Chapter 31. Croup

Croup (acute laryngotracheobronchitis) is a respiratory illness of childhood and one of the most common causes of upper airway obstruction in children. Physicians should be comfortable with the disease as it will be one of the most frequent presentations of acute stridor in children to the office or emergency setting. In the United States, it is estimated to affect around 3% of the population and is most common in children aged 6 months to 6 years with the largest number of cases seen in those between 1 and 2 years of age.1 Reinfection and recurrence of croup is common. The ratio of males to females with croup is 1.43:1.1 There are two seasonal peaks of croup in North America, the first in autumn and the second in late winter.1 Because of biennial increases in viral epidemics, the number of croup cases is 50% higher in odd-numbered years when compared to even-numbered years.2

Clinical symptoms of croup include a hoarse voice, a seal-like barky cough and stridor. As croup symptoms worsen, respiratory distress and occasionally cyanosis can appear. Symptoms typically worsen when the child is agitated and at nighttime. Fortunately croup symptoms are short-lived with the majority (60%) having resolution within 48 hours,3 and only a small portion having symptoms lasting up to 1 week.3 The majority of children with croup can be managed as outpatients with less than 5% requiring admission.4–6 For those children requiring hospitalization, the need for endotracheal intubation is rare (1–5%)7 and mortality is extremely rare.7,8

Localized inflammation of the upper airway caused by an upper respiratory tract infection leads to varying degrees of airway obstruction and the range of symptoms seen in croup. Specifically, the infection causes the mucosa of the vocal folds and subglottis become erythematous and swollen.9 The subglottic area is the narrowest part of the airway and any edema affects the lumen negatively. This narrowing disrupts airflow resulting in the barky seal-like cough, stridor and increased work of breathing (indrawing).

The most common viral etiologic agents for croup are parainfluenza viruses types 1 and 3. One study showed they were responsible for greater than 65% of the cases of croup.1 Most recently, human metapneumovirus has been identified as another etiologic agent for croup.10

Table 31–1 lists the most common infectious and noninfectious causes of croup.

The clinical history for children that present with croup is fairly typical. Parents will tell the health care providers that their child was well during the day apart from upper respiratory tract infection symptoms. If fever is present, it is usually mild. They may or may not have symptoms of a hoarse voice. Within 24 hours the symptoms acutely worsen and the child often develops stridor. This rapid change prompts the family to seek medical attention.

Croup symptoms are usually classified into mild, moderate, and severe and are based upon the Westley croup score (Table 31–2).11 Symptoms of croup (barky seal-like cough and stridor) almost always begin in the night time. If the child develops severe respiratory distress, they may appear agitated but do not drool or appear toxic. Respiratory failure is often preceded by a change in mental status such as fatigue, pallor or cyanosis, and decreasing stridor, breath sounds, and chest wall retractions.11–14

The diagnosis of croup is a clinical one. Most children presenting with an acute onset of upper airway obstruction with hoarse voice, barky ‘seal like’ cough and stridor will have croup.3,6Table 31–3 lists the most common differential diagnoses for croup. Of those listed, particular note should be made of both bacterial tracheitis and epiglottitis. These two diseases may be confused with croup but often the symptoms are more severe and the child appears much more toxic. Bacterial tracheitis, a true infection of the trachea and a complication of croup,15 occurs as a secondary bacterial superinfection in patients with a viral respiratory disease.16–18 The most common bacterial agents that have been implicated in bacterial tracheitis are: Staphylococcus aureus, group A Streptococcus, and Moraxella catarrhalis. Streptococcus pneumoniae and Haemophilus influenzae have also been cultured but are less common because of current immunization practices.15,18–22 Children who have a high fever, appear toxic, and have a poor response to initial treatment of croup should be considered to have bacterial tracheitis.15,18 Administration of broad-spectrum antibiotics is the mainstay of treatment in bacterial tracheitis along with close monitoring of the patients airway status in the intensive care unit. Intubation rates vary from 57% to 80% and mortality figures are zero to 21%.16,17,23,24

Epiglottitis, although rare since wide spread use of the H. influenzae B vaccine,25,26 is another important potential diagnosis. Children present with a high fever and toxic appearance that is typically abrupt in onset. They will also have symptoms of stridor, drooling, and dysphagia and may be quite anxious. Children often sit in the forward “sniffing” position which aids in maintaining airway patency. If epiglottitis is suspected, leave the child in a position of comfort (usually with the parent), decrease stimuli, and have someone who is skilled in advanced airway management prepare to secure the child's airway.

