Continuous Interscalene Brachial Plexus Block via an Ultrasound-Guided Posterior Approach: A Randomized, Triple-Masked, Placebo-Controlled Study

Interscalene perineural catheters placed using the anterolateral approach provide a number of benefits after painful shoulder surgery.1–3 However, using this approach, nonstimulating catheters may have a failure rate of up to 20%,2,4 and stimulating catheters may take too long to insert (sometimes >30 min).3,5–7 Other challenges related to the anterolateral approach include avoiding the external jugular vein, superficial placement potentially leading to catheter dislodgement and inclusion of the catheter site in the sterile surgical field. A posterior approach to the brachial plexus may avoid these problems.8,9 The continuous cervical paravertebral block introduces the needle between the levator scapulae and trapezius muscles and directs the catheter anteriorly to lay along the brachial plexus.10–12 The needle is often advanced in an anterior direction until it contacts cervical vertebra, then further anterior and laterally until the brachial plexus is located using electrical stimulation.9,11,12 Recently, a case report described a new ultrasound-guided posterior approach using real-time imaging allowing needle/catheter insertion without requiring cervical vertebra contact.13 Unlike the anterolateral approach, the posterior approach has not been examined in a controlled investigation; and thus its benefits and risks remain unknown. Therefore, the objective of this randomized, triple-masked (patients, investigators, and statisticians), placebo-controlled study was to test the hypothesis that, compared to a single-injection ropivacaine interscalene block, an ultrasound-guided continuous posterior interscalene block provides superior postoperative analgesia after moderately painful shoulder surgery. The primary end point was average shoulder pain the day after surgery.