Hypoxic-ischemic encephalopathy (HIE) is a brain injury caused by oxygen deprivation, or birth asphyxia, compounded by a decrease in blood flow to the brain. HIE is a leading cause of death among newborns, contributing to around 840,000 annual neonatal deaths worldwide, according to Medscape.
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Neonatal Hypoxic Ischemic Encephalopathy
HIE is extremely prevalent among premature babies, but also affects many newborns who are carried to term. Brain injuries can result in a wide range of severe developmental impairments, as well as the neuro-musculur disorder cerebral palsy.
In fact, recent MRI studies have shown that more than 75% of all neonatal brain disorders are caused by hypoxic brain damage that was sustained during or close to the time of birth.
Most cases of hypoxic-ischemic encephalopathy are sustained during or shortly before a newborn’s delivery, although appropriate medical intervention can often limit the extent of brain damage caused by birth asphyxia. In some cases, the injury is entirely preventable.
Brain Hypoxia At Birth
A child’s body can only compensate for a decrease in oxygen intake momentarily.
When oxygen levels drop abnormally, no matter the cause, a child’s body will automatically begin to redistribute the flow of blood, re-routing the fluid to organs that must continue working for the infant to survive. The heart and brain, along with the adrenal glands, receive a large boost in blood flow, but this surge cannot be maintained indefinitely.
As oxygen deprivation continues, cerebral blood flow will eventually decline, depriving brain tissue of the oxygen it needs. Brain cells begin to die off, and the ultimate result is hypoxic-ischemic encephalopathy, an irreversible form of brain injury.
Symptoms & Early Signs Of Neonatal Encephalopathy
As a clinical syndrome, hypoxic-ischemic encephalopathy is characterized by the following signs:
- epilectic brain activity on EEG readings
- hypotonia, or poor muscle development
- impaired feeding abilities
- depressed level of consciousness (usually lasting from seven to fourteen days)
But it should be noted that the signs and symptoms of HIE will vary greatly depending on the duration of asphyxia and extent of brain damage. Sometimes, the symptoms can even seem contradictory. For example, mild cases of hypoxic-ischemic encephalopathy can be accompanied by increases in muscle tone, while severe cases are generally marked by low muscle development.
Thus it’s impossible to write up a master list of symptoms, and two babies may show remarkably different clinical presentations. With that being said, other signs and symptoms of HIE may include:
- abnormally low heart rate
- low or absent infant breathing rate
- acidosis, an increased acidity in the blood or other body tissues
- meconium-stained amniotic fluid
- diminished or absent reflex response
- bluish or pale skin due to insufficient oxygen levels in the blood
- an Apgar score lower than three that lasts longer than five minutes
In general, doctors rely on diagnostic tests, rather than signs and symptoms, to accurately diagnose hypoxic-ischemic encephalopathy. MRI, or magnetic resonance imaging, ultrasound and echocardiography are most common.
Medical Terminology: What Is HIE?
As a medical term, hypoxic-ischemic encephalopathy denotes three interrelated concepts:
- hypoxia – a decrease in the amount of oxygen reaching body tissues
- ischemia – a restriction in blood flow to body tissues, which causes a shortage of oxygen and glucose, nutrients necessary to keep body tissues alive
- encephalopathy – a general term for diseases or disorders that affect the brain
Blood carries oxygen throughout the body, nourishing every organ and tissue. Thus, whenever blood flow decreases precipitously, oxygen deprivation is likely to occur on the tissue level. In other words, ischemia causes hypoxia in all but the rarest cases. But hypoxia, a lack of oxygen, may or may not itself lead to ischemia. In some cases, the latter condition, a restriction in blood flow, can be prevented through emergency treatment measures.
Hypoxia & Ischemia
Both hypoxia and ischemia can cause cellular damage and brain injury, but ischemia is generally considered the more serious condition. Decreases in blood flow throughout the body make it impossible for cells to create the energy they need to survive. To compound the problem, ischemia often leads to a buildup of acids in the blood. These toxins can actually be absorbed by cells, restricting their ability to absorb oxygen as they would normally, and worsening the injury.
