The purpose of this study is to compare the effect of frova and stylet on the success rate of tracheal intubation when using a video laryngoscope.

Inclusion Criteria:

• 1. adult patients aged over 19 years who are undergoing endotracheal intubation for elective surgery.
• 2. Patients who have one of the predictors of difficult intubation such as Mallampati classification 3 or 4, limited the movement of the neck, body mass index less than 35 kg/m2, a distance from the tip of the chin to the thyroid cartilage of less than 6.5 cm, a interincisor distance less than 3.5 cm, inability to protrude of lower incisors over the upper incisors, or a diagnosis of obstructive sleep apnea.

Exclusion Criteria:

• 1. Patients receiving emergency surgery
• 2. Pregnant women
• 3. Patients scheduled for oral surgery such as tonsillectomy, vocal cord surgery
• 4. Patients who have a history of ankylosing spondylitis or have a large tumor of 4 cm or more on the tongue and need an awake intubation
• 5. Patients who are at risk of vomiting due to not fasting time