Croup

Croup (Laryngotracheobronchitis) – High‑Yield Study Guide for Medical Students

Croup is a common pediatric respiratory illness characterized by upper airway inflammation leading to the classic triad of barking cough, hoarseness, and inspiratory stridor. Understanding its pathophysiology, clinical course, and evidence-based management is essential for safe pediatric practice.

Definition

Croup, or acute laryngotracheobronchitis, is an acute viral infection causing inflammation and edema of the larynx, trachea, and proximal bronchi, resulting in upper airway obstruction and stridor in young children.

Clinically, the term “croup” usually refers to viral croup, distinguishing it from other causes of upper airway obstruction such as epiglottitis, bacterial tracheitis, and foreign body aspiration.

Epidemiology

Croup is one of the most common causes of acute stridor in children.

• Age: Typically affects children aged 6 months to 3 years; peak incidence around 18–24 months. Older children can be affected but less commonly and usually less severely.
• Sex: Slight male predominance.
• Seasonality: Most common in late fall and early winter, mirroring the circulation of common respiratory viruses.
• Etiology: Most commonly due to parainfluenza viruses (especially types 1 and 3). Other implicated viruses include RSV, influenza A and B, adenovirus, and rhinovirus.
• Burden: High number of outpatient and ED visits; a small fraction require hospitalization, and very few require intubation in the era of routine corticosteroid use.

Pathophysiology

Croup results from viral infection of the upper airway mucosa, with a characteristic anatomic and physiologic response in young children.

• Site of pathology: Involves the larynx (especially subglottic region), trachea, and proximal bronchi. The subglottic area is the narrowest portion of the pediatric upper airway and is encircled by the rigid cricoid cartilage, so even small amounts of edema significantly reduce the lumen.
• Edema and narrowing: Viral infection triggers mucosal inflammation, capillary leak, and edema in the subglottic space. According to Poiseuille’s law, a small reduction in radius causes a large reduction in airflow, especially during inspiration when negative intrathoracic pressure promotes airway collapse.
• Inspiratory stridor: Turbulent airflow through the narrowed, edematous upper airway produces the characteristic harsh inspiratory noise.
• Cough and hoarseness: Inflammation of the larynx and vocal cords causes the barking “seal-like” cough and hoarse voice.
• Dynamic obstruction: Distress, agitation, and crying increase respiratory drive, further exacerbating negative intrathoracic pressure and worsening airway narrowing, creating a vicious cycle.

Clinical Presentation

Typical History

• Prodrome: 1–3 days of nonspecific upper respiratory symptoms such as rhinorrhea, low-grade fever, and mild cough.
• Onset: Abrupt appearance of barking cough and hoarseness, often at night. Parents may describe it as “seal-like” or “dog-bark” cough.
• Stridor: Initially inspiratory stridor only with agitation; may progress to stridor at rest with increasing severity.
• Course: Symptoms often worse at night, frequently peak at 24–48 hours, and typically resolve within 3–7 days.

Physical Examination

• General appearance: Child may appear in mild to moderate respiratory distress; assess mental status (alert vs lethargic), hydration, and overall work of breathing.
• Vital signs:
  • Tachypnea proportional to severity.
  • Tachycardia due to fever, distress, or hypoxia.
  • Fever: Usually low-grade; high fever suggests alternate or concomitant diagnosis (e.g., bacterial tracheitis or pneumonia).
  • Oxygen saturation: Usually normal in mild to moderate croup; desaturation is a late and concerning sign.
• Respiratory exam:
  • Characteristic barking cough and hoarse voice.
  • Stridor: Inspiratory, harsh, often heard without a stethoscope in more severe cases.
  • Work of breathing: Nasal flaring, suprasternal and intercostal retractions, tachypnea; paradoxical chest/abdominal movement in impending failure.
  • Lung auscultation usually reveals clear or transmitted upper airway sounds; lower airway wheeze or crackles suggest alternative or additional pathology.
• Hydration and perfusion: Assess mucous membranes, capillary refill, urine output (by history), and peripheral pulses.

Severity Assessment

Several clinical scoring systems exist, the most commonly referenced being the Westley croup score. In practice, clinicians often classify severity as mild, moderate, or severe.