Many experts, including those at HopeForHIE.org, distinguish between two stages of the brain injury:
- immediately after oxygen deprivation begins to occur, brain cells sustain damage
- when normal blood flow returns to the brain, the damaged cells begin to release the absorbed toxins, leading to “reperfusion injury”
Since hypoxic-ischemic encephalopathy is so complex, and brain injuries can be the result of numerous different factors, treatment will depend on the extent and causes of the damage.
How Is Hypoxic-Ischemic Encephalopathy Treated?
After suffering birth asphyxia, many newborns need to be resuscitated. Following preliminary stabilization, treatment turns to the dual task of preventing further brain injury and supporting basic organ functions.
Doctors will attempt to maintain appropriate oxygen delivery, often relying on mechanical ventilation to do so. Many newborns require several days of artificial ventilation to survive after sustaining a brain injury. Blood flow is another concerns, and physicians will check to ensure that blood glucose levels remain within a normal range.
Seizures present a significant risk of further brain trauma, and can also threaten the proper functioning of lungs and the cardiovascular system. Most infants will be placed on drugs like phenobarbital or a benzodiazepine to control their seizures.
To learn more about the treatment options for HIE, check out this guide from doctors at the University of Virginia Health System.
Hypothermia treatment is now the treatment-of-choice for many babies with birth-related hypoxic-ischemic encephalopathy. By lowering a baby’s body temperature to approximately 91 degrees Fahrenheit, and maintaining that temperature for around 72 hours, cellular activity is slowed considerably. This allows the cells, including those in the brain, to recover from injury.
Hypothermia treatment is also designed to prevent further damage that can be caused if blood flow is allowed to return too quickly.
In most hospitals, hypothermia is mandatory after an HIE diagnosis. A wealth of clinical evidence has shown that hypothermia treatment can improve clinical outcomes for infants, and failure to perform this life-saving treatment is often an example of medical malpractice.
How Can HIE Affect A Child?
In full-term infants, the effects of a hypoxic brain injury are largely determined by which part of the brain is injured, as well as the degree and duration of oxygen deprivation.
Severe cases generally involve damage to the brain’s deep gray matter, including the hippocampus, regions of the brain thought to control emotion, memory and the autonomic nervous system, and the basal ganglia, a complex of structures involved in motor movement, learning and habit-formation.
For most children, the brain’s white matter is spared from injury, even after profound (or “near total”) oxygen deprivation. White matter is generally believed to coordinate activity between brain regions.
HIE can cause a wide range of impairments, from neuro-muscular impairments to cognitive impairment. Epilepsy and cerebral palsy are possible, along with developmental delays.
The severity of impairment, however, is unlikely to become apparent until a child reaches the age of 3 or 4.
What Causes Lack Of Oxygen To The Brain?
Hypoxic-ischemic encephalopathy is usually caused by oxygen deprivation, or asphyxia. But the potential causes of birth asphyxia itself are far more various:
- umbilical cord complications, including knots, compression and cord prolapse
- acute maternal low blood pressure, or hypotension, along with maternal blood clotting conditions
- poorly functioning lungs in the infant
- placental insufficiency
- blood clots in the placenta
- uterine rupture
- placental abruption
- physical trauma during the delivery process
- shoulder dystocia
While some of these complications are truly unavoidable, many are not. Cautious, knowledgeable doctors are often able to diagnose potentially-dangerous conditions at an early stage, and then mitigate their effects during labor and delivery.
By the same token, doctors can make mistakes, missing maternal health conditions entirely or addressing emergent issues ineffectively. When insufficient medical care leads to hypoxic-ischemic encephalopathy, a family may have every right to demand accountability from negligent healthcare professionals in a medical malpractice lawsuit.
How Common Is HIE?
Estimates on hypoxic-ischemic encephalopathy vary, with most suggesting that between one and three out of every 1,000 full-term births will be affected by the injury.
Of those newborns, approximately 15% to 20% will die soon after delivery, according to the Journal of Biomedicine and Biotechnology. Another 25% of the infants born with this type of brain injury will develop permanent severe neuro-psychological disorders.