Croup

Viral croup (i.e., acute laryngotracheobronchitis) is an inflammation of the upper airway that occurs in young children. It is most often caused by the parainfluenza virus. This condition is characterized by a barking cough, hoarse voice, and inspiratory stridor, all of which often worsen at night. More severe symptoms are associated with higher degrees of airway obstruction and include signs of respiratory distress, which can rarely progress to respiratory failure. Croup is primarily a clinical diagnosis, and diagnostic studies are only performed for severe disease, diagnostic uncertainty, or recurrent episodes of croup. All patients with viral croup should receive glucocorticoids (preferably dexamethasone) and supportive treatment. Patients with moderate or severe croup should also be evaluated for admission and receive nebulized racemic epinephrine and supplemental oxygen. The prognosis of uncomplicated croup is good, and complete recovery typically occurs within seven days of onset.

• Peak incidence: 6 months to 3 years
• Most common in fall and winter

References:^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Most common pathogen: parainfluenza viruses (75% of cases) ^[2]
• Other pathogens: respiratory syncytial virus (RSV), adenovirus, influenza virus, SARS-CoV-2 (COVID-19) ^[3][4]

• Important membrane-bound virulence factors of parainfluenza virus include:
  • Hemagglutinin: binds sialic acid → viral entry
  • Neuraminidase: release and spread of virions
• Viral infection → inflammation of the upper airway with edema formation and infiltration of inflammatory cells → narrowing of subglottic airway (inspiratory stridor) and increased work of breathing

• Prodromal phase: 1–2 days of upper respiratory tract infection symptoms (rhinitis, low-grade fever, sore throat) ^[3][5]
• Symptoms of croup ; last 2–7 days and typically manifest in the late evening/night. ^[3]
• Characteristic features include seal-like barking cough, hoarseness, and inspiratory stridor due to subglottic narrowing. ^[3][5]
  • Mild croup: Stridor may be absent or only manifest in agitated individuals.
  • Moderate croup
    • Stridor and dyspnea may be present at rest.
    • Thoracic retractions are typically visible.
    • Affected individuals may be tachycardic or tachypneic.
  • Severe croup
    • Severe stridor and dyspnea are present at rest.
    • Air entry is decreased.
    • Hypoxemia, an altered mental state, and/or other signs of impending respiratory failure may be present.
    • Upper airway obstruction can cause pulsus paradoxus. ^[6]
    • Agitation can worsen symptoms and precipitate complete airway obstruction.

Do not examine the throat of a child with significant stridor because the resulting agitation may precipitate complete airway obstruction. ^[7]

General principles ^[3][8][9]

• Croup is most commonly diagnosed based on the presence of characteristic clinical features of croup.
• Diagnostic studies are not routinely required; do not delay treatment in unstable patients to obtain studies.
• Indications for diagnostic studies include:
  • Atypical presentation or diagnostic uncertainty, to rule out differential diagnoses of pediatric stridor
  • Severe disease
  • Recurrent episodes of croup

Do not delay treatment of stridor to perform diagnostic studies.

Imaging

• X-ray chest and neck (anteroposterior and lateral) ^[9]
  • May identify subglottic narrowing ; on anteroposterior view (steeple sign)
  • May show concurrent lower airway involvement ^[10]
• CT chest and neck: usually performed for differential diagnoses or suspected underlying congenital abnormalities ^[3][11]
• Laryngoscopy/bronchoscopy: may be performed for suspected foreign bodies or atypical croup ^[12]

The steeple sign is not specific to croup; it may also be present with bacterial tracheitis, epiglottitis, and noninfectious etiologies such as thermal injuries and neoplasms. ^[3]

Laboratory studies

• Respiratory viral panel
  • Usually reserved for patients who do not respond to initial treatment ^[3]
  • Most commonly shows parainfluenza; coinfections are common. ^[5]
• CBC: may help distinguish between bacterial and viral infections ^[3]
• Blood gas ^[13]
  • Indicated for severe respiratory symptoms, e.g., signs of impending respiratory failure
  • May show hypoxemia and/or CO₂ retention

Approach ^[3][8][9]

• Keep the patient calm and minimize distress.
  • Allow the patient to maintain a comfortable position (usually semi-upright). ^[7]
  • Examine the child in the parent's lap. ^[14]
  • Avoid examining the throat as this may precipitate airway obstruction. ^[7]
• Hypoxemia/signs of impending respiratory failure: Initiate immediate stabilization (e.g., supplemental oxygenation, intubation).
• Perform a croup severity assessment to guide treatment; consider using a scoring system (e.g., Westley croup score).
  • All patients: dexamethasone and supportive care as needed (e.g., antipyretics, IV fluids)
  • Patients with moderate/severe croup: Add nebulized racemic epinephrine.
• Regularly reassess patients. ^[8]
• Admit patients with admission criteria for croup, e.g., severe croup, age < 6 months.

Agitation can worsen symptoms and precipitate complete airway obstruction; keep children calm and defer distressing procedures (e.g., IV placement) until facilities are in place for immediate intubation if required. ^[15]

Nebulized racemic epinephrine rapidly relieves symptoms of respiratory distress. Dexamethasone provides longer symptom relief but takes up to 6 hours to reduce airway swelling. ^[3]

Humidified air, both in the hospital and as a home remedy (e.g., steam inhalation), has been used to treat croup, but there is no evidence that it is effective. ^[3][5][16]

Immediate stabilization ^[3]

• Contact anesthesia or ENT early because children with croup have difficult airways.
• Initiate respiratory support.
  • Hypoxemia (e.g., pulse oximetry < 92%) and/or signs of respiratory distress
    • Start supplemental oxygen (typically humidified).
    • Consider modifications to oxygen delivery to prevent worsening agitation. ^[7][17]
  • Respiratory failure or signs of impending respiratory failure ^[10]
    • Endotracheal intubation is required.
    • Bring the difficult airway cart to the bedside.
    • The most experienced physician should perform the intubation.

Individuals with croup have difficult airways due to glottic and subglottic stenosis; if intubation is needed, notify anesthesia or ENT as early as possible. ^[3]

Evidence on the efficacy of helium-oxygen (heliox) mixtures in croup is mixed; routine use is not recommended. ^[18]

Croup severity assessment

• Follow local or institutional protocols where available.
• Croup scoring systems are susceptible to interobserver variability. ^[19]
• The most commonly used score is the Westley croup score. ^[19]

Over 80% of croup cases are mild. ^[21]

Treatment

• Give dexamethasone (off-label). ^[3][22]
  • Reduces airway swelling within 6 hours
  • Effects last up to 72 hours.
• Start supportive care. ^[3][21]
  • Ensure recommended daily fluid intake (oral or IV).
  • Offer antipyretics if febrile.
  • Educate the family on concerning features, e.g., signs of respiratory distress, signs of significant dehydration.
• Moderate croup/severe croup: Add nebulized epinephrine. ^[3][10]
  • Preferred: racemic epinephrine ^[3][10]
    • Reduces airway swelling within 30 minutes
    • Monitor for 2–4 hours for return of symptoms. ^[3][9]
    • Dose may be repeated as needed.
  • Alternative: L-epinephrine ^[3]

Suspect other causes of pediatric stridor if there are no symptoms of an upper respiratory infection and if symptoms do not respond to treatments for croup.

Disposition

• Discharge home with return precautions can be considered in the following cases:
  • Mild croup
  • Moderate croup that has responded to a single nebulized epinephrine treatment
• Patients with severe croup or other risk factors should be admitted; consider pediatric ICU.

Admission criteria for croup ^[8][10]

• Severe croup
• Need for oxygen or IV fluids
• > 1 treatment with nebulized epinephrine
• Age < 6 months
• Persistent tachypnea or tachycardia
• Complex medical history (congenital cardiac or pulmonary disease, premature birth)

Overview

Additional differential diagnoses ^[3]

• Asthma/virus-induced wheeze
• Pneumonia
• Retropharyngeal abscess
• Bacterial tracheitis
• Tracheomalacia
• Laryngomalacia
• Subglottic stenosis
• Subglottic hemangioma
• Anaphylaxis

The differential diagnoses listed here are not exhaustive.

• Respiratory failure (rare)
• Pulmonary edema
• Pneumothorax
• Pneumomediastinum
• Secondary bacterial infection (e.g., bacterial tracheitis)
• Cardiac arrest and death

We list the most important complications. The selection is not exhaustive.

• The prognosis in uncomplicated cases is good, with full recovery.
• Parents should be aware that croup tends to recur.
  • Most often within a week after recovery
  • If croup recurs within the peak incidence age (six months to three years), airway abnormalities should be suspected.
  • If croup recurs outside the peak incidence age, atopic conditions, airway lesions or gastroesophageal reflux should be suspected.

• Keep the child calm and allow them to choose a comfortable position.
• Assess for signs of impending respiratory failure; if present contact ENT/anesthesia and prepare for difficult intubation.
• Start supplemental oxygen if needed.
• Give dexamethasone.
• Assess for features of moderate and severe croup; if present give nebulized racemic epinephrine.
• Regularly reassess the patient; start continuous monitoring for patients given nebulized racemic epinephrine.
• Screen for admission criteria for croup and arrange admission if present.