[Fentanyl reduces the MAC of sevoflurane].

OBJECTIVE: To determine the interaction between fentanyl and sevoflurane following a bolus injection of fentanyl after induction iwth sevoflurane inhalation only. METHODS: Sixty children aged 5-10 years who were diagnosed as having VSD or ASD were randomly allocated into three groups. The first group received sevoflurane in oxygen without any other drugs. The second group received sevoflurane in oxygen with fentanyl 3 ng/kg, and the third group received sevoflurane in oxygen with fentanyl 6 ng/kg. MAC determination, in response to the stimulus of skin incision, was made using the "up-down" method. RESULTS: The MAC of sevoflurane in oxygen was (2.72 +/- 0.08)%. Fentanyl 3 ng/kg bolus injection produced a fentanyl plasma concentration of (0.64 +/- 0.13) microgram/L at skin incision and resulted in a MAC for sevoflurane of (1.03 +/- 0.07)%. Fentanyl 6 ng/kg bolus injection produced a fentanyl plasma concentration of (1.51 +/- 0.18) micrograms/L at skin incision and resulted in a MAC for sevoflurane of (0.64 +/- 0.01)%. By the stimulation of skin incision, the Hr, MAP of group I increased 39%, 29%, compared with group II 14%, 15%, group III 20%, 14%, respectively. These results were significantly different (P < 0.01). CONCLUSION: The MAC of sevoflurane is significantly reduced 20 minutes after a single dose of 3 ng/kg of fentanyl and that increasing the fentanyl dose to 6 ng/kg produces a little further decrease in MAC of sevoflurane.