Which regional block is appropriate for anesthesia of a humeral shaft fracture?

Brachial Plexus Block via Infraclavicular or Axillary Approach

For humeral shaft fracture anesthesia, an infraclavicular or axillary brachial plexus block is the most appropriate choice, avoiding interscalene or supraclavicular approaches to minimize respiratory complications. 1

Rationale for Block Selection

The humeral shaft requires complete brachial plexus coverage (C5-T1 distribution). While multiple approaches can achieve this, guideline evidence specifically recommends choosing blocks that minimize respiratory interference 1. The 2020 Anaesthesia guideline explicitly states that "axillary or infraclavicular brachial plexus block may be chosen over supraclavicular brachial plexus block" when respiratory function preservation is a priority 1.

Why Avoid Higher Approaches

• Interscalene blocks carry near-universal risk of hemidiaphragmatic paresis (approaching 100%), making them inappropriate for humeral shaft fractures despite being commonly used for proximal humerus injuries 2, 3, 4
• Supraclavicular blocks also pose significant phrenic nerve involvement risk 1
• The guideline explicitly recommends avoiding these approaches when alternatives exist 1

Optimal Block Technique

Primary Recommendation: Infraclavicular Block

• Provides complete C5-T1 coverage necessary for humeral shaft surgery
• Minimal respiratory compromise
• Lower risk of pneumothorax compared to supraclavicular approach
• Must use ultrasound guidance to reduce local anesthetic systemic toxicity risk 1

Alternative: Axillary Block

• Equally appropriate with no respiratory effects
• May be technically easier in some patients
• Complete upper extremity coverage when properly performed

Critical Technical Considerations

Ultrasound guidance is mandatory - the guideline emphasizes this reduces local anesthetic systemic toxicity risk 1. Calculate safe local anesthetic doses before injection.

Procedural Safeguards

• Allow adequate onset time (20-30 minutes) before surgical incision 1
• Thoroughly test block success before proceeding to prevent emergent conversion to general anesthesia 1
• Test all dermatomes: lateral arm (axillary nerve), medial arm (medial brachial cutaneous), forearm (radial, median, ulnar distributions)
• Consider reduced sedation doses to avoid respiratory compromise 1

Common Pitfalls to Avoid

1. Choosing interscalene block - while case reports describe its use 2, 5, this violates guideline recommendations for shaft fractures where respiratory-sparing alternatives exist
2. Inadequate block testing - rushing to surgery before confirming complete sensory blockade leads to intraoperative conversion
3. Excessive local anesthetic volume - calculate maximum safe dose based on patient weight
4. Skipping ultrasound guidance - increases complication risk significantly

Special Circumstances

For pathological fractures with systemic disease, regional anesthesia becomes even more advantageous by avoiding general anesthesia risks 2. However, maintain the same principle: choose infraclavicular/axillary over interscalene approaches.

If combined approaches are needed (rare for shaft fractures), ultrasound guidance allows reduced volumes at each site 5, but this adds complexity without clear benefit for straightforward shaft fractures.