Duchenne Muscular Dystrophy: Pulmonary Management

1. Duchenne Muscular Dystrophy:Pulmonary Management

2. Introduction • Ambulant boys normally have few respiratory difficulties • Progressive loss of muscle strength leads to risk of respiratory complications over time: • Ineffective cough • Nocturnal hypoventilation • Sleep disordered breathing • Daytime respiratory failure • Staged progression: planned/proactive approach to respiratory care, aiming to prevent/manage these complications • Team to include a doctor and therapist skill in initiation/management of • Non-invasive ventilation and associated interfaces • Lung-volume recruitment techniques • Manual and mechanically assisted cough • Specific guidelines for respiratory care in DMD have also been published

3. Surveillance: Ambulatory • Minimal assessment to include pulmonary function • e.g. sitting Forced Vital Capacity (FVC) at least annually • Enables familiarity of patient with equipment • Allows care team to assess maximum respiratory function achieved

4. Surveillance: Non-ambulatory (clinic measurements) • Main need for pulmonary care is after loss of independent walking • [Figure 2, TLN p181] • Clinic measurements at least every 6 months • Sitting FVC • Peak cough flow • Oxyhaemoglobin saturation by pulse oximetry • Maximum inspiratory and expiratory pressures • Awake end-tidal CO2 level should be measured by capnography, if patient non-ambulatory and has any of • Suspected hypoventilation • FVC <50% prediceted • Current use of assisted ventilation

5. Surveillance: Non-ambulatory (home measurements) • [See Figure 3, TLN p181]

6. Family Awareness • Family should be aware of the symptoms of hypoventilation or a weak cough, which should be reported to medical caregivers • Prolonged, apparently minor upper respiratory infections (e.g. recovery from common colds is slow, with colds progressing to chest congestion and bronchitis often requiring antibiotic therapy) • More tiredness than is usual • Shortness of breath, difficulty catching breath or finishing sentences • Headaches all the time or in the morning • Sleepiness for no reason • Trouble sleeping, frequent waking from sleep, nightmares • Wakes trying to catch breath, or can feel heart pounding • Trouble paying attention • Family should keep copies of the latest breathing test results to show to attending doctors

7. Prevention of Problems • Immunisation with 23-valent pneumoccocal polysaccharide vaccine for patients ≥ 2 years • Annual immunisation with trivalent inactivated influenza vaccine for patients ≥ 6 months • Both can be given to patients on steroids, though immune response to vaccination may be diminished • Detailed information on immunisation indications, contraindications, and schedules can be obtained from national sources • It is essential to keep up to date with vaccination policies as they can change regularly according to new threats • If chest infection occurs, then in addition to manually and mechanically assisted cough, antibiotics should be prescribed early

8. Interventions • Specific interventions are dependent on the disease phase • Staged progression: • Volume recruitment/deep lung inflation techniques • Manual/mechanically assisted cough techniques • Nocturnal ventilation • Daytime ventilation • Tracheostomy

9. Step 1: Volume Recruitment & Deep Lung Inflation Techniques • By self-inflating manual ventilation bag, or mechanical insufflation/exsufflation • When FVC <40% predicted

10. Step 2: Manual and Mechanically Assisted Cough Techniques • Necessary when • Respiratory infection present and baseline peak cough flow < 270 L/minute • Baseline peak cough flow < 160 L/min or max expiratory pressure < 40cm water • Baseline FVC < 40% predicted or < 1.25 L in older teenagers/adults

11. Step 3: Nocturnal Ventilation • Indicated in patients who have any of • Signs/symptoms of hypoventilation (patients with FVC < 30% predicted are at especially high risk) • Baseline SpO2 <95% and/or blood or end-tidal Co2 >45 mm Hg while awake • An apnoea-hypopnoea index >10 per hour on polysomnography or four or more episodes of SpO2 <92% or drops in SpO2 of at least 4% per hour of sleep • Optimally, use of lung volume recruitment assisted cough techniques should always precede initiation of non-invasive ventilation

12. Step 4: Daytime Ventilation • In patients already using nocturnally assisted ventilation daytime ventilation is indicated for • Self-extension of nocturnal ventilation into waking hours • Abnormal deglutition due to dyspnoea, which is relieved by ventilator assistance • Inability to speak a full sentence without breathlessness and/or • Symptoms of hypoventilation with baseline SpO2 <95% and/or blood or end-tidal Co2 >45mm Hg while awake • Continuous non-invasive assisted ventilation (with mechanically assisted cough) can facilitate endotrachealextubation for patients who were intubated during acute illness or anaesthesia, followed by weaning to nocturnal non-invasive assisted ventilation if applicable

13. Step 5: Tracheostomy • Indications for tracheostomy include • Patient and clinician preference • Patient cannot successfully use non-invasive ventilation • Inability of local medical infrastructure to support non-invasive ventilation • 3 failures to achieve extubation during critical illness despite optimum use of non-invasive ventilation and mechanically assisted cough • The failure of non-invasive methods of cough assistance to prevent aspiration of secretions into the lung and drops in oxygen saturation below 95% or the patient’s baseline, necessitating frequent direct tracheal suctioning via tracheostomy

14. Surgery • Lung function should be checked before surgery • DMD patients should never be given inhaled anaesthesia or succinylcholine

15. CAUTION: Supplemental Oxygen • In later stages of DMD, supplemental oxygen therapy should be used with caution • Can apparently improve hypoxaemia while masking underlying cause (e.g. atelactasis or hypoventilation) • Might impair central respiratory drive, exacerbating hypercapnia • If patient has hypoxaemia due to hypoventilation, retained respiratory secretions and/or actelectasis, then manual and mechanically assisted cough and non-invasive ventilatory support are necessary • Substitution of these methods by oxygen therapy is dangerous

16. References & Resources • The Diagnosis and Management of Duchenne Muscular Dystrophy, Bushby K et al, Lancet Neurology 2010 9 (1) 77-93 & Lancet Neurology 2010 9 (2) 177-189 • Particularly references, p186-188 • The Diagnosis and Management of Duchenne Muscular Dystrophy: A Guide for Families • TREAT-NMD website: www.treat-nmd.eu • CARE-NMD website: www.care-nmd.eu