Lung Ultrasound and Lung Clearance Index After Preterm Birth: A Structure‐Function Framework for Bronchopulmonary Dysplasia and Post‐Prematurity Respiratory Disease

BACKGROUND: Bronchopulmonary dysplasia (BPD) and post-prematurity respiratory disease (PPRD) are heterogeneous consequences of disrupted lung development after preterm birth. Diagnostic frameworks anchored to oxygen requirement and respiratory support at fixed postmenstrual ages incompletely capture structural injury, ventilation heterogeneity, and long-term trajectories. OBJECTIVE: To synthesize evidence on neonatal lung ultrasound (LUS) and multiple-breath washout (MBW-derived lung clearance index (LCI) after preterm birth and to propose a pragmatic, time-dependent structure-function surveillance framework. METHODS: Targeted, non-systematic PubMed searches and reference screening were performed for (1) BPD/PPRD definitions and guidance; (2) neonatal LUS standards, scoring systems, and cohorts evaluating BPD prediction and later morbidity; and (3) MBW/LCI methodological standards, device/method considerations, and reference equations informing interpretation across childhood and adulthood. RESULTS: Serial LUS provides a repeatable bedside structural signal during the NICU course when acquisition and scoring are standardized. Early LUS trajectories, particularly within the first two postnatal weeks, show prognostic value for subsequent moderate-to-severe BPD, and modified scores may relate to later respiratory morbidity. LCI offers a complementary global functional readout of ventilation inhomogeneity, often detecting peripheral airway dysfunction during tidal breathing when spirometry is insensitive or infeasible; however, infant LCI is constrained by dead-space effects and method/device sensitivity. CONCLUSIONS: LUS and LCI are complementary, stage-specific tools. A pathway that anchors early surveillance in standardized LUS and extends longitudinal follow-up with MBW/LCI from preschool age onward is clinically feasible within PPRD frameworks. Prospective studies linking neonatal LUS trajectories with later LCI and patient-important outcomes are needed.