Cough Assist (MI-E)

Cough Assist (Mechanical Insufflation–Exsufflation)

An effective cough is the airway's emergency clearance system. When the muscles that power coughing are too weak — as in many neuromuscular conditions — a cough assist machine (mechanical insufflation–exsufflation, or MI-E) does the work for them.

How it works

The device delivers a deep positive-pressure breath in (insufflation), then rapidly switches to a strong negative pressure to pull air out (exsufflation). This sudden reversal recreates the high expiratory flow of a natural cough and drags secretions up toward the mouth, where they can be cleared or suctioned. An optional oscillation can be added to help shear mucus from the airway wall.¹

Who it helps

MI-E is used where the cough is weak: motor neurone disease (MND/ALS), muscular dystrophy, spinal muscular atrophy, post-polio syndrome, high cervical spinal cord injury, and some patients with severe COPD and a feeble cough. The trigger to introduce it is a falling cough peak flow — commonly considered when it drops below about 270 L/min, and clearly inadequate below 160 L/min, particularly during a chest infection.²

Settings

Pressures are titrated to the individual, often in the range of ±30 to ±50 cmH₂O, to achieve an effective cough. Lower pressures are used where there is bulbar weakness or a tendency to upper-airway collapse; higher pressures where airways are narrow or secretions thick. MI-E can be delivered via a face mask, mouthpiece or tracheostomy, and is usually given in sets of several cycles followed by a rest.³

Cautions

MI-E is avoided or used with caution in bullous emphysema, recent pneumothorax or barotrauma, recent facial or oral surgery, and haemodynamic instability. As with all airway clearance, it is introduced and titrated by a trained clinician.

Evidence and guidance

MI-E improves cough effectiveness and is recommended for airway clearance in neuromuscular disease⁴ — for example, in the NICE guideline on motor neurone disease (NG42)⁵ — and is frequently paired with airway clearance techniques and, where needed, non-invasive ventilation.

References & evidence base

1. Chatwin M, Toussaint M, Gonçalves MR, et al. Airway clearance techniques in neuromuscular disorders: a state of the art review. Respir Med 2018;136:98–110.
2. Toussaint M, Chatwin M, Gonzales J, Berlowitz DJ. 228th ENMC International Workshop: airway clearance techniques in neuromuscular disorders. Neuromuscul Disord 2018;28(3):289–298.
3. Auger C, Hernando V, Galmiche H. Use of mechanical insufflation–exsufflation devices for airway clearance in subjects with neuromuscular disease. Respir Care 2017;62(2):236–245.
4. Morrow B, Zampoli M, van Aswegen H, Argent A. Mechanical insufflation–exsufflation for people with neuromuscular disorders. Cochrane Database Syst Rev 2013;(12):CD010044.
5. National Institute for Health and Care Excellence. Motor neurone disease: assessment and management (NG42). London: NICE, 2016.

References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.