Treatment of Neonatal Encephalopathy With Oral Sildenafil Suspension to Repair Brain Injury Secondary to Birth Asphyxia

The investigators will enroll neonates with HIE treated with TH from NICUs in a multicentre, randomized, double-blind, placebo-controlled phase 2 clinical trial to evaluate the safety and efficacy of sildenafil to repair brain injury. Neonates with moderate-severe HIE on admission and with brain injury on a day-2 brain MRI (during TH) will be randomized to sildenafil or placebo (allocation 2:1) for 7 consecutive days. Aim 1: Evaluate the efficacy of sildenafil to improve brain injury (primary outcome). The investigators will determine whether sildenafil reduces brain injury on a day-30 MRI compared to the baseline day-2 MRI. Aim 2: Determine the safety of sildenafil (secondary outcome). The investigators will assess the safety of sildenafil by recording the incidence of adverse events. Aim 3: Evaluate the efficacy of sildenafil to improve cardiopulmonary hemodynamics (secondary outcome). The investigators will determine whether sildenafil improves pulmonary pressure and right/left ventricular function on day 4 of life (after TH completion) compared to baseline day-2 measurements