The purpose of this study is to find an optimal inspiratory pressure to provide adequate tidal volume and prevent gastric insufflation in pediatric patients.

The children under 5 years old are randomly assigned to muscle relaxation group and non-relaxation group. For muscle relaxation group, routine anesthesia induction is performed with muscle relaxant and mask ventilation is started by pressure-controlled mechanical ventilation. Gastric auscultation and abdominal ultrasonography are performed simultaneously during mask ventilation to detect inflow of air. Initial inspiratory airway pressure is 10 cmH2O and increased gradually by 2 cmH2O until gastric insufflation is detected by either of two methods. Tracheal intubation is done after detection of gas.

For non-relaxation group, mask ventilation is performed in a same manner, without muscle relaxant. After detection of gas by any of the two methods, rocuronium 0.6 mg/kg is administered and tracheal intubation is performed.

The purpose of this study is to find an optimal inspiratory pressure to provide adequate tidal volume and prevent gastric insufflation in pediatric patients.

The children under 5 years old are randomly assigned to muscle relaxation group and non-relaxation group. Stratum was constructed based on age and randomization scheme was performed separately within each stratum. Block randomization was done to ensure balance of the age groups.

For muscle relaxation group, routine anesthesia induction is performed with muscle relaxant and mask ventilation is started by pressure-controlled mechanical ventilation. Gastric auscultation and abdominal ultrasonography are performed simultaneously during mask ventilation to detect inflow of air. Initial inspiratory airway pressure is 10 cmH2O and increased gradually by 2 cmH2O until gastric insufflation is detected by either of two methods. Tracheal intubation is done after detection of gas.

For non-relaxation group, mask ventilation is performed in a same manner, without muscle relaxant. After detection of gas by any of the two methods, rocuronium 0.6 mg/kg is administered and tracheal intubation is performed.

Tidal volume and oxygen saturation are recorded during study period.

Inclusion Criteria:

• Pediatric patients scheduled for elective surgery under general anesthesia
• BMI < 30
• ASA class 1 or 2

Exclusion Criteria:

• with difficult airway
• preexisting pulmonary disease
• upper respiratory tract infection
• intestinal obstruction
• with risk of pulmonary aspiration
• history of stoke or moyamoya disease