• Kumiko Yamada, Shinichi Inomata, and Makoto Tanaka.
• From the Faculty of Medicine, Division of Clinical Medicine, Department of Anesthesiology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
• Anesth. Analg. 2016 Jul 1; 123 (1): 175-8.

BackgroundTo the best of our knowledge, the ropivacaine concentration required for ultrasound-guided ilioinguinal and iliohypogastric nerve block (INB) has not been reported. We designed this study to examine the 50% effective concentration (EC50) of ropivacaine for ultrasound-guided INB in children anesthetized with 2% sevoflurane.MethodsWe studied 30 consecutive children (age range, 6 months to 11 years) ASA physical status I to II undergoing unilateral open inguinal hernia repair. General anesthesia was induced by sevoflurane and maintained with 2% end-tidal concentration of sevoflurane in air and oxygen (FIO2 = 0.4). Ultrasound-guided INB was performed using a 3 mL ropivacaine solution. The first child received 0.3% ropivacaine, and subsequent concentrations were determined by the response of the previous patient to initial skin incision using Dixon up-and-down method. The testing interval was set at 0.1%, and the lowest concentration was 0.05% (0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%). The EC50 for INB of ropivacaine was analyzed using probit test.ResultsThe concentration at which all patients showed complete block was 0.50%, according to the up-and-down method. The EC50 was 0.21% (95% confidence interval, 0.03-0.34).ConclusionsThe EC50 of ropivacaine for ultrasound-guided INB was 0.21% (95% confidence interval, 0.03-0.34), in pediatric patients anesthetized with 2% sevoflurane.

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