Hypoxic-Ischemic Encephalopathy (HIE)

Definition

Hypoxia refers to a reduction in the supply of oxygen to organs including the brain. Ischemia refers to an inadequate supply of blood to the organs. Encephalopathy is a term used to describe any form of generalized brain dysfunction. Hypoxic-Ischemic Encephalopathy (or HIE) is a non-specific term for brain dysfunction caused by a lack of blood flow and oxygen to the brain. Sometimes, HIE is also referred to as birth asphyxia, but this term only pertains to a very strict criteria of infants with brain injury.

Alternate names

HIE

Causes, incidence and risk factors

How and when does HIE occur?

There are many problems during pregnancy, labor, delivery, and after delivery that can cause HIE. However, in many cases the cause of HIE is not known.

Possible problems during pregnancy

Preeclampsia, maternal diabetes with vascular disease, congenital infections of the fetus, drug and alcohol abuse, severe fetal anemia, cardiac disease, lung malformations, problems with blood flow to the placenta.

Problems during labor and delivery

Umbilical cord accidents, rupture of the placenta or uterus, excessive bleeding from the placenta, abnormal fetal position, prolonged late stages of labor, very low blood pressure in the mother (caused by drugs, bleeding, anesthesia.)

Problems after delivery

Severe prematurity, severe lung or heart disease, serious infections (especially meningitis or sepsis), trauma to the brain or skull, congenital malformations of the brain, very low blood pressure in the baby.

How common is HIE?

Regarding full-term infants, HIE occurs in approximately 3-20 per 1000 live births. In the preterm infant, HIE occurs in up to 60% of live births.

Types

  • Mild HIE: Less than 5% of these infants will have a severe handicap.
  • Moderate HIE: 25% to 75% of these infants will have a severe handicap or potentially die early in life.
  • Severe HIE: 75% or more of these infants will have a severe handicap or potentially die early in life.

Signs and symptoms

Before Birth

  • Measurements of fetal movement and/or heart rate variability before birth.
  • The presence of meconium (the baby’s first stool) in the amniotic fluid. This is a poor predictor of increased risk for HIE, but may indicate the fetus was in distress prior to birth.

Clinical Evaluation

  • APGAR Score (scores given to infants after birth as a measure of the infant’s well-being)
  • APGAR scores remaining low for more than 10 minutes may correlate with HIE severity.
  • An abnormal neurologic exam is essential for making the diagnosis of HIE. Some of the abnormal findings on physical exam are:
    • Changes in mental status (decreased alertness)
    • Increased or decreased muscle tone
    • Seizures
    • Abnormal pupils
    • Changes in reflexes
    • Changes in breathing and heart rate
  • The exam is repeated 2-3 times a day for the first several days of life to help the doctor determine if the infant is improving or worsening.
  • EEG: electrodes are placed on the infant’s scalp to evaluate the brain’s electrical activity. EEG finding can help identify seizure activity and also may correlate to the infant’s outcome. EEG data is read by a pediatric neurologist

Tests, treatments

Laboratory Evaluation

Blood tests can evaluate for evidence of other injured organs caused by HIE. This is because a decrease in blood flow and oxygen can affect all organs and not just the brain. The kidneys, liver, heart, and lungs are the most common organs affected by HIE. Umbilical cord blood samples may show an increase acid build-up. This can be a sign that the infant was in distress prior to birth.

Radiological Evaluation

Brain imaging, using Ultrasound, CT scans (computed tomography) and MRI (magnetic resonance imaging) may be used to evaluate for an underlying brain malformation and to look for evidence of brain injury. Currently, MRI is the most sensitive way to look for brain injury, but the infant may be too sick to transport for MRI or he/she may not tolerate the long scanning time (approximately 45 minutes).

How is HIE treated?

Unfortunately, there is no definitive treatment for infants with HIE. Most therapies are directed at supporting the infant’s affected organs including:

    • Supporting the heart and blood pressure
    • Sustaining kidney and liver function
    • Mechanical ventilation may be required if the infant cannot breath completely on their own
    • If the baby has seizure, they must be controlled with medications

Currently, the only brain-specific therapy that has been proven to reduce the risk of long-term neurodevelopmental handicaps is brain or whole body hypothermia (cooling the infant’s body temperature to approximately 33.5 degrees Celsius or 92 degrees Fahrenheit) for 3 days. See Hypothermia.

Support groups

Expectations (prognosis)

The disabilities infants with HIE display as they grow vary with the severity of HIE. While infants with mild HIE exhibit little to no long-term disabilities, infant who have suffered moderate to severe HIE may die in the newborn period or have medical conditions including Cerebral Palsy, Mental Retardation, feeding difficulties, learning disabilities, visual or hearing impairment and seizures.

Prognosis based on clinical classification is as follows:

      • Mild HIE: Less than 5% of these infants will have a severe handicap.
      • Moderate HIE: 25% to 75% of these infants will have a severe handicap or potentially die early in life.
      • Severe HIE: 75% or more of these infants will have a severe handicap or potentially die early in life.