Asthma is the most common chronic disease of childhood.¹ The International Study of Asthma and Allergies in Childhood (ISAAC) has identified differences in the prevalence of asthma internationally, ranging from 1.6% in Indonesia to 36.7% in the United Kingdom.² Prevalence of asthma in the United States is estimated at 8.4%, affecting an estimated 6.2 million children under 18 years of age.³ The overall prevalence is highest in developed countries and is highest in urban versus rural areas. Most children develop asthma under 5 years of age.

Acute exacerbations of asthma are often managed in emergency departments (EDs). The Centers for Disease Control (CDC) reported that in 2013 approximately 571,000 US children (<15 years old) were treated for an acute exacerbation of asthma in the ED.⁴

Asthma has been defined as intermittent, reversible obstructive airway disease and is a chronic inflammatory disorder of the airways with acute exacerbations. The most recent National Heart, Lung, and Blood Institute (NHLBI) expert panel guidelines (2007) define asthma as “a common chronic disorder of the airways that is complex and characterized by variable and recurring symptoms, airflow obstruction, bronchial hyper responsiveness, and an underlying inflammation.” The interaction of these features determines the clinical manifestations, severity of asthma, and response to treatment.⁵

The major pathophysiology of asthma includes increased airway responsiveness, inflammation, mucus production, and submucosal edema. Airway responsiveness is defined as the ease with which airways narrow in response to various non-allergic stimuli. The level of airway responsiveness correlates with the severity of symptoms and medication requirements. Airway inflammation plays a critical role in the development of obstruction and the degree of hyper responsiveness. Increased mucus production and submucosal edema add to the obstruction. There are anatomic and physiologic differences in a child compared with an adult which make them more prone to obstruction and more vulnerable to respiratory failure. The peripheral airways are smaller and thus offer greater resistance to airflow. Infants do not possess collateral channels for ventilation that are present in older children and adults. In infancy, the diaphragm is the primary muscle of respiration and possesses muscle fibers that are more prone to fatigue. Any degree of abdominal distension will interfere with diaphragmatic function and lead to secondary ventilatory insufficiency.

Children with acute exacerbations of asthma often seek care in an ED (Fig. 35-1). Exacerbations are characterized by decreases in expiratory airflow that can be documented and quantified by simple measurement of lung function (spirometry). These objective measures more reliably indicate the severity of an exacerbation than does the severity of symptoms.⁵ Unfortunately, spirometry is difficult to obtain in young children.⁶ Obtain an initial focused history and physical examination to guide treatment and then obtain a detailed history during treatment. Classification of the severity of the exacerbation is important in selecting therapy. Tables 35-1 and 35-2 illustrate the classification of asthma severity recommended by the NHLBI expert panel report.⁵ Numeric asthma scores can classify severity and measure effectiveness of treatment.^7–9 Scores which have been developed and validated include the pediatric asthma severity score (PASS) and the pediatric respiratory assessment measure (PRAM).¹⁰

The brief history should assess⁵:

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  Time of onset and any potential causes or triggers of the current exacerbation

  
  
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  Severity of symptoms especially compared with previous exacerbations

  
  
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  Treatment given before arrival to the ED, and response to this treatment

  
  
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  All current medications and time of last dose, especially of asthma medications

  
  
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  Estimate of number of previous unscheduled office visits, ED visits, and hospitalizations for asthma, particularly within the past year

  
  
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  Any prior episodes of respiratory insufficiency or intensive care unit admissions due to asthma

  
  
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  Other potentially complicating illness

Complete a rapid physical examination and start treatment. Focus on the severity of the exacerbation (see Table 35-2). Gauge the level of parental concern, and obtain a general assessment of distress. Important clues include alertness, anxiety, general health, positioning, ability to speak, fluid status, and presence of cyanosis. Vital signs may have some prognostic value. Fever, unusual in asthma, may point to a more complicated course and significant underlying disease. Increased pulse rate may be a sign of hypoxia. Pulsus paradoxus (a drop in systolic blood pressure of 10 mmHg or more with inspiration) was believed to correlate with a worsening status but its usefulness has been questioned. Increased respiratory rates are usually seen in asthmatic exacerbations, but respiratory rate may decrease with fatigue in severe asthma. The lung examination may reveal a number of findings including diffuse wheezing. Wheezing results from turbulent airflow and occurs first on expiration alone, progressing to both inspiration and expiration. The wheezing may be localized and may shift in location with time, as the relative degree of obstruction may vary. If airway obstruction is severe, there will be little airflow and the chest may be quiet. Thus wheezing is not a reliable indicator of the degree of obstruction. Lung examination may also reveal diffuse or localized rales or as a persistent cough with a clear lung examination. The presence of rales in asthma may be misinterpreted as indicative of concomitant pneumonia. Accessory muscle use is a more reliable indicator of degree of obstruction. The presence of air leak is suggested by asymmetric breath sounds, tracheal deviation, or subcutaneous edema.

