Obtunded patients
Uncooperative patients
Vomiting or inability to protect the airway (aspiration risk)
Facial trauma or burns
Facial, esophageal, or gastric surgery
Poor mask fit
Noninvasive ventilation
Mechanical ventilation 
Bag valve mask ventilation
Extracorporeal membrane oxygenation
High frequency oscillation ventilation
Lung recruitment maneuver
Needle cricothyrotomy
Surgical cricothyrotomy