The 90% effective dose of spinal ropivacaine for external cephalic version: A sequential dose-finding study

ObjectiveAlthough spinal anesthesia can improve the success of external cephalic version, the optimal analgesic dose of ropivacaine remains undefined, and higher doses may increase potential risks. This study aimed to determine the 90% effective dose of intrathecal ropivacaine for external cephalic version.MethodsIn this double-blind, prospective, sequential dose-finding study, 40 parturients scheduled for external cephalic version received spinal anesthesia with ropivacaine (initial dose, 2.5 mg) combined with 10 µg fentanyl. Subsequent doses were determined using a biased coin up-and-down design based on the analgesic efficacy outcome of the preceding participant. Efficacy was defined as a procedural visual analog scale pain score ≤30 mm. The 90% effective dose was estimated using isotonic regression and bootstrapping.ResultsThe estimated 90% effective dose of intrathecal ropivacaine co-administered with 10 µg fentanyl was 3.22 mg (95% confidence interval: 2.80-3.36). The median (interquartile range) visual analog scale scores were 30.0 (20.0, 42.5), 30.0 (20.0, 30.0), and 10.0 (10.0, 25.0) mm in the 2.5, 3.0, and 3.5 mg dose groups, respectively (p < 0.05). Maternal and fetal hemodynamics remained stable.ConclusionsA dose of 3.0 mg ropivacaine combined with 10 µg fentanyl provided a favorable balance between analgesic efficacy and safety for spinal anesthesia during external cephalic version and is recommended for clinical use.Trial Registration: Chinese Clinical Trial Registration Centre (http://www.chictr.org.cn); Registration Number: ChiCTR2400084126; Registration Date: 10 May 2024.