Comparison of Ultrasound-guided Location of Laryngeal Mask With Air Leakage Test

Inclusion Criteria: * patients selected for this study must meet all of the following criterion: 1. Age is between 17 to 65 years old; 2. ASA (Amecican Society of Anesthesiology ) scores I-II; 3. Actual weight is between 30 to 100 kilogram; 4. Patients undergo selective supine operations under general anesthesia (laryngeal mask); 5. Patients agree to participate in our study and sign Informed Consent Form Exclusion Criteria: * Patients cannot participate in this study if they have any of the following conditions: 1. Airway stenosis, history of airway masses etc, whicn may cause obstruction to ventilation; 2. Swelling of the neck caused by huge mass in the neck and history of neck surgery etc, which doesn't contribute to ultrasound observation; 3. Stomach fullness, intestinal obstruction, gastroesophageal reflux disease etc, which may cause reflux aspiration.