CoolCap Trial, Treatment of Perinatal Hypoxic-Ischemic Encephalopathy

Inclusion Criteria: Infants are assessed sequentially by criteria A, B and C listed below. Infant must meet all three criteria to be eligible for trial enrollment. * Criteria A: Infants \>= 36 weeks gestation admitted to the NICU with ONE of the following: * Apgar score of \<= 5 at 10 minutes after birth; * Continued need for resuscitation, including endotracheal or mask ventilation, at 10 minutes after birth; * Acidosis defined as either umbilical cord pH or any arterial pH within 60 minutes of birth \< 7.00; or * Base Deficit \<= -16 mmol/L in umbilical cord blood sample OR any blood sample within 60 minutes of birth (arterial or venous blood). * Criteria B: Moderate to severe encephalopathy consisting of altered state of consciousness (as shown by lethargy, stupor, or coma) AND at least one or more of the following: * Hypotonia; * Abnormal reflexes, including oculomotor or pupillary abnormalities; * An absent or weak suck; * Clinical seizures * Criteria C: At least 20 minutes duration of amplitude integrated EEG (aEEG/CFM) recording that shows abnormal background aEEG/CFM activity or seizures. The aEEG/CFM is to be performed from one hour of age. If subsequently an abnormal aEEG/CFM is recorded before 5.5 hours of age, the infant is then eligible for enrollment. The aEEG is not to be performed within 30 minutes of IV anticonvulsant therapy as this may cause suppression of EEG activity. In particular, high dose prophylactic anticonvulsant therapy (e.g., \>20 mg/kg phenobarbitone) is not to be given prior to performing the aEEG/CFM. Exclusion Criteria: * Infant expected to be \> 5.5 hours of age at the time of randomization * Prophylactic administration of high dose anticonvulsants (e.g., \>20 mg/kg phenobarbitone). After trial entry phenobarbitone or other anticonvulsant therapy is allowed to be given as clinically indicated to treat seizures. * Major congenital abnormalities, such as diaphragmatic hernia requiring ventilation, or congenital abnormalities suggestive of chromosomal anomaly or other syndromes that include brain dysgenesis * Imperforate anus * Evidence of head trauma or skull fracture causing major intracranial hemorrhage * Infant \< 1,800 g birth weight * Head circumference \< (mean - 2SD) for gestation if birth weight and length are \> (mean - 2SD) * Infant "in extremis" (i.e. an infant for whom no other additional intensive management would be offered in the judgment of the attending neonatologist) * Unavailability of essential equipment (e.g., Cool-Cap, aEEG/CFM) * Planned concurrent participation in other experimental treatments