AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Croup, also termed laryngotracheitis or laryngotracheobronchitis, is a viral respiratory tract infection. It is primarily a pediatric illness and, as its alternative names indicate, generally affects the larynx and trachea but may also extend to the bronchi. It is the most common etiology for stridor in febrile children. Croup manifests as hoarseness, a seal-like barking cough and a variable degree of respiratory distress. However, morbidity is secondary to narrowing of the larynx and trachea below the level of the glottis, causing the hallmark inspiratory stridor.

Pathophysiology

Acute infectious croup is spread through inhalation of the responsible virus. The initial port of entry is the nose and nasopharynx. The infection spreads and eventually involves the larynx and trachea. Although the lower respiratory tract may also be affected, some authors consider laryngotracheobronchitis a separate entity, with bacterial superinfection as the potential cause.

Inflammation and edema of the subglottic larynx and trachea, especially near the cricoid cartilage, are most clinically significant. This is the narrowest part of the pediatric airway. Accordingly, swelling can significantly reduce the diameter, limiting airflow. This narrowing leads to stridor. Endothelial damage and loss of ciliary function occurs. A fibrinous exudate partially occludes the lumen of the trachea. Decreased mobility of the vocal cords due to edema leads to the associated hoarseness. In severe disease, fibrinous exudates and pseudomembranes may develop, causing even greater airway obstruction. Hypoxemia may occur from progressive luminal narrowing and impaired alveolar ventilation and ventilation-perfusion mismatch.

Spasmodic croup (laryngismus stridulus) may be a noninfectious variant of the disorder, with a clinical presentation similar to that of the acute disease but with less coryza. In such cases, subglottic edema occurs without the inflammation typical in viral disease. Although viral illnesses may trigger spasmodic croup, the reaction may be allergic rather than a direct result of infection.

Frequency

United States

Croup is the most common pediatric infection that causes stridor, accounting for approximately 15% of clinic and ED visits for pediatric respiratory infections. In North America, incidence peaks in the second year of life at 5-6 cases per 100 children. Approximately 5% of children experience more than one episode. Croup is most common in late fall and early winter but may be seen at any time of year.

Mortality/Morbidity

Hospitalization rates vary widely among communities, with rates from 1.5-30% and typically averaging 2-5%. Throughout the 1990s, US hospitalizations averaged approximately 41,000 per year but appear to have decreased over the last decade. Fewer than 2% of hospitalized children require intubation. Although exact mortality is unknown, one 10-year study found a mortality rate of less than 0.5% in intubated patients.

Sex

Male-to-female ratio is approximately 1.5:1.

Age

Croup is primarily a disease of infants and toddlers, with most cases affecting children aged 6 months to 3 years. Incidence peaks in the second year. Although the disease is rare after age 6 years, it may be seen as late as age 12-15 years.

CLINICAL

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History

Croup usually begins with nonspecific respiratory symptoms, including rhinorrhea, sore throat, and cough. Fever is generally low grade (38-39°C) but can exceed 40°C. Within 1-2 days, the characteristic signs of hoarseness, barking cough, and inspiratory stridor develop, often suddenly, along with a variable degree of respiratory distress. Most ED visits occur from 10 pm to 4 am, and symptoms are perceived as worsening at night. Symptoms typically resolve within 3-7 days but can last as long as 2 weeks.

Spasmodic croup typically presents at night with the sudden onset of "croupy" cough and stridor. The child may have mild upper respiratory complaints but more often appears completely well prior to the onset of symptoms.

Physical

The physical presentation of croup widely varies. Most children have no more than a croupy cough and hoarse cry. Some may have stridor only upon activity or agitation, whereas others have audible stridor at rest and evidence of respiratory distress. Paradoxically, the severely affected child may have "quiet" stridor secondary to the degree of airway obstruction. The child with croup does not appear toxic.

The child's symptoms range from minimal inspiratory stridor to severe respiratory failure secondary to airway obstruction. In mild cases, respiratory sounds at rest are normal; however, mild expiratory wheezing may be heard. Children with more severe cases have inspiratory and expiratory stridor at rest with suprasternal, intercostal, and subcostal retractions. Air entry may be poor. Lethargy and agitation may be a result of hypoxemia. Other warning signs of severe respiratory disease include tachypnea, tachycardia out of proportion to fever, and hypotonia. Children may be unable to maintain adequate oral intake, which results in dehydration. Cyanosis is often a late ominous sign.

