[Measurement of the minimum alveolar concentration of sevoflurane during combined anesthesia with sevoflurane, small-dose dexmedetomidine and fentanyl].

OBJECTIVE: To determine the minimum alveolar concentration (EC(50) and EC(95)) of sevoflurane in body movement response to surgical incision during combined anesthesia with dexmedetomidine, sevoflurane and fentanyl. METHODS: Twenty-six ASA class I or II patients (aged 18-60 years) underwent selective surgery for lumbar disc herniation under general anesthesia with the combination of with dexmedetomidine, sevoflurane and fentanyl. All the patients received infusion with 0.5 mg/kg dexmedetomidine for 10 min before anesthesia induction with intravenous injection of 3 µg/kg fentanyl 8% sevoflurane inhalation. Upon loss of consciousness, sevoflurane concentration was reduced to 5% with intravenous injection of 1-2 mg/kg succinylcholine, and intubation was started after muscles relaxation. Anesthesia was maintained by sevoflurane and dexmedetomidine (0.2 µg·kg(-1)·h(-1)). Before the surgery, a steady state end-tidal sevoflurane concentration was maintained for at least 10 min. The first patient of the series was tested with 1.5% sevoflurane, and the concentration was adjusted according to modified Dixons up-and-down method (with a step size of 0.2%). Probit analysis was used for calculating EC(50), EC(95) and the 95% confidence interval (CI). RESULTS: The EC(50) of sevoflurane was 0.94% (95%CI of 0.76%-1.07% ) and EC(95) was 1.23% (95%CI 1.09%-2.05% ). CONCLUSION: The EC(50) and EC(95) of sevoflurane are 0.94% and 1.23%, respectively, for suppressing body movement in response to surgical incision during combined anesthesia with sevoflurane, dexmedetomidine and fentanyl.