Key point The interscalene block deposits local anaesthetic around the C5–C6 roots / superior trunk in the interscalene groove. It provides dense analgesia for the shoulder and proximal humerus but spares the inferior trunk (C8–T1), so the ulnar border of the forearm and hand is typically not covered — and hemidiaphragmatic paresis is expected in the great majority of patients.
Anatomy
The brachial plexus is formed by the anterior rami of C5–T1. At the interscalene level — roughly at the cricoid cartilage (C6) — the plexus lies as roots and emerging superior/middle trunks in the groove between the anterior and middle scalene muscles. This is the most cephalad point at which the plexus can be blocked, and it favours the upper roots (C5, C6) that supply the shoulder.
Coverage & sparing
- Reliably blocked: C5–C6 (± C7) — shoulder, lateral clavicle, proximal humerus, and the suprascapular/axillary territories
- Frequently spared: inferior trunk (C8–T1) — the ulnar nerve territory (medial forearm/hand). This is expected, not a failure
- Frequently co-blocked: phrenic nerve (C3–5), producing hemidiaphragmatic paresis; cervical sympathetic chain (Horner syndrome); recurrent laryngeal nerve (hoarseness)
- The skin over the “cape” of the shoulder derives from the supraclavicular nerves (superficial cervical plexus, C3–4); a separate superficial cervical plexus block may be needed for some posterior/superior incisions
Indications
The interscalene block is the reference regional technique for shoulder and proximal humerus surgery, as anaesthesia (with sedation/GA) or for postoperative analgesia.
| Surgical Site | Block Role | Notes |
|---|---|---|
| Total shoulder arthroplasty | First-line | PROSPECT-supported; consider continuous catheter or adjuvants to address rebound pain |
| Rotator cuff repair, arthroscopy (Bankart, SLAP) | First-line | Excellent analgesia; low-volume approaches reduce phrenic effect |
| Proximal humerus ORIF | First-line | Good coverage of the surgical field |
| Clavicle (lateral third) | Partial | Often combined with superficial cervical plexus block for full coverage |
| Elbow / forearm / hand surgery | Avoid | Inferior trunk sparing — use supraclavicular / infraclavicular / axillary instead |
Contraindications
Respiratory reserve is the pivotal consideration. A standard interscalene block causes ipsilateral hemidiaphragmatic paresis in close to 100% of patients, reducing FVC and FEV₁ by roughly 25–30%. Patients dependent on diaphragmatic function may not tolerate this.
Absolute
- Patient refusal
- Infection at injection site
- Local anaesthetic allergy
- Contralateral phrenic nerve palsy or pneumonectomy (bilateral diaphragm compromise)
Relative
- Severe respiratory disease (e.g. FEV₁ <50%, severe COPD)
- Contralateral recurrent laryngeal nerve palsy
- Coagulopathy / therapeutic anticoagulation
- Pre-existing neuropathy (document carefully)
Technique — Ultrasound-Guided
Real-time ultrasound guidance is standard. A key safety point is distinguishing the C5/C6 roots from a small nerve traversing the middle scalene (commonly the dorsal scapular or long thoracic nerve) to avoid needle injury and mistaken targeting.
Equipment & position
- Probe: high-frequency linear (10–15 MHz), transverse across the neck at cricoid level
- Needle: 50 mm short-bevel insulated, in-plane from the lateral (postero-lateral) side
- Position: supine or semi-sitting, head turned ~30–45° to the contralateral side, slight bed head-up to improve venous drainage
Step-by-step
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Trace-back from the supraclavicular view (recommended)
Identify the plexus lateral to the subclavian artery in the supraclavicular fossa, then slide the probe cephalad, following the plexus as it “lines up” vertically in the interscalene groove. This is more reliable than starting at the neck de novo.
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Identify the “stoplight” sign
At the interscalene groove the C5, C6 (often bifid) and C7 roots appear as 2–3 stacked round hypoechoic structures between the anterior and middle scalene muscles, deep to the SCM. Confirm the carotid/IJV medially and avoid them.
-
Needle insertion — lateral to medial, in-plane
Insert at the lateral end of the probe, advancing through (or superficial to) the middle scalene toward the groove. Aim to place the tip adjacent to, not within, the target roots — typically between C5 and C6.
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Incremental injection with monitoring of spread
Aspirate, then inject in 3–5 mL aliquots watching for circumferential spread within the interscalene sheath. High injection pressure or intraneural swelling mandates immediate needle withdrawal. Low-volume techniques (5–10 mL) achieve analgesia while reducing phrenic spread.
Sonoanatomy
The hallmark of the interscalene view is the “stoplight” (traffic-light) sign: the C5, C6 and C7 roots stacked as round-to-oval hypoechoic structures in the groove between the anterior and middle scalene muscles, immediately deep to the sternocleidomastoid.
/images/interscalene-us-nysora.png.
Sonoanatomy tip: If the roots are hard to find at the neck, drop caudally to the supraclavicular view (plexus lateral to subclavian artery) and trace them cephalad into the groove. Beware the small round nerve within the middle scalene (dorsal scapular / long thoracic) — it is not a target and can be injured.
