• Hypoxic‑ischemic encephalopathy (HIE) is a brain injury caused by a lack of oxygen and blood flow to the brain, often around the time of birth.
• HIE is a leading cause of cerebral palsy and other lifelong disabilities, but outcomes vary widely depending on how severe and how long the lack of oxygen lasted.
• Rapid recognition and treatment, including therapeutic hypothermia (cooling) started in the first hours after birth, can reduce the risk of death and severe disability in some infants.

---

What Is Hypoxic‑Ischemic Encephalopathy (HIE)?

HIE injury is a significant cause of Cerebral Palsy. Alissa Palaszynski, the founder of The BRIGHT Foundation’s daughter, suffered from an HIE injury at birth due to an Amniotic Fluid Embolism. Read a deeply personal account of Alissa’s birth story and early years after Amniotic Fluid Embolism & HIE. HIE is a brain injury that is caused by lack of oxygen “asphyxia” (ie, hypoxia, acidosis). HIE can occur before birth, during labor and delivery, or shortly after birth when the baby’s brain does not receive enough oxygen and/or blood flow. The resulting injury can range from mild and temporary to severe and permanent, depending on how long and how completely oxygen was interrupted.

The WHO (World Health Organization) reports 23% of neonatal deaths worldwide are due to some form of birth related HIE. HIE is also a major contributor to long‑term disabilities such as cerebral palsy, epilepsy, learning difficulties, and developmental delay in children who survive the initial injury.

---

How HIE Damages the Brain

HIE is a brain injury that is caused by lack of oxygen “asphyxia” (ie, hypoxia, acidosis). The underlying problem is that the brain is deprived of both oxygen and adequate blood flow, which are together required for normal energy production in brain cells. When this happens, brain cells cannot maintain normal function, toxic substances build up inside and around the cells, and a cascade of injury and cell death unfolds over hours to days.

Damage to the brain cells occurs at the time of the HIE event, but cell death continues for the next 48–72 hours. This “secondary” phase of injury is why treatments that slow metabolism and protect the brain, such as cooling, can make a difference even after the initial event is over.

In moderate to severe HIE, the injury can also affect other organs such as the heart, lungs, kidneys, liver, and intestines. Babies may show signs of multi‑organ dysfunction and often require support in a neonatal intensive care unit (NICU).

---

Obstetric Causes of HIE in Full‑Term Infants

HIE injuries in full term infants can be caused by a number of factors including placenta abruption or placenta previa. Abruption occurs when the placenta separates from the uterus and previa occurs when the placenta covers the cervix. Both cause excessive bleeding during labor and delivery and cause the baby to suffer from lack of oxygen.

Other causes include a ruptured Uterus (where the wall of the Uterus tears), and twisting, knotting, compression or prolapsing of the unbilical cord. These umbilical cord problems can abruptly cut off or severely reduce blood flow and oxygen to the baby and are considered emergencies. Finally, in rare cases an Amniotic Fluid Embolism (AFE) can occur. This a rare delivery complication where the amniotic fluid enters the mothers blood stream and causes colapse of the respiratory and cardiovascular systems. The prognosis for mother and child are often catestrophic with HIE often effecting both mother and child.

Other pregnancy and labor‑related factors that can contribute to HIE include things like maternal high blood pressure or preeclampsia, severe maternal infection, very long or very difficult labors, excessive uterine contractions, and delays in performing a needed cesarean section. Severe maternal blood loss or very low blood pressure can also reduce blood flow to the placenta and fetus and set the stage for HIE.

---

Non‑Birth Causes of HIE

HIE can also be caused by cardiac arrest, respiratory arrest, near‑drowning, near‑hanging, and other forms of incomplete suffocation, carbon monoxide and other poisonous gas exposures. In these situations, the mechanism of brain injury is similar: the brain does not receive adequate oxygen and blood flow for a period of time, and the same cascade of cellular injury and delayed cell death occurs.

In infants and children outside the newborn period, HIE may follow severe breathing problems, serious infections that affect the heart or circulation, choking events, or exposure to toxins that interfere with the body’s ability to deliver oxygen.

---

When During Pregnancy HIE Occurs Matters

HIE can occur at earlier points in the pregnancy. Depennding on when HIE occurs the part of the brain injured is different. This is becuase the developing brain requires more oxygen in areas of high metabolic activity, in different critical areas at differnet times. A severe lack of oxygen early in pregnancy may interfere with overall brain formation, while a late‑pregnancy or birth‑related HIE event usually produces more specific patterns of injury.

When HIE injury occurs in a full term infant, the damage is typically to the upper brainstem, thalamus, cerebellum, basal ganglia, medial temporal structures (especially the CA1 field of the hippocampus), cortical layers 3, 5, and 6, as well as the cerebral hemispheric deep white matter. These regions are highly active and particularly vulnerable to oxygen deprivation.

---

Signs and Diagnosis of HIE in Newborns

Clinicians usually suspect HIE when there has been a clear problem around the time of birth (such as an abruption, uterine rupture, or cord accident) and the baby then shows signs of neurologic depression. Common features include:

• Low Apgar scores beyond the first few minutes of life.
• Needing resuscitation or breathing support at birth.
• Poor muscle tone (a limp or “floppy” baby).
• Abnormal level of alertness (very sleepy, unresponsive, or in a coma).
• Abnormal reflexes or weak feeding and sucking.
• Seizures in the first hours or days of life.

Standard diagnostic tools in many centers include:

• Blood gases and other blood tests shortly after birth to look for acidosis and organ dysfunction.
• Electroencephalography (EEG) or amplitude‑integrated EEG (aEEG) for continuous or frequent monitoring of brain activity and seizures.
• Brain MRI in the first week of life (often between days 3 and 7) to define the pattern and severity of brain injury.
• Cranial ultrasound and, when needed, other imaging tests to evaluate bleeding or structural abnormalities.

Diagnosis blends the story from labor and delivery, physical examination, blood test results, and findings from EEG/aEEG and MRI.

---

Outcomes and Long‑Term Effects

The outcome after HIE varies widely. Some babies with mild HIE may recover with little or no obvious long‑term impairment. Others may develop one or more of the following:

• Cerebral palsy.
• Seizure disorders and epilepsy.
• Learning and intellectual disabilities.
• Speech, vision, or hearing problems.
• Behavioral and attention difficulties.
• Ongoing feeding and growth challenges.

In the most severe cases, HIE can be fatal in the newborn period or later in childhood. Because many difficulties may not be obvious in the first months of life, children who have experienced HIE typically need scheduled developmental assessments through early childhood, along with early physical, occupational, and speech therapy, to identify and address problems as soon as possible.

---

Brain Cooling and Body Cooling (Therapeutic Hypothermia)

In recent years, brain cooling and body cooling have proven to be effective mechanisms to stop the destructive effects of an HIE injury. Damage to the brain cells occur at the time of the HIE event, but cell death continues for the next 48‑72 hours. Cooling has proven to slow down the metabolic activity of the brain cells and thus spares them from further damage.

Therapeutic hypothermia usually involves lowering the baby’s core body temperature to about 33–34 degrees Celsius (approximately 91–93 degrees Fahrenheit) for 72 hours, under close monitoring in a neonatal intensive care unit. This can be done as whole‑body cooling or as selective head cooling, depending on the center. After the cooling period, the baby is rewarmed slowly, usually over several hours, to avoid sudden changes in blood flow or metabolism.

Unfortunitly, the window of oppertunity for cooling is very short. If the infant is not cooled in the first hours after birth, the technique will not help. Most treatment protocols require that cooling be started within the first several hours of life in babies who meet specific criteria (such as evidence of asphyxia and moderate to severe encephalopathy).

Even when cooling is provided promptly and correctly, some babies will still have significant disability. However, cooling has been shown to reduce the risk of death and severe disability in many infants with moderate to severe HIE, and it is now standard care in many centers.

---

Supportive Care and Rehabilitation

Beyond cooling, babies with HIE require careful supportive care of breathing, blood pressure, blood sugar, and body temperature, as well as treatment of seizures and any organ problems. They often need:

• Mechanical ventilation or other breathing support.
• Medications to support blood pressure and heart function when needed.
• Antiseizure medications to control clinical and electrical seizures.
• Careful fluid and nutrition management, sometimes including feeding tubes.

As the baby grows, early physical, occupational, and speech therapy, along with regular developmental assessments, help identify challenges early and support the best possible outcomes. Families may also benefit from counseling, social work support, and connection to community resources and support groups to help them navigate medical, educational, and emotional needs over time.

---

Prevention and Monitoring

Preventing HIE begins with good prenatal care, early recognition and treatment of maternal conditions such as high blood pressure, diabetes, and infections, and careful monitoring during labor and delivery. Key steps include:

• Regular prenatal visits.
• Monitoring fetal growth and well‑being.
• Appropriate use of labor‑inducing and labor‑augmenting medications.
• Continuous or frequent fetal heart rate monitoring when indicated.
• Rapid response to emergencies such as placental abruption, uterine rupture, or umbilical cord prolapse.

Even when all precautions are taken, some HIE events cannot be predicted or prevented. In those cases, rapid recognition, timely resuscitation, early transfer to a facility that can provide therapeutic hypothermia, and close neurologic monitoring give the best chance of limiting brain injury.