Neuromuscular respiratory failure and airway clearance — branching viva

Opening — framing the problem

The examiner begins: a 13-year-old boy with Duchenne muscular dystrophy, now a full-time wheelchair user, has morning headaches, daytime sleepiness and three chest infections this winter with a weak cough. How do you frame his respiratory problem? [1] [2]

I would frame it as the two-part respiratory failure of neuromuscular disease. Weak inspiratory muscles cause hypoventilation that appears first in sleep, which explains the morning headaches and daytime sleepiness, and weak expiratory and bulbar muscles cause an ineffective cough with secretion retention, which explains the recurrent chest infections. His lungs are structurally normal, so I would treat the pump and the cough as two separate problems. [1] [6]

Branch A — confirming each problem

How would you confirm each of these two problems? [1]

For the pump I would measure the forced vital capacity sitting and supine, where a large supine fall indicates diaphragm weakness, and I would study sleep with overnight oximetry and transcutaneous or end-tidal carbon dioxide, because carbon dioxide rises before oxygen falls and detects nocturnal hypoventilation early. For the cough I would measure the peak cough flow, which tells me whether he can clear secretions and whether assisted cough is needed. [1] [7]

Branch B — the two parallel treatments

The studies confirm nocturnal hypoventilation and a low peak cough flow. What treatment does he need? [6]

He needs two treatments in parallel. For the hypoventilation I would start nocturnal non-invasive ventilation, which reverses the morning headaches and daytime sleepiness and rests the respiratory muscles. For the weak cough I would put airway clearance in place, laddered from manual assisted cough and breath stacking or lung volume recruitment to mechanical insufflation-exsufflation, so that clearance is ready before the next infection. I would also review his cardiac status given the associated cardiomyopathy. [6] [2]

Branch C — the sick infant with spinal muscular atrophy

Now an infant with spinal muscular atrophy arrives with a viral chest infection, a weak cough and increasing work of breathing. What is your governing rule? [4]

This is a respiratory emergency because she has almost no reserve, and the governing rule is to clear the secretions and support ventilation rather than merely give oxygen. I would intensify airway clearance with the cough assist machine and assisted cough, support breathing with non-invasive ventilation, start antibiotics promptly, and monitor carbon dioxide rather than relying on the oxygen saturation. Oxygen is added only on top of adequate clearance and ventilation. [1] [4]

Closing — the safety rule

Give me the single rule you would write on this child's illness action plan. [1]

In any chest infection, clear the secretions and support ventilation, and do not simply give oxygen, because oxygen alone masks the rising carbon dioxide and does nothing for the retained secretions that are the real problem. [1] [6]