Sildenafil Plus Hypothermia to Treat Neonatal Encephalopathy

Inclusion Criteria: * 1/Neonates born at or after 36 weeks' gestation, treated by therapeutic servo-controlled hypothermia for neonatal hypoxic ischemic encephalopathy. Therapeutic hypothermia should be decided according to French national guidelines. * 2/ Social security coverage * 3/ Informed consent of one of the two holders of parental authority. Exclusion Criteria: * 1/ Chromosomal aberrations and major malformations evidenced after birth * 2/ Decision for "comfort care only" before study drug administration, * 3/ Uncontrolled hemorrhagic syndrome, * 4/ Severe hemodynamic failure at initiation, requiring at least two therapies (including either volume expansion, hydrocortisone or inotropes) * 5/ Known hypersensitivity to the active substance or to any of the excipients * 6/ Concomitant administration of nitrates or nitric oxide donors, Inhaled Nitric Oxide, other PDE5 inhibitors, inhibitors of CYP3A4 * 7/ Participation in another interventional study