Laryngotracheobronchitis, commonly known as croup, is caused predomi- nantly by viral illnesses and is the most common cause of upper airway obstruction in children (Sobol & Zapata, 2008).
Epidemiology
The incidence of croup is estimated to be 1.5–6.0% and most commonly affects children age 6 months to 5 years, but can affect children up to the age of 12. Boys are affected 1.5 times more than girls (Knutson & Aring, 2004). Croup can occur at any time of the year; however, there is a seasonal variability with most cases occurring in the fall and winter (Roosevelt, 2007). Parainfluenza virus type I is the most common causative organism, responsible for 50–70% of cases. Other viral pathogens include parainflu- enza types II and III, respiratory syncytial virus, adenovirus, influenza viruses A and B, and, less commonly, varicella, herpes simplex virus, measles, and enteroviruses. Mycoplasma pneumoniae may also be the caus- ative organism in school-age children, though still relatively uncommon.
In remote cases, bacteria such as staphylococcus and streptococcus are possible organisms and can cause a significant bacterial tracheitis (see Chapter 5), which is far more serious and can cause considerable airway obstruction, often requiring intravenous antibiotics and possible
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intubation. Fungi and atypical bacteria are extremely uncommon patho- gens for croup, and, if found to be the source of the infection, then consid- eration for an underlying immune deficiency should be made (Sobol &
Zapata, 2008).
Pathophysiology
The virus is transmitted via the inhalation route infecting the epithelial cells of the mucosa in the larynx and trachea, and subsequently results in swelling and inflammation. The subglottis is the narrowest part of the pediatric airway and the only region of the airway bounded by a complete cartilaginous ring; any swelling in this area can result in significant airway obstruction. Even 1 mm of edema in the normal pediatric subglottis reduces its area by more than 50% (Sobol & Zapata, 2008).
Signs and symptoms
The child with viral croup will typically present with a low-grade fever, hoarse voice, cough, and coryza over the first 24–72 hours. There is a classic
“barky” cough notable, which intensifies at night. Most cases of croup are mild; however, progression to inspiratory or biphasic stridor may occur with increasing respiratory distress. Children tend to prefer to sit upright and demonstrate an improvement in their symptoms in this position.
While most children have mild cases of croup, in some cases, respiratory distress can become moderate to severe with the child developing nasal flaring, intercostal and suprasternal retractions, and tachypnea. The sever- ity of the symptoms is related to the degree of narrowing of the larynx and trachea due to inflammation and swelling (Kliegman, 2007).
Diagnosis
Diagnosis is typically made by clinical history and exam; however, in some cases, radiograph confirmation is necessary. The classic finding visualized on the anteroposterior neck radiograph is the “steeple sign” (Figure 6.5), although this is only seen about 50% of the time (Knutson & Aring, 2004).
This is due to the swelling and inflammation of the airway at the subglottic region.
Management
The treatment of croup is directed toward reducing inflammation of the airway. In most cases, children will only need supportive measures which include fluids, antipyretics, rest, and letting the child assume a position of comfort. Historically, pediatric providers advised parents to either provide warm mist typically in the form of shower steam in a closed-door environ- ment or alternately to provide cool mist or air by bringing the child out in
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the cold. Theoretically, cool air results in vasoconstriction of the airway with a resultant decrease in inflammation, soothes inflamed mucosa, and thins mucus; warm, humidified air may also soothe the inflamed mucosa, which in turn decreases coughing due to mucosal irritation, eases symp- toms, and may allow for an easier air exchange and improvement of symptoms (Knutson & Aring, 2004). More recently, Scolnik et al. (2006) completed a randomized controlled study on the use of humidified mist for children with moderate croup, which showed no significant benefit.
If croup results in stridor at rest and/or a trip to the hospital, other therapies have proven to be beneficial. Use of corticosteroids has been studied and has been shown to have a clinical benefit within 6 hours of administration (Klassen, 1997). Steroids can be given in a variety of forms, including oral, intramuscular, or nebulized form. A single dose of 0.6 mg/
kg of dexamethasone has been shown to be equally effective to the same dose delivered by intramuscular injection and has, in general, become the standard of care for children with moderate croup (Rittichier & Ledwith, 2000). Researchers have also looked at the potential for a lower dose of oral dexamethasone to 0.15 mg/kg with one study showing equal efficacy to Figure 6.5 Steeple sign on chest X-ray (AP view).
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higher dosing (Geelhoed & Macdonald, 1995). Nebulized budesonide has been compared to oral dexamethasone for the treatment of croup, and comparatively, both therapies were found to have similar decreases in croup scores and can be a consideration for treatment (Klassen et al., 1998).
In addition, nebulized vaponephrine, otherwise known as racemic epi- nephrine, had been used for many years as a standard therapy for moder- ate to severe croup and continues to be used today. It works by decreasing mucosal edema by vasoconstriction and by reducing bronchial and tra- cheal secretions. Onset of action is typically within 10–30 minutes and generally lasts about 2 hours. Children given vaponephrine are observed in the emergency department for 3 hours after administration to ensure they do not experience a rebound effect when the beneficial effects of the medication subside (Kliegman, 2007). Heliox, a mixture of oxygen and helium, has also been used for children with severe croup in an effort to avoid intubation. This mixture of gas allows for easier diffusion of oxygen across the narrowed compromised airway (McGarvey & Pollack, 2008). In almost all cases, prompt appropriate treatment of croup results in excellent outcomes, and in very few cases, hospitalization or a more critical airway intervention such as intubation will be necessary.
If a child is not responding to routine therapy for croup, other diagnoses must be considered, including epiglottitis, bacterial tracheitis, airway burns, and structural lesions, which may have become more obstructive with laryngotracheobronchitis. Furthermore, with instances of recurrent croup, gastroesophageal reflux may be a contributing factor.
Complications
Complications from croup are very rare. In some instances, pneumonia develops. Most children do very well with standard therapy, but in the event croup becomes severe and respiratory failure develops, there is potential for complete airway obstruction and respiratory arrest.