Risk of Delayed Symptomatic Pneumothorax After Interscalene Nerve Block
Delayed symptomatic pneumothorax after interscalene nerve block is exceedingly rare, with an overall pneumothorax incidence of approximately 0.2%, and most cases present acutely within the first hour rather than hours later. 1
Incidence and Timing
The overall incidence of pneumothorax following interscalene brachial plexus block is approximately 0.2% (1 in 520 patients) in a large prospective study of standardized technique. 1
Most pneumothoraces from lung procedures are detectable within 1 hour, with 98% visible on chest radiographs taken either immediately or at 1 hour post-procedure. 2
Delayed pneumothoraces presenting more than 24 hours after a procedure are documented but remain exceptional, even in lung biopsy literature where the risk is substantially higher than nerve blocks. 2
Clinical Presentation Pattern
When pneumothorax occurs after interscalene block, it typically presents acutely during or immediately after the procedure with ipsilateral chest pain, dyspnea, and potentially diminished breath sounds. 2
The single documented case of pneumothorax in the large prospective interscalene study presented acutely, not in a delayed fashion. 1
Tension pneumothorax has been reported even with ultrasound-guided technique, but these cases manifested during the surgical procedure under general anesthesia, not hours later in a delayed presentation. 3
Key Distinguishing Features from Other Nerve Blocks
Interscalene blocks have a significantly lower pneumothorax risk compared to intercostal nerve blocks (0.2% vs 1.4-8.7%) because the needle trajectory is directed away from the pleura. 1, 4
The anatomical approach for interscalene blocks targets the brachial plexus at the level of C6, which is considerably distant from the pleural dome when proper technique is employed. 1
Patient Counseling and Monitoring
Patients should be informed of pneumothorax risk as part of informed consent, though the absolute risk is very low. 2
Patients should remain in a monitored setting for at least the first hour where staff can be alerted if new symptoms develop, as this captures the vast majority of potential complications. 2
Patients discharged after the procedure should receive explicit instructions to return immediately for any new-onset breathlessness or chest pain, as delayed presentations beyond 24 hours, while rare, have been documented in procedural literature. 2
Clinical Bottom Line
The chance of a truly delayed (hours after the block) symptomatic pneumothorax is exceptionally low, likely well under 0.1%, given that the overall pneumothorax rate is only 0.2% and most present immediately. 1 The primary monitoring window is the first hour post-procedure, after which the risk becomes negligible but not zero. 2