Complications and Side Effects of Interscalene and Supraclavicular Blocks
Both interscalene and supraclavicular brachial plexus blocks carry risks of local anesthetic systemic toxicity, nerve injury, and hematoma, but interscalene blocks cause significantly more respiratory complications—specifically hemidiaphragmatic paresis occurs in up to 100% of cases—making supraclavicular blocks the preferred alternative when respiratory function preservation is critical.
Common Complications by Block Type
Interscalene Block Complications
Respiratory complications are the defining concern with interscalene blocks:
- Hemidiaphragmatic paresis: Occurs in 73.7-100% of patients 1, 2
- This results from phrenic nerve blockade due to the proximity of the injection site to C3-C5 nerve roots
- Patients requiring supplemental oxygen or with baseline respiratory compromise should avoid this approach 1
Neurologic side effects are frequent:
- Horner's syndrome: 59.6% incidence 3
- Hoarseness: Common due to recurrent laryngeal nerve involvement 4
- Peripheral nerve injury: 14% symptomatic at 10 days, 7.9% at 1 month, with 0.2% having persistent dysesthesia at 9 months 5
- Serious permanent neurologic injuries documented in closed claims data 6
Other complications:
- Pneumothorax: 0.2% 5
- Central nervous system toxicity: 0.2% 5
- Cardiovascular complications: Documented but rare 6
Supraclavicular Block Complications
Significantly lower respiratory impact:
- Hemidiaphragmatic paresis: 0-23.7% (dramatically lower than interscalene) 2
- This makes supraclavicular blocks safer for patients with respiratory concerns
Reduced neurologic side effects:
- Horner's syndrome: 19.6% (versus 59.6% with interscalene) 3
- Hoarseness: Lower incidence than interscalene 7
- Motor blockade may be more extensive in distal nerve distributions (radial, ulnar, median) 3
Shared risks with interscalene:
- Local anesthetic systemic toxicity (mitigated by ultrasound guidance) 1
- Nerve injury
- Hematoma formation
- Vascular puncture
Risk Mitigation Strategies
Ultrasound guidance is mandatory to reduce local anesthetic systemic toxicity risk 1. Calculate safe local anesthetic doses before injection.
Block selection algorithm:
- Choose supraclavicular over interscalene when respiratory function preservation is important 1
- Consider axillary or infraclavicular approaches over supraclavicular for even greater respiratory sparing 1
- Reduce pre-procedural sedation doses to avoid respiratory compromise 1
For continuous catheters: The interscalene space is anatomically confined, making catheter displacement common with neck or shoulder movement 8. This can lead to loss of efficacy or migration causing new complications. The proximal longitudinal oblique supraclavicular approach may offer more stable catheter positioning 2.
Critical Pitfalls
Experience matters: Less experienced anesthesiologists have higher complication rates with interscalene blocks 6. Serious complications including deaths have been reported in national closed claims data 6.
Persistent symptoms require investigation: If paresthesias, dysesthesias, or pain persist beyond the expected block duration, evaluate for:
- Ulnar nerve entrapment (sulcus ulnaris syndrome)
- Carpal tunnel syndrome
- Complex regional pain syndrome
- True plexus injury 5
These conditions require specific treatment and may be unrelated to the block itself.
The 0.4% severe long-term complication rate for interscalene blocks includes disabling permanent injuries 5. When balanced against the near-universal hemidiaphragmatic paresis, supraclavicular blocks provide comparable analgesia with substantially better safety profiles 4, 7, 2.