What is the recommended anesthetic technique for performing shoulder arthroplasty using an ultrasound‑guided interscalene brachial plexus block?

Ultrasound-Guided Interscalene Brachial Plexus Block for Shoulder Arthroplasty

Interscalene brachial plexus block is the first-choice regional anesthetic technique for shoulder arthroplasty, and should be performed using ultrasound guidance with 20-30 mL of local anesthetic (ropivacaine 0.2-0.5% or bupivacaine 0.25-0.5%), combined with intravenous dexamethasone 10 mg to prolong block duration. 1

Core Technique Specifications

The 2019 PROSPECT guidelines explicitly recommend interscalene brachial plexus blockade as the first-choice regional analgesic technique for shoulder surgery 1. While these guidelines focused on rotator cuff repair, the principles directly apply to shoulder arthroplasty given similar pain pathways and surgical trauma.

Ultrasound Guidance is Essential

• Always use ultrasound guidance to visualize local anesthetic spread and reduce the risk of local anesthetic systemic toxicity 2
• Ultrasound enables precise needle placement and reduces required local anesthetic volumes while maintaining efficacy 3
• The technique has higher success rates compared to landmark-based approaches 4

Optimal Local Anesthetic Dosing

Volume considerations:

• Use 20-30 mL of local anesthetic for single-shot blocks 3
• Volumes <20 mL significantly increase intraoperative opioid consumption (55.6% of patients required fentanyl vs. 22-31% with higher volumes) 3
• Volumes >30 mL increase cardiovascular instability without improving analgesia 3
• The optimal volume appears to be 24 mL, which minimizes hypotensive bradycardic events (9.1% incidence) 3

Concentration matters:

• Ropivacaine 0.2% reduces postoperative opioid consumption for 72 hours compared to 0.1% 1
• Bupivacaine 0.25-0.5% or ropivacaine 0.5% are effective alternatives 1, 5, 6
• Higher concentrations (0.2% vs 0.1%) provide superior analgesia without significantly increasing motor block 6

Mandatory Adjunct: Intravenous Dexamethasone

Administer dexamethasone 10 mg intravenously at the time of block placement 1:

• Prolongs block duration significantly
• Reduces pain scores for the first 48 hours postoperatively 1
• Decreases analgesic consumption (paracetamol and NSAIDs) 1
• Provides anti-emetic effects
• No difference in efficacy between perineural and intravenous administration - IV route is safer and equally effective 1

Continuous vs. Single-Shot Technique

Consider continuous interscalene block for major shoulder arthroplasty:

• Continuous blocks provide superior analgesia on postoperative days 1-3 compared to single-shot 1
• Lower pain scores at 6h, 24h, and 72h postoperatively 1
• Reduced opioid consumption for 48 hours 1
• For continuous infusions, use ropivacaine 0.2% at 4-5 mL/hour with patient-controlled boluses 1
• Higher concentrations (0.3% vs 0.2%) reduce opioid consumption without increasing pain scores 1

Multimodal Analgesia Framework

The block must be integrated into a comprehensive regimen 1:

Pre-operative/Intra-operative:

• Paracetamol (acetaminophen) 1g IV or PO
• COX-2 inhibitor or NSAID
• Dexamethasone 10 mg IV (as discussed above)
• Interscalene block

Postoperative:

• Continue paracetamol scheduled dosing
• Continue NSAID/COX-2 inhibitor
• Opioids reserved strictly for rescue analgesia only 1

Critical Safety Considerations

Phrenic nerve blockade is inevitable with traditional interscalene blocks:

• Occurs in nearly 100% of cases with standard technique
• Usually clinically insignificant in healthy patients
• Screen high-risk patients (COPD, obesity, sleep apnea) for respiratory compromise
• Consider alternative techniques (suprascapular + axillary nerve blocks) in patients with severe respiratory disease 1

Avoid these common pitfalls:

• Using volumes <20 mL leads to inadequate analgesia and increased opioid requirements 3
• Using volumes >30 mL increases hemodynamic instability without benefit 3
• Omitting dexamethasone shortens block duration significantly 1
• Failing to establish multimodal analgesia increases opioid consumption and side effects 1

Alternative: Suprascapular + Axillary Nerve Block

If interscalene block is contraindicated due to respiratory concerns:

• Suprascapular nerve block combined with axillary nerve block provides effective analgesia 1
• Lower pain scores compared to suprascapular block alone 1
• This is the second-line option, not first-choice 1
• Does not provide complete shoulder anesthesia but spares phrenic nerve function

Block Assessment Before Surgery

Thoroughly test block success before surgical incision 2:

• Allow adequate onset time (20-30 minutes minimum)
• Verify sensory blockade in C5-C6 dermatomes
• This prevents emergent conversion to general anesthesia
• Document block extent for medicolegal purposes