Optimal end-tidal concentration of sevoflurane to test an ankle clonus in children

Study Design. A prospective randomized study on the end-tidal concentrations of sevoflurane at which ankle clonus existed. Summary of Background Data. The ankle clonus reflex is a transient neurologic abnormality, which normally occurs in patients during emergence from general anesthesia. Objective. To determine the optimal end-tidal concentration of sevoflurane to test an ankle clonus in children during emergence from general anesthesia. Methods. We studied 30 children (aged 5 -15 years). General anesthesia was induced with thiopental sodium. Anesthesia was maintained with sevoflurane, oxygen, and air. At completion of surgery, 3% volume of the end-tidal sevoflurane concentration was maintained for at least 10 minutes. Ankle clonus was checked at 1.0% to 0.1% volume of the end-tidal sevoflurane concentration with an interval of 0.05% volume. Results. Of children, 80% had bilateral ankle clonus, which was found most frequently when patients responded poorly to verbal commands. The median of the end-tidal sevoflurane concentration for a reactive ankle clonus was 0.45% volume (interquartile range 0.5% to 0.4% volume). Conclusions. The ankle clonus should be tested at 0.45% volume of end-tidal sevoflurane concentration in children undergoing scoliosis surgery during emergence from the general anesthesia.