Asthma

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38 Asthma

Asthma, a chronic inflammatory disorder of the airways, is one of the most prevalent pediatric pulmonary disorders, affecting an estimated 6.8 million American children younger than 18 years of age. Acute asthma exacerbations are responsible for 700,000 emergency department (ED) visits per year and are the third leading cause of hospitalization in the United States for children younger than 15 years of age. Treatment is expensive—direct health care costs total $14.7 billion per year, of which $6.2 billion is spent on asthma prescriptions. Approximately 12.8 million school days are lost each year secondary to absenteeism from asthma exacerbations.

Instituting proper asthma management—by initiating appropriate therapy, providing patient and parent education, and monitoring patient symptoms and response to therapy—will reduce symptom frequency and severity, improve quality of life, and cut excess healthcare expenditures. This chapter discusses classical atopic asthma as it pertains to children and adolescents.

Etiology and Pathogenesis

Asthma is characterized by the presence of three airway components: inflammation, obstruction, and hyperresponsiveness. Chronic airway inflammation establishes baseline airway edema and obstruction, which sets the stage for acute exacerbations. During acute exacerbations, inciting triggers (Box 38-1) cause inflammation and bronchoconstriction of already hyperresponsive airways. Key cellular components involved in the pathogenesis of asthma include mast cells; eosinophils; and, to some degree, neutrophils, T cells, macrophages, and epithelial cells (Figures 38-1 and 38-2).

Figure 38-1 Steps in the pathogenesis of asthma.

Figure 38-2 Pathology of an acute asthma attack.

Although downstream symptoms are relatively uniform (e.g., respiratory distress, wheezing), upstream predisposing factors are broader in their scope. Asthma is likely the result of interplay among environmental and genetic causes. Environmental factors, such as respiratory pathogens, allergens, and pollutants, can cause airway inflammation and irritation, immune system dysregulation, or both, leading to the development of asthma. Environmental factors can also worsen existing disease. Genetic factors, such as a family history of atopic disease or an altered cytokine profile, can also result in abnormal modulation of the immune system and predispose a patient to developing asthma. For example, a T-helper cell type 2 (Th2)–cytokine profile likely correlates with the development of asthma and allergy. Currently, the genetics of asthma remain complex and multifactorial in nature; in the future, the genetic identification of particular genotypes and phenotypes may allow for the categorization of asthma into distinct subtypes that will aid in tailoring treatment plans.

Clinical Presentation

When providing a patient history, parents of a child with asthma often recall symptoms secondary to episodic airway obstruction. The most common reported symptom is persistent cough, which frequently is the only symptom, and may occur more often while the child is asleep. Nighttime cough caused by asthma, which occurs several hours into sleep, must be differentiated from cough caused by gastroesophageal reflux (GER) or postnasal drip, which occurs soon after a child is recumbent.

Although wheezing is a hallmark symptom of asthma, parents rarely report hearing an audible wheeze. Other symptoms a parent may recall include shortness of breath, chest pain, exercise intolerance, and variable degrees of respiratory distress. Subacute presentations of any of these symptoms, including the presence of chronic cough, are much more commonly encountered than life-threatening episodes of airway obstruction.

A patient or family history of allergy and atopic skin disease may be present. It is important to inquire about the setting(s) in which symptoms occur because a variety of inciting triggers exist (Box 38-1 and Figure 38-3). A patient should also be assessed for comorbid medical conditions, including GER, allergic rhinitis, sinusitis, and obesity, all of which can exacerbate asthma symptoms. For a patient with a previous asthma diagnosis, it is useful to inquire about the frequency of ED visits and hospital admissions, oral steroid use, and any history of severe complications (e.g., endotracheal intubation or admission to the intensive care unit [ICU]).

Figure 38-3 Asthma triggers.

The physical examination of a patient with well-controlled asthma is generally unrevealing. The physical examination of a patient with asthma during an acute exacerbation will most frequently demonstrate heterophonous wheezing (inspiratory, or expiratory, or both). To properly assess for the presence of wheezing, adequate airflow is required; it may be necessary to “squeeze the wheeze” and compress the chest wall to ensure forced exhalation or to ask an older child to exhale forcefully with the mouth wide open. Heterophonous or polyphonic wheezing results from turbulent air flow through multiple obstructed small airways; the different “musical” pitches are a consequence of varying degrees of obstruction. Heterophonous wheezing should be differentiated from homophonous or monophonic wheezing, which typically occurs with obstruction of larger airways.

