HIE - Hypoxic Ischemic Encephalopathy

Brain InjuriesPerinatal hypoxic-ischemic encephalopathy (HIE) is one of the most serious and life-threatening types of infant brain damage that can occur during childbirth. HIE occurs when both oxygen and blood supply to a baby's brain is restricted or interrupted during childbirth (perinatal asphyxia) which causes brain cells to die after short periods.

What Is Hypoxic Ischemic Encephalopathy (HIE)?

HIE is a very serious type of infant brain damage that occurs during childbirth when the baby’s brain is deprived of blood and oxygen. The blood and oxygen deprivation causes cells in the baby’s brain to die within minutes.

Encephalopathy is a medical word that is used to reference various related conditions resulting from injury to the brain. Hypoxic ischemic encephalopathy (HIE) is a specific type of brain injury triggered by a combination of (1) hypoxia -- an interruption of oxygen circulation; and (2) ischemia - - blood flow restriction. Perinatal HIE occurs when blood and oxygen to the brain are simultaneously reduced or cutoff during childbirth or immediately after. HIE is a relatively rare event, occurring in about 3 out of every 1,000 births.

What Causes Hypoxic Ischemic Encephalopathy (HIE)?

HIE is caused by acute loss of blood and oxygen flow to a baby’s brain during childbirth or during pregnancy. The deprivation of oxygen and blood causes cells in the baby’s developing brain to rapidly decay and then die. The oxygen deprivation that causes HIE is usually caused by obstetric complications during the labor and delivery process, but it can also result from prenatal complications or events. Complications that can cause HIE include:

Labor & Delivery Complications:

Neonatal Complications:

Effects of HIE

HIE is an extremely serious type of brain injury. Even though it only occurs in less than .05% of all births, HIE is one of the leading causes of infant mortality in the U.S. every year.

Aside from being life-threatening, HIE also causes permanent brain damage. Somewhere between 15-20% newborns diagnosed with HIE will die in the first week. From the remainder that survives, 25% will suffer permanent brain damage to various degrees of severity. Brain injuries from HIE often result in physical disabilities and cognitive impairment.

A smaller percentage of babies with HIE have great outcomes. These children fully recover and experience only mild, if any, symptoms of neurologic injury.  There is no data on life expectancy for the 80-85% of children with HIE how survive the first week of life.  But clearly in severe cases, there is an impact on predicted life expectancy. 

Symptoms of HIE

HIE symptoms immediately after birth will vary significantly based primarily on the severity of the underlying brain damage:

Mild HIE

  • Tendon reflexes are abnormal and muscles are stiff in the  first few days
  • Extreme irritability, feeding problems, and excessive crying or sleeping
  • Symptoms of mild HIE often resolve within a few weeks

Moderate HIE

  • Lack of muscle tone (floppy baby syndrome) with an absence of reflexes
  • Cannot grasp and has a poor sucking reflex
  • Sporadic apnea
  • Seizures (typically within the first day)

Severe HIE

  • Extreme seizures which increase in frequency in first 2 days
  • Not responsive to external stimulus
  • Irregular breathing
  • Extreme hypotonia (like a rag doll)
  • Abnormal eye control or movement with dilated pupils
  • Abnormal heart rate and blood pressure
  • Cardiorespiratory failure (often fatal)
Treatment for HIE

The primary treatment for HIE that has gained steam in recent years is body and head cooling. This treatment is commonly referred to as therapeutic hypothermia. Therapeutic hypothermia aims to bring the baby’s body temperature below normal immediately after birth. This effectively slows down the cellular decay and damage process within the brain. By slowing down this process hypothermia therapy aims to minimize the long term impact of HIE Unfortunately, damage to the brain from newborn hypoxia is permanent and cannot simply be fixed with surgery or medications. So HIE is a permanent injury. Treatment options involve therapy and medication to help manage the effects of any brain damage. Babies with severe HIE injuries will often need life-long support and accommodations.

But there are also amazing HIE recovery stories where the child was through to have a permanent injury who has a fantastic outcome. Success stories after HIE are not uncommon.  Ultimately, the scope of the child's injury, and this is no consolation to parents, is often not fully understood until the child is much older. 

Scientific Sources

Yıldız, et al. "Neonatal hypoxic ischemic encephalopathy: an update on disease pathogenesis and treatment." Expert review of neurotherapeutics 17.5 (2017): 449-459.

Molloy, Eleanor J., and Cynthia Bearer. "Neonatal encephalopathy versus hypoxic-ischemic encephalopathy." (2018): 574-574.

Finder, Mikael, et al. "Two-year neurodevelopmental outcomes after mild hypoxic ischemic encephalopathy in the era of therapeutic hypothermia." JAMA pediatrics 174.1 (2020): 48-55.

Greco, P., et al. "Pathophysiology of hypoxic–ischemic encephalopathy: a review of the past and a view on the future." Acta Neurologica Belgica 120.2 (2020): 277-288.