One-handed E-C clamp mask holding technique, two-handed mask ventilation with jaw thrust, and two-handed mask ventilation with triple airway maneuver are three common airway management maneuvers. Sniffing position may improve ventilation between these three maneuvers. The investigators hypothesize that ventilation efficiency may be different between these three maneuvers whether the patient is in sniffing position or neutral position. The investigators would like to quantify this effect by measuring the expired tidal volume, airway pressure, EtCO2 slope and hemodynamic change between these three maneuvers during anesthesia induction.

Mask ventilation is considered a important skill for airway management during general anesthesia induction and for apneic unconscious patients. One-handed E-C clamp mask holding technique, two-handed mask ventilation with jaw thrust, and two-handed mask ventilation with triple airway maneuver are three common airway management maneuvers. However, the efficiency of ventilation between these three maneuvers has to be clarified. Besides, whether sniffing position or neutral position may improve ventilation between these three maneuvers is to be determined. The investigators will collect airway parameters of the patients receiving general anesthesia and measure the expired tidal volume, airway pressure, EtCO2 slope and hemodynamic change between these three maneuvers during anesthesia induction.

Inclusion Criteria:

• adult patients(ASA I-III) scheduled for elective surgery requiring general anesthesia with endotracheal intubation.

Exclusion Criteria:

• pneumothorax
• SpO2<96%(without additional oxygen supply)
• vocal cord palsy
• congenital airway abnormality
• facial trauma or deformity
• acute upper airway disease
• inadequate fasting time
• neck or potential cervical spine disease
• temporal-mandible joint abnormality
• head and neck tumor
• status post radiotherapy
• pregnancy
• long term sedative or opioid drug use
• patient refuse