Mechanically assisted cough in motor neurone disease

Motor Neurone Disease (MND) is a disabling and inevitably fatal disease, usually with a life expectancy of 2-3 years from symptom onset. It is characterised by progressive wasting and weakness in bulbar, limb and respiratory muscles. There is no cure and treatment is mainly symptomatic. Neuromuscular respiratory failure, with or without a chest infection, is the commonest cause of death in MND patients. It has been shown that supporting respiratory function with non-invasive ventilation, improves survival and quality of life despite progression of the disease. The patients with respiratory muscle weakness may also have a weak cough and significant difficulty in clearing their airways of respiratory secretions. This causes much discomfort, predisposes to chest infections and adversely affects quality of life. Due to lack of evidence in this area, there is no clear consensus or guideline about how best to help such patients. This work aimed to establish the role of cough augmentation techniques in MND.
A total of 40 eligible patients with MND were randomised to the breath-stacking technique (n=21) or Mechanical Insufflator-Exsufflator MI-E (n=19) and followed-up at 3 monthly intervals for at least 12 months or until death. All patients were diagnosed with respiratory failure and offered non-invasive ventilation (NIV). The primary outcome measure was the number of days with symptoms of chest infection, treated with antibiotics, in the community or in hospital. Survival and quality of life benefit, assessed by short form 36 mental component summary (MCS) and sleep apnoea quality of life index symptoms domain (sym), were the secondary outcome measures.
There were 13 episodes of chest infection in the breath-stacking group and 19 episodes in MI-E group (p=0.87), requiring 90 and 95 days of antibiotics respectively (p=0.85). There were 6 episodes of hospitalisation in each group (p=0.87). The mean duration of symptoms per chest infection was 6.9 days in the breath-stacking group and 3.9 days in MI-E group (p=0.16). The chance of hospitalization, in the event of a chest infection was 0.46 in the breath-stacking group and 0.31 in MI-E group (p=0.47). Median survival in the breath-stacking group was 535 days and 266 days in the MI-E group. The MCS score was maintained above 75% of baseline for a median of 329 days in the breath-stacking group and 205 days in MI-E group (p=0.41). A non-significant improvement in quality of life, compared to baseline was observed in both interventional groups.
In MND patients with respiratory failure, cough augmentation is likely to help maintain quality of life in the presence of the distressing symptom of weakened ability to cough. This study was not powered to assess the potential impact on life expectancy. There was no significant difference in terms of pulmonary morbidity between the two groups. A trend towards fewer chest infections was observed in the breath-stacking group, and a trend for reduced duration of antibiotic use and decreased chance of hospitalization in the event of a chest infection was observed in the MI-E group, though these changes did not reach statistical significance. These results are insufficient to draw firm conclusions, but support routine domiciliary use of a suitable cough augmentation technique in patients with ALS requiring respiratory support. The breath-stacking technique may be prescribed for domiciliary use with the onset of respiratory failure. MI-E may be useful in the event of a chest infection when it has the potential to reduce the duration of antibiotic use and chance of hospitalisation or when breath-stacking is no longer sufficient to maintain patient comfort. The results of this trial provide data useful for the power calculations required for a larger-scale multi-centre randomised trial.