Mei, aged 2, presents because of a harsh cough and difficulty breathing.

She developed a cold with a runny nose three days ago and has been unwell. Her mother said that she was awake most of the previous night with a barking cough and noisy breathing.

Examination reveals an otherwise healthy child with persistent
inspiratory stridor and lower rib retraction at rest.
Her vital signs are:
Pulse 130
Respiration 40/min
BP 90/60
Temperature 37.2
There is no cyanosis and no other abnormal physical signs.