In immunocompromised patients, Acute Respiratory Failure (ARF) is associated with a high case-fatality, particularly when invasive Mechanical Ventilation (MV) is required. In the most hypoxemic patients, oxygen administration through High Flow Nasal Cannula (HFNC) has been reported as an alternative to the venturi mask. The aim of this study is to compare HFNC and venturi mask on early respiratory deterioration and patient's comfort in that setting. The investigators planned a prospective randomized study in 4 Intensive Care Units (ICUs). As respiratory deterioration occurs early after ICU admission, patients are randomized to receive two hours of oxygen therapy either through HFNC or venturi mask. The primary endpoint is defined as the need for invasive or noninvasive MV in the 2-hour period. Secondary endpoints include comfort, dyspnea and thirst.

Inclusion Criteria:

• Age over 18 years.
• Admission to ICU for ARF. ARF was defined with the need of oxygen over 6l/min to maintain SpO2 over 95% or symptom of respiratory distress (intercostal recession or tachypnea >30/min or dyspnea at rest).
• Immunosuppression. Immunosuppressed conditions were solid tumor, hematological malignancy, steroid treatment or other immunosuppressive treatment, or HIV infection.

Exclusion Criteria:

• Hypercapnia (above 47 mmHg)
• Chronic respiratory failure
• Previous mechanical ventilation in the days before admission
• Need of immediate NIV or intubation
• Refusal
• Pregnancy