Merck Manual

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Rajeev Bhatia

, MD, Phoenix Children's Hospital

Reviewed/Revised Jan 2022 | Modified Sep 2022
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Croup is acute inflammation of the upper and lower respiratory tracts most commonly caused by parainfluenza virus type 1 infection Parainfluenza Virus Infections . It is characterized by a brassy, barking cough and inspiratory stridor. Diagnosis is usually obvious clinically but can be made by anteroposterior neck x-ray. Treatment is antipyretics, hydration, nebulized racemic epinephrine, and corticosteroids. Prognosis is excellent.

Croup affects mainly children aged 6 months to 3 years.

Etiology of Croup

The most common pathogens are

Less common causes are respiratory syncytial virus Respiratory Syncytial Virus (RSV) and Human Metapneumovirus Infections (RSV) and adenovirus Adenovirus Infections followed by influenza viruses Influenza A and B, enterovirus Overview of Enterovirus Infections , rhinovirus, measles virus Measles Measles , and Mycoplasma pneumoniae Mycoplasmas . Croup caused by influenza may be particularly severe and may occur in a broader age range of children.

Seasonal outbreaks are common. Cases caused by parainfluenza viruses tend to occur in the fall; those caused by RSV and influenza viruses tend to occur in the winter and spring. Spread is usually through the air or by contact with infected secretions.

Pathophysiology of Croup

The infection causes inflammation of the larynx, trachea, bronchi, bronchioles, and lung parenchyma. Obstruction caused by swelling and inflammatory exudates develops and becomes pronounced in the subglottic region. Obstruction increases the work of breathing; rarely, tiring results in hypercapnia. Atelectasis may occur concurrently if the bronchioles become obstructed.

Symptoms and Signs of Croup

Croup is usually preceded by upper respiratory infection symptoms. A barking, often spasmodic, cough and hoarseness then occur, commonly at night; inspiratory stridor Stridor may be present as well. The child may awaken at night with respiratory distress, tachypnea, and retractions. In severe cases, cyanosis with increasingly shallow respirations may develop as the child tires.

The obvious respiratory distress and harsh inspiratory stridor are the most dramatic physical findings. Auscultation reveals prolonged inspiration and stridor. Crackles also may be present, indicating lower airway involvement. Breath sounds may be diminished with atelectasis. Fever is present in about half of children. The child’s condition may seem to improve in the morning but worsen again at night.

Recurrent episodes are often called spasmodic croup. Allergy or airway reactivity may play a role in spasmodic croup, but the clinical manifestations cannot be differentiated from those of viral croup. Also, spasmodic croup usually is initiated by a viral infection; however, fever is typically absent.

Diagnosis of Croup

  • Clinical presentation (eg, barking cough, inspiratory stridor)

  • Anteroposterior (AP) and lateral neck x-rays as needed

Diagnosis of croup is usually obvious by the barking nature of the cough. Similar inspiratory stridor can result from epiglottitis Epiglottitis Epiglottitis , bacterial tracheitis Bacterial Tracheitis Bacterial Tracheitis , airway foreign body, diphtheria Diphtheria Diphtheria , and retropharyngeal abscess Retropharyngeal Abscess Retropharyngeal Abscess . Epiglottitis, retropharyngeal abscess, and bacterial tracheitis have a more rapid onset and cause a more toxic appearance, odynophagia, and fewer upper respiratory tract symptoms. A foreign body may cause respiratory distress and a typical croupy cough, but fever and a preceding upper respiratory infection are absent. Diphtheria is excluded by a history of adequate immunization and is confirmed by identification of the organism in viral cultures of scrapings from a typical grayish diphtheritic membrane.

If the diagnosis is unclear, patients should have AP and lateral x-rays of the neck and chest; subepiglottic narrowing (steeple sign) seen on AP neck x-ray supports the diagnosis. Seriously ill patients, in whom epiglottitis is a concern, should be examined in the operating room by appropriate specialists able to establish an airway ( see Treatment Treatment Epiglottitis is a rapidly progressive bacterial infection of the epiglottis and surrounding tissues that may lead to sudden respiratory obstruction and death. Symptoms include severe sore throat... read more Treatment ). Patients should have pulse oximetry, and those with respiratory distress should have arterial blood gas measurement.

Pearls & Pitfalls

  • Epiglottitis, retropharyngeal abscess, and bacterial tracheitis cause a more toxic appearance than croup and are not associated with a brassy, barking cough.

Treatment of Croup

  • For outpatients, cool humidified air and possibly a single dose of a long-acting corticosteroid

  • For inpatients, humidified oxygen, racemic epinephrine, and corticosteroids

The illness usually lasts 3 to 4 days and resolves spontaneously. A mildly ill child may be cared for at home with hydration and antipyretics. Keeping the child comfortable is important because fatigue and crying can aggravate the condition. Humidification devices (eg, cold-steam vaporizers or humidifiers) may ameliorate upper airway drying and are frequently used at home by families but have not been shown to alter the course of the illness. The vast majority of children with croup recover completely.

Hospitalization is typically indicated for

  • Increasing or persistent respiratory distress

  • Tachycardia

  • Fatigue

  • Cyanosis or hypoxemia

  • Dehydration

Pulse oximetry is helpful for assessing and monitoring severe cases. If oxygen saturation falls below 92%, humidified oxygen should be given and arterial blood gases should be measured to assess CO2 retention. A 30 to 40% inspired oxygen concentration is usually adequate. CO2 retention (PaCO2 > 45 mm Hg) generally indicates fatigue and the need for endotracheal intubation, as does inability to maintain oxygenation.

Nebulized racemic epinephrine 5 to 10 mg in 3 mL of saline every 2 hours offers symptomatic relief and relieves fatigue. However, the effects are transient; the course of the illness, the underlying viral infection, and the PaO2 are not altered by its use. Tachycardia and other adverse effects may occur. This drug is recommended mainly for patients with moderate to severe croup.

High-dose dexamethasone 0.6 mg/kg IM or orally once (maximum dose 10 mg) may benefit children early in the first 24 hours of the disease. It can help prevent hospitalization or help the child who is hospitalized with moderate to severe croup; hospitalized children who do not respond quickly may require several doses. The viruses that most commonly cause croup do not usually predispose to secondary bacterial infection, and antibiotics are rarely indicated.

Key Points

  • Croup is an acute, viral, respiratory tract infection affecting infants age 6 to 36 months and is typically caused by parainfluenza viruses (mainly type 1).

  • A barking, often spasmodic cough and sometimes inspiratory stridor (caused by subglottic edema) are the most prominent symptoms; symptoms are often worse at night.

  • Diagnosis is usually clinical, but an anteroposterior x-ray of the neck and chest showing classic subepiglottic narrowing (steeple sign) supports the diagnosis.

  • Give cool, humidified air or oxygen, and sometimes corticosteroids and nebulized racemic epinephrine.

Drugs Mentioned In This Article

Drug Name Select Trade
Adrenaclick, Adrenalin, Auvi-Q, Epifrin, EpiPen, Epipen Jr , Primatene Mist, SYMJEPI, Twinject
AK-Dex, Baycadron, Dalalone, Dalalone D.P, Dalalone L.A, Decadron, Decadron-LA, Dexabliss, Dexacort PH Turbinaire, Dexacort Respihaler, DexPak Jr TaperPak, DexPak TaperPak, Dextenza, DEXYCU, DoubleDex, Dxevo, Hemady, HiDex, Maxidex, Ocu-Dex , Ozurdex, ReadySharp Dexamethasone, Simplist Dexamethasone, Solurex, TaperDex, ZCORT, Zema-Pak, ZoDex, ZonaCort 11 Day, ZonaCort 7 Day
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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