Lee — a 39-year-old male with a history of eczema, asthma and mild scoliosis — presents to his GP with a few weeks of worsening dyspnoea on exertion and orthopnoea. He also reports excessive daytime sleepiness, generalised weakness and lethargy, and recent weight gain.

On examination, Lee has gained 5kg in three months, giving him a BMI of 26kg/m². Vital signs are within acceptable limits, as well as cardiorespiratory, thyroid and neurological examination.

Initial investigations are unremarkable except for an elevated haemoglobin and ECG demonstrating a new right bundle branch block. Chest X-ray demonstrates a small pleural effusion. Lee is referred to a respiratory physician promptly for evaluation.

By the time he attends this appointment, a week later, his dyspnoea has worsened, he has features of respiratory distress and his oxygen saturation is 85%. He is referred to ED.