Three groups of patients are going to have minor surgery under general anesthesia with inhaled anesthetics and different ventilatory setting (Tidal volume: 8, 10, 12 ml/kg, respiratory rate: 10/min each). Group A (Sevoflurane) will use sevoflurane, group B (Desflurane) will use desflurane, and group C (Isoflurane) will use isoflurane. It will be observed differences among the groups for ventilatory effects on speed of induction.

Duration of this randomised controlled trial will be about 3 months. Estimated sample size will be 36 patients(12 in each group).

No premedicant will be given. The anesthetic workstation and a circulatory circuit will be prefilled with 1.0 MAC of inhaled anesthetic that will be selected randomly.

• Group A (n=12): Sevoflurane 2.0 vol%
• Group B (n=12): Desflurane 6.0 vol%
• Group C (n=12): Isoflurane 1.2 vol%

Each group has 3 subgroups according to the ventilatory setting that will also be randomly determined.

• Hypoventilation: tidal volume 8 ml/kg, respiratory rate 10 /min
• Normoventilation: tidal volume 10 ml/kg, respiratory rate 10 /min
• Hyperventilation: tidal volume 12 ml/kg, respiratory rate 10 /min

Patients will be preoxygenated with 100% oxygen (5 L/min) for 5 minutes under pulse oximeter, EKG, and noninvasive blood pressure monitoring. Bispectral index (BIS) monitor will be applied.

The induction of general anesthesia will start with propofol (2 mg/kg), rocuronium (0.8 mg/kg) and remifentanil infusion (0.1 mcg/kg/min). The size of a tracheal tube will be 7.5 mm (ID) for male, 7.0 mm (ID) for female. After intubation, anesthesia workstation will be connected to the tracheal tube. Ventilation will start, and that point will be time 0. During 720 seconds, inspiratory (PIgas) and end-tidal concentration of inhaled anesthetics (ETgas), end-tidal partial pressure of carbon dioxide, and BIS will be measured at time 0, 30, 60, 90, 120 ,150, 180, 240, 300, 360, 480, 600, and 720 seconds. Mean blood pressure and heart rate will also be recorded every 2 minutes. Fresh gas flow will be kept at 6 L/min with 100% oxygen.

The fraction of ETgas/PIgas will be analyzed with nonlinear mixed effects modeling.

Estimated sample size will be 36 patients (12 in each group, 4 in each ventilatory settings).

Inclusion Criteria:

• ASA PS I, II
• Age: 20-60 years male and female
• Elective schedule with minor surgery
• BMI < 30

Exclusion Criteria:

• Patients with pulmonary, cardiac, endocrinal, neuromuscular and neurological diseases or past history
• Upper airway anomaly or deformity
• ASA PS III or higher
• Pregnant women
• BMI >= 30