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Background General anaesthesia and interscalene brachial plexus block (ISB) are the main anaesthesia methods for patients undergoing shoulder arthroscopy. However, they usually result in severe complications, such as postoperative nausea and vomiting (PONV), postoperative cognitive dysfunction (POCD), and hemi-diaphragmatic paralysis (HDP). Compared with ISB, superior trunk block (STB) is associated with a lower incidence of HDP and greater hand strength. Previous studies of STB have proven that it could provide surgical anaesthesia and noninferior postoperative analgesia, but the incidence of partial HDP was still very high, which may be fatal for some specific populations, such as patients with preexisting pulmonary impairments. Moreover, a high dose of local anaesthetic (LA) can result in prolonged postoperative numbness and weakness in the affected upper limb. Adverse events can be avoided by reducing the dose of LA, namely by using the minimum effective volume (MEV) or concentration (MEC). In this study, we aimed to explore the MEV of ropivacaine 0.25%, providing satisfactory surgical anaesthesia during the performance of an STB. Methods/design Our study is a prospective cohort trial to determine the minimum effective volume of ropivacaine 0.25% in 90% of patients (MEV90) on the provision of surgical anaesthesia for shoulder arthroscopy. Trial designs apply the up-and-down Biased Coin Design (BCD) methodology, which has been adopted in recent years in dose-finding studies for regional anaesthesia. Participants will be enrolled and receive STB with different volumes of ropivacaine 0.25%. The volume of ropivacaine administered to each patient depends on the outcome of the previous one. A volume of 5 ml is chosen for the initial case on the basis of prior clinical experience. In case of failure, the next patient will receive a higher volume (defined as the previous volume with an increment of 2 ml). The successful block will be defined as not only achieving a minimal score of 9 points (out of 10 points) after 30 minutes of STB using a sensory composite scale but also completing the surgery with only STB without general anaesthesia. The volume of LA for the subsequent case is then randomized according to the BCD principle. Discussion This research will determine the MEV90 of ropivacaine 0.25% of STB in patients undergoing shoulder arthroscopy. The results of the study will be important for guiding clinical practice and making it possible to enhance recovery after surgery for patients in day wards undergoing shoulder arthroscopic surgery. |