As mentioned earlier, the diagnosis of croup is a clinical one. Radiological studies are useful to help exclude other diagnoses but are rarely helpful in diagnosing croup.27 Therefore, for those patients who present with the classic history and clinical symptoms of croup, treatment should not be delayed for radiographs.28 If radiographs are preformed after initial management, the lateral and anteroposterior neck X-rays will show the classic “steeple sign” which is caused by subglottic narrowing (Figure 31–1). A membrane in the trachea as well as a ragged tracheal contour suggests bacterial tracheitis15,20,29,30 (Figure 31–2). Findings of thickened aryepiglottic folds and epiglottis suggest epiglottitis.31 A widened soft tissue space of the posterior pharynx is suspicious for retropharyngeal abscess31 (Figure 31–3).

Two Canadian studies recommended against the use of routine bronchoscopy in croup and stated that bronchoscopy should only be used when the diagnosis is severely in question, when the case is prolonged, or nonresolving in spite of optimal medical management.32,33 Both studies also stated that if endoscopy is used, caution should be taken to avoid further damage to the vocal chords and subglottic area.32,33

Table 31–4 and Figure 31–4 outline recommended medications and management used in the treatment of croup in the emergency department (ED) setting.

Cold Air

Of those children who present to the ED with croup, the parents will often state that their child's symptoms have improved en route to the hospital. Although not clinically or scientifically proven, parents will anecdotally attribute the resolve of symptoms to cold air exposure. It is hypothesized that the cold air soothes the airway and helps to decrease the swelling of the subglottic area.

Mist Therapy

Often parents will also state that they have tried some form of mist therapy prior to arrival in the ED. It is thought that the act of comforting the child in the parent's arms while mist is being administered may soothe the airways and improve symptoms. Unfortunately, there has been no published evidence to support the use of mist in the treatment of croup.14,34–37 In 2007, a Cochrane review by Moore and Little concluded that the croup score of children that are managed in the ED will not improve greatly with the inhalation of humidified air.35 There are also potential risks to using mist in the treatment of croup. Several studies have demonstrated that there may be bacterial contamination in the mist that may cause infection or hypersensitivity reactions that could worsen the disease process.38–41 Mist tents, often used to administer mist therapy, are also discouraged because they worsen the child's anxiety by separating him from the parents, preclude rapid and accurate evaluation of the child, and may precipitate bronchospasm in susceptible children, potentially compounding the croup-related respiratory distress.

Corticosteroids

Corticosteroids for the treatment of croup have been debated since the early 1970s.42–44 The use of an anti-inflammatory agent to treat inflammation and edema of the subglottic area makes intuitive sense.45 Several forms of corticosteroids have been used in the treatment of croup; the most common being dexamethasone followed by budesonide.46 However methylprednisolone, betamethasone, and fluticasone have also been used46,47 (Table 31–4). The onset of action of corticosteroids to decrease symptoms in croup was initially thought to be approximately 6–8 hours, but recent studies have demonstrated that the beneficial effects of corticosteroids occur as early as 2 hours after corticosteroid administration.48–50 One dose of dexamethasone is usually all that is needed because of its long half-life and bioavailability (up to 82 h).51 Most children will have resolution of symptoms approximately 72 hours after medical assessment and administration of corticosteroids.52

Several well-designed, randomized, placebo-controlled clinical trials and systematic reviews have all demonstrated the effectiveness of corticosteroids in reducing symptoms in all forms of croup (mild, moderate, and severe) in both the inpatient and outpatient setting.4,46,52–55 For mild croup (Westley score < 3), there have been three studies that have demonstrated a clear benefit in the administration of corticosteroids.52,56,57 In one study patients received a single dose of 0.15 mg/kg of dexamethasone compared to placebo. The treatment group had a significant reduction in repeat visits to medical care with ongoing croup symptoms compared with the placebo group.56 Another study looked at those patients with mild croup and allocated them to receive either 0.6 mg/kg of oral dexamethasone, 160 μg of inhaled budesonide, or placebo. Both steroid groups had a faster resolution of croup symptoms compared with the placebo group and were less likely to seek medical attention in the week-after treatment.57 The most recent study by Bjornson et al. demonstrated that those children who received a single dose of 0.6 mg/kg of dexamethasone when compared to placebo had a significantly less chance of returning to medical care and faster resolution of symptoms.52 Other added benefits in the 48 hours after treatment was a decrease in parental anxiety and less lost sleep.52 The authors also concluded that there was a small but significant economic benefit to both the health care system and families in the dexamethasone group.52 An average savings of $21 was seen per child.52

