In a previous study, NCT03147469, the investigators found that the vocal cords were more easily visualized by fiberoptic bronchoscopy with neck extension positioning. On the basis of this finding, the investigators are going to conduct a randomized controlled trial to evaluate the effect of neck extension on the success rate of blind intubation through laryngeal mask.

Participants undergoing general anesthesia will be randomly assigned to group E (with neck extension) or group C (with neutral position). Ambu® AuraGain™ laryngeal mask will be placed first, and then, a lubricated endotracheal tube will be gently intubated through the laryngeal mask. The participants will be mechanically ventilated with an endotracheal tube if blind intubation succeed. Blind intubation will be performed with a maximum of two attempts. If all attempts failed, the laryngeal mask will be removed and the tube will be intubated using a direct laryngoscopy.

The primary outcome of this study is the success rate of blind intubation within a first attempt. Secondary outcomes included overall success rate of blind intubation within a maximum of two attempts, time for blind intubation, the incidence of postoperative hoarseness, cough, and sore throat, and any obvious complications related to airway management such as bleeding, airway trauma, dental fracture, aspiration, or bronchospasm.

Inclusion Criteria:

• Adult patients undergoing general anesthesia with endotracheal intubation

Exclusion Criteria:

• Emergency operation
• History of esophageal, oropharyngeal, or laryngeal disease
• History of cervical spine surgery
• Insufficient NPO time
• Loosening teeth
• Mouth opening less than 2cm