Non-invasive ventilation and home respiratory support — structured clinical encounter

Station brief (candidate)

You are the paediatric registrar in a respiratory and long-term ventilation clinic. A 13-year-old boy with Duchenne muscular dystrophy, a full-time wheelchair user, is referred with morning headaches, daytime sleepiness and a weakening cough; his last chest infection took two weeks to clear, and his daytime blood gas is normal. The team asks you to establish what is happening, order and interpret the investigations, choose the ventilatory treatment, address the cough, and plan for safe home ventilation. You have 12 minutes with the team and 5 minutes for examiner discussion. [6]

Information available on request

• Morning headaches and unrefreshing sleep; daytime sleepiness and reduced concentration at school. [6]
• Cough feels weaker to the family; prolonged recovery from the last respiratory infection. [3]
• Examination: alert, wheelchair user; kyphoscoliosis; reduced chest expansion; paradoxical abdominal movement lying flat; no distress at rest. [3]
• Daytime capillary blood gas (on request): normal carbon dioxide. [6]
• Overnight study with carbon dioxide monitoring (on request): sustained nocturnal rise in carbon dioxide with dips in oxygen saturation, worst in rapid-eye-movement sleep. [2]
• Cough peak flow (on request): falling toward the low hundreds of litres per minute. [7]

Tasks

1. Give the respiratory problem and explain why the daytime blood gas can be normal. [6]
2. Outline the investigation of choice and the limitation of overnight oximetry alone. [2]
3. State the ventilatory treatment and the evidence for its timing. [5]
4. Describe how you assess and support the cough. [3] [7]
5. Outline what must be in place for safe home ventilation. [1]

Marking anchors

Must-hit

• Recognises nocturnal hypoventilation from the symptoms, and explains that hypoventilation appears first in sleep — especially rapid-eye-movement sleep when accessory muscles are inhibited and a weak diaphragm works alone — so the daytime blood gas can be normal while sleep is already dangerous. [6]
• Chooses an overnight study with carbon dioxide monitoring (polysomnography with capnography, or oximetry plus transcutaneous or end-tidal carbon dioxide), stating that oximetry alone can miss hypoventilation because the saturation may hold while carbon dioxide rises. [2]
• States that treatment is nocturnal bilevel non-invasive ventilation, and that Ward and colleagues showed nocturnal ventilation should start when nocturnal hypoventilation appears and not prophylactically before it. [5]

Merit

• Assesses cough by cough peak flow and introduces mechanical insufflation-exsufflation (cough assist) with airway clearance before the next infection, citing Chatwin; and outlines safe discharge with trained caregivers, back-up equipment and power, a written emergency plan and shared community follow-up with re-titration as the child grows. [3] [7] [1]

Fail

• Reassures the family because the daytime blood gas is normal and arranges no sleep study or ventilatory support despite the symptoms of nocturnal hypoventilation. [6]
• Prescribes nocturnal oxygen alone for a child who is retaining carbon dioxide, masking the hypoventilation. [2]