Study Overview: This study is testing the safety of a drug called sildenafil in premature babies with a lung condition known as severe bronchopulmonary dysplasia (BPD). BPD is a lung problem that affects infants, especially those who were born too early. This research involves comparing sildenafil to a placebo (a harmless pill that doesn't have any effect) in babies in Neonatal Intensive Care Units (NICUs).

• The study lasts for up to 28 days, with a follow-up period of 28 days after stopping the study drug.
• Participants will have regular medical checks, including heart and breathing tests.
• Adverse effects will be monitored closely throughout the study.

Eligibility: Babies who were born before 29 weeks and are receiving breathing help may qualify. Parents must give consent for their baby to participate. Babies can't join if they've taken sildenafil or certain other medications recently or have certain heart or liver conditions.

Considerations: The study requires consent from a parent or guardian, involves frequent health checks, and monitors any potential side effects closely. Participants receive no direct benefits, but the study aims to help improve future treatments for BPD.