Respiratory issues are a leading cause of severe health problems in those with the earlier onset form of SMA. The main issues are:
- Due to a weak cough, it may not be possible to clear mucus from the lungs, which may lead to chest infections
- Muscle weakness may mean someone is not able to take a big enough breath to exchange carbon dioxide for oxygen (hypoventilation) which can cause low oxygen levels in the blood (oxygen desaturation). Hypoventilation and low oxygen first occur during sleep when the muscles for breathing are most relaxed and gradually the difficulty exchanging carbon dioxide for oxygen extends to when the person is awake also.
As breathing problems are common and more likely to be severe, breathing management should be started early and take place regularly, even if there are no symptoms (this is called ‘proactive’ treatment). A specialist respiratory doctor should be involved as soon as possible after diagnosis.
All infants with SMA who are unable to sit should be seen at least once every three months in clinic when they should have a physical examination. If they are not breathing effectively (hypoventilating), carbon dioxide can build up. It is important therefore that they have their carbon dioxide levels checked at the end of a breath out. They should also have regular sleep studies so that their overnight breathing can be tested for hypoventilation and low oxygen saturation. These tests will help joint decision making around whether to begin using a machine to help with breathing (non-invasive Ventilation or NIV – see over) during sleep.
Colds can lead to chest infections which are common and are made worse when someone is unable to cough up mucus and other secretions well enough. Chest physiotherapy combined with machines that make it easier to cough (e.g. Cough Assist®, Vital Cough®) should be available to all non-sitters. Anyone with an ineffective cough and swallow should also be provided with a machine to suck out (suction) oral secretions. Parents and carers should be given training and support so that they can follow through with medical advice and use machines effectively.
Non-invasive ventilation (NIV) is the recommended way to improve low oxygen saturations and high carbon dioxide levels during sleep (hypoventilation). NIV is also called ‘bi-level positive airway pressure’ (BiPAP) which is delivered by a machine which gives two levels of air pressure via an individually fitted mask for the nose or the nose and mouth. A higher pressure is given while inhaling to give a bigger breath than the person can take on their own during sleep. The machine pressure then drops to a lower pressure while exhaling. NIV is designed to synchronise with normal breathing. The settings should be set to give a big enough breath so that oxygen is not needed.
Other breathing supports such as ‘continuous positive airway pressure’ (CPAP) are not recommended because they do not facilitate carbon dioxide exchange for oxygen.
Following a detailed discussion between clinicians and the family, invasive ventilation is an option that may be considered for those for whom NIV does not work. This is surgery that creates an opening in the windpipe that allows breathing through a tube called a tracheostomy tube rather than through the nose and mouth. This is generally long-term. The options for breathing support should be discussed with the medical team at a time of good health. Any decision should focus on what is best for the person with SMA.
Medications used to open the airways (nebulised bronchodilators) should be available if there is high suspicion of asthma or if a clear improvement in breathing is seen after it has been given. Medications to reduce salivary secretions (such as glycopyrrolate) should be used carefully and, with medical guidance, the dose changed as needed. This is to avoid the possibility of the secretions drying out too much, which makes them harder to remove. Long-term daily use of medications to break down secretions (Pulmozyme® or hyptertonic saline) is not recommended. Antibiotic use during illness should be discussed on an individual basis with the medical team.
In addition to the annual influenza vaccine and pneumococcal vaccinations and other recommended routine vaccinations, it is recommended that infants up to the age of 2 years are vaccinated with Palivizumab which acts against a common virus – respiratory syncytial virus (RSV) that can cause breathing problems. As discussed in the Section, Nutrition, Growth and Bone Health, there can be other factors which exacerbate breathing problems and should also be treated, such as reflux.