Feasibility of Preoxygenation by Supraglottic Jet Ventilation Before Endotracheal Intubation

The study assumed that supraglottic jet ventilation is an alternative solution as a safe way to do the preoxygenation before endotracheal intubation by contrasting it with mask pressurized ventilation. The investigators also expected that supraglottic jet ventilation won't increase the occurrence of esophageal reflux. The investigators randomly divided the patients into 2 groups:Group C and Group S.Patients in Group C will be preoxygenation with mask pressurized ventilation while patients in Group S with supraglottic jet ventilation by Wei NASAL JET（WNJ）.The tracheal intubation will be done after the 3 minutes preoxygenation. The investigators will measure the PaCO2 before and after preoxygenation, and the investigators will take the stomach-ultrasonography to find if there are too much gas in the gastro. If pulse oximetry is lower than 95% during the preoxygenation, the investigators will adjust the position of the Wei NASAL JET（WNJ) or use the change the way that the investigators hold the mask or change the pressure of ventilation on the basis of the group.