RSV and Pediatric Respiratory Distress

Respiratory syncytial virus infects the respiratory epithelium. The resulting inflammation causes swelling, necrosis, and shedding of small-airway cells, while excess mucus accumulates in the bronchioles. These changes narrow or plug the airways and create the obstruction characteristic of bronchiolitis. The infant’s small airway has little reserve. A modest amount of wall oedema occupies a much larger proportion of the lumen than it would in an older child. Air then moves less effectively, especially during exhalation, when the bronchioles naturally become narrower. Uneven obstruction causes air trapping in some areas and poor ventilation in others, producing ventilation–perfusion mismatch and hypoxaemia. Wheeze reflects turbulent airflow through narrowed airways; crackles may occur as air moves through secretions or reopens partially collapsed small airways. The disease is not primarily a problem of reversible bronchospasm, which explains why bronchodilators do not routinely improve typical bronchiolitis. Increased work of breathing is initially compensation. Nasal flaring, intercostal or subcostal retractions, grunting, and tachypnoea show that the child is generating more effort to maintain ventilation. As fatigue develops, the pattern may become quieter rather than better: poor air...