A chest radiograph is rarely indicated in acute asthma exacerbations and rarely provides additional useful information.¹¹ Obtaining a chest radiograph may be important for the child with first-time wheezing, as there are many illnesses that can present with wheezing (see Differential Diagnosis below). Thereafter, specific indications for a chest radiograph include clinical suspicion of consolidation, effusion, pneumothorax, or impending respiratory failure. Typical chest radiograph findings are hyperinflation, peribronchial cuffing, and areas of subsegmental atelectasis (Fig. 35-2). These findings are nonspecific.

Spirometry can assess a patient’s degree of respiratory compromise. However, many children are unable to cooperate. The simplest spirometry test, peak expiratory flow rate (PEFR), is reliable in children older than 5 years,⁶ but is probably not practical to assess severity in children younger than 8 years. A PEFR of less than 30% to 50% of predicted or of the patient’s personal best indicates severe airway obstruction.

Oximetry is another tool that may help assess severity. It correlates with ventilation perfusion mismatching and thus degree of obstruction. An initial pulse oximetry may assess severity but not predict the need for hospital admission.¹²

Blood gases may be useful in severe exacerbations but are not necessary for management. Hypoxia will be present early due to ventilation perfusion mismatch. PCO₂ will be decreased early in the disease secondary to compensatory hyperventilation. As the obstruction progresses, the number of alveoli being adequately ventilated and perfused decreases and CO₂ retention occurs. Thus, a “normal” or slightly elevated PCO₂ in a patient with an asthma exacerbation may be a sign of muscle fatigue and impending respiratory failure. Eventually, the hypoxia and hypercapnia lead to acidosis. If a blood gas is warranted, a venous sample is usually acceptable.

Demonstrating episodic and reversible airway disease allows one to make a definitive diagnosis of asthma. This is most reliably accomplished by performing pulmonary function tests (PFTs). As outlined, children younger than 8 years are generally unable to perform the tasks needed to get accurate PFTs in the ED. The diagnosis in young children is usually made on a clinical basis. Consider the diagnosis of asthma in children with recurrent wheezing and symptom-free intervals, especially if there is a family history of asthma, atopy, or allergies. A personal history of atopy or allergies is also suggestive of the diagnosis of asthma. Some children with asthma have their first episode prior to 6 months of age. In infants, as in older children, viral infections are the most common trigger for asthma. Both infants who have asthma and those who do not may become infected with respiratory syncytial virus (RSV) or other viruses, and develop bronchiolitis as their first episode of wheezing.¹³ Therefore, in an infant with wheezing it is impossible to clinically differentiate between bronchiolitis and asthma. The most important clue to infantile asthma is a history of recurrent episodes of wheezing or persistent cough, especially a nocturnal cough.

Other possible etiologies for wheezing in an infant or child are provided in Table 35-3. A history of prematurity or ventilatory support will help in identifying the infant with bronchopulmonary dysplasia (BPD). Clinical signs which favor a congenital heart or cardiac cause for wheezing include digital clubbing, cyanosis, organomegaly, an audible murmur, and an active precordium. An association of signs and symptoms with feeding may suggest a tracheoesophageal fistula, gastroesophageal reflux, or recurrent aspiration. Clues to identifying the presence of a lower airway foreign body may come from the history (sudden onset and observed aspiration), chest examination (asymmetry), or radiographic studies (localized air trapping). It is often quoted that all that wheezes is not asthma. This is especially true in children, and remember that even patients with a previous diagnosis of asthma may have another etiology for wheezing.

Obtain a cardiopulmonary assessment on every patient with an acute asthma exacerbation on arrival to the ED. The choice and intensity of therapy depends on the severity of the exacerbation and the patient’s response to initial treatment. Recommended doses for asthma therapies are summarized in Table 35-4. Though typically not necessary, consider applying oxygen in all ED patients with an acute exacerbation of their asthma (24% (1L/min) by facemask in children <5 years old; low flow oxygen, by facemask or nasal cannula, in children between 6 and 11 years old; titrate arterial oxygen saturation to between 94% and 98% in patients <11 years old and to between 93% and 95% in children >11 years old).¹⁴ Hypoxia can lead to hypoventilation and acidosis, which can cause pulmonary vasoconstriction, pulmonary hypertension, and right heart failure. Check for signs of dehydration due to decreased intake or vomiting and provide intravenous (IV) fluids if needed. However, in acute asthma exacerbations, there may be increased secretion of antidiuretic hormone and increased capillary permeability, thus IV fluids should be used in moderation to avoid overhydration resulting in pulmonary edema. Antibiotics should be used only if evidence of concurrent infection exists. However, most exacerbations are secondary to viral upper respiratory infections and hence antibiotics are rarely indicated.