A 4-year-old boy presents with a history of a severe cough that has been present for the past 3 weeks. The cough occurs in short bursts with an inspiration followed by a succession of hacking coughs. He occasionally vomits after coughing. His mum states that the cough is worse at night. On examination his chest is clear but you note that he has two small subconjunctival haemorrhages and some petechiae on his face.