Inclusion Criteria:  age above 20 years Anesthesiologists I-II who required orotracheal intubation for elective surgery  Exclusion Criteria:  nasotracheal intubation awake tracheal intubation emergency surgery required rapid-sequence intubation (RSI) those in pregnancy with possible difficult intubation(with oropharyngeal pathology, limited neck mobility, previous head and neck surgical history) anticipated difficult intubation assessed by preoperative Airway Difficult Score (≥ 7) with allergy history of common anesthetics agents any underlying comorbidities which refrain them from receiving common anesthetic agents