Standard monitoring with continuous electrography (ECG), non-invasive blood pressure(NIBP) monitoring and pulse oximetry will be used for all patients. A baseline blood pressure, heart rate, respiratory rate, oxygen saturation (SaO2) and ETCO2 will be recorded. During preoperative period, a 20-gauge, radial artery catheter was inserted under aseptic technique. It is used to obtain arterial blood gas measurement of partial pressure oxygen and carbon dioxide (PaO2, PaCO2) Blood gas will be analyzed by using ABL 800 flex blood gas analyzer (Radiometer Medical ApS, Denmark) with calibrations recommended by the manufacturer. No sedation will be given during preoperative period.