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Types & Forms of HIE

There are three levels of HIE: mild, moderate, and severe. The severity of HIE is determined using Sarnat staging, which takes into account clinical presentation, exam results, seizure presence, and illness duration.  Mild HIE is classified as Sarnat Grade I, and severity increases up to a maximal Stage III.

Mild

Mild Hypoxic Ischemic Encephalopathy (HIE) is a type of brain injury that occurs when a baby’s brain doesn't get enough oxygen (hypoxia) and/or blood flow (ischemia) around the time of birth. “Mild” refers to the least severe form of this condition. During labor, delivery, or shortly after birth, a baby may experience reduced oxygen and blood flow to the brain. This can damage brain cells and affect brain function, depending on how long and severe the lack of oxygen was.

What does “Mild HIE” mean?

In mild HIE, babies may:

  • Be slightly irritable or jittery

  • Have trouble feeding initially

  • Show slightly abnormal muscle tone (e.g., a bit floppy or stiff)

  • Recover quickly within a few days

Unlike moderate or severe HIE, mild HIE often doesn’t cause long-term problems, but close monitoring is still important because:

  • Some subtle developmental or cognitive issues might emerge later

  • Early intervention, if needed, can help reduce risks

Diagnosis & Monitoring

Doctors typically diagnose HIE through a combination of:

  • Apgar scores (at birth)

  • Physical signs

  • Imaging like MRI

  • Umbilical cord blood gases (to check for acidosis)

  • EEGs to monitor brain activity

Good To Know

Many babies with mild HIE go on to develop normally.

  • Follow-up care with developmental specialists is common to catch any early signs of issues.

  • Cooling therapy (hypothermia treatment) is usually reserved for moderate to severe cases, not mild ones.

Moderate

Moderate HIE is a middle-level brain injury caused by a reduction in oxygen (hypoxia) and/or blood flow (ischemia) to a baby’s brain, typically around the time of birth. It’s more serious than mild HIE, and babies with this diagnosis usually show clear signs of neurological distress.

What does “Moderate HIE” mean?

In moderate cases, babies may:

  • Be very sleepy or lethargic—not waking or feeding well

  • Have low muscle tone (floppy limbs)

  • Show weak or absent reflexes (like sucking or grasping)

  • Experience seizures

  • Have abnormal breathing patterns

  • Often require support in the NICU

Diagnosis & Monitoring

Moderate HIE is typically diagnosed through:

  • Physical exam: Noting neurological signs and behavior

  • MRI or ultrasound: To visualize any brain injury

  • EEG: To check for seizures or abnormal brain activity

  • Blood tests: To assess for acidosis or organ function

  • Cooling therapy (therapeutic hypothermia) is standard for moderate HIE. It involves lowering the baby’s body temperature for 72 hours to help protect the brain and limit further damage.

Prognosis & Outcomes

Many babies with moderate HIE recover well, especially with early treatment like cooling therapy.

  • Some may have long-term effects, such as:

    • Mild to moderate motor delays

    • Learning differences

    • Attention or coordination challenges

  • Close follow-up with neurology, developmental pediatrics, and therapy services is often recommended.

Severe

Severe HIE is the most serious form of brain injury caused by a significant lack of oxygen and/or blood flow to a baby’s brain, usually around the time of birth. This level of injury often affects multiple areas of the brain and requires immediate, intensive medical care.

What does “Severe HIE” mean?

In severe cases, babies may:

  • Be unresponsive or comatose

  • Have very low or no muscle tone (extremely floppy)

  • Show no normal reflexes (like sucking, grasping, or even breathing without help)

  • Experience frequent, hard-to-control seizures

  • Have difficulty regulating basic functions (heart rate, temperature, blood pressure)

  • Often require a ventilator and full NICU support

Diagnosis & Treatment

Severe HIE is diagnosed through:

  • Neurological exam showing very poor or absent brain function

  • MRI/CT scan showing extensive brain injury

  • EEG showing severely abnormal brain activity

  • Blood and organ function tests, as multiple systems may be affected

  • Cooling therapy may still be attempted in some severe cases, but outcomes are less predictable than in moderate cases.

  • Some families are also faced with difficult decisions about life support and long-term care early on.

Prognosis & Long-Term Outlook

Many children with severe HIE will have lasting disabilities, including:

  • Cerebral palsy

  • Severe developmental delays

  • Epilepsy

  • Feeding difficulties (may require a feeding tube)

  • Vision or hearing impairments

  • Some babies with very severe injury may not survive the newborn period

  • Every child is different—but outcomes tend to reflect the extent and location of brain injury