BACKGROUND: To 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.
METHODS: We 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.
RESULTS: The 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).
CONCLUSIONS: The EC50 of ropivacaine for ultrasound-guided INB was 0.21% (95% confidence interval, 0.03–0.34), in pediatric patients anesthetized with 2% sevoflurane.
From the Faculty of Medicine, Division of Clinical Medicine, Department of Anesthesiology, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Accepted for publication February 27 2016.
The authors declare no conflicts of interest.
Reprints will not be available from the authors.
Address correspondence to Shinichi Inomata, MD, Faculty of Medicine, Division of Clinical Medicine, Department of Anesthesiology, University of Tsukuba, Tsukuba City, Ibaraki 305, Japan. Address e-mail to email@example.com.