This study is to investigate the efficiency and safety of fibreoptic bronchoscopy assisted intubation during noninvasive positive pressure ventilation in respiratory failure patients. Half of the participants will receive preoxygenation with noninvasive ventilator and fibreoptic bronchoscopy intubation during NIPPV. While the other half using usual preoxygenation(bag-mask ventilation ).

Respiratory failure is very common for critically ill patients, Main complication associated with intubation was desaturation. Usual preoxygenation( bag-mask ventilation) have been show that marginally effective in critically ill patients. As a result, there is a need to optimize the technique of preoxygenation to prolong the safe duration of apnea during the intubation procedure in critically ill patients. Noninvasive ventilation provides continuous positive airway pressure is effective in increasing the efficiency of gas exchange and in reducing the decrease in oxyhemoglobin saturation during fiberoptic bronchoscopy in hypoxemic patients.

Therefore, our aim was to study whether NIPPV is more effective at reducing desaturation than usual preoxygenation in hypoxemic, critically ill patients requiring intubation in ICU.

Inclusion Criteria:

• Acute respiratory failure requiring intubation,
• Age greater than or equal to 18 years

Exclusion Criteria:

1. Nasal polyps，Nasopharyngeal cancer，Nasal bleeding，Rhinitis，Sinusitis and so on Nasal disease
2. Basal skull fracture
3. Severe coagulopathy, blood platelet counts <50×10*9/L
4. Nose and facial deformities, trauma
5. Cardiac arrest
6. Pregnancy or puerpera