Abstract
This chapter provides an overview of pediatric asthma. The author reviews the pathophysiology, precipitating factors and clinical symptoms of asthma. The preoperative plan for patients with asthma is reviewed. A comprehensive discussion on anesthetics for the asthmatic is presented as is the management of perioperative asthma exacerbation. Each of the medications commonly used for pediatric asthma are reviewed.
A five-year-old male with a history of asthma and eczema presents for laparoscopic orchiopexy. His home regimen includes fluticasone, two puffs twice daily, and albuterol as needed. His mother reports he had an upper respiratory tract infection (URI) a few weeks ago, and since then has been using his albuterol inhaler more frequently. Ten days ago, the wheezing worsened and she took him to the emergency department where he was treated with nebulized albuterol and discharged home with a three-day course of oral corticosteroids. Since then he has returned to his usual state of activity, URI symptoms have resolved, and he has not used albuterol in the past three days. According to mom, she was told to hold all medications in preparation for surgery; therefore, he did not take fluticasone this morning.
His current vital signs are: heart rate 127, respiratory rate 28, blood pressure 101/70, SpO2 95% on room air, with an axillary temperature of 37.0°C.
On physical exam, the child is alert and interactive. Respirations are unlabored, without nasal flaring or intercostal retractions. Chest auscultation reveals mild expiratory wheezes bilaterally.
What Is the Definition of Asthma?
Asthma is a common chronic disorder of the airways that is characterized by variable and recurring bronchial hyperresponsiveness, airflow obstruction, mucus secretion, and inflammation.
What Are the Important Differential Diagnoses to Consider?
Not all wheezing is asthma. Other diagnoses to consider include: tracheomalacia, bronchomalacia, bronchiolitis, bronchial foreign body, bronchopulmonary dysplasia, cystic fibrosis, tracheal web/stenosis, and bronchial stenosis.
What Is the Prevalence of Asthma?
Asthma is the most common chronic disease of childhood in industrialized countries, affecting more than 6 million children in the United States. The prevalence of asthma in US children is approximately 10%, and its incidence has increased by an average of 4.3% each year.
The Pathophysiology of Asthma
Although much remains unknown about the exact pathophysiologic mechanisms, the development of asthma appears to be a complex process involving the interaction of host factors and environmental exposures, leading to chronic airway inflammation and excessive airway reactivity.
One of the key drivers in the pathophysiology of asthma is inflammation, by the interaction of mast cells and eosinophils, which, when activated by interaction with antigen, release cytokines and lipid mediators that result in bronchial inflammation and airflow limitation. Airflow obstruction is caused by a combination of several factors including bronchoconstriction, airway edema, hypersecretion, and mucus plugging. This leads to increased work of breathing, ventilation-perfusion mismatch, air trapping, hyperinflation, hypoxemia, diaphragmatic fatigue, hypercapnia and, if left untreated, respiratory failure.
What Are Some Precipitating Factors of Acute Asthma?
Environmental factors, including airborne allergens and viral respiratory infections, play a crucial role in asthma exacerbation (Table 10.1). Emotional stimuli – including stress, fear, anxiety, and excitement – are also known triggers of asthma. Airway manipulation, such as occurs during induction of general anesthesia, may trigger or exacerbate asthma symptoms.
Table 10.1 Common precipitating factors for asthma
| Precipitating factors of asthma |
|---|
| Respiratory infection (RSV) |
| Airway irritants (tobacco smoke, inhaled anesthetics) |
| Allergens |
| Exercise |
| Emotional stress |
| Dry/cold air |
| Chronic gastroesophageal reflux disease |
| Drugs (aspirin, beta-blockers) |
| Airway manipulation/stimulation |
What Are the Clinical Symptoms of Asthma?
Acute exacerbations of asthma may include wheezing, dyspnea on exertion, chest tightness, or dry cough. When severe, it may be manifest as chest wall retractions, use of accessory muscles of respiration, and prolonged expiratory phase due to bronchospasm.
Are There Any Chronic Consequences of Asthma?
Airway remodeling describes permanent airway changes that develop from chronic inflammation. Structural changes include smooth muscle hypertrophy, hyperplasia, blood vessel proliferation, epithelial thickening, and fibrosis. This results in progressive loss of lung function that is not prevented or fully reversible by current available treatments.
What Are the Different Pharmacologic Agents Available for Asthma?
Medications available to treat acute exacerbations and long-term control consist of bronchodilators and anti-inflammatory drugs in six different classes:
Beta2-adrenergic agonists: induce bronchial smooth muscle relaxation and bronchodilation. Short-acting beta2-adrenergic agonists are the first line treatment in acute asthma exacerbation. Long-acting beta2-agonists are used in combination with inhaled corticosteroids in moderate or severe persistent asthma.
Corticosteroids: the most potent and effective anti-inflammatory agents used in the long-term control of asthma. They block late-phase reactions, reduce airway hyperreactivity, and inhibit inflammatory cell activation. Most often used inhaled, with oral use reserved for severe or persistent asthma.
Leukotriene inhibitors: antagonize the leukotriene receptor leading to inhibition of leukotriene-induced bronchial smooth muscle constriction. They are mainly used as an alternative, not preferred, treatment of asthma, and often used as an adjunctive therapy to corticosteroids.
Methylxanthines: mild to moderate bronchodilator used as an alternative, not preferred, and as adjunctive therapy with corticosteroids. Monitoring of serum level is essential due to narrow therapeutic index.
Cromolyn sodium: pulmonary mast cell stabilizer that diminishes the IgE antibody-induced release of inflammatory mediators. Used as an alternative, but not preferred, medication in mild persistent asthma, or as a preventive treatment in exercise-induced asthma.
Anticholinergics: inhibit muscarinic cholinergic receptors, reducing the intrinsic vagal tone of bronchial smooth muscle. Can be used in combination with, or as an alternative to beta2-adrenergic agonists.
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