Spontaneous respirations
Gag reflex
Significant facial trauma
Restricted mouth opening
Obstruction
Distorted<unk> 
Stiff lungs (chronic pulmonary disease, obesity) or neck (C-spine collar, limited neck extension)
Supraglottic airway
Oropharyngeal airway
Nasal foreign body
Pterygium
Ear foreign body
Subglottic stenosis
Epiglottitis
Ranula