• Many authors have attempted to devise croup scores to assist the examiner in assessing the degree of respiratory compromise. One of the most commonly cited is the Westley score. Although widely used to evaluate treatment protocols, its clinical efficacy has not been extensively studied. According to the Westley scale, a score of less than 3 represents mild disease; a score of 3-6 represents moderate disease; and a score greater than 6 represents severe disease. The score uses the following 5 dimensions:
• • Inspiratory stridor
  • • None - 0 points
    • Upon agitation - 1 point
    • At rest - 2 points
  • Retractions
  • • Mild - 1 point
    • Moderate - 2 points
    • Severe - 3 points
  • Air entry
  • • Normal - 0 points
    • Mild decrease - 1 point
    • Marked decrease - 2 points
  • Cyanosis
  • • None - 0 points
    • Upon agitation - 4 points
    • At rest - 5 points
  • Level of consciousness
  • • Normal - 0 points
    • Depressed - 5 points
• Mild disease consists of occasional barking cough, no stridor at rest, and mild or nonexistent suprasternal or subcostal retractions.
• Moderate disease includes frequent cough, audible stridor at rest, and visible retractions, but little distress or agitation.
• Severe disease consists of frequent cough, prominent inspiratory (and, occasionally, expiratory) stridor, conspicuous retractions, decreased air entry on auscultation, and significant distress and agitation.
• Lethargy, cyanosis, and decreasing retractions are harbingers of impending respiratory failure.

Causes

The parainfluenza viruses (I, II, III) are responsible for as many as 80% of croup cases, with parainfluenza I accounting for most episodes and for 50-70% of hospitalizations. 

Other infectious causes of croup include adenovirus, respiratory syncytial virus (RSV), measles, coxsackievirus, rhinovirus, echovirus, reovirus, metapneumovirus, and influenza A and B. Influenza A is associated with severe disease. Influenza A has been implicated in children with severe respiratory compromise.

Mycoplasma pneumoniae has been implicated in a few cases.

DIFFERENTIALS

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Other Problems to be Considered

Angioneurotic edema
Aspirated foreign body
Laryngeal web
Laryngeal papillomatosis
Laryngeal hemangioma
Spasmodic croup
Subglottic hemangioma
Vocal cord paralysis
Measles
Uvulitis
Laryngeal tuberculosis
Laryngeal fracture

WORKUP

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Lab Studies

• The diagnosis of croup is largely clinical, based on the presenting history and physical examination findings.
• Laboratory test results rarely contribute to the diagnosis. The CBC count is usually nonspecific, although the WBC count and differential may reveal a viral pattern with lymphocytosis. Identification of specific viruses is also not typically necessary but may be useful in determining isolation needs or, in the case of influenza A, deciding whether antiviral therapy is indicated.

Imaging Studies

• Plain films can verify a presumptive diagnosis or exclude other disorders, such as an aspirated foreign body, epiglottitis, bacterial tracheitis, or retropharyngeal abscess.
• Plain films should not be used as the only means of making a diagnosis and are not required in uncomplicated cases.
• The posterior-anterior chest radiograph classically reveals a steeple sign, which signifies subglottic narrowing, whereas the lateral view may reveal a distended hypopharynx (ballooning) during inspiration. However, these findings are not observed in as many as 50% of children with croup. Also, a steeple sign may be observed in patients without croup, representing a false positive.

Other Tests

• Although pulse oximetry findings are within the reference range in most patients, such monitoring is helpful to assess the degree of respiratory compromise in severe cases. 
• Arterial blood gases are unnecessary and show neither hypoxia nor hypercarbia unless respiratory fatigue ensues.

Procedures

• Laryngoscopy is required only in unusual circumstances (eg, the course of illness is not typical, the child has symptoms that suggest an underlying anatomic or congenital disorder).  It may also be required in patients with bacterial tracheitis to obtain the necessary cultures.

TREATMENT

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Medical Care

ED treatment depends on the degree of distress. For example, a child who presents with only a croupy cough may require nothing more than parental reassurance, and the parents may only need education regarding the course of the disease. Any child who presents with respiratory complaints must have a thorough evaluation to ensure the patency of the airway and maintenance of effective oxygenation and ventilation. Infants with severe respiratory distress or compromise require 100% oxygenation with ventilation support initially with a bag-valve-mask device. If the airway and breathing require further maintenance, the patient should be intubated with an endotracheal tube. Intubation should be accomplished with an endotracheal tube that is 0.5-1 mm smaller than predicted.

