Sildenafil to Repair Brain Injury Secondary to Birth Asphyxia

Inclusion Criteria: * Male and female neonates meeting the criteria for induced hypothermia: * Gestational age ≥ 36 weeks and birth weight ≥ 1800 g; * Evidence of fetal distress, i.e., history of an acute perinatal event, cord pH ≤ 7.0 or base deficit ≤ - 16 mEq/L; * Evidence of neonatal distress, such as an Apgar score ≤ 5 at 10 minutes, postnatal blood gas pH obtained within the first hour of life ≤ 7.0 or base deficit ≤ - 16 mEq/L, or a continued need for ventilation initiated at birth and continued for at least 10 minutes; * Evidence of moderate to severe neonatal encephalopathy by an abnormal neurological exam and/or an amplitude-integrated electroencephalogram (aEEG). * Evidence of brain injury on a brain magnetic resonance imaging (MRI) performed on day 2 of life. Exclusion Criteria: * Neonates with complex congenital heart disease * Neonates with cerebral malformations * Neonates with genetic syndrome * Neonates with intraventricular and/or intraparenchymal hemorrhage on MRI performed on day 2 of life