Hypoxic Ischemic Encephalopathy (HIE) is a type of neonatal encephalopathy. When neonatal encephalopathy is indisputably due to hypoxic ischemic (anoxic) brain injury it is referred to as such. This type of brain injury occurs when there is a lack of adequate blood flow to the brain, a lack of adequate inspired oxygen, or inadequate oxygen-carrying capacity in the blood.
This can be caused by many things including impaired maternal oxygenation, inadequate blood flow in the placenta, umbilical cord issues like true knot formation, placental abruption, uterine rupture, cord prolapse, and fetal issues like hemorrhage or thrombosis.
HIE is a dangerous condition that requires immediate medical intervention. Per the National Institutes of Health (NIH), HIE affects approximately 1.5-2.5 out of every 1,000 full-term births in developed countries. The incidence rate in babies who are severely premature (born at 32 weeks gestation or earlier) is up to 60% of all live births.
What is Hypoxic Ischemic Encephalopathy?
HIE is a brain dysfunction caused by a lack of oxygen or blood flow to the brain. This lack of perfusion causes damage to the brain and other organs. Hypoxia means not enough oxygen. Ischemia means not enough blood flow. The term, encephalopathy refers to brain dysfunction. Thus, hypoxic ischemic encephalopathy is oxygen deprivation that generally occurs close to labor and delivery.
What Causes HIE?
There are a number of different possible causes of HIE, any of which can occur before, during or after the baby is born. Various problems or medical complications may cause HIE during pregnancy in the antepartum period, or just before birth. These include:
- Maternal diabetes with vascular disease
- Problems with blood circulation to the placenta
- Chronic hypertension
- Cardiac disease
- Congenital infections of the fetus
- Drug and alcohol abuse
- Severe fetal anemia
- Lung malformations
HIE can also occur during labor and delivery, or the intrapartum period. Common intrapartum causes may include:
- Excessive bleeding from the placenta
- Maternal low blood pressure
- Umbilical cord issues
- Prolonged late stages of labor
- Abnormal fetal presentation
- Rupture of the placenta or the uterus
In addition, infants can develop HIE due to complications that occur in the postpartum period, or after delivery. Premature babies are particularly at risk of suffering brain injury or even death if HIE occurs after delivery. The most common causes of postpartum HIE include:
- Severe cardiac or pulmonary disease
- Serious Infections, including sepsis and meningitis
- Severe prematurity
- Low neonatal blood pressure
- Brain or skull trauma
- Cardiac arrest
- Respiratory failure
In some cases, there are no identifiable causes for infant HIE.
Symptoms of HIE
There are a number of symptoms associated with HIE, including:
- Low Apgar scores, <5 at 5 minutes and 10 minutes
- Floppiness, or unreactive to sights or sounds, or more tense and agitated
- Low heart rate
- Low blood pressure
- Poor muscle tone and absent reflexes
- Weak breathing, no breathing at all, or rapid breathing
- Weak cry
- Bluish or pale skin color
- Excessive acid in the blood
- Seizures or abnormal movements
- Problems feeding
How HIE Affects Children
The effects of HIE vary from patient to patient depending on whether the infant has mild, moderate or severe symptoms. Infants with mild HIE may have minimal symptoms, which may not impact their lives in significant ways. Those with more moderate or severe HIE typically have more significant symptoms. Infants who suffer severe HIE at birth have a higher rate of infant mortality (death) in the days following birth.
Effects of HIE may include:
- Developmental delays
- Cerebral palsy
- Cognitive issues
- Motor skill development delays
- Neurodevelopmental delays.
Some patients require the assistance of a PEG tube for feeding and a tracheostomy, with or without ventilator support for breathing assistance. Many of the developmental issues associated with HIE are difficult to determine until the child is older.
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Tests to Confirm an HIE Diagnosis
General assessments to determine if an infant has HIE include an evaluation of respiratory status, need for respiratory support, cardiac status, neurological status, laboratory results and monitoring of urinary output.
Labs tests include blood gasses, CBC (complete blood count), blood sugar, renal function studies, creatinine, electrolytes, and liver function studies like bilirubin, ALT (alanine transaminase) and AST (aspartate transaminase). Infectious disease labs like blood cultures and CRP (C-reactive protein) are often drawn.
Tests to further evaluate HIE include computerized tomography (CT scan), magnetic resonance imaging (MRI), echocardiography and an ultrasound of the head. Optional tests may include electrocardiogram (EKG), electroencephalogram (EEG) and evoked potential tests. Generally, patients with HIE are evaluated to determine the severity of the injury, which can be mild, moderate or severe.
Doctors have various options to treat HIE. These options depend on the cause of the condition and the amount of damage to the baby’s brain. This makes it impossible for physicians to develop a definitive treatment for neonatal cases of HIE. Therefore, the primary goal of HIE treatment is to support the baby’s affected organs. Treatment options include:
- Mechanical ventilation to help a baby who can’t breathe without assistance.
- Cooling, or therapeutic hypothermia. The baby’s brain or body is cooled in order to reduce swelling and brain injuries.
- Hyperbaric oxygen treatment in cases where the cause of HIE is carbon monoxide intoxication.
- Medications to control seizures.
- Treatments to assist the baby’s heart function and control blood pressure.
Determining the prognosis for a child with HIE depends on a variety of factors, including his or her overall health. It can be difficult to predict long-term outcomes or complications, but doctors have found certain criteria can help. Consider the following:
- A