Additionally, a symptomatic patient with asthma is frequently short of breath and tachypneic. The patient may also have other signs of airway obstruction, including decreased air entry, prolongation of the expiratory : inspiratory ratio, and hyperexpansion of the chest (a widened anteroposterior diameter). Nasal flaring and the use of accessory muscles (e.g., the sternocleidomastoid, intercostal, pectoralis major, and abdominal muscles) are also commonly observed.

Careful attention should be paid to the skin examination for signs of atopic disease, such as eczema or atopic dermatitis, and to the upper respiratory exam for signs of allergic rhinitis, including mucosal swelling, nasal polyps, and rhinorrhea. The presence of nasal polyps should trigger evaluation for cystic fibrosis. Digital clubbing is never a component of uncomplicated asthma and should prompt further evaluation.

Differential Diagnosis

If considering a diagnosis of asthma, the time-worn axiom must be remembered that “all that wheezes is not asthma.” Before a diagnosis of asthma can be confirmed, alternative diagnoses must be considered (Table 38-1). Furthermore, not all wheezes are equal. For example, monophonic wheezing associated with foreign body aspiration is distinct from polyphonic wheezing associated with asthma.

Table 38-1 Differential Diagnosis of Asthma in Children

Differential Diagnosis		Suggested Confirmatory Tests
Upper airway diseases	Allergic rhinitis or sinusitis	Physical examination, sinus CT scan
Obstruction of large airways	Foreign body in trachea or bronchus Vocal cord dysfunction Vascular rings or laryngeal webs Tracheomalacia Tracheal- or bronchostenosis Enlarged lymph nodes or tumor	Chest radiography Laryngoscopy Barium swallow, chest MRI Laryngoscopy, flexible bronchoscopy Chest radiography, chest CT scan, bronchoscopy Chest radiography, chest CT scan
Obstruction of small airways	Viral bronchiolitis Bronchiolitis obliterans Cystic fibrosis Bronchopulmonary dysplasia Heart disease	History, chest radiography, viral antigen or PCR testing Chest CT scan, lung biopsy Chest radiograph, sweat chloride test, genetic test Prenatal history, chest radiography, chest CT scan Chest radiograph, ECG, echocardiography
Other causes	Gastroesophageal reflux Oromotor dysfunction leading to chronic aspiration Pulmonary edema Tracheoesophageal fistula	pH probe, barium swallow, nuclear milk scan Modified barium swallow, speech pathology evaluation Chest radiography Chest radiography, fluoroscopy, chest CT

CT, computed tomography; ECG, electrocardiography; MRI, magnetic resonance imaging; PCR, polymerase chain reaction.

Adapted from the Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma. Washington, DC, U.S. Department of Health and Human Resources, 2007, p 12. Available at http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm.

Within the respiratory system, upper respiratory infections and allergic rhinitis are the most common causes of recurrent cough and wheezing. Other potential causes include foreign body aspiration, vocal cord dysfunction, tracheal or bronchial compression (by vessels, strictures, or masses), cystic fibrosis, and bronchopulmonary dysplasia (chronic lung disease of prematurity).

Nonrespiratory system causes should be excluded. Cardiac pathology—such as congenital heart disease, pulmonary edema, or vascular abnormalities compressing the respiratory tree—must be considered. GER; aspiration pneumonitis; and less frequently, tracheoesophageal fistula can all cause recurrent wheezing and so mimic asthma.

Evaluation

Chronic Disease

It is useful to classify a patient’s different symptoms into categories of severity (Table 38-2), which can guide stepwise treatment. Historical data provide the most useful information in establishing a diagnosis of asthma. When a tentative diagnosis of asthma is suspected based on a patient’s history and physical findings, further evaluation with spirometry is warranted.

Table 38-2 Classifying Asthma Severity in Children 5 to 12 Years Old

Spirometry is useful in quantifying pulmonary function, as well as for demonstrating a response to a trial of bronchodilators in patients who are old enough to cooperate with the test (usually older than 5 years of age, although the reliability of spirometry is being investigated in younger populations). After a challenge with a bronchodilator, an improvement in a patient’s FEV₁ (forced expiratory volume in 1 second) of at least 12% demonstrates significant bronchodilator responsiveness and so is strongly suggestive of asthma in the proper historical context. Additionally, the flow-volume curve will reveal a typical concave obstructive pattern. For a patient with an existing asthma diagnosis, trends in spirometry data can reflect the severity and relative control of a patient’s disease.

