Organised secretions can build up in a tracheal tube. This increases airway resistance so during a spontaneous breathing trial in a patient being considered for extubation the patient may have increased work of breathing and unfairly fail the trial, delaying extubation.
How can you spot it? Increased airways resistance can increase peak airway pressure. However inspiratory plateau pressure will not be affected (obtained by performing an inspiratory hold). Identifying a big difference between peak and plateau pressures should prompt a search for increased airway resistance, which includes a narrowed tracheal tube lumen. The amount of accumulated secretion is not necessarily related to the duration of intubation.
Increases in endotracheal tube resistance are unpredictable relative to duration of intubation
Chest 2009; 136:1006-1013