What is the recommended phrenic nerve sparing block for shoulder surgery?

Phrenic Nerve Sparing Blocks for Shoulder Surgery

For shoulder surgery requiring regional anesthesia, the superior trunk block or costoclavicular block should be used instead of the traditional interscalene block when phrenic nerve preservation is a priority, as both provide equivalent surgical anesthesia and analgesia while dramatically reducing hemidiaphragmatic paralysis from 71-84% to less than 6%. 1, 2, 3

Primary Recommendation: Superior Trunk Block

The superior trunk block is the most rigorously studied phrenic-sparing alternative and should be considered first-line when respiratory function preservation is critical 3:

• Provides noninferior surgical anesthesia compared to interscalene block while reducing hemidiaphragmatic paralysis incidence from 71.4% to 4.8% (adjusted odds ratio 0.02,95% CI 0.01-0.07, P < 0.001) 3
• Maintains equivalent pain control in the recovery room with median worst pain scores of 0 in both groups 3
• Preserves respiratory parameters completely, unlike interscalene block which significantly impairs pulmonary function 3
• Associated with higher patient satisfaction and lower incidence of hoarseness 3
• Actually provides superior pain control on postoperative day 1 compared to interscalene block 3

Alternative: Costoclavicular Block

The costoclavicular block represents another excellent phrenic-sparing option with even more recent evidence 2:

• Reduces hemidiaphragmatic paralysis incidence to 5.9% compared to 84.4% with interscalene block (P < 0.001) 2
• Maintains effective analgesia with no significant difference in opioid consumption throughout the postoperative period 2
• Causes minimal diaphragmatic excursion reduction (0.25 cm vs 3.87 cm with interscalene block, P < 0.001) 2
• Results in significantly less impairment of forced vital capacity and forced expiratory volume compared to interscalene block 2

When Traditional Interscalene Block Remains Appropriate

If phrenic nerve sparing is not a concern, continuous interscalene block remains the gold standard 1:

• Continuous interscalene block is preferred over single-shot due to longer analgesia duration and reduced rebound pain 1
• Provides lower pain scores and reduced opioid consumption on postoperative days 1,2, and 7 1
• Should be combined with IV dexamethasone to increase analgesic duration 1
• Use ropivacaine 0.2-0.3% for continuous infusions 1

Technical Modifications to Reduce Phrenic Nerve Involvement

If interscalene approach must be used but phrenic sparing is desired, consider these modifications 4:

• Use ultrasound guidance with injection 4 mm outside the brachial plexus fascia (extrafascial technique) to reduce spread to phrenic nerve 4
• Employ lower volumes of local anesthetic (10 ml rather than 20 ml) to limit medial spread 4, 3
• These modifications reduce but do not eliminate hemidiaphragmatic paralysis risk 4

Blocks to Avoid for Shoulder Surgery

The posterior suprascapular nerve block alone and PECS II block should not be used as primary anesthesia for shoulder surgery 1, 4:

• Posterior suprascapular nerve block provides inferior analgesia compared to interscalene block unless combined with infraclavicular block 4
• PECS II block is explicitly listed as "not medically necessary or unproven" for shoulder surgery postoperative pain control 1
• Anterior suprascapular nerve block shows high hemidiaphragmatic paralysis prevalence despite being more distal 4

Clinical Decision Algorithm

For patients with normal respiratory function:

• Use continuous interscalene block with IV dexamethasone 1

For patients with compromised pulmonary function, COPD, or requiring supplemental oxygen:

• First choice: Superior trunk block 5, 3
• Second choice: Costoclavicular block 2
• Third choice: Combined posterior suprascapular + infraclavicular block 4

For patients where interscalene is contraindicated entirely:

• Axillary nerve block with or without suprascapular nerve block 1

Critical Technical Considerations

Always use ultrasound guidance to reduce local anesthetic systemic toxicity risk by 50% and improve block success rates 5, 6:

• Calculate safe local anesthetic doses carefully (maximum ropivacaine 300 mg) 6, 7
• For brachial plexus blocks, supraclavicular approaches show 92% success rates compared to 56-86% for axillary approaches 7
• Avoid excessive sedation during block performance as this may compromise respiratory function, particularly in patients with respiratory comorbidities (risk ratio 2.5) 6

Multimodal Analgesia Framework

Regardless of block choice, combine with 1:

• Regular paracetamol and NSAIDs/COX-2 inhibitors initiated preoperatively 1
• Single dose IV dexamethasone (not perineural) to increase block duration 1
• Reserve opioids for rescue analgesia only 1

Common Pitfalls

• Do not choose infraclavicular or axillary blocks as primary anesthesia for shoulder surgery - these are appropriate for elbow, forearm, and hand procedures but provide inadequate shoulder coverage 5, 6
• Do not use supraclavicular block when phrenic sparing is the goal - this approach carries significant hemidiaphragmatic paralysis risk similar to interscalene 5, 7
• Do not assume lower volumes alone will prevent phrenic involvement with standard interscalene technique - anatomic approach modification (superior trunk or costoclavicular) is more reliable 4, 3