Since neurological testing during neurosurgery, such as somato-sensory evoked potentials, motor-evoked potentials, auditory evoked potentials and visual evoked potentials are well maintained their wave-form reactivity with total intravenous anaesthesia technique better than inhalational anesthetic techniques, the standard anesthesia method for neurosurgery is usually total intravenous anaesthesia technique. Nonetheless, after finishing recording the evoked potential responses during surgery, facilitation of recovery from general anesthesia is getting important, because the real neurological physical examination is much more sensitive than above electrical evoked potentials to evaluate the results of surgical operation.

We propose to evaluate the recovery parameters after conversion from total intravenous anaesthesia technique to Desflurane anesthesia during long term neurosurgery procedures. The conversion will be initiated upon completion of the neurophysiological electric evoked potentials assessment. Based on the pharmacological properties of desflurane, we hypothesize that recovery after conversion to Desflurane will be faster compared to recovery after total intravenous anaesthesia alone.

Inclusion Criteria:

• Patients undergoing elective craniotomy
• American Society of Anesthesiology Physical Status Ⅰ, II and III
• Age: between 20 to 65 years
• Sex: male or female
• Patients who are postmenopausal or surgically sterilized
• Expected Operation time is longer than 4 hours.

Exclusion Criteria:

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