Association Between High-Flow Nasal Cannula Duration and Bronchopulmonary Dysplasia Severity in Very Preterm Infants

Background: High-flow nasal cannula (HFNC) is widely used during respiratory weaning in very preterm infants, but its relationship with bronchopulmonary dysplasia (BPD) is unclear. Methods: This retrospective cohort included infants born at <32 weeks’ gestation (2017–2025) who started HFNC before BPD assessment at 36 weeks’ postmenstrual age (PMA) or discharge. The exposure was HFNC days before assessment; a landmark analysis restricted exposure to the period before 32 weeks’ PMA. Logistic and ordinal logistic regression were used. Results: Of 641 infants, 232 (36.2%) developed BPD. Each additional HFNC day before assessment was associated with higher odds of BPD (adjusted OR 1.043, 95% CI 1.022–1.065) and greater severity (adjusted OR 1.047, 95% CI 1.027–1.067). HFNC days accrued before 32 weeks’ PMA were not associated with BPD after adjustment (OR 1.023, 95% CI 0.988–1.060). Most infants with Grade 3 BPD started HFNC only after assessment. Conclusions: Among very preterm infants who progressed to HFNC before BPD assessment, longer HFNC duration was associated with BPD, mainly reflecting persistence on HFNC close to assessment rather than early exposure. HFNC duration is not an independent marker of BPD severity and should not be used for early prediction.