This is a randomized controlled trial (RCT) on the use of Inhaled prostaglandin E1 (IPGE1) in Neonatal Hypoxemic Respiratory Failure (NHRF). Fifty patients recruited at 10 high volume sites within the NICHD Neonatal Research Network will constitute a pilot sample to evaluate the feasibility and safety of prolonged IPGE1 administration and determination of optimal dose. In this Pilot RCT, two doses of IPGE1 (300 and 150 ng/kg/min) will be administered over a maximum duration of 72 hours and compared with placebo. Once feasibility and safety of IPGE1 administered over 72 hours has been demonstrated in the pilot trial, a full scale randomized controlled trial will be planned.