Inclusion Criteria:  - A. Age 18-60  B. Patients with difficult airway assessed by two anesthesiologists according to the difficult airway score who needed to undergo nasal endotracheal intubation for oral and maxillofacial surgery in Peking University Stomatological Hospital.  C. BMI between 18 to 30 kg/m2 D.ASA Grade I to II E. NYHA grade I F. Patients requiring arterial hemodynamics monitoring and blood gas analysis due to surgical requirements G. Signed the informed consent  Exclusion Criteria:  - A.Respiratory diseases: respiratory failure, COPD, pulmonary fibrosis, asthma and other diseases. Patients with ventilatory dysfunction or airway obstruction.  B. NYHA cardiac function grade greater than I, or NYHA cardiac function grade I but with a history of coronary heart disease.  C. Conditions affecting the monitoring of peripheral oxygen saturation, such as poor peripheral circulation perfusion and application of vasoconstrictor, are present.  D. Indoor oxygen saturation below 92%. E. Patients who cannot tolerate rapid exchange ventilation with nasal humidification.  F. Patients with a history of easy nasal bleeding. G. Inability to understand or express pain scores. H. Menstrual period and lactation period of female patients. I. The patient has mental illness. J. Patients with severe intraoperative complications should be removed after surgery