Distant Extrafascial Injection vs Subfascial Injection for Interscalene Block: Acute Pain Outcomes and Rates of Complications

This is a prospective randomized controlled double-blinded trial on patients undergoing shoulder surgery (shoulder arthroscopy or open shoulder surgery), aged between 18 and 85 years old.

The exclusion criteria will be contraindications to brachial plexus block (e.g., allergy to local anesthetics, coagulopathy, malignancy or infection in the area); existing neurological deficit in the area to be blocked; severe respiratory disease; inability to understand the informed consent and patient refusal.

Prior to the procedure, all patients will be fully informed about the risks and benefits of participating in the study and written informed consent will be obtained.

Interscalene brachial plexus block will be performed with the patient lying lateral on the non-operative side, following our routine clinical practice, with twenty milliliters of local anesthetic containing bupivacaine 0.5% with 1:200,000 epinephrine. For patients in the subfascial injection group, the needle tip will be positioned lateral to the brachial plexus at a distance of 4 mm, measured with a caliper.

Block assessment and definition of a successful block Evaluation of sensory and motor blockades will be performed by a blinded research assistant every 5 min, for a total of 30 min, after local anesthetic (LA) injection. Sensory block and motor blockades will be tested in the C4, C5, C6, C7, and C8 dermatomes using a blunt tip needle pinprick test and muscular testing. A successful block will be defined as complete sensory and motor blockade in the distribution of the C5 and C6 nerve roots within 30 minutes of performing the ISB. In cases of a failed block, the ISB will be repeated at the discretion of the attending anesthesiologist and these patients will be excluded from the intraoperative and postoperative secondary outcome analyses.