Hypoxic ischemic encephalopathy (HIE) is a brain injury that occurs around birth and is caused by a lack of blood flow to the brain. Babies with HIE are at risk of long-term physical and cognitive impairments.

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Hypoxic ischemic encephalopathy (HIE) is a brain injury that occurs due to a lack of oxygen.

The name can be broken down into three parts:

  • hypoxic, meaning to have too little oxygen
  • ischemic, meaning restricted blood flow
  • encephalopathy, meaning altered brain function

HIE is a complication that can occur in babies before, during, or immediately after birth. It’s called neonatal HIE when it occurs in infants. Moderate to severe HIE can cause potentially life threatening complications or lifelong disability.

HIE can occur in older children and adults too, often as a result of conditions like cardiac arrest or asphyxiation.

This article focuses on neonatal HIE. Read on to learn more about its symptoms, treatment options, and potential complications.

Hypoxic ischemic encephalopathy (HIE) happens when a baby's brain doesn't get enough oxygen. Share on Pinterest
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The brain needs oxygen to function. With a complete lack of oxygen in the brain, permanent brain injury and death can occur in under 5 minutes.

Neonatal HIE happens when a baby’s brain is deprived of oxygen-rich blood. This typically occurs during labor and delivery, but it can occur before or soon after birth. A lack of blood flow to the brain can lead to brain injury or even death if oxygen flow isn’t reestablished.

Brain injury tends to be more severe the longer oxygen flow is disrupted and the lower the baby’s oxygen level drops. As a result of this, HIE can range from mild to severe. Mild HIE may cause few to no long-term complications. Moderate to severe HIE can lead to a number of physical and cognitive impairments.

Brain injury occurs in three stages:

  1. immediate brain cell injury from lack of oxygen and glucose
  2. a latent period of about 6 hours where some brain cells recover
  3. a second injury phase over the next 24 to 48 hours as blood flow increases and toxic neurotransmitters spread

Treatments initiated during this time frame can have a significant effect on long-term outcomes.

How common is HIE?

HIE occurs in 1 to 5 births per 1,000 in developed countries and in as many as 20 per 1,000 births in low- to middle-income countries.

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Symptoms of HIE can vary in severity from mild to severe. They’re typically apparent shortly after birth, but they can sometimes be missed. Symptoms of neonatal HIE may include:

  • decreased muscle tone (hypotonia), which may appear as “floppiness”
  • atypical eye movements or pupil reflexes
  • poor or no ability to feed
  • periods of breathing cessation (apnea)
  • deeper than usual breaths (hyperpnea)
  • seizures

Most cases occur during difficult births. HIE can happen during labor or during the delivery itself. It can also appear after birth if your baby needs resuscitation or experiences other complications.

Potential causes of HIE include:

  • disrupted blood flow to the placenta (placental insufficiency)
  • placental abruption, or early separation of the placenta from the uterus
  • high or low blood pressure in pregnant person
  • low oxygen levels in the blood in pregnant person
  • umbilical cord compression or prolapse
  • meconium aspiration syndrome, when your baby inhales a mix of amniotic fluid and their first feces
  • uterine rupture
  • severe infection
  • low blood count or blood pressure in baby
  • lung or heart failure in baby
  • problems with lung or heart development

Risk factors

Potential risk factors for HIE include:

A doctor or nurse will perform the Apgar test shortly after birth to measure how well your baby functions outside the womb. These tests are usually performed at 1 and 5 minutes after birth. They evaluate:

  • breathing
  • heart rate
  • muscle tone
  • skin color
  • reflexes

If your child has a low Apgar score, the healthcare professional may suspect that your baby isn’t getting adequate oxygen, especially if there were complications during the delivery.

A doctor may perform other tests to look for potential complications, such as:

  • blood tests
  • umbilical cord or placenta blood testing
  • heart function tests
  • head ultrasound to look for fluid buildup in the brain
  • electroencephalography to check brain activity

To help diagnose HIE, the American College of Obstetricians and Gynecologists (ACOG) recommends a brain MRI within 24 to 96 hours of birth.

Your baby’s doctor will use test results, clinical signs, and other information to help them make an HIE diagnosis. Because action needs to be taken immediately, your baby may be treated before receiving an HIE diagnosis.

The doctor might not make a diagnosis for several days.

ACOG recommends another MRI 10 days after birth to evaluate the extent of brain injury. But the true extent of the damage might not be realized for some time.

What to expect during a postnatal MRI?

MRI is an imaging technique that can show doctors which parts of the brain have damage. Your baby will need to remain still during the scan for 15 to 90 minutes. To achieve this, healthcare professionals may swaddle or sedate your baby.

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The standard treatment for moderate to severe HIE is therapeutic hypothermia, also known as cooling therapy. There’s strong evidence that it can minimize brain damage.

Cooling therapy involves lowering your baby’s temperature with a special blanket or cap and a machine. Your child will have their vitals such as their heart rate and brain wave activity monitored closely during the treatment.

Therapeutic hypothermia is ideally initiated during the first 6 hours after birth. The standard therapy is 33°C to 34°C for 72 hours. This period is usually followed by a 6- to 12-hour period of rewarming, usually increasing the temperature by 0.5°C every 1 to 2 hours.

An MRI is often performed shortly after rewarming to reassess brain damage.

The Canadian Paediatric Society recommends following up with babies who receive hypothermia treatment for at least 2 years and ideally until they reach school age.

HIE can cause a number of different complications. They’ll depend on which parts of the brain are damaged and the severity of that damage.

About 20% to 50% of newborns with HIE die shortly after birth.

Surviving babies with moderate to severe HIE can develop long-term brain damage that can lead to complications such as:

Some of the complications of HIE, like learning disabilities, may not become noticeable until your child is school-aged.

What is brain plasticity?

Neuroplasticity, or brain plasticity, is the ability of the cells in your brain to create new pathways to adapt to damaged areas. It’s thought that neuroplasticity plays an important role in recovery from brain injury. Researchers are still investigating the role neuroplasticity plays in healing from HIE.

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Long-term outlook

About 25% to 60% of surviving infants have long-term complications. More severe HIE is associated with a higher chance of complications or death.

Prompt treatment with therapeutic hypothermia can significantly decrease the chances of long-term complications. Infants with moderate to severe HIE who receive hypothermic treatment within their first 6 hours of life have a significantly lower risk of death or lifelong complications.

If complications are severe, your child may need lifelong care. However, most children are still able to live typical lives.

  • Neonatal HIE is a brain injury that occurs around birth and is caused by a lack of blood flow to the brain.
  • There are many potential causes of HIE, such as disrupted blood flow to the placenta or chord problems.
  • Cooling therapy is the standard treatment for HIE. It involves cooling your baby for 72 hours to limit brain damage.
  • Initiating cooling therapy promptly within 6 hours of birth gives your baby the best chance of avoiding long-term complications.