Remifentanil and Midazolam on Propofol for Loss of Consciousness

Propofol in combination with remifentanil or midazolam can result in synergistic or additive effect. The patients who are scheduled to undergo general anesthesia are enrolled in this study. 120 patients will be randomly allocated to 3 groups(P, PR, PMR). The patients in group P will receive general anesthesia only with propofol and group PR and PMR will receive 0.25 mcg/kg/min remifentanil infusion prior to propofol. The patients in group PMR will receive 0.03 mg/kg bolus dose of midazolam 1 min after start of the remifentanil infusion. 'Success' is defined as loss of both verbal response and eyelash reflex in 2 min after propofol administration. When 'success', the next patient will receive the same dose(in 18/19 probability) or 0.25 mg/kg lower dose(in 1/19 probability) of propofol. When 'failure', the next patient will receive 0.25 mg/kg higher dose of propofol at induction period.