One of the most common conditions of childhood is viral croup, which typically occurs during fall or early winter. For most children, it is a mild condition that never involves EMS, but, occasionally, it can present more severely. In this article, I will review the pathophysiology of croup and its treatment.
Viral croup usually affects young children with a peak incidence between 6 months to 3 years of age. It is rare to see it beyond the age of six. Several viruses can cause croup, the most common being Parainfluenza Virus Type 1. Coronavirus has also become a more frequent cause. And of course, RSV is a contributor. Therefore, in addition to stridor and cough, they frequently also have nasal discharge and fever.
The main symptom, which is what raises concern, is partial blockage of the upper airway. When the virus invades the mucosa of the upper respiratory tract it causes swelling of the subglottic region due to inflammation.
Small children have relatively narrow airways and their trachea wall tends to be floppier. Additionally, the cricoid cartilage, being a ring, prevents expansion. Therefore, all the swelling tends to narrow the airway. In severe cases, the diameter of the subglottic airway can be reduced to as little as 1-2 mm.
Despite the narrow floppy airways of small children, only a small percentage of children with respiratory viruses get croup. There are some other predisposing factors.
There seems to be some genetic component, as children whose parents had croup as a child are more prone to get it. Contributing factors include tracheomalacia (which is a condition of having an extra floppy trachea), laryngeal clefts, subglottic stenosis, vallecular cysts, or subglottic hemangiomas. It’s also possible that children with reactive airways are more susceptible.
The condition usually starts with rhinorrhea, congestion, and fever. The child usually doesn’t have a sore throat. This is followed by the onset of respiratory stridor and barky-sounding cough.
Typically, children present during the night between 10pm to 4am with acute onset of respiratory distress. Stridor is caused by inspiration as the vacuum created to pull air into the lungs causes further narrowing of the subglottic area and extrathoracic trachea, resulting in a coarse wheeze.
This is usually just on inspiration, but if the narrowing becomes very severe it can occur on expiration as well as inspiration. Other signs of respiratory distress can be present including indrawing, paradoxical breathing, and restlessness.
Often the condition improves on the way to the hospital as the child is exposed to the outside air, which during croup season tends to be cool. The cool air helps reduce the swelling. In most children, this is a self-limiting condition lasting 24-72 hours. Of those children that are seen in the ER only about 5% end up being admitted.
Racemic epinephrine given via nebulizer is usually very effective in quickly resolving the stridor and respiratory distress. A single dose of dexamethasone orally is usually also administered in the ER to reduce the likelihood of recurrence of stridor and respiratory distress. If Racemic epinephrine is given then the child is observed for 4 hours afterwards before discharge to be sure there is no relapse.
