Initial Ventilation Strategy for Adult Immunocompromised Patients With Acute Respiratory Failure

Inclusion Criteria: * Adult (18 years old ≤ age ≤ 80 years old) immunocompromised patients admitted to hospital with moderate to severe ARF diagnosed within the last 72 hours, which meets the indications for ventilatory support. * Patients are considered as moderate to severe ARF when the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) is between 85 and 170 while the patient is breathing oxygen through a Venturi mask, or clinically diagnosed as the following: 1. 30 mmHg \< PaO2 \< 50 mmHg on room air; 2. Clinical evidence of respiratory distress (intercostal recession, polypnea \>35/min or dyspnea at rest). * Patients are considered as immunocompromised when clinically diagnosed as at least one of the following: 1. HIV infection; 2. Hematologic malignancy or solid tumor under chemotherapy; 3. Solid organ or stem cell transplant; 4. Long-term (\>30 days) or high dose steroids (\>1 mg/kg/d prednisone equivalent) usage and/or any other immunosuppressive drugs; 5. Neutropenia (defined as a neutrocyte count of \< 0.50×109/L) showing for at least 48 hours Exclusion Criteria: * Age\<18 or \>80 years old; * Partial pressure of arterial carbon dioxide (PaCO2) \> 50 mmHg or arterial pH \< 7.20; * PaO2/FiO2 \>170 or PaO2/FiO2\< 85; * Patients have been treated with NIV or IMV within 30 days. * NIV is contraindicated or IMV is definitely indicated, including PaO2/FiO2\< 85, respiratory arrest, hemodynamic instability, inability to fit the face mask, pneumothorax, vomiting, development of airway bleeding, inability to protect the airway, or copious respiratory secretions; * Comorbided with other severe diseases, including New York Heart Association functional class ≥ II, valvular heart disease, dilated cardiomyopathy, cardiogenic pulmonary edema, implanted cardiac pacemaker, unstable angina, myocardial infarction, or cardiac surgery within the previous 3 months; systolic arterial pressure \<90 mmHg after optimal fluid therapy; history of chronic obstructive pulmonary disease (COPD) or asthma; impaired consciousness (Glasgow Coma Scale score \<13); postoperative acute respiratory failure; pregnancy or breastfeeding; * Lack of consent, do-not-intubate decision, and any other situations where obvious bias are expected