Determination of the ED90 and ED99 of Liposomal versus Conventional Bupivacaine for Ultrasound-Guided Stellate Ganglion Block: A Biased-Coin Design Study

Background: Local anesthetics commonly used for ultrasound-guided stellate ganglion block (SGB) have a relatively short duration of action (6-12 hours). Liposomal bupivacaine, utilizing a multivesicular liposome sustained-release technology, can extend the block duration to over 72 hours, offering a potential option for prolonged sympathetic blockade. Determining its optimal effective dose relative to conventional bupivacaine is crucial for balancing prolonged efficacy with safety. Methods: All patients received ultrasound-guided SGB, successful blockade was explicitly defined as the onset of Horner syndrome (ptosis, miosis, anhidrosis) within 30 minutes post-injection. For the 0.5% bupivacaine hydrochloride group, the initial volume was 1.6 mL. The volume was adjusted using a biased-coin up-and-down sequential design with a step size of 0.2 mL. The study endpoint was 45 successful blocks, and the ED90 was calculated using isotonic regression. The liposomal bupivacaine group followed an identical design with an initial volume of 1.6 mL (266 mg/20 mL) and a step size of 0.4 mL. Results: The ED90 for 0.5% bupivacaine hydrochloride was 2.07 mL (95% CI: 1.99, 2.57), and the ED99 was 2.37 mL (95% CI: 2.33, 3.05 mL). The ED90 for liposomal bupivacaine was 3.75 mL (95% CI: 2.90, 5.17 mL), and the ED99 was 4.35 mL (95% CI: 4.22, 5.36 mL). Conclusion: Volumes of approximately 2.1 mL of bupivacaine hydrochloride and 3.8 mL of liposomal bupivacaine can be expected to achieve near-complete stellate ganglion blockade. While liposomal bupivacaine holds promise for long-duration therapy, dosing must be cautious due to the prolonged course of potential complications.