Croup
Viral laryngotracheobronchitis causes subglottic mucosal swelling at the narrowest, fixed-diameter part of a young child's airway, producing a barking cough and stridor whose severity is read directly off the degree of narrowing.
In a nutshell
Viral inflammation swells the subglottic mucosa, the one segment of the airway fixed in diameter by the cricoid ring, so a small amount of oedema causes a disproportionate obstruction. This produces the barking cough and stridor, worsened by crying and agitation. A single dose of dexamethasone reduces the oedema directly; severe cases get nebulised adrenaline as a temporary bridge.
Classic presentation
A two-year-old with a coryzal prodrome, barking cough, hoarse voice and inspiratory stridor, worse at night.
Key points
- The cricoid ring is the only completely cartilage-encircled part of the airway, so subglottic oedema there causes disproportionate narrowing compared with elsewhere.
- Stridor severity and the barking cough are direct readouts of airway calibre: crying and lying flat worsen both by increasing turbulence and mucosal engorgement.
- Every child with croup gets oral dexamethasone, regardless of severity, because it treats the oedema directly and shortens the illness.
- Nebulised adrenaline is temporary symptom relief for severe obstruction (vasoconstriction), not a cure: effects wear off and the child needs observation for rebound.
- Do not examine the throat or distress the child: agitation can precipitate worsening obstruction, and this is also how epiglottitis is protected against being missed as the wrong diagnosis.
First-line investigation
None: croup is a clinical diagnosis made on the barking cough, hoarse voice and stridor without invasive examination.
First-line management
Oral dexamethasone for every child, with nebulised adrenaline reserved for severe or worsening obstruction.
Exam traps
- Drooling, high fever and a toxic, still child point to epiglottitis, not croup: do not examine the throat, call anaesthetics/ENT urgently.
- Hypoxia is a late sign in upper airway obstruction; a normal saturation does not exclude significant obstruction.
- Nebulised adrenaline is not a substitute for dexamethasone: both may be needed, and the child must be observed after adrenaline for rebound symptoms.
Educational content pending clinical review. Not medical advice.