Laryngotracheobronchitis

Etiology

Croup is most often a viral infection that affects the subglottic airway, commonly caused by the parainfluenza virus. Other viruses that are known to cause croup include the respiratory syncytial virus (RSV), rhinovirus, enterovirus, influenza, and adenovirus.[4][5]

Epidemiology

Croup occurs more commonly in boys than in girls. It frequently occurs in children aged 6 months to 6 years old, with a peak incidence in children 12 months to 2 years of age. Most cases of croup occur from late autumn to early spring. Recurrent croup is rare unless there is a family history of the illness. Only a small percentage of patients require hospital admission. A population study conducted from 1999 to 2005 found that only 5.6% of children with croup required admission. Most patients can be safely discharged from the emergency department after appropriate management as discussed below.

Pathophysiology

Inhalation of the virus causing croup first infects the nasal and pharyngeal mucosal epithelia, then spreads to the subglottic space. For children 8 years and younger, the subglottic space is the most narrow part of the airway. The cricoid cartilage forms a complete cartilaginous ring that is nonexpanding. This inability of the cricoid to expand leads to a significant narrowing of the subglottic region secondary to the inflamed mucosa. When the child cries or becomes agitated, further dynamic obstruction can occur at and below the cartilaginous ring. These factors lead to the common high-pitched stridor heard at rest and when the patient becomes agitated. Extension into the bronchi, as occurs with laryngotracheobronchitis, can lead to wheezing, crackles, air trapping, and increased tachypnea; a clinical picture that can be confused with acute asthma.

History and Physical

One to three days of rhinorrhea, nasal congestion, and fever usually precedes croup. Typical symptoms of croup include a barky or a seal-like cough, hoarse voice, and high pitched inspiratory stridor that parents may incorrectly describe as “wheezing.”

Several scoring systems can evaluate the severity of respiratory distress. The Westley score assesses the following:

• Cyanosis
• Level of consciousness
• Inspiratory stridor
• Retractions
• Air entry

Evaluation

Evaluation of the patient must include ruling out other causes of stridor (discussed in the differential diagnosis section) and prompt recognition of the rapid progression or worsening of airway obstruction. Radiographs are not necessary to diagnose croup but can be obtained if the diagnosis is unclear. The “steeple sign,” due to subglottic narrowing, can be seen on plain films of the chest in patients with croup.[6][7][8]

Patients should be evaluated while sitting comfortably on the caretaker's lap to prevent agitation and further narrowing of the airway. Croup is a clinical diagnosis made when patients present with a barky cough with or without stridor. Patients with the extension of inflammation into the lower airway, or laryngotracheobronchitis, can also have wheezing, crackles, decreased air movement, and tachypnea. 

Patients with croup can be placed into 3 groups: mild, moderate, or severe, as seen in Table 1 below. Careful evaluation of worsening stridor, work of breathing (chest wall/subcostal retractions, nasal flaring, sitting in a sniffing position, suprasternal retractions, grunting, accessory muscle use), vitals, mental status, hydration status, and air movement help determine the treatment and disposition. The presence of wheezing, crackles, or decreased air movement on lung auscultation suggests laryngotracheobronchitis.

Treatment / Management

The goal of treatment is to decrease airway obstruction. Treatment includes nebulized epinephrine, corticosteroids, and at least 3 hours of observation after the last dose of epinephrine. Supplemental oxygen via blow by or nasal cannula can also be used for hypoxic patients with croup.[9][10][11]

Nebulized Epinephrine

Racemic epinephrine 2.25% 0.05 mL/kg nebulized with a maximum of 5 mL or L-epinephrine 0.5 mL/kg nebulized with a maximum of 5 mL is reserved for moderate and severe croup. Admit patients requiring more than 1 to 2 doses of nebulized epinephrine in the emergency department.

Corticosteroids

Regardless of severity, all patients with croup benefit from oral steroids. Dexamethasone 0.15 mg/kg to 0.6 mg/kg by mouth with a maximum of 10 mg as a one-time dose is the typical dose (the intravenous dose can be given by mouth).

Observation

Patients with croup should be observed for a minimum of 3 hours after the completion of each dose of nebulized racemic epinephrine. Watch for worsening or recurrence of symptoms, including persistent stridor at rest, increased work of breathing, and hypoxia, during the observation period. Admit patients requiring more than one or two doses of nebulized epinephrine in the emergency department.

Heliox

Several trials have been conducted on helion in the management of croup, and the results are mixed. Overall, there is no harm from trying heliox because most anecdotal reports indicate that it helps ease breathing.

Intubation

Intubation is reserved for severe cases of croup not responding to medical treatment. The endotracheal tube size should be smaller than typical for the patient's age and size to avoid trauma to the already edematous airway.

Differential Diagnosis

Differential diagnosis

For a patient younger than 6 months old with stridor:

• laryngotracheomalacia
• subglottic stenosis
• vocal cord paralysis
• hemangioma
• vascular ring
• foreign body aspiration
• anaphylaxis
• asthma
• peritonsillar abscess
• retropharyngeal abscess

For patients older than 6 months with stridor:

• foreign body aspiration
• bacterial tracheitis
• epiglottitis
• peritonsillar abscess
• parapharyngeal abscess
• retropharyngeal abscess
• anaphylaxis.

Prognosis

The prognosis for most children with croup is excellent. Most cases can be managed with outpatient care. Fewer than 2% of patients require hospitalization. The use of nebulized epinephrine and steroids has markedly lowered the need to intubate many patients.

Complications

Complications are rare but can occur in some cases. They include:

• Hospitalization
• Secondary bacterial infection
• Pneumothorax
• Otitis media
• Dehydration
• Lymphadenitis