To assess the safety and efficacy of noninvasive positive pressure ventilation for patients with intro-pulmonary pulmonary acute lung injury and compare this with high-concentration oxygen therapy.

Inclusion Criteria:

1. acute onset;
2. a clinical presentation of respiratory distress;
3. arterial oxygen tension/inspired oxygen fraction (PaO2/FIO2) < 300 mmHg but > 200 mmHg while breathing oxygen delivered by a conventional Venturi device at a maximum concentration (50%);
4. presence of bilateral pulmonary infiltrates on posteroanterior chest radiograph;
5. no evidence of left heart failure as assessed by echocardiography and/or a pulmonary artery wedge pressure of <18 mm Hg.
6. the cause of ALI is consider to be intro-pulmonary.

Exclusion Criteria:

1. age <18 yrs;
2. Glasgow Coma Scale < 11;
3. airway or facial injury;
4. pneumothorax or pneumomediastinum;
5. unable to spontaneously clear secretions from the airways;
6. cardiogenic shock or severe hemodynamic instability (systolic blood pressure <90 mmHg associated with decreased urinary output (<20 mL.h-1) despite fluid repletion and use of vasoactive agents) of other causes;
7. severe ventricular arrhythmia or unstable myocardial ischemia;
8. severe organ dysfunction (Sequential Organ Failure Assessment score > 3);
9. end-stage patients who were expected to survive < 6 months;
10. severe abdominal distension;
11. refusal to receive NPPV;
12. the cause of ALI is consider to be extrapulmonary;
13. unable to cooperate with NPPV application;
14. active upper gastrointestinal bleeding.