This study will be conducted in Ain Shams University Hospital in the general intensive care unit after ethical committee approval number (FMASU R 9/2020) .It is a prospective randomized controlled study. Eligible patients will be randomized by computer system to one of two groups either High Flow Nasal Oxygen (HFNO) group or Non Invasive Ventilation (NIV) group. Inclusion criteria includes admitted immunocompromised patients to our general 34 beds ICU with acute hypoxemic respiratory failure (ARF).

ARF is characterized by respiratory rate more than 25/min, PaO2/FiO2 less than 300 under standard O2 10 L/min, or findings of persistent pulmonary infiltrates in radiographs.

Immunocompromised patients have one or more of the following criteria hematological malignancy (either active or remitting in the last 5 years), bone marrow transplantation (in the last 5 years), severe leucopenia less than 1000 white blood cells in cubic millimeter, solid organ transplantation, steroid therapy more than 0.5 mg/kg/day for at least 3 weeks, or cytotoxic therapy for non malignant disease.

Patients included in the study will be randomized after admission to ICU to one of two groups, HFNC group or NIV group. Patients enrolled in HFNC group will receive immediate connection to HFNC with a flow of 60L/min, and FIO2 adjusted to have SpO2 of 92% or more, through a heated humidifier and a oxygen blender of the same machine. In case of patient intolerance to high flow, flow will be diminished to the highest tolerated by the patient. Patients will be encouraged to have their mouth closed during HFNC to augment positive end expiratory pressure (PEEP) created by high flow.NIV group, patients will be connected to ICU ventilator on NIV mode for at least 4 hours, through a NIV continuous positive airway pressure (CPAP)mask with ventilator settings; pressure support (PS) level of 8 cmH2O and PEEP level of 5 cmH2O,which can be increased to 10 cmH2O

Inclusion Criteria:

• . Inclusion criteria includes admitted immunocompromised patient to ICU with acute hypoxemic respiratory failure (ARF).
• Hematological malignancies.
• Post bone marrow transplantation

Exclusion Criteria:

• Need of emergency intubation.

• patient with deterioration of conscious level with hypoxemia with FiO2 less than 90% in spite of maximum O2 support.

  • hemodynamic instability with need of vasoconstrictor support.

Not yet decided that patient participating will accept for share their information or no.