C5–C7) → reliable for shoulder/proximal arm
  • Lower trunk (C8–T1) often spared → ulnar nerve and medial forearm/hand may have incomplete anaesthesia
  • For distal upper limb: supraclavicular/infraclavicular/axillary blocks provide more complete coverage
Compare interscalene block with supraclavicular block for upper limb surgery.

Compare level, indications, coverage, and complications.

  • Level: interscalene = roots/trunks, supraclavicular = trunks/divisions (compact plexus)
  • Indications: interscalene best for shoulder, supraclavicular best for arm/forearm/hand (dense block)
  • Coverage: interscalene may miss ulnar (C8–T1), supraclavicular more complete
  • Complications: interscalene higher phrenic palsy and RLN/Horner’s, supraclavicular higher pneumothorax risk (reduced with US) and vascular puncture
What are the key safety strategies to reduce the risk of nerve injury during interscalene block?

Think: visualization, injection pressure, patient feedback, and dose strategy.

  • Ultrasound: keep needle tip in view, avoid entering nerve, aim for spread around nerve structures
  • Injection technique: incremental injection, frequent aspiration, stop if pain/paraesthesia or high resistance, consider pressure monitoring
  • Avoid deep sedation during injection so patient can report symptoms (practice dependent, balance comfort and safety)
  • Use appropriate LA dose/volume, avoid multiple needle passes, document pre-existing deficits

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