Video laryngoscope has become recommended option during difficult intubation. Guidelines of ASA at 2013 had suggested using video laryngoscope after failure intubation of direct laryngoscope. Varieties of video laryngoscope had been invented with different curves. We call the one which has the same curve of Macintosh laryngoscope as conventional video laryngoscope in this study. Mostly, the way of using conventional video laryngoscope is suggested as Macintosh method. However, with the front positioning camera, Miller method can theoretically improve the glottic opening. We intend to discuss whether using Miller approach with conventional video laryngoscope can improve glottic opening or not.

Video scope can provide better glottic opening by increase the tilting angle of the tip, and the position of camera can provide larger vision angle. However, while the angle increases, the endotracheal tube must fallow the curve, which may require learning curve of the operator. In Glidescope as example, increase the tilting angle can help with glottic exposure, however the steep curve will simultaneously increase the difficulty of inserting the tube or using Magill forceps, especially while intubating double lumen or nasal endotracheal tube. Conventional video laryngoscope in this study indicates the video laryngoscope blade which has the same curve as Macintosh laryngoscope. It mainly improves the glottic view by front positioning camera.

Anesthesiologist usually place the tip of the blade at vallecula to expose the glottic which is the conventional ways of using Macintosh blade which we name it as Macintosh method. Placing the tip below the epiglottis and lift it up directly is the way of using Miller blade. Theoretically, the Miller method with conventional video laryngoscope may improve the scale of glottic exposure measured with Cormack-Lehane grade. This is a one-group pretest-posttest study to compare the Cormack-Lehane grade with two different methods in the same patient. This study tends to discuss whether this combination can improve the glottic exposure and preserve the advantage of direct laryngoscope.

Inclusion Criteria:

1. Aged>20
2. Scheduled to received operation that required general anesthesia with endotracheal tube [3] ASA I, II

Exclusion Criteria:

1. Emergent surgery
2. pregnant
3. Limited mouth opening
4. Poor dental condition
5. Airway obstruction (oral tumor, hypopharyngeal cancer….etc)
6. Deep neck infection
7. Allergic to any anesthetic

We had no experience of making IPD. If it's helpful to other researcher, then we'll try figure out how to do it.