nasal mask for Mechanical Ventilation Complication

Recently, the investigators demonstrated that nasal route ventilation is superior to the nasal-oral combined ventilation in the absence of jaw thrust and chin up maneuvers. The investigators hypothesize nasal mask ventilation may reduce the incidence of difficult mask ventilation during the induction of general anesthesia by: 1) producing a better seal than full face mask, and 2)establishing a greater airway patency and more effectively ventilate than full face mask ventilation. The investigators intend to test this hypothesis on adult patients during the induction of general anesthesia in the absence of muscle relaxation.