Clinical meaning
Pediatric airways differ significantly from adult airways, making children more vulnerable to respiratory distress. The pediatric airway is shorter, narrower, and more compliant. The larynx is higher (C3-C4 vs C4-C6 in adults) and more anterior. The epiglottis is omega-shaped and angled differently. Crucially, the narrowest point is at the cricoid cartilage (subglottic area) rather than the glottis as in adults. Per Poiseuille's law, airway resistance is inversely proportional to the radius to the fourth power — even 1 mm of mucosal edema in a pediatric airway can reduce cross-sectional area by 50-75%, dramatically increasing work of breathing. Croup (laryngotracheobronchitis) is caused primarily by parainfluenza virus (types 1 and 3), causing subglottic edema and the characteristic barky (seal-like) cough and inspiratory stridor. The steeple sign on neck X-ray shows subglottic narrowing. Epiglottitis is a bacterial infection (historically H. influenzae type b, now more commonly S. aureus, S. pneumoniae, and Group A Strep due to Hib vaccination) causing rapid, severe swelling of the epiglottis and supraglottic structures. This is a true airway emergency — the thumbprint sign on lateral neck X-ray shows the swollen epiglottis. Bronchiolitis is a lower airway disease (bronchioles) caused primarily by respiratory syncytial virus (RSV), causing bronchiolar edema, mucus plugging, and air trapping. It is the most common lower respiratory tract infection in infants <1 year, peaking at 2-6 months.