The main purpose of the present study is to verify whether, as compared with conventional weaning, early weaning with high-flow nasal cannula oxygenation or noninvasive positive pressure ventilation may more effective in shortening the duration of invasive ventilation, hence reducing the rates of complications and mortality in patients with acute hypoxemic respiratory failure.

Inclusion Criteria:

1. Orotracheal intubation；
2. PaO2 <60mmHg（venturi mask，FiO2=0.5），and PaCO2 ≤45mmHg；
3. Meeting criteria for weaning readiness；
4. Spontaneous breathing trial failure.

Exclusion Criteria:

1. Age<18；
2. Duration of invasive ventilation <48h；
3. Tracheotomy；
4. Percentage of cuff leak volume in tidal volume<15.5%；
5. Unable to spontaneously clear secretions from their airway；
6. Recent oral，nasal，facial or cranial trauma or surgery；
7. Recent gastric or esophageal surgery；
8. Active upper gastro-intestinal bleeding；
9. Severe abdominal distension；
10. Lack of co-operation；
11. Chronic respiratory disease such as chronic obstructive pulmonary disease, asthma, interstitial lung disease and neuromuscular disease.