A Comparison of Three Methods for Improving Expiratory Cough Flow and Lung Volume in Children With Neuromuscular Diseases

Current options for respiratory care in children with NMDs include numerous devices and treatments have been proposed for improving secretion clearance and lung function in very weak patients. Unfortunately treatment decisions are still based on little more than personal opinion. In particular, there are almost no carefully conducted studies on the best forms of respiratory therapy in children with NMDs. Commonly used treatment options are best listed under the following headings:

1. Chest physiotherapy. This broad term covers a range of therapies that includes postural drainage, manual percussion and chest vibrations. These treatments are often preceded by inhaled medications intended to mobilize secretions (humidification, hypertonic saline, Dornase alpha). Chest physiotherapy has been studied extensively in cystic fibrosis(13) but there are no prospective studies of its use in children with NMDs. The lack of any evidence of clear long-term benefit combined with the need for a trained assistant, has limited the application of chest therapy to in-patient treatment of acute exacerbations.
2. Breath stacking. Inspiratory lung volume can be increased by 'stacking' repeated inhalations. This allows a greater cough flow with improved secretion clearance. The simplest method is to use a bag, face mask and a one-way valve. Inspiratory volume can also be augmented using mechanical or non-invasive ventilators although care must be taken to avoid over-inflation and barotrauma(14). The cough phase after insufflation is often augmented by external compression of chest or abdomen (manually assisted cough). While there is evidence that breath stacking, with or without manually assisted coughing, can increase lung volume and peak cough flows(15), there are no prospective studies to study long term effects.
3. Mechanical insufflation-exsufflation. Devices in this group inflate the lung with an inspiratory positive pressure phase followed rapidly by a negative pressure exhalation phase(16). They are widely used and recommended but prospective research support is lacking. As with breath stacking, there is evidence of short term improvement in lung volume and cough flows(17) following MI-E treatment. There are also retrospective reviews to suggest that the technique is effective and well tolerated in children(18). However, there are no prospective controlled studies of MI-E either in adults or children.
4. Airway oscillation. Various devices have been developed to superimpose an oscillatory wave flow over normal breathing. The oscillating pressure wave is intended to help mobilise secretions and expand atelectatic areas of the lung. This can be achieved by an external vibrating vest or delivered directly to the airway through a face mask. Prospective study of the vibrating vest showed that it had no benefit(19). However, research exists that oscillation via mask is beneficial both in short(20) and longer term studies(21).

The newcomer to this important topic would be forgiven for finding the lack of research evidence difficult to believe. Children with NMDs are very complex management problems and they consume a lot of hospital resources. The mechanical devices paid for by insurance companies, or governments, cost many thousands of dollars each - surely all this money and time should be based on some form of evidence? Unfortunately this is not the case. Two large reviews of the management of NMDs by both the British(2) and the American(22) thoracic societies emphasized this lack of evidence. Both concluded that the major requirement in the management of these children is research.

The principal question in the management of children with NMDs is whether early introduction of effective respiratory therapy will slow the decline in lung function and help to keep these children out of hospital. That requires long term studies of the use of therapies known to be effective, at least in the short term. Such evidence - even short term evidence of efficacy, is not available. Our study is not a case of comparing a new treatment to an established therapy, it is a case of assessing current widely used treatments in order to determine whether they have any measurable benefits. The best of the three techniques studied will then form the basis for a long term early intervention study.

OBJECTIVES.