Hypoxic-Ischemic Encephalopathy (HIE)

Hypoxic-ischemic encephalopathy (HIE) is a life-threatening brain injury caused by impaired blood and oxygen supply to an infant’s brain. When the brain is deprived of oxygen and nutrients, the resultant damage can be severe and permanent. HIE is one of the leading causes of cognitive impairment, physical disability, and death in infants.

What Causes Hypoxic-Ischemic Encephalopathy?

HIE is often the result of asphyxia during a traumatic birth. High-risk pregnancies and signs of maternal and fetal distress during labor should be monitored closely to minimize the risk of asphyxia. The following are possible causes of asphyxia:

  • Severely low maternal blood pressure
  • Prolapsed umbilical cord
  • Uterine rupture
  • Placental abruption
  • Hemorrhage during labor
  • Impaired breathing or lung function of the infant
  • Compression of the umbilical cord

What Happens to the Brain?

In HIE, an infant’s brain does not receive sufficient oxygen- and nutrient-rich blood. Within minutes, brain cells are damaged and can no longer function. In severe asphyxia, cell death may occur. Once blood flow returns to the brain, the infant is at risk for subsequent injury (referred to as “reperfusion injury”) caused by the release of toxins from damaged cells or hemorrhage to the blood vessels of the brain.

Depending on the gestational age of the infant and the severity of the asphyxia, varying degrees of brain damage occur. In premature newborns, the white matter of the brain is most often affected, a condition known as periventricular leukomalacia (PVL). Although term infants may also suffer PVL, as well as injury to the deeper, gray structures, such as the basal ganglia, thalamus, and hippocampus.

Complications of HIE

Infants with HIE are at risk for many of the following complications:

  • Low blood pressure
  • Damage to other organs (kidneys, heart, liver) caused by low blood pressure
  • Seizures
  • Stupor or coma
  • Stroke
  • Hypotonia and muscle weakness
  • Difficulty feeding
  • Apnea

Long-term complications resulting from HIE depend on the severity of blood and oxygen deprivation. Cognitive impairment, cerebral palsy, seizure disorder, and deficits in behavior, motor skills, and visual function are examples of permanent and debilitating effects of HIE.

Diagnosing HIE

After a hypoxic-ischemic event, the injury can be detected through ultrasound, CT scan, or MRI of the brain. Depending on the severity of the injury and the gestational age of the newborn, brain imaging will reveal varying patterns of injury to white matter, gray matter, or deep gray matter. Brain imaging may also determine whether the injury occurred prior to or during birth.

Damage from a hypoxic-ischemic event that occurred during delivery will appear on a brain imaging study within 24 hours after birth. After the first few days of life, brain scans may appear falsely normal. However, two to three weeks following birth, scans will begin to reveal loss of brain matter and abnormal accumulation of fluid in the brain’s ventricles.

Treatment for HIE

Priority treatment involves immediate resuscitation after delivery. The infant may be placed on a ventilator for supportive breathing. Goals for treatment include maintaining sufficient blood flow to the brain and the rest of the body, preventing swelling in the brain, and managing seizures. Therapeutic hypothermia—or cooling of the infant’s brain (and possibly the whole body)—has been shown to help slow progression of brain damage. Long-term treatment is individualized depending on the severity of the cognitive, motor, and sensory impairments.