Patients are admitted to the preoperative unit 15 minutes before the procedure. After intravenous access is established by a 20 gauge cannula, all patients are monitored with non-invasive blood pressure (NIBP), electrocardiogram (ECG) and peripheral oxygen saturation (SpO2) (Drager-Primus Anesthesia Device Monitor, Drager Medical Systems, Inc 16 Electronics Avenue, Denver, MA 01923 USA) in the operating room before the beginning of procedure. Patients are randomly allocated into two groups in a 1:1 ratio by a computer-generated list. Allocation is provided with sealed envelopes containing group named paper.