Phrenic-Sparing Strategies
Because hemidiaphragmatic paresis limits use in patients with respiratory compromise, a range of diaphragm-sparing strategies has been described. The trade-off is generally between diaphragm preservation and analgesic reliability/onset.
| Strategy | Rationale | Trade-off |
|---|---|---|
| Low volume (5–10 mL) | Less cephalad/anterior spread to the phrenic nerve on ASM | Reduces but does not abolish phrenic effect; shorter duration |
| More caudal injection | Deposit further from the C3–5 phrenic contributions | Technique-dependent |
| Superior trunk block | Target the superior trunk distal to the C5/C6 root confluence, away from the phrenic nerve | Emerging evidence; comparable shoulder analgesia with less diaphragm effect |
| Supraclavicular block | More distal plexus; lower phrenic incidence than interscalene | Less complete shoulder coverage than a well-placed ISB |
| Anterior suprascapular ± axillary nerve block | Selective articular innervation of the shoulder, largely diaphragm-sparing | More technically involved; two injections |
Practical approach: for the patient with borderline respiratory reserve who still needs shoulder analgesia, a diaphragm-sparing option (superior trunk, or suprascapular + axillary) is often preferable to a standard interscalene block. Discuss the risk–benefit explicitly and document.
Local Anaesthetics & Dosing
Respect maximum mg/kg limits. Interscalene volumes are relatively small, so toxicity risk is lower than high-volume blocks — but vascular structures are close, so aspirate and inject incrementally. Verify doses against local formulary and current SmPC.
| Agent | Concentration | Volume | Onset | Duration (plain) |
|---|---|---|---|---|
| Ropivacaine | 0.5% | 10–20 mL | 10–20 min | 10–14 h |
| Ropivacaine (low-vol) | 0.5% | 5–7 mL | 10–20 min | 8–12 h |
| Bupivacaine / Levobupivacaine | 0.25–0.5% | 10–20 mL | 15–25 min | 10–16 h |
| Lidocaine (fast surgical) | 1.5–2% | 15–20 mL | 5–10 min | 2–4 h |
Ropivacaine 0.5% — 10–15 mL
+ Dexamethasone 4–8 mg IV to extend duration and blunt rebound pain. Consider a continuous catheter for major shoulder arthroplasty.
Ropivacaine 0.5% — 5–7 mL (low volume) OR superior trunk / suprascapular + axillary approach
Lower volume reduces cephalad spread to the phrenic nerve. For meaningful respiratory compromise, prefer a diaphragm-sparing block.
Adjuvants
| Adjuvant | Dose | Route | Effect | Evidence |
|---|---|---|---|---|
| Dexamethasone | 4–8 mg | IV (or perineural) | Extends duration by 6–8 h, attenuates rebound pain | Strong |
| Dexmedetomidine | 0.5–1 mcg/kg | Perineural or IV | Prolongs block by 4–6 h; sedation/bradycardia possible | Moderate |
| Adrenaline | 2.5–5 mcg/mL | With LA | Intravascular marker; modest prolongation of short-acting LA | Strong |
Rebound pain — a sharp increase in pain as a single-shot interscalene block regresses (often overnight) is well described after shoulder surgery. Mitigate with IV dexamethasone, a pre-emptive multimodal oral regimen timed to block offset, clear patient counselling, or a continuous catheter.
Complications
| Complication | Incidence | Risk | Mitigation |
|---|---|---|---|
| Hemidiaphragmatic paresis | ~90–100% (standard); lower with low-volume | Expected | Low volume; diaphragm-sparing alternatives; avoid in respiratory compromise |
| Horner syndrome | Common | Low | Self-limiting; warn patient (ptosis, miosis, anhidrosis) |
| Hoarseness (recurrent laryngeal n.) | 10–20% | Low | Self-limiting; caution with contralateral vocal cord palsy |
| Vascular puncture | Low | Moderate | Identify carotid/IJV/vertebral vessels; colour Doppler; in-plane visualisation |
| LAST | <0.1% | Low | Aspirate; incremental injection; lipid emulsion immediately available |
| Epidural / intrathecal / vertebral artery injection | Rare | High severity | Avoid medial/deep needle trajectory; strict in-plane tip visualisation |
| Persistent neuropathy | <0.1% | Low | Avoid intraneural injection; low injection pressure; document pre-existing deficits |
Lipid emulsion 20% must be immediately available for any peripheral nerve block. Ensure a full LAST resuscitation kit and follow the Association of Anaesthetists / ASRA guidance.
Video Resources
Educational videos embedded from YouTube educational/institutional channels.
Interscalene Block — Technique
Anatomy, sonoanatomy, and ultrasound-guided technique walkthrough.
Sonoanatomy & Scanning
Identifying the stoplight sign and tracing the plexus between the scalenes.
Video IDs are placeholders — replace with your preferred verified clips before publishing.
References
- El-Boghdadly K, Chin KJ, Chan VWS. Phrenic Nerve Palsy and Regional Anesthesia for Shoulder Surgery: Anatomical, Physiologic, and Clinical Considerations. Anesthesiology. 2017;127(1):173–191.
- Tran DQH, Elgueta MF, Aliste J, Finlayson RJ. Diaphragm-Sparing Nerve Blocks for Shoulder Surgery. Reg Anesth Pain Med. 2017;42(1):32–38.
- ESRA PROSPECT Working Group. Procedure-specific postoperative pain management. esraeurope.org/prospect ↗
- NYSORA. Ultrasound-Guided Interscalene Brachial Plexus Block. nysora.com ↗
- Neal JM et al. ASRA Practice Advisory on Local Anesthetic Systemic Toxicity. Reg Anesth Pain Med. 2018;43(2):113–123.
- Desmet M et al. Intravenous dexamethasone and peripheral nerve block duration. Br J Anaesth. 2017;117(6):799–807.
- Abdallah FW, Brull R. Perineural dexmedetomidine as an adjuvant: systematic review. Br J Anaesth. 2013;110(6):915–925.
Literature identified via PubMed (National Library of Medicine). Verify current guidance before clinical application.