AMERICAN ACADEMY OF PEDIATRICS Section on Allergy and Immunology Management of Asthma

Asthma can be regarded as a complex syndrome of reversible airway obstruction characterized by bronchial hyperirritabiity following exposure to various stimuli. Some of the stimuli include extrinsic allergens, viral respiratory infections, and various factors that stimulate irritant receptors in the airways, (eg, vigorous exercise, cold air, cigarette smoke, and air pollutants). The threshold for bronchial hyperreactivity varies among asthmatic mdividuals and, from time to time, in the same individual. Infection, exercise, exposure to specific allergens, climatic factors, and nonspecffic irritants can lower this threshold, and antiasthmatic medications can raise it. If sensitivity to specific allergens can be demonstrated, avoidance of these allergens or, in selected instances, immunotherapy with specific allergens can raise the threshold for the reagmic (IgE) induced hyperreactivity. Advances of clinical pharmacology and pulmonary physiology have significantly improved the management of asthma in children and adolescents. Application of these advances requires consideration of the frequency and severity of reversible airway obstruction, the chronicity of symptoms between acute episodes, the various specific factors that may trigger the irritable airways of asthma, and the persistance of airway obstruction based on measurements of pulmonary function. The management of asthma is directed toward the reversal of the altered physiology and the prevention of subsequent symptoms and signs of the disease. The pathophysiology of the airway obstruction includes contraction of bronchial smooth muscle, edema of bronchial mucosa, and excess secretions caused by stimulation of the mucous glands of the respiratory tract. These factors cause either partial or complete obstruction and result in impaired yentilation and pulmonary gas exchange. Partial obstruction of the airways results in increased airway resistance, decreased flow, air trapping, and hypoxemia. Areas of complete obstruction may result in atelectasis, which can be confused radiologically with pneumonia. Age is not a factor in the diagnosis. The traditional euphemisms of asthma in infancy (eg, recurrent bronchiolitis or bronchitis, asthmatic bronchitis, and wheezy bronchitis) may only delay appropriate treatment until the patient is older and the presentation more classical. More than 50% of children with asthma have an onset ofsymptoms during the first two years of life, and at least 25% of these children had an onset of symptoms before they were 1-year-old.’ In infants and younger children with asthma, mucosal edema and mucus secretions may predominate over bronchospasm. These patients may appear to respond less well to bronchodilator medication.2 However, earlier notions that infants have no functioning bronchial smooth muscle to cause bronchospasm are not true, and the apparent bronchodilator unresponsiveness of infants with asthma is relative and not absolute.