• The first rule of management is to keep the child as comfortable as possible, allowing the patient to remain in a parent's arms and avoiding unnecessary painful interventions. Persistent crying increases oxygen demands and respiratory muscle fatigue and worsens the obstruction.
• Careful monitoring of the heart rate, respiratory rate, respiratory mechanics, and pulse oximetry are important to detect early hypoxia.
• Throughout the 19th and most of the 20th century, cool mist administration was the mainstay of treatment. Hospitals had "croup rooms" filled with mist. Theoretically, mist moistens airway secretions, decreases their viscosity, and soothes the inflamed mucosa. Animal data show that microaerosol inhalation activates mechanoreceptors that produce a reflex slowing of respiratory flow rate and leads to improved airflow. Despite its continued widespread use, little evidence supports the clinical efficacy of cool mist. Randomized studies of children with moderate-to-severe croup revealed no difference in outcome between those who received cool mist and those who did not.¹ In addition, the use of hot steam should be avoided because scalding has been reported.
• The current cornerstones of treatment are glucocorticoids and nebulized epinephrine, although steroids have proven beneficial in severe, moderate, and even mild croup. Corticosteroids are beneficial because of their anti-inflammatory action, whereby laryngeal mucosal edema is decreased. They also decrease the need for salvage nebulized epinephrine. A single dose of dexamethasone has been shown to be effective in reducing the overall severity of croup if administered within the first 24 hours after onset of illness. It has the same efficacy if administered intravenously, intramuscularly, or orally. Inhaled budesonide has also proven to be effective but is more expensive. Corticosteroids should not be administered to children with varicella or untreated tuberculosis.
• Nebulized racemic or L-epinephrine is typically reserved for patients in moderate-to-severe distress. It works by adrenergic stimulation, which causes constriction of the precapillary arterioles, thereby decreasing capillary hydrostatic pressure. This leads to fluid resorption from the interstitium and improvement in the laryngeal mucosal edema. Its beta-2-adrenergic activity leads to bronchial smooth muscle relaxation and bronchodilation. Although a child who is symptomatic enough to receive epinephrine may be discharged after at least 3 hours of observation, anyone receiving epinephrine should also be given corticosteroids.
• Antibiotics are not indicated.
• Heliox is a metabolically inert, nontoxic gas that is combined with oxygen. It has low viscosity and low specific gravity, which allows for greater laminar airflow through the respiratory tract. Helium decreases the force necessary to move the gas through the airways and decreases the mechanical work of respiratory muscles. Several trials of heliox have demonstrated no advantage over conventional modalities; however, other trials have shown it to be equally effective in moderate-to-severe croup when compared with racemic epinephrine. It has also been shown to improve symptoms in very severe croup that failed to improve with racemic epinephrine.

MEDICATION

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Drug Category: Corticosteroids

Although a subject of controversy throughout the 1980s and 1990s, corticosteroids have since become a routine part of ED management of croup. Steroids are thought to decrease airway edema via their anti-inflammatory effect. In mild disease, corticosteroids have been proven to reduce the number of children returning to the ED for further treatment. In moderate-to-severe disease, they improve croup scores within 12-24 hours and decrease hospitalization rates. Most trials have used dexamethasone at 0.6 mg/kg (intramuscular or oral), but oral doses as low as 0.15 mg/kg are effective. Oral and intramuscular routes appear equally beneficial. Prednisolone (1 mg/kg) has been proven effective but may be associated with a greater return of children to the ED. 

Inhaled corticosteroids also have demonstrated efficacy, with most trials using budesonide. However, according to most authors, the relative ease, speed, and cost of administration make systemic corticosteroids preferable to nebulized formulations.

Drug Name	Prednisone (Deltasone) or prednisolone (Prelone)
Description	Several studies have shown improvement in clinical symptoms and croup score in patients who were hospitalized or treated in the ED. Corticosteroids exert beneficial effect via anti-inflammatory action in which laryngeal mucosal edema is decreased. In calculating an appropriate prednisone dose, dexamethasone is 6.67 times more potent and has a long half-life of 36-56 h vs a median half-life of 18-36 h for prednisone.
Pediatric Dose	Not established; one randomized controlled trial demonstrated decreased duration of intubation in children receiving prednisolone 1 mg/kg PO q12h until 24 h after extubation; not to exceed 60 mg/24 h
Contraindications	Documented hypersensitivity; systemic fungal infections; tuberculosis; varicella or exposure to varicella; peptic ulcer disease; hepatic dysfunction
Interactions	Coadministration with barbiturates, phenytoin, or rifampin can decrease effectiveness; coadministration with estrogens can decrease clearance; concurrent use with digoxin may cause digitalis toxicity secondary to hypokalemia
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Prolonged use has been associated with adrenal insufficiency, psychosis, immunosuppression, peptic ulcer disease, CHF, anaphylaxis, osteoporosis, pseudotumor cerebri, pancreatitis, nausea, vomiting, dyspepsia, edema, headache, dizziness, mood swings, insomnia, anxiety, hypokalemia, hypertension, hyperglycemia, cushingoid features, menstrual irregularities, ecchymosis, acne, skin atrophy, and impaired wound healing

Drug Name	Budesonide (Pulmicort Respules)
Description	Clinical studies have documented improvement in symptoms and decrease in hospital admissions with nebulized budesonide in children with croup. Corticosteroids exert beneficial effect via anti-inflammatory action in which laryngeal mucosal edema is decreased.
Pediatric Dose	2 mL (0.5 mg) of solution inhaled via nebulizer
Contraindications	Documented hypersensitivity; active bacterial or fungal infection
Interactions	None reported
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Prolonged use may increase the systemic absorption of corticosteroids; hypothalamic-pituitary axis suppression; hyperglycemia; glycosuria

Drug Category: Nebulized vasoconstrictors

Epinephrine stimulates alpha- and beta2-receptors. It constricts the precapillary arterioles, thus decreasing airway edema. Because of the potential adverse effects of tachycardia and hypertension, it is reserved for children with moderate-to-severe disease. The effects of epinephrine are transient, and most trials show alleviation of symptoms for no longer than 2 h. In the 1980s and early 1990s, a rebound phenomenon was thought to occur, necessitating admission of all children who received the drug. However, in recent years, patient discharge after 3-4 hours of observation has become acceptable as long as they have no stridor at rest, normal air entry, normal color, normal consciousness, and have received a dose of steroids.

Drug Name	Epinephrine (Adrenalin)
Description	Levo isomer. Stimulates alpha-, beta1-, and beta2-adrenergic receptors, which results in bronchodilatation, increased peripheral vascular resistance, hypertension, increased chronotropic cardiac activity, and positive inotropic effects. Causes alpha-adrenergic receptor–mediated vasoconstriction of edematous tissues, thus reversing upper airway edema.
Pediatric Dose	5 mL (5 mg) of 1:1000 solution diluted in 2 mL saline administered via nebulization; may repeat q20-30min
Contraindications	Documented hypersensitivity; cardiac arrhythmias; angle-closure glaucoma; during labor (may delay second stage of labor)
Interactions	Increases toxicity of beta- and alpha-blocking agents and that of halogenated inhalational anesthetics
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Caution in cardiovascular disease, tachycardia (especially with HR >200 bpm), diabetes mellitus, hyperthyroidism, and cerebrovascular insufficiency

FOLLOW-UP

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Further Inpatient Care

• Hospital admission is advised if, after optimal ED management, the child exhibits the following:
• • Cyanosis, hypoxia, or both
  • Depressed sensorium
  • Moderate respiratory distress
  • Stridor at rest
  • Progressive symptoms
  • Poor oral intake, dehydration, or both
• Hospital admission is also advised if the child is young or if the family is unable to properly care for the child at home or cannot return to the ED if needed.
• Hospital care is largely supportive, including careful monitoring, supplemental oxygen as needed, and rehydration. Nebulized epinephrine may be administered, and some providers administer additional doses of dexamethasone, although the safety and efficacy of this practice has not been well studied.

Complications

• Complications are rare. In most series, fewer than 5% of children who present with croup require hospitalization, and fewer than 2% of those who are hospitalized are intubated. Death occurs in approximately 0.5% of intubated patients.
• Bacterial superinfection may result in pneumonia or bacterial tracheitis.
• Pulmonary edema, pneumothorax, lymphadenitis, and otitis media have also been reported.

Prognosis

• Prognosis is excellent.
• Some evidence suggests that hospitalization for croup may be associated with a future development of asthma. In at least one study, children admitted for croup later demonstrated higher levels of bronchial hyperresponsiveness and an allergic response to skin testing.

Patient Education

• For more information, see eMedicine's patient education article Croup.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Patients who receive epinephrine in the ED should be observed for at least 3 hours and should be discharged only if they demonstrate healthy color, air entry, consciousness, and no stridor at rest and have received a dose of corticosteroids.
• Corticosteroids may be warranted even in children who present with mild symptoms.
• Although croup is the most common cause of stridor in the pediatric population, other disorders, such as aspirated foreign bodies and epiglottitis, must be considered.

MULTIMEDIA

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Media file 1:  Steeple sign on radiograph.
	View Full Size Image
Media type:  Radiograph

REFERENCES

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41. Luria JW, Gonzalez-del-Rey JA, DiGiulio GA, et al. Effectiveness of oral or nebulized dexamethasone for children with mild croup. Arch Pediatr Adolesc Med. Dec 2001;155(12):1340-5. [Medline].
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43. Marx A, Torok TJ, Holman RC, et al. Pediatric hospitalizations for croup (laryngotracheobronchitis): biennial increases associated with human parainfluenza virus 1 epidemics. J Infect Dis. Dec 1997;176(6):1423-7. [Medline].
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Article Last Updated: Sep 19, 2007