The ED90 of Liposomal Bupivacaine for Motor-Sparing After Interscalene Brachial Plexus Block: A Dose-Finding Study

In adult arthroscopic rotator cuff repair, interscalene brachial plexus block using liposomal bupivacaine has been proven to effectively provide analgesic effects. However, concerns about motor-blocking may restrict its widespread clinical application. This study aimed to determine the 90% minimum effective dose (ED90) of liposomal bupivacaine for successful sensory blockade with motor-sparing following ultrasound-guided interscalene brachial plexus block.

A total of 55 patients undergoing arthroscopic rotator cuff repair received an ultrasound-guided interscalene block using liposomal bupivacaine. The study employed an up-and-down sequential method with a biased-coin design. The primary outcome was the ED90 of liposomal bupivacaine in middle-aged patients undergoing motor-sparing (sensory score of 1 or 2 and a motor score of >2 during 3-72 hours after surgery) ultrasound-guided interscalene brachial plexus block. Secondary outcomes included Numerical Rating Scale (NRS) and numbness scores; as well as the percentage change in diaphragmatic excursion and pulse oxygen saturation (SpO₂) from baseline to the Post-Anesthesia Care Unit (PACU).

In total, 53 patients completed the study. The estimated ED90 of liposomal bupivacaine was 46.55 mg [90% confidence interval (CI), 39.36-48.41]. There was no significant difference observed in diaphragmatic excursion (P=0.164) and SpO₂ (P=0.820) in the PACU between the motor-sparing group and motor-blocking group. There was no severe pain (Scores 7-10) on movement or at rest and no severe numbness (Scores=3) during the 72 hours after blocking. There were no reports of other complications, except for two female patients who developed nausea and vomiting after completion of the blocks.

Motor-sparing ultrasound-guided interscalene brachial plexus block using liposome bupivacaine with a dose of 46.55 mg enables successful sensory blocks in 90% of middle-aged adults after excluding cases with failed sensory blockade.