All patients will receive iv propofol 2 mg/kg as induction agent and succinyl choline 1.5 mg/kg for intubation. Then the ventilation will be controlled to achieve end-tidal CO2 30-35 mmHg with O2:N2O 1:1 L/min with desflurane 12%. Time to achieve alveolar concentration of desflurane at 1, 2, 3, 4, 5 and 6% will be recorded and analyzed. After that, the concentration of desflurane and anesthetic technique will be adjusted to requirement of anesthesiologist.