Indications include Acute exacerbations of COPD (chronic obstructive pulmonary disease), eg, with PaCO2 > 45 mm Hg or pH < 7.30 Cardiogenic pulmonary edema with impending respiratory failure Obesity-hypoventilation syndrome Immunocompromised patients with impending respiratory failure in whom intubation poses a higher risk of infection Hypoxemic respiratory failure Patients with do-not-intubate advance directives who would otherwise require intubation The optimal patient is alert and cooperative and has minimal airway secretions.