Key Concepts
Introduction
Bronchiolitis (primarily RSV) involves viral invasion of bronchiolar epithelial cells causing necrosis, edema, mucus hypersecretion, and small airway obstruction. In infants with bronchiolar lumens less than 1 mm, even 1 mm of edema reduces cross-sectional area by 75%, creating a ball-valve mechanism with air trapping, hyperinflation, and hypoxemia. Croup (laryngotracheobronchitis, primarily parainfluenza virus) involves subglottic inflammation below the cricoid cartilage, the narrowest portion of the pediatric airway. Subglottic edema of 1 mm reduces the infant airway cross-sectional area by approximately 60%, producing the classic triad of barking (seal-like) cough, inspiratory stridor, and hoarseness. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit. If the stem names a license or role, reread that line; scope errors are classic trap answers even when the clinical topic is familiar. Run a 60-second scan: breathing work and oxygenation, perfusion and end organs, neuro baseline, likely infection sources, and devices that can fail quietly. When two answers feel partly right, pick the one that reduces imminent harm and matches orders for the role you were given. Train yourself...