In treatment of patients with moderate croup (Westley score 3–8), a systematic review found that there was a significant reduction in the Westley score at both 6 and 12 hours posttreatment. Fewer readmissions and/or return visits to medical care as well as decreased length of stay in the ED or hospital were also noted. Of note there was also a decrease in the usage of racemic epinephrine treatment when compared with placebo.46

For inpatients that had severe croup (Westley score >8), several well-designed studies promote the use of steroids for treatment. First, a 1989-meta-analysis found that in those patients who received corticosteroid treatment when compared to placebo, there was a significant reduction in symptoms and clinical improvement at both 12 and 24 hours posttreatment.55 There were also significantly fewer intubations of patients with croup for the same time period.55 This was additionally supported by a second study from Western Australia.48 This study reviewed admitted croup patients over a 16-year period that received corticosteroids. The authors found them to have a decrease in number of ICU days, intubations, and overall length of stay in the hospital48; therefore, leading to their recommendation that all patients should receive corticosteroids in the treatment of croup.48 Finally, two randomized controlled trials by Rivera58 and Tibballs59 comparing intubated croup patients receiving either placebo or prednisolone until extubation showed that the patients who received prednisolone had a statistically significant reduction in the duration of endotracheal intubation and the need for reintubation.58,59

The most common dose of dexamethasone that is used today is 0.6 mg/kg. This is most frequently given orally but may be given intramuscularly if needed. The oral route is preferred because it is less traumatic to the patient, has excellent absorption and serum concentrations peak as fast as with intramuscular injection.51,60 The oral dose is also tolerated well with vomiting being a rare occurrence.52

As far as the dose that is most effective in croup, a meta-analysis in 1989 showed that higher doses of corticosteroids (0.3–0.6 mg/kg) are more effective than lower doses.55 This resulted in a clinically significant improvement of patients at 12 hours post corticosteroid dose.55 There has been one study that compared a single dose of 0.15 mg/kg versus 0.3 mg/kg versus 0.6 mg/kg in the effectiveness in the treatment of croup. The authors found no difference in improvement of croup symptoms in each of the treatment groups.61 Unfortunately the study was not designed to test equivalence and the study size in each group may have been too small to detect a clinically important difference between all three dosing groups.46,61

The route of administration of corticosteroids has been debated also. As a result, there have been a total of seven randomized controlled studies comparing parenteral, intramuscular or oral, versus inhaled corticosteroid administration.26,49,57,62–66 All studies concluded that the oral route was superior to the intramuscular route with regards to ease of administration and was less traumatic to the patient. Also, there was no evidence that the intramuscular group provided any additional benefit when compared to the oral route. If the patient is vomiting, the inhaled or intramuscular routes may be used as an alternative.

Racemic Epinephrine

The first description of using racemic epinephrine in the treatment of croup was back in 1971 by Adair and colleagues.67 A dose of 0.5 mL of a solution of 2.25% of racemic epinephrine is given via nebulizer over 5–10 minutes. If racemic epinephrine is not available, a dose of 5 mL of L-epinephrine (1:1000) may be given to achieve the same effect.68,69 Since then, there have been several studies demonstrating the effectiveness of racemic epinephrine when compared to placebo in improving croup scores within the first 30 minutes after receiving treatment.11,12,26,34,70 The clinical effect of racemic epinephrine is present for at least 1 hour and essentially nonexistent after 2 hours.11,12,34 With the addition of oral dexamethasone or inhaled budesonide, the child, who has been treated with racemic epinephrine and observed for a period of 2–4 hours if symptom free, may be safely discharged home from the ED.50,62,71–73

Heliox

The use of helium for therapy in upper airway obstruction has been reported since 1934 by Barach.74 Since then there have been several small studies that have looked at its use in the form of heliox (a helium–oxygen mixture at a ratio of 80:20 or 70:30) administered by a non–rebreather mask for the alleviation of croup symptoms. Heliox is thought to provide increased laminar airflow through the narrowed airway, thereby decreasing the mechanical work of breathing. Heliox cannot be used to treat children who require supplemental oxygen >30%. Most authors concluded that although heliox may alleviate symptoms of croup, it is not superior to other conventional treatments (i.e., racemic epinephrine).75–78

Only 2% of children with croup require hospitalization; of these, less than 1.5% require endotracheal intubation. Factors that should prompt hospitalization include a history of severe obstructive symptoms prior to presentation, a congenital or acquired airway anomaly (e.g., subglottic stenosis), age younger than 6 months, stridor at rest, inadequate oral intake, extreme parental anxiety, or worsening symptoms.