Objective To observe the effects of Midazolam combined with Fentanyl on energy motabolism in general anesthesia.Methods 35 selected neurosurgical adult patients,ASA class Ⅰ-Ⅱ,received total intravenous general anesthesia with Midazolam combined with Fentanyl.Oxygen consumption( VO 2 ) ,carbon dioxide production(VCO 2),respiratory quotient(RQ),and metabolism rate(MR) were measured.Results VO 2 and MR increased when patients' posture changed or there existed strong operative stimulation.VO 2 and MR during postinduction were 91.09% and 91.29 % of the level before anesthesia respectively(P<0.05),and were 93.58% and 94.93% of that during operation respectively(P<0.05).As anesthesia duration lasted,RQ decreased gradually from 0.95±0.29(before anesthesia) to 0.79±0.09,VCO 2 showed a stable trend during both postinduction and operation.Conclusion (1) Change of VO 2 and MR are related to the degree of operative stimulation in neurosurgical patients with Midazolam-Fentanyl anesthesia.(2)RQ trend shows gradually decreasing during anesthesia.