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Pediatric Asthma Exacerbations

Pediatric Asthma Exacerbations: Pathogenesis and clinical findings Non-allergic asthma (not triggered by allergens) Allergic asthma (triggered by allergens) (e.g., pollen, animal dander, dust mites) Viral respiratory tract infections Extreme weather Physical exertion Pollutants (e.g. cigarette smoke) Allergen inhalation activates IgE on mast cells Virus invades epithelial cells in airway Inhalation of cold ↑ Minute ventilation or dry air dries ↑ Air flow irritates & dries airway mucosa airway mucosa Inhaled irritants damage airway Epithelial barrier breakdown releases inflammatory mediators epithelium & activate immune cells Immune system releases inflammatory mediators (e.g., histamine, leukotrienes, prostaglandins, cytokines) into airway Histamine & leukotrienes stimulate smooth muscle cells in the airway to constrict Cytokines attract white blood cells (e.g., eosinophils, neutrophils, monocytes) Inflammatory mediators stimulate epithelial goblet cells Inflammatory mediators ↑ vascular permeability in airway mucosa Bronchoconstriction (bronchioles narrow) Airway inflammation persists & intensifies Goblet cells produce excess mucus plugs & obstruct small airways Airway wall swells (mucosal edema) Asthma Exacerbation Acute or sub-acute episode marked by a progressive ↑ in asthma symptoms & a measurable ↓ in lung function compared to patient’s baseline Bronchial hyperresponsiveness (an exaggerated & easily triggered constricting response of the airways to various stimuli) Narrowed bronchioles mechanically obstructs air flow & ↓ ventilation ↓ Ventilation impairs elimination of carbon dioxide (CO₂) from blood More force is required to expel air Turbulent airflow through narrowed bronchioles during expiration Severe airflow obstruction prevents airflow into distal lung regions ↓ Ventilation traps air in alveoli Prolonged expiratory phase Inflammatory mediators & mucous hypersecretion sensitize afferent nerves in airway ↑ Arterial partial pressure of CO2 (PaCO2)) triggers hyperventilation ↑ Work of breathing Expiratory wheeze ↓ Breath sounds Afferents activate cough reflex via Trapped air ↑ intra- Air trapping alveolar pressure overinflates vagus nerve above pleural pressure lungs Cough ↓ PaCO2 ↑ blood pH Tachypnea (↑ respiratory rate) Exhaustion of respiratory muscles ↓ strength & respiratory rate Air trapping limits oxygen (O2) exchange in alveoli ↑ Pressure ruptures alveoli ↓ Diaphragmatic excursion Hyperinflation on chest X-ray Pneumothorax (air collects in pleural space) ↓ Oxygenation of blood (hypoxemia) Respiratory alkalosis Normocapnia, can progress to hypercapnia (↑ PaCO2) Engagement of accessory respiratory muscles Respiratory failure ↓ O2 delivery to peripheral tissues Legend: Authors: Fares Senjar, Jody Platt Hypoxemic hypoxia (SpO2 < 90% on room air) Reviewers: Merry Faye Graff, Emily J. Doucette, Central cyanosis (bluish discoloration of skin & mucous membranes) Elizabeth De Klerk, Yan Yu, Alexander Arnold, Naminder Sandhu*, Jonathan Liu* Tachycardia (↑ heart rate) *MD at time of publication Complications Published Dec 2, 2013; updated Nov 15 2025 on www.thecalgaryguide.com Pathophysiology Mechanism Sign/Symptom/Lab Finding