17th February 2025

A 19-year-old woman attends A&E with difficulty in breathing.

A 19-year-old woman attends A&E with difficulty in breathing. She is tachycardic, with saturations of 90% on air. On examination she has a bilateral wheeze and is unable to complete full sentences. She is treated for an acute severe asthma attack with salbutamol and ipratropium nebulisers, steroids, oxygen and magnesium sulphate. Her symptoms improve and she is admitted for monitoring. 

You are called to see her 3 hours later as she is complaining of left-sided chest pain and worsening shortness of breath. Her oxygen requirement has increased from 2 L via nasal cannula to a 40% Venturi mask. On examination she has reduced breath sounds on the left side, with a quiet wheeze on the right side. The left side of her chest is hyperresonant to percussion, compared with the right. Which investigation is most likely to be diagnostic for the cause of her deterioration?