Non-compliant patients (i.e. severe anxiety)
Impossible NT tube positioning caused by anatomic abnormalities (i.e. turbinate hypertrophy, nasal polyps, narrow nasal cavity).
Hyperventilation is not allowed because of the small Inner Diameter of NT tube, even if it is adequate for spontaneous breathing at rest (it could be necessary to sedate the patient and apply PSV).
Need for nasogastric tube because of the impossible oral feeding (the presence of NT tube causes incomplete closure of the glottis during swallowing).
Dangerous accidental dislodgment (i.e. in case of hypersecretion with severe cough). It causes a rapid re-obstruction of the glottis with new ARF.
Table 1: Limitations and shortcomings of PSE technique.