The patients will receive both standard frontal and nasal BIS monitoring during general anesthesia.

• All patient will receive standard monitoring (EKG, Blood pressure, pulse oximetry), and BIS transducer placement at standard frontal area before anesthesia.
• Sedative medication can be given as appropriate.
• Anesthesia induction by inhalation induction with sevoflurane (if intravenous line not presented) or intravenous induction with thiopental 5-6 mg/kg IV
• Other medication including fentanyl 1 mcg/kg IV and cisatracurium 0.1-0.2 mg/kg IV will be given and the patient will be intubated.
• The second BIS will be installed on the bridge of the nose and temporal on the same side as frontal BIS.
• The patient will be maintained with sevoflurane and other anesthetic drugs as appropriate, adjusted per frontal BIS (40-60).
• The frontal BIS and the nasal BIS will be measured until the endotracheal tube is being removed. If the patient has moved until it was impossible to measure the BIS or has any necessity to cancel the BIS measurement. The BIS measurement can be stopped.

BIS is a processed electroencephalogram (range from 0-100), the optimal value of BIS during general anesthesia is 40-60. We aim to define the differences between standard frontal BIS and nasal BIS using Bland-Altman analysis.

SQI (range from 0-100) determines the quality of signal of the primary outcome (BIS). We aim to define the differences of SQI of BIS between standard frontal and nasal positions.