Describe the acute Laryngotracheobronchitis of Croup.

Definition

• Croup (acute laryngotracheobronchitis) is a common viral infection causing inflammation of the larynx, trachea and bronchi, leading to upper-airway obstruction.
• It typically affects children aged 6 months to 3 years and is the commonest cause of acute stridor with fever in this age group.

Etiology

• Parainfluenza virus (types 1 & 3) — the commonest cause.
• Others — RSV, influenza, adenovirus, and (rarely) measles.
• It occurs in autumn/winter; subglottic oedema in a narrow infant airway causes the obstruction.

Pathophysiology

Viral infection of the larynx & subglottis → Inflammation & oedema of the subglottic region → Narrowing of the already-small infant airway → Turbulent airflow → inspiratory stridor + barking cough

Clinical Features

• A preceding coryza and low-grade fever for 1–2 days.
• The classic triad — barking ('seal-like') cough, inspiratory stridor, and a hoarse voice.
• Symptoms are typically worse at night and with crying/agitation.
• Signs of increasing obstruction — stridor at rest, chest indrawing, tachypnoea, restlessness, and (late/ominous) cyanosis, drowsiness or a silent chest.

Assessment of Severity (westley Score Concept)

• Mild: barking cough, no stridor at rest, no/mild indrawing — the child is playful and feeding.
• Moderate: stridor at rest with chest indrawing, but no agitation.
• Severe: stridor at rest with marked indrawing, agitation/distress.
• Impending respiratory failure: lethargy, decreasing stridor with fatigue, cyanosis.

Investigations

• A clinical diagnosis — avoid distressing the child.
• If done, a neck X-ray (AP) may show the 'steeple sign' (subglottic narrowing).
• Do not examine the throat or perform painful procedures if severe obstruction is suspected.

Management

• Keep the child calm (crying worsens obstruction); allow the parent to comfort them.
• Corticosteroids for all — a single dose of oral dexamethasone (0.15–0.6 mg/kg) (or nebulised budesonide) reduces oedema and severity.
• Moderate–severe: add nebulised adrenaline (rapid but temporary relief — observe for rebound for 2–4 hours) and give oxygen.
• Impending failure: senior/anaesthetic help and airway management (intubation) in a controlled setting.
• Maintain hydration; most mild cases are managed and discharged home with advice.

Differential Diagnosis of Acute Stridor

Epidemiology

• Commonest in children aged 6 months–3 years; occurs in autumn/winter.
• The commonest cause of acute stridor with fever in this age group.

Spasmodic (recurrent) Croup

A variant with sudden night-time barking cough and stridor without preceding fever/coryza, often recurrent, with an allergic/atopic tendency. It settles quickly and is managed like viral croup.

Criteria for Hospital Admission

• Stridor at rest, moderate–severe chest indrawing, or hypoxia.
• Poor response to steroids/adrenaline; toxic appearance or diagnostic doubt; young infant or poor social support.

Prognosis

Most croup is mild and self-limiting, resolving in 3–5 days; steroids markedly reduce severity and the need for admission. Serious airway obstruction is uncommon but must be anticipated.

Medications at a Glance

Home Advice (mild Croup)

• Keep the child calm and comfortable; ensure adequate fluids.
• Return urgently if there is stridor at rest, chest indrawing, drooling, cyanosis or the child looks unwell.

WHY You Must Not Upset the Child

• The most important practical rule in a child with stridor is understanding why agitating the child can turn a partial airway obstruction into a complete one.
• Stridor arises from turbulent flow through a narrowed EXTRAthoracic airway.
• Now consider the mechanics: on inspiration, the pressure inside the extrathoracic airway falls below atmospheric — so the narrowed, floppy segment is sucked further inward.
• The harder and faster the child breathes, the more negative that inspiratory pressure becomes — and the more the airway collapses.
• So a crying, struggling, frightened child generates powerful negative pressures and worsens their own obstruction — while simultaneously increasing their oxygen consumption.
• This is why the cardinal rule of paediatric airway management is: keep the child calm.
• Leave them on the parent's lap, in whatever position they choose; do not lie them down; do not attempt to cannulate them; do not force an oxygen mask on them; and — above all — DO not examine the throat if epiglottitis is suspected, since a tongue depressor can precipitate complete obstruction and death.

WHY Every Child with Croup Gets Steroids

• A remarkable and evidence-based point is understanding why a single dose of dexamethasone is given to every child with croup — even the mildest case.
• Croup is caused by a virus (usually parainfluenza) producing inflammation and oedema of the subglottic region — the narrowest part of a child's airway, and one encircled by rigid cricoid cartilage, so the swelling can only expand inwards.
• Because of the fourth-power law, even a millimetre of oedema causes a huge rise in resistance.
• Corticosteroids reduce that oedema — and the trials are unambiguous: a single dose of dexamethasone (0.15–0.6 mg/kg, oral or IM) reduces the severity and duration of symptoms, reduces return visits and admissions, and reduces the need for intubation — in all grades of severity, including mild croup.
• The benefit begins within 2–3 hours and it is cheap and safe.
• Nebulised adrenaline is added in moderate-to-severe croup — it acts within minutes by vasoconstricting the mucosa, but its effect wears off in 2 hours, so the child must be observed for rebound.
• Humidified air, long used, has no proven benefit.