Depending on the presence of atypical or comorbid symptoms, other studies may be indicated, including a chest radiograph. Although more useful in the acute setting, a chest radiograph can demonstrate hyperinflation and retrosternal air trapping and can aid in ruling out pulmonary infection, heart disease, tumor, and foreign body aspiration.

Acute Exacerbation

A patient experiencing an acute asthma exacerbation should be promptly evaluated and triaged based on the severity of his or her symptoms (Table 38-3). Standardized criteria should be used within an institution, although many different schemes exist. Criteria are primarily based on symptom assessment, and concerning symptoms and signs include tachypnea, breathlessness, increased work of breathing, accessory muscle use, and decreased pulse oximetry values. For a child old enough to perform the maneuver, obtaining peak flow measurements can aid in determining the severity of an exacerbation, with peak expiratory flows of less than 40% predicted signaling a severe exacerbation requiring further assessment in an ED. However, peak flows are not a reliable measure because they measure large airway obstruction, and one can experience a 25% decrease in small airway flow before there is any decrease in peak flow. Spirometry is a much more sensitive measure of both small and large airway function and can also be used in the acute setting to assess both severity of the exacerbation and acute response to therapy.

Table 38-3 Classifying Asthma Exacerbation Severity in Children Younger Than 12 Years Old

	Symptoms and Signs	Clinical Course
Mild	• Dyspnea with activity • Tachypnea with activity • Expiratory wheezing • Normal oxygen saturations

• Usually cared for at home

• Prompt relief with inhaled SABA

• Possible benefit from course of oral corticosteroids

Moderate

• Dyspnea interferes with activity

• Tachypnea interferes with activity

• Expiratory wheezing

• Mild increased work of breathing

• Some accessory muscle use

• Normal oxygen saturations

• Usually requires office or ED visit

• Relief from frequent inhaled SABA

• Oral systemic corticosteroids

Severe

• Dyspnea at rest

• Tachypnea at rest

• Breathlessness or inability to talk

• Expiratory and inspiratory wheezing

• Significantly increased work of breathing

• Decreased air entry

• Accessory muscle use

• Oxygen saturations <92%

• Usually requires ED visit and hospitalization

• Partial relief from frequent inhaled SABA

• Oral systemic corticosteroids

• Additional therapies often indicated

Life threatening

• As above in severe category

• Altered mental status

• Sleepiness

• Requires ED visit and hospitalization

• Possible ICU admission

• Minimal or no relief from frequent inhaled SABA

• IV corticosteroids

• Additional therapies indicated

• Monitor blood gases, electrolyte

• Prepare for intubation

ED, emergency department; ICU, intensive care unit; IV, intravenous; SABA, short-acting bronchodilator agent.

Adapted from the Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma. Washington, DC, U.S. Department of Health and Human Resources, 2007, p 54. Available at http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm.

A child who scores in the severe classification should immediately be placed on cardiorespiratory and pulse oximetry monitors and further acute testing may be indicated, such as checking serum electrolytes and arterial blood gas values. The medical team must make frequent reassessments of such a patient. The majority of patients who have repeated pulse oximetry values less than 92% or continued symptoms 1 to 2 hours after initiation of acute therapy generally require inpatient hospital admission.

Management

For patients requiring therapy, the mainstays of treatment include administration of bronchodilators and inhaled or systemic corticosteroids (Figures 38-4 and 38-5).

Figure 38-4 Mechanisms of asthma medications.

Figure 38-5 Proper administration of inhaled bronchodilators and corticosteroids.

Chronic Disease

For long-term control, an inhaled corticosteroid is the preferred treatment. In general, patients with asthma should receive the minimal therapy indicated to control their symptoms (Table 38-4). If comorbid medical conditions are present, they should also be treated (i.e., a patient with allergic rhinitis should receive intranasal corticosteroids or oral antihistamine therapy). Depending on the severity of a patient’s asthma symptoms, he or she should be reassessed at regular intervals after initiation of treatment to evaluate response to therapy and the need for adjustment of therapy.

Table 38-4 Stepwise Approach for Managing Asthma Long Term in Children 5 to 12 Years Old