• Mild croup:
  • Occasional barking cough.
  • No stridor at rest (may have stridor only with agitation).
  • No or minimal retractions.
  • Normal mental status and air entry.
• Moderate croup:
  • Frequent barking cough.
  • Stridor at rest.
  • Marked retractions (suprasternal, intercostal, subcostal).
  • No or minimal agitation, but child may appear uncomfortable.
  • Good air entry, no fatigue.
• Severe croup:
  • Prominent inspiratory (and possibly biphasic) stridor at rest.
  • Marked retractions, possibly paradoxical breathing.
  • Agitation, anxiety, or conversely lethargy (ominous).
  • Reduced air entry; may have cyanosis or hypoxemia.
  • Signs of impending respiratory failure: decreased stridor (due to poor airflow), bradypnea, or poor respiratory effort.

Diagnosis

Clinical Diagnosis

Croup is primarily a clinical diagnosis based on history and physical examination.

• Key features:
  • Age 6 months–3 years.
  • Viral prodrome followed by barking cough, hoarseness, and inspiratory stridor.
  • Symptoms worse at night.
  • Typically afebrile or low-grade fever, non-toxic appearance in uncomplicated cases.
• Routine laboratory tests (CBC, inflammatory markers) are not required for typical cases and do not change management.
• Viral testing (e.g., PCR panels) is usually unnecessary, but may be considered in hospitalized patients or in the context of infection control or epidemiologic surveillance.

Imaging

• Neck radiography is not routinely indicated but may be considered when the diagnosis is uncertain or to evaluate for alternative causes of upper airway obstruction.
• The classic finding on anteroposterior neck film is the “steeple sign”: symmetric subglottic narrowing resembling a church steeple. Note that this finding is neither specific nor necessary for diagnosis.
• Radiographs should only be obtained in a stable patient and should not delay treatment.

Differential Diagnosis

It is crucial to distinguish croup from other causes of acute upper airway obstruction and stridor, many of which require different and more urgent management.

• Epiglottitis:
  • Rapid onset, high fever, toxic appearance.
  • Dysphagia, drooling, muffled “hot potato” voice.
  • Child often sits leaning forward in the tripod position.
  • Cough is usually minimal or absent, unlike barky cough of croup.
• Bacterial tracheitis:
  • Severe illness with high fever, toxic appearance.
  • May follow viral croup but worsens instead of improving.
  • Thick purulent tracheal secretions; may present with severe respiratory distress and poor response to standard croup therapy.
• Foreign body aspiration:
  • Sudden onset of choking and respiratory distress.
  • Focal wheeze, unilateral decreased breath sounds, or stridor depending on location.
  • Lack of viral prodrome.
• Allergic reaction / anaphylaxis:
  • Acute onset after exposure to allergen.
  • Stridor with signs of angioedema, urticaria, hypotension.
• Spasmodic croup:
  • Similar presentation to viral croup but more abrupt onset, often at night, and frequently without fever or viral prodrome.
  • Likely has allergic or hyperreactive airway component.

Management

Management of croup focuses on airway assessment, alleviation of upper airway obstruction, and supportive care. Early use of corticosteroids and, when indicated, nebulized epinephrine has significantly reduced the need for intubation and hospitalization.

General Principles

• Assess airway and severity first: Evaluate work of breathing, stridor at rest, oxygen saturation, mental status, and ability to maintain hydration.
• Minimize agitation: Keep the child calm; allow parental presence; avoid unnecessary procedures that can worsen obstruction via increased respiratory effort and dynamic collapse.
• Administer corticosteroids to all patients with croup (including mild cases) as they reduce symptom severity, improve scores, and decrease return visits and need for additional interventions.
• Use nebulized epinephrine for moderate to severe croup with stridor at rest and significant work of breathing.

Pharmacologic Therapy

Corticosteroids

Dexamethasone is the preferred corticosteroid due to its long half-life and efficacy.

• Dose: Commonly 0.6 mg/kg (maximum 10–12 mg), given once. Lower doses (e.g., 0.15–0.3 mg/kg) have also shown benefit in some studies, but 0.6 mg/kg remains standard in many guidelines.
• Route: Oral, intramuscular, or IV depending on the child’s ability to tolerate oral medication and clinical status. Oral route is generally preferred in a stable child.
• Onset and effect: Clinical improvement usually begins within 2–3 hours and persists for 24–72 hours.

Nebulized budesonide is an alternative when oral or parenteral dexamethasone is not feasible.

• Dose: Typically 2 mg via nebulizer as a single dose.
• Studies show that systemic dexamethasone is at least as effective and often preferred for ease and low cost.

Nebulized Epinephrine

Racemic or L-epinephrine provides rapid but temporary relief of airway obstruction by causing alpha-adrenergic vasoconstriction of edematous mucosa.

