Viral Croup

Definition And Epidemiology

• Acute inflammatory upper airway obstruction.
• Characterized by bark-like or metallic/brassy cough, hoarseness, inspiratory stridor, and respiratory distress.
• Highest incidence among preschool children, peaking between 6 months to 3 years of age.
• Peak incidence in the second year of life.
• Predominantly affects males.
• Seasonal variation observed with higher occurrence during autumn and winter months.
• Hospitalization required in <5% of cases; intensive care needed in 1-2% of hospitalized cases.
• Mortality rate extremely low (<0.5%).

Etiology

• Viral infection of the glottic and subglottic regions.
• Parainfluenza virus types 1 and 3 account for >70% of cases.
• Other viral agents: Parainfluenza type 2, Influenza A and B, Adenovirus, Respiratory Syncytial Virus (RSV), Metapneumovirus, Coronavirus, and Measles.
• Mycoplasma pneumoniae rarely isolated, causes mild disease.

Pathophysiology

• Viral infection spreads to larynx and trachea.
• Inflammation leads to edema, abnormal secretions, and cellular debris.
• Decreased laryngeal and subglottic airway diameter causes obstruction.
• Small caliber of pediatric airways dramatically increases airway resistance with minimal mucosal edema.
• Inspiratory stridor results from turbulent airflow through narrowed extrathoracic airway.
• Alveolar gas exchange remains normal; hypoxia occurs only with impending complete airway obstruction.

Clinical Manifestations

• Upper respiratory infection (URI) prodrome: Rhinorrhea, pharyngitis, mild cough, low-grade fever lasting 1-3 days.
• Sudden onset of distinctive barking cough, hoarseness, and inspiratory stridor.
• Symptoms worsen at night.
• Agitation and crying significantly aggravate symptoms and signs.
• Physical examination reveals normal to moderately inflamed pharynx, tachypnea, nasal flaring, and chest retractions.
• Preference to sit upright in bed.

Croup Variants

• Spasmodic Croup:
  • Occurs in children aged 1-3 years.
  • Sudden onset in early morning hours.
  • Absence of viral prodrome, coryza, or fever.
  • Resolves rapidly within a few hours.
  • High recurrence rate; possible allergic component or associated with gastroesophageal reflux disease (GERD).

Clinical Severity Assessment

Clinical severity guides management. Assessed using sensorium, distress, stridor, heart rate, and oxygen saturation.

Stridor Severity

Weasley Croup Score

Differential Diagnosis

Must differentiate from other causes of acute upper airway obstruction.

Investigations

• Diagnosis is primarily clinical.
• Avoid distressing interventions (phlebotomy, IV access, throat examination) to prevent sudden airway obstruction.
• Radiology:
  • Anteroposterior (AP) Neck X-ray: "Steeple sign" (subglottic narrowing).
  • Lateral Neck X-ray: Helps rule out Epiglottitis ("thumb sign") or retropharyngeal abscess.
  • Caution: Never shift an unstable child for X-rays before stabilization. Radiographic findings are neither completely sensitive nor specific.
• Laboratory:
  • Complete Blood Count (CBC): Neutrophilic leukocytosis (nonspecific).
  • C-Reactive Protein (CRP): Elevation suggests bacterial etiology (Tracheitis/Epiglottitis).

Management

Initial Stabilization

• Keep infant on mother’s lap; separation worsens stridor.
• Administer oxygen in a nonthreatening manner to maintain SpO2 >95%.
• Withhold throat examination with tongue depressor until airway secured.
• Avoid sedation.

Mild Croup

• Corticosteroids:
  • Single dose oral Dexamethasone (0.6 mg/kg) OR nebulized Budesonide (2 mg).
• Discharge home if stable.
• Counsel parents on natural course (resolution in 48-72 hours) and warning signs (poor feeding, altered sensorium, worsening stridor).
• No role for antibiotics or beta-agonist bronchodilators.

Moderate to Severe Croup

• Hospitalization preferred.
• Nebulized Adrenaline (L-epinephrine):
  • Dose: 0.5 mL/kg of undiluted 1:1000 adrenaline (maximum 5 mL).
  • Mechanism: Constricts precapillary arterioles via beta-adrenergic receptors, decreasing laryngeal mucosal edema.
  • Duration of action: <2 hours. Requires minimum 2-4 hours observation for rebound symptoms.
  • Repeat dose after 2 hours if necessary.
• Corticosteroids:
  • Mandatory even if responsive to adrenaline (adrenaline effect wanes).
  • Dexamethasone 0.6 mg/kg (maximum 8 mg) via Oral, IV, or IM route.
  • Nebulized Budesonide 2 mg.
• Provide supplemental oxygen for SpO2 <95%.

Indications for Intubation / Intensive Care

• Depressed sensorium (lethargy, unresponsive).
• Severe retractions with declining intensity (muscle fatigue).
• Cyanosis or SpO2 <90% despite oxygen therapy.
• Procedure: Secure airway in a controlled setting. Use an endotracheal tube 0.5 - 1.0 mm smaller than estimated for age/height.

Discharge Criteria

• Observation for at least 2-3 hours post-adrenaline nebulization.
• No stridor at rest.
• Normal air entry.
• Normal pulse oximetry.
• Normal level of consciousness.
• Received systemic corticosteroids.

Complications And Prognosis

• Complications: Occur in ~15% of cases.
  • Extension of infection: Otitis media, terminal bronchiolitis, pneumonia.
  • Bacterial superinfection: Bacterial tracheitis.
  • Rare: Toxic shock syndrome (if associated with S. aureus or S. pyogenes tracheitis).
• Prognosis:
  • Excellent overall prognosis.
  • Majority of deaths result from laryngeal obstruction prior to medical intervention or tracheotomy complications.