Snapshot A 5-year-old is brought to his pediatrician’s office by his parents because he cannot keep up with his friends while playing outside because he is short of breath. His parents report that they notice him occasionally coughing at night but he is otherwise healthy. On physical exam, respiratory rate is within normal limits and slight end expiratory wheezing is appreciated diffusely. Introduction Clinical definition a reversible, intermittent obstructive disease of the small airways characterized by inflammation and hyperresponsiveness Epidemiology Can present at any age Most common chronic pediatric disease Risk factors atopy strongest identifiable factor atopic dermatitis food allergies allergic rhinitis family history smoking obesity air pollution ETIOLOGY Pathogenesis acute, subacute, or chronic inflammation an elevated level of IgE binds mast cells and triggered by an antigen to release histamine and initiate an inflammatory cascade common triggers allergies (house dust mites) upper respiratory infection cold air exercise obstruction secondary to airway hyperresponsiveness, edema, mucus plugging, and smooth muscle hypertrophy CLASSIFICATION Classification based on daytime and nighttime symptoms Asthma Classification Severity Symptom Frequency Pulmonary Function Test Intermittent ≤2 days/week ≤2 nights/month FEV1 > 80% of predicted Mild persistent > 2/week but < 1/day > 2 nights/month FEV1 ≥ 80% of predicted Moderate persistent Daily daytime > 1 night/week FEV1 60-80% of predicted Severe persistent Continual daytime Frequent nighttime FEV1 < 60% of predicted Presentation Symptoms often worse in the early morning and at night wheezing productive cough shortness of breath chest tightness Physical exam chronic asthma possibly normal wheezing acute exacerbation wheezing accessory muscle usage paradoxical breathing decreased breath sounds prolonged expiratory phase tachypnea pulsus paradoxus hyperresonance Special presentations Samter triad aspirin and nonsteroidal anti-inflammatory drug sensitivity, asthma, and nasal polyps exercise induced bronchoconstriction only associated with exercise cough variant only cough symptoms imaging Chest radiograph may be normal hyperinflammation if severe studies pulmonary function tests gold standard peak expiratory flow rate can be used at home to monitor obstruction < 50% of personal best indicates a severe obstruction arterial blood gas mild hypoxia with early respiratory alkalosis due to tachypnea normalization of PCO2 could indicate fatigue and impending respiratory failure interpret in the context of the overall clinical picture if severe, respiratory acidosis due to CO<sub>2</sub> retention diffusing capacity of carbon monoxide normal Differential Anaphylaxis distinguishing factors swollen mouth, hypotension, and gastrointestinal symptoms Foreign object lodged in the respiratory tract distinguishing factors foreign object visualized on chest radiograph Post nasal drip distinguishing factors frequent throat clearing, nonproductive cough, normal FEV1 and cardiopulmonary exam treatment: first-generation antihistamines (e.g. diphenhydramine) Congestive heart failure distinguishing factors volume overload visualized on chest radiograph and physical exam Gastroesophageal reflux disease distinguishing factors sour taste, regurgitation, and burning sensation DIAGNOSIS Diagnostic testing diagnostic approach in acute exacerbation of asthma provide supportive care and lifesaving treatments first use peak expiratory flow rate to monitor pulmonary function test as an outpatient later Diagnostic criteria pulmonary function tests an obstructive pattern of FEV1/FVC < 70% is consistent with diagnosis if consistent with obstructive lung disease, reverse with a beta-agonist increase of ≥ 12% from baseline and ≥ 200 mL if normal in a well patient but high clinical suspicion, induce with a methacholine challenge decrease of ≥ 20% from baseline increased residual volume and TLC normal DLCO Treatment of Acute Exacerbations Management approach administer lifesaving treatments and monitor serially with for signs of respiratory failure physical examinations peak expiratory flow rate ABG Medical first-line humidified O2 β2-agonists via metered dose inhaler or nebulizer magnesium relaxes smooth muscle reduces hospital admissions second-line intravenous methylprednisone indication if poor response to first-line treatment aminophylline Interventional non-invasive positive pressure indication if poor response to medical management above only appropriate for alert patients with intact airway intubation indications if continued threat of airway obstruction despite first-line and second-line treatment if unable to protect airway due to reduced consciousness if PCO<sub>2</sub> normalizes or is elevated (patient should be hyperventilating leading to low PCO<sub>2</sub>, if the patient becomes fatigued, PCO<sub>2</sub> will begin to increase) Treatment of Chronic Asthma Management approach based on a step-wise approach building upon existing therapy all patients should have a short-acting β2-agonists as needed Therapy based on the classification intermittent treat with short-acting β2-agonists as needed no daily long-term treatment needed mild persistent add low-dose inhaled corticosteroid predisposes to oral candidiasis ("thrush") moderate persistent add long-acting β2-agonist to inhaled low-dose corticosteroid alternative: add leukotriene modifier or theophylline alternative: inhaled medium-dose corticosteroid only severe persistent inhaled medium- or high-dose corticosteroid with long-acting inhaled β2-agonist if continued poor control, consider oral corticosteroids or omalizumab (anti-IgE) Other medical management strategies cromolyn indication exercise prophylaxis montelukast indication exercise prophylaxis or aspirin-induced asthma inhaled β2-agonists indication prior to exposure to triggers such as exercise Lifestyle modifications including allergy avoidance Complications Acute respiratory failure Status asthmaticus Atelectasis Pneumothorax Use of non-specific β-blockers (i.e., blocking β2) can close airways leading to death