• Indication: Moderate to severe croup (stridor at rest, significant retractions, distress) or impending respiratory failure.
• Dosing options (institutional protocols vary):
  • Racemic epinephrine 2.25%: 0.5 mL diluted in 2.5–3 mL normal saline via nebulizer.
  • L-epinephrine (1:1000, 1 mg/mL): 0.5 mL/kg (maximum 5 mL) nebulized, often used when racemic form unavailable.
• Onset and duration: Improvement is typically noted within minutes; effect lasts about 1–2 hours, after which symptoms may recur (“rebound”).
• Monitoring: Children receiving nebulized epinephrine should be observed for at least 2–3 hours after treatment to monitor for recurrence of significant symptoms.

Other Medications and Measures

• Antipyretics (e.g., acetaminophen, ibuprofen) for fever and discomfort.
• Humidified air (cool mist) has traditionally been used; evidence for benefit is limited. It may provide subjective comfort but does not replace pharmacologic therapy.
• Heliox (helium-oxygen mixture) may reduce work of breathing in severe cases by decreasing airflow turbulence, but its role is limited and generally reserved for specialized settings.
• Antibiotics are not indicated for typical viral croup. Consider them only if bacterial complications (e.g., bacterial tracheitis, pneumonia) are suspected.
• Antitussives and decongestants are not recommended and may cause adverse effects without meaningful benefit.
• Nebulized bronchodilators (e.g., salbutamol/albuterol) have limited role because pathology is upper airway; they may be considered if concurrent lower airway disease (e.g., asthma, bronchiolitis) is suspected.

Supportive Care and Disposition

• Oxygen: Administer supplemental oxygen in children with hypoxemia (e.g., saturations < 92–94%) or signs of significant respiratory distress; use the least-agitating method (e.g., blow-by).
• Hydration: Encourage oral intake in mild cases; consider IV fluids if moderate to severe distress, poor oral intake, or risk of dehydration.
• Observation: Children with moderate or severe croup or those treated with epinephrine should be observed until stable, with no significant stridor at rest and minimal work of breathing.
• Criteria often used for safe discharge (may vary by institution):
  • No or minimal stridor at rest.
  • Normal or only mildly increased work of breathing.
  • Normal mentation, able to take oral fluids.
  • Stable for several hours after epinephrine, if given.
• Indications for admission may include persistent moderate to severe symptoms, recurrent need for epinephrine, hypoxemia, poor oral intake/dehydration, or significant comorbidities.

Complications

• Respiratory failure: Rare with appropriate management but can occur in severe cases; risk increases with fatigue, hypoxemia, and delayed treatment.
• Bacterial superinfection: Croup can be followed by or complicated by bacterial tracheitis or pneumonia, especially if course is severe or fails to improve with standard therapy.
• Post-intubation subglottic stenosis: In children requiring intubation for severe croup, prolonged intubation may lead to subglottic scarring and stenosis.

Key Clinical Pearls

• Think croup in a child aged 6 months–3 years with barking cough, hoarseness, and inspiratory stridor, especially at night with a viral prodrome.
• Corticosteroids (dexamethasone) should be given to all patients with suspected croup, regardless of severity, due to strong evidence of benefit in reducing symptoms and healthcare utilization.
• Nebulized epinephrine is indicated for moderate to severe croup and provides rapid but temporary improvement. Always observe for several hours afterward to monitor for recurrence.
• Minimize agitation; a crying, distressed child with croup can deteriorate quickly due to dynamic airway collapse.
• High fever, toxic appearance, drooling, or dysphagia are red flags suggesting alternative diagnoses such as epiglottitis or bacterial tracheitis rather than simple viral croup.
• Spasmodic croup presents similarly but with abrupt onset and minimal or no fever; management overlaps with viral croup.
• Most children with croup have a self-limited course and can be managed as outpatients with a single dose of dexamethasone and careful observation.

Summary for Exams

• Etiology: Mostly parainfluenza virus type 1 (others: type 3, RSV, influenza).
• Age group: 6 months–3 years, fall and winter predominance.
• Classic triad: Barking cough, inspiratory stridor, hoarseness.
• Key management: Dexamethasone for all; nebulized epinephrine for moderate–severe cases; supportive care and close monitoring.
• Differentiate from epiglottitis: Epiglottitis – drooling, dysphagia, high fever, tripod position, toxic appearance, minimal cough.

This structured understanding of croup will help you recognize, risk-stratify, and manage affected children effectively, and will serve you well in both clinical practice and exam settings.