The Effective Ropivacaine Concentration for Transversus Thoracic Muscle Plane Block in Adult Cardiac Surgery: A Dose-Finding Trial Protocol

Background Median sternotomy in cardiac surgery is associated with severe pain, and opioid-based analgesia is currently standard. In recent years, various ultrasound-guided nerve block types have been used in cardiac surgery to reduce opioid use and facilitate postoperative recovery, including ultrasound-guided transversus thoracic muscle plane block. However, the 90% effective concentration of ropivacaine used for ultrasound-guided transverse thoracic muscle plane block (TTPB) in cardiac surgery remains undetermined. This study aims to evaluate the 90% effective concentration of ropivacaine for ultrasound-guided transversus thoracic muscle plane block in adult cardiac surgery using the biased coin up-and-down sequential method. Methods This study is a single-center, prospective, sequential allocation dose-finding trial. Participants will be adult patients with American Society of Anesthesiologists physical status (ASA-PS) II-IV undergoing elective cardiac surgery with median sternotomy. Ultrasound-guided transversus thoracic muscle plane block will be performed after induction of general anesthesia at 0.4 ml.kg^-1 ropivacaine per side (0.8 ml.kg^-1 bilaterally), with concentrations pre-determined by biased coin up-and-down sequential method. Successful transversus thoracic muscle plane block is to be defined as less than a 20% increase in heart rate or blood pressure from the baseline value within one minute after the skin incision in the midline of the chest. The 90% effective concentration of ropivacaine will be estimated using isotonic regression. Conclusions The results of this study will help establish guidelines for transversus thoracic muscle plane block in cardiac surgery and may facilitate the optimization of healthcare resources.