The cricothyroid membrane is the most common position that the invasive airway secure is performed, but it is not easy to identify the cricothyroid membrane by tactile perception. Although it is recommended to use the laryngeal handshake method for identifying the cricothyroid membrane in difficult airway society 2015 guidelines for management of unanticipated difficult intubation in adults, there is only suggestion without clinical data about how much the laryngeal handshake method improves the accuracy of identification of the cricothyroid membrane So we made the hypothesis that the cricothyroid membrane is identified more correctly when the laryngeal handshake method is used than when that method is not used. And we try to find out whether there is actual difference about identification of the cricothyroid membrane between using the laryngeal handshake method and not using that method. By identifying the difference between them, we are going to support the recommendation of guidelines and make the evidence for educating the doctors who have any possibility to perform the criocthyroidotomy to use the laryngeal handshake method skillfully in the 'cannot intubate, cannot oxygenate' situation.

Inclusion Criteria:

• patients who underwent nose or ear surgery in Seoul National University Hospital and Seoul Metropolitan Government Seoul National University Boramae Medical Center

Exclusion Criteria:

• those whose ASA class was over 3, those who rejected to participate study or had impaired capacity to agree, those who was going to undergo neck surgery, those who had anatomical anomaly or skin lesion at neck, and those who were pregnant were excluded.