Comparing the effects of ' Cricoid pressure' or 'Paralaryngeal pressure' during endotracheal intubation procedure.

Applying Cricoid pressure is widely used procedure to prevent gastric contents regurgitation during endotracheal intubation. To find out effectiveness external pressure is applied, the investigators will evaluate the relative position of esophagus and trachea. And also comparing the effects of Cricoid pressure and Paralaryngeal pressure during whole tracheal intubation procedures.

1. Confirm the relative positions between esophagus and trachea in awake patients by using ultrasonography.
2. Compare the effect of 'Cricoid pressure' and 'Paralaryngeal pressure' to esophageal opening during tracheal intubation procedure as below points.

1) Awake states. (Before sedation) 2) Anesthetized states. (After muscle relaxation) 3) During direct intubation procedure.

Inclusion Criteria:

• Who would be scheduled any surgery under general anesthesia and agree with the purpose of the study

Exclusion Criteria:

• Diseases or anatomical abnormalities in the neck, larynx, pharynx or esophagus,
• Aspiration tendency
• Known or predicted difficult airway.

Who has any surgery under general anesthesia and agree with the purpose of the study