Noninvasive ventilation is increasingly used method of respiratory management in both the emergency room and critical care. Noninvasive ventilation delivers mechanically assisted breaths without the placement of an artificial airway and has become an important mechanism of ventilator support inside and outside the intensive care unit.

Noninvasive ventilation is further subdivided into negative pressure ventilation which is the iron lung, first used in 1928 and the Hayek oscillator, is a more recently designed to provide negative pressure during inspiration and positive pressure during expiration. Noninvasive positive pressure ventilation can be used as continuous positive airway pressure or bi-level positive airway pressure.

Inclusion Criteria:

• obstructive sleep apnea syndrome
• acute exacerbation Chronic obstructive pulmonary disease
• pneumonia
• interstitial lung diseases

Exclusion Criteria:

• Patients refuse Non invasive ventilation
• Patients with absolute indication for Mechanical ventilator (in respiratory arrest or unstable cardiorespiratory status, trauma or burns involving the face, or gastric surgery, reduced consciousness, Pneumothorax
• Patients with contraindication to Non invasive ventilation

All patients who admitted to the Respiratory intensive care unit and the attending team conducted him to Non invasive ventilation