Airway clearance techniques have the potential to improve mucociliary clearance during NPPV therapy or immediately after extubation by reducing mucus plugging and enhancing the removal of secretions. It is important to distinguish between secretion mobilization techniques (clearance of peripheral airways), including postural drainage, chest wall vibration, positive expiratory pressure therapy, high-frequency chest compression, and high-frequency chest wall oscillation, and cough augmentation techniques (clearance of central and upper airways), including manually and mechanically assisted coughing. Among cough augmentation aids, mechanically assisted coughing (MAC) can be delivered by a device consisting of a two-stage axial compressor that provides positive pressure to the airway, then rapidly shifts to negative pressure, thereby generating a forced expiration. It is usually applied via a facemask. It commonly produces a decrease in pressure by approximately 80 cm H₂O in 0.2 s; the insufflation and exsufflation pressure and time are independently adjustable. The device can deliver maximum positive and negative pressures of about 60 cm H₂O.

The use of mechanical insufflation-exsufflation (MI-E) devices for MAC has been proposed as a complement to NPPV in patients with NMD with an inability to generate an effective cough who develop an intercurrent respiratory tract infection, with the goal to expel secretions, allay secretion-associated dyspnea, and increase oxyhemoglobin saturation and pulmonary parameters.

Ability to effectively cough can be evaluated by measuring peak cough flow (PCF), the maximum airflow generated by the patient during cough, which is dependent on lung volume, airway caliber, compliance of the respiratory system, and inspiratory and expiratory muscle strength. Normal individuals may produce a PCF as great as 720 l/min (occasionally higher in healthy individuals). The minimum effective PCF was inferred from patients who were being weaned from mechanical ventilation, showing that successful extubation requires at least 160 l/min (2.7 l/s). Bach and Saporito [1], in fact, conducted a mixed-population study in 49 patients that found that those with PCF below 160 l/min, irrespective of the ability to breathe, failed extubation or decannulation. On this basis, indications for the use of MI-E in the acute setting have been considered as the following: