Hypoxic-Ischaemic Encephalopathy
Hypoxic-ischaemic encephalopathy is a serious brain injury that occurs when a newborn’s brain doesn’t receive enough oxygen and blood during birth or shortly after. While some children recover completely, others may face lifelong challenges affecting their movement, learning, and development.
Table of contents
- What is hypoxic-ischaemic encephalopathy?
- Other names for this condition
- How common is HIE?
- What causes HIE?
- Who is at higher risk?
- Signs and symptoms
- Levels of severity
- How is HIE diagnosed?
- Treatment options
- Long-term effects and complications
- What is the outlook?
What is hypoxic-ischaemic encephalopathy?
Hypoxic-ischaemic encephalopathy, commonly known as HIE, is a type of brain injury that happens when a baby’s brain does not receive enough oxygen and blood flow[1]. This condition typically occurs before birth, during labor and delivery, or shortly after birth[2].
The term describes three important aspects of the condition. Hypoxic means the brain did not receive enough oxygen. Ischaemic means blood flow to the brain was restricted. Encephalopathy refers to a brain disorder or dysfunction[5].
Brain tissue requires a constant supply of oxygen and nutrients delivered through blood. When this supply is interrupted, brain cells begin to break down and die. These dying cells release substances that are toxic to other cells, creating a chain reaction that causes brain injury to spread over hours or days[8].
The severity of HIE and its long-term effects depend on several factors: how long the brain was without oxygen or blood flow, how much of the brain was affected, and how the individual’s brain repairs itself[1]. Brain damage from HIE can also affect other organs in the body, including the heart, lungs, kidneys, and liver[1].
birth asphyxia, neonatal encephalopathy, perinatal asphyxia, perinatal encephalopathy
Other names for this condition
Healthcare providers may use different terms when referring to HIE. You might hear it called birth asphyxia, neonatal encephalopathy, perinatal asphyxia, or perinatal encephalopathy[1][2]. All these terms describe the same basic problem: a brain injury caused by lack of oxygen and blood flow around the time of birth.
How common is HIE?
HIE affects an estimated 1 to 6 infants out of every 1,000 births[2]. In the United States, this equals approximately 9,000 to 12,000 newborns each year[2]. Some sources estimate it occurs in 2 to 4 of every 1,000 births[5].
Globally, birth asphyxia causes 840,000 or 23% of all newborn deaths worldwide[7]. Many infants who survive sustain significant brain injury and develop long-term health problems[16].
What causes HIE?
HIE is caused by an interruption of blood and oxygen supply to the brain[2]. This interruption can happen at different times: during pregnancy (the prenatal period), during labor and delivery, or following birth (the postnatal period)[5].
During pregnancy
Problems during fetal development that can lead to HIE include abnormal development or function of the baby’s heart or lungs, infections such as toxoplasmosis or CMV, blood pressure that is too high or too low in the pregnant mother, low oxygen levels in the pregnant mother, severe fetal anemia, fetal heart disease, and fetal lung malformations[2][5].
During labor and delivery
Many complications during labor and delivery can restrict oxygen and blood flow to the baby. These include problems with the umbilical cord (such as the cord dropping out of place before the baby, compression of the cord, or knots in the cord), the placenta separating from the uterus before birth (placental abruption), the placenta blocking the cervix (placenta previa), the uterus tearing open (uterine rupture), prolonged labor, bleeding from the placenta, slow fetal heart rate, and maternal infections[2][3][5].
After birth
Following birth, HIE can result from prematurity, trauma to the brain or skull during delivery, lung or heart disease, infections such as sepsis, low blood pressure in the baby during delivery due to maternal or placental complications, respiratory failure, or cardiac arrest[5].
Often the exact cause of HIE is unknown[3]. In many cases, multiple factors contribute to the oxygen deprivation.
Who is at higher risk?
While most cases of HIE cannot be prevented, certain factors can make it more likely[1].
Factors related to the baby include low birth weight, contamination of the amniotic fluid (the fluid surrounding the baby in the womb), and delayed fetal development where certain organs like the lungs did not develop completely[2].
Factors related to the pregnant parent include preeclampsia (high blood pressure during pregnancy), low blood pressure during delivery, gestational diabetes, prolonged labor, substance use disorder, problems with the uterus or placenta, emergency cesarean section (C-section), maternal infections, and poor positioning during delivery (such as the baby’s shoulders getting stuck for prolonged periods)[1][2][3].
Very premature births and physical trauma to the brain or skull also increase the risk[1].
Signs and symptoms
Symptoms of HIE can appear immediately during or after birth, or they may become apparent over the first few hours or days of life. The signs can vary from baby to baby and depend on which parts of the brain were damaged and how severely[3].
Immediately during or after the brain injury, the infant may show a low heart rate, breathing problems, too much acid in body fluids (acidosis), seizures or unusual movements, stained meconium (a newborn’s first stool), low muscle tone, blue or very pale skin, and low reflexes[1].
Other early symptoms include an unusual state of being awake and aware (such as being highly alert or having very low energy), trouble breathing, not eating properly, trouble with hearing or vision, muscle problems (either floppy, weak muscles called hypotonia, or tense, stiff muscles called hypertonia), a weak cry, seizures or other neurological problems, slow heart rate, and organ failure[3][5].
In more severe cases, symptoms include little to no response to touch or sound, poor reflexes, abnormal breathing patterns, an irregular or slow heartbeat, seizures, and loss of consciousness[2].
The full extent of damage from HIE may not be understood for several months or years after the brain injury occurs[1]. Sometimes problems are not identified until the child begins attending school or starts missing developmental milestones such as crawling or walking[8].
Levels of severity
Healthcare providers classify HIE based on the severity of symptoms. These classifications help predict outcomes and guide treatment decisions. All levels of HIE require immediate medical attention[2].
Mild HIE
Babies with mild HIE may show behavioral issues such as poor feeding, irritability, excessive crying or sleepiness (often in an alternating pattern). Muscle tone may be slightly increased and reflexes may be brisk during the first few days. Symptoms typically resolve within 24 hours[5][7][9].
Moderate HIE
In moderate HIE, the infant is lethargic with significant weakness and diminished reflexes. The grasping, Moro (startle reflex), and sucking reflexes may be sluggish or absent. The infant may experience occasional periods when breathing stops temporarily (apnea). Seizures typically occur early, within the first 24 hours after birth. Full recovery within one to two weeks is possible and is associated with a better long-term outcome[7][9].
Severe HIE
Severe HIE symptoms are far more serious. The baby may be in a stupor or coma and not respond to any physical stimulus except the most painful. Breathing is often irregular and the baby may require a breathing tube and machine to help with breathing. There is generalized weakness and depressed reflexes. Neonatal reflexes such as sucking, swallowing, and grasping are absent. Unusual eye movements may occur, such as eyes pointing in different directions, jerky movements, or bobbing. Pupils may be dilated, fixed, or poorly reactive to light[7][9].
Seizures can be delayed and severe in cases of severe HIE, and may initially resist conventional treatments. Problems with heart rate and blood pressure are common. As the injury progresses, the soft spot on the baby’s head (fontanelle) may bulge, suggesting increasing swelling in the brain (cerebral edema)[7].
How is HIE diagnosed?
Doctors often suspect HIE in a newborn shortly after birth based on the child’s symptoms, such as seizures, and any problems that occurred during pregnancy, labor, or delivery[3][9].
Several types of tests help confirm the diagnosis and determine the extent of brain injury. Blood tests can measure oxygen levels, acid levels in body fluids, and organ function. These tests help assess how severely the lack of oxygen affected the body[1].
Brain imaging studies provide detailed pictures of the brain to identify areas of damage. Ultrasound uses sound waves to create images of the brain through the soft spot on the baby’s head. Magnetic resonance imaging (MRI) uses magnets and radio waves to produce detailed pictures of brain structures and can show areas where cells have been damaged. Computed tomography (CT) scans use X-rays to create cross-sectional images of the brain[10].
An electroencephalogram (EEG) measures electrical activity in the brain. This test can detect seizures, including those that may not be visible on the outside, and help assess brain function. In severe HIE, the EEG may show very little brain activity or a burst suppression pattern[7][10].
Doctors also evaluate the newborn’s responsiveness, muscle tone, reflexes, and ability to breathe on their own. They review the baby’s Apgar scores, which are measurements of a baby’s condition taken at one minute and five minutes after birth[9].
Treatment options
Treatment for HIE focuses on preventing further brain injury and supporting the baby’s vital functions. The most important treatment for moderate to severe HIE is therapeutic hypothermia, also called cooling therapy[11].
Therapeutic hypothermia (cooling therapy)
Therapeutic hypothermia involves carefully lowering the baby’s body temperature to reduce brain damage. The baby’s body is cooled to about 33.5 degrees Celsius (92.3 degrees Fahrenheit) for 72 hours, then slowly warmed back to normal temperature[13].
This treatment must be started within six hours after birth to be effective[11]. Cooling therapy works by slowing down the chain reaction of cell death that happens after the brain is deprived of oxygen. It can help prevent or minimize permanent brain damage[8][13].
Studies have shown that therapeutic hypothermia can reduce the mortality rate and the severity of brain damage caused by HIE[13]. It is now the standard of care for infants with moderate-to-severe HIE[11].
Supportive care
In addition to cooling therapy, babies with HIE need careful supportive care. This includes ensuring adequate oxygen delivery and breathing support, sometimes using a breathing machine (ventilator). Blood pressure and heart function must be carefully monitored and maintained at appropriate levels. Healthcare providers must avoid low blood sugar (hypoglycemia) and high blood sugar (hyperglycemia), as both can worsen brain injury[11].
Fluid levels and electrolytes (minerals in the blood) need careful management. Preventing fever (hyperthermia) is critical, as increased body temperature can worsen brain damage[11].
Treatment of seizures
Many babies with HIE experience seizures, which can cause additional brain injury. Doctors treat seizures with anti-seizure medications. In most cases, these medications can be stopped before the baby leaves the hospital, depending on brain function and EEG findings[11].
Ongoing care and therapies
After the initial treatment, babies with HIE often need ongoing care and therapies. Physical therapy can help with movement and motor skills. Occupational therapy assists with daily living skills. Speech and language therapy helps with communication and feeding problems. Some children may need assistive devices such as walkers or wheelchairs[11].
Long-term effects and complications
HIE is a serious condition that can be fatal or lead to permanent brain damage. The extent of long-term effects varies widely depending on the severity of the initial injury and how well the brain recovers[2].
Brain injuries from HIE can cause developmental delays, where children are slower to reach milestones such as sitting, crawling, walking, or talking. Intellectual disabilities may affect learning and problem-solving abilities. Epilepsy, a condition causing repeated seizures, can develop. Cerebral palsy, which affects muscle tone, movement, and posture, is one of the most common long-term effects of HIE[1][2].
Children may also experience hearing or vision problems, feeding difficulties, trouble with coordination, behavior problems, and cognitive or emotional challenges[5].
Because brain damage can affect other organs as well, children with HIE may have heart problems or cardiac arrest, lung problems, kidney problems, or liver problems[1].
It is important to note that some children who experience HIE at birth may not have any long-term consequences. Others can experience mild to severe disabilities[1]. The severity of these symptoms may not become apparent until ages three to four, when developmental differences become more noticeable[3].
What is the outlook?
The outlook for children with HIE varies greatly depending on the severity of the brain injury. Children with mild HIE generally have a good prognosis, with symptoms often resolving within 24 hours and minimal long-term effects[7].
For moderate HIE, full recovery within one to two weeks is possible and is associated with better long-term outcomes[7]. However, some children may still develop disabilities.
Severe HIE carries a much more serious prognosis. After an HIE diagnosis, 40% to 60% of infants either do not survive past two years of age or suffer a severe intellectual disability[13]. However, cooling therapy has been shown to improve these outcomes for many babies[13].
Once permanent brain damage has occurred, there is no cure for HIE. However, many treatments and therapies can improve symptoms and function in children with HIE[8]. Early intervention services, ongoing medical care, and supportive therapies can help children reach their full potential.
Close monitoring and regular follow-up care are essential after discharge from the hospital. Physical therapy and developmental evaluations help track progress and address problems early[11]. Even after discharge, children with HIE benefit from continued support and regular check-ups to optimize their development and quality of life.