ACUTE LARYNGOTRACHEOBRONCHITIS (CROUP)

Saturday, August 16, 2008

Essentials of Diagnosis

• Most often in children ages 6 mo to 6 y, peak is at 2 y.

• Fever, hoarseness of voice followed by paroxysms of nonproductive, brassy cough that ends with a characteristic inspiratory stridor.

• The child appears anxious and has tachypnea, inspiratory stridor, retraction of intercostal muscles, and associated rhonchi or wheezing.

• Anterior-posterior x-ray view of the neck shows the subglottic obstruction.

• Microbiologic diagnosis can be established by serology, viral or bacterial cultures from the pharynx, or rapid antigen detection enzyme immunosorbent assays such as for RSV or influenza type A.

General Considerations

Acute laryngotracheobronchitis (LTB) or croup is subglottic inflammation and edema caused by a viral or bacterial infection of the larynx, trachea, and bronchi (Box 9-5). Croup is the most common cause of upper respiratory tract obstruction in children between the ages of 6 mo and 6 y, with the peak occurrence at 2 y old. It is caused mostly by viruses, primarily parainfluenza virus types I and II, although others, such as influenza type A or B, RSV, and adenovirus are also implicated. Occasionally M pneumoniae can cause LTB.

Clinical Findings

A. Signs and Symptoms. Most children have hoarseness of voice and a brassy cough with an associated inspiratory or even an expiratory stridor. Fever, rhinorrhea, sore throat, and cough usually precede this. Symptoms may vary in intensity and last ~ 3-4 d if mild. Patients appear apprehensive and tend to lean forward. The child may have tachypnea and might be using accessory respiratory muscles. Inspiratory or expiratory stridor is prominent. Pulmonary examination may reveal rhonchi, crepitations, or wheezing. Breath sounds may be diminished if upper airway obstruction is severe and air entry is greatly decreased.

B. Laboratory Findings. The white blood cell count may be normal or mildly elevated. Noninvasive pulse oximetry to monitor the oxygen saturation is recommended. Arterial blood gas assessment shows hypoxemia and/or hypercapnia, depending on the severity of the disease.

C. Imaging. Lateral neck x-rays show overdistended hypopharynx, subglottic narrowing that is wider on expiration than inspiration, thickened vocal cords, and a normal epiglottis. Anterior-posterior views of the neck show edematous subglottic walls converging to create a characteristic "steeple sign" (Figure 9-1). There may also be diffuse narrowing of the trachea and bronchi (Figure 9-2).

Differential Diagnosis

Acute epiglottitis is a major differential diagnosis to be considered when a child presents with these symptoms. Radiographs of the neck can easily help differentiate the two conditions. Other causes of similar symptoms include foreign-body aspiration, which can be determined by history, x-rays, or endoscopic evaluation. Membranous croup or bacterial tracheitis should also be considered if the child presents with a clinical picture similar to croup but appears more toxic and has subglottic narrowing on radiographs of the neck.

Complications

Severe croup, as may occur with influenza type A, may require tracheotomy or intubation in = 13% of patients and have an associated mortality of 0-2.7%. A small percentage of children with prolonged intubation or severe disease may develop subglottic stenosis. A few follow-up studies have shown an increase in hyperactive airways in children with a history of croup.

Treatment

Antibiotics are not routinely recommended for the treatment of croup unless the patient has symptoms or cultures suggestive of bacterial etiology (Box 9-6). Cool air humidification and supportive care are essential to keep the child calm, to prevent further tachypnea and distress. Respiratory rate is the best predictor of hypoxemia. Noninvasive pulse oximetry or arterial blood gas testing for PaO2 or PaCO2 should aid in assessment of the patient's condition and response to therapy. Noninvasive monitoring is preferred to prevent further anxiety in the child.

Nebulized racemic epinephrine is important in the therapy for croup because the a and ß agonists decrease edema and relieve obstruction by vasoconstriction. Racemic epinephrine nebulization is well tolerated, even by the younger children, and may decrease the need for intubation. Children receiving racemic epinephrine should be observed for relapse because epinephrine has a short half-life and rebound vasodilatation and edema can occur. Racemic epinephrine nebulization should be used cautiously in children with left ventricular outflow tract obstruction such as tetralogy of Fallot or idiopathic hypertrophic subaortic stenosis. In severe croup, corticosteroids (eg, dexamethasone) decrease subglottic edema, the number of racemic epinephrine treatments, and intubations.

Some children will fail medical management and require intubation. Intubation should be done in fully equipped units and preferably via the nasotracheal route. Extubation is usually attempted in ~ 5-7 d if extubation criteria are met. Extubation criteria include decreased secretions, decreased leakage around the endotracheal tube (which indicates decreased edema), and an alert child. Failure to extubate should prompt further endoscopic evaluation.

Prognosis

Croup is mostly a self-limited disease with complete uncomplicated resolution. As mentioned above, some children may develop hyperactive airways or become predisposed to recurrent croup. A few may develop subglottic stenosis caused by severe disease or prolonged intubation.

Prevention & Control

Good handwashing and cleanliness can help decrease transmission from an infected patient, particularly at daycare centers or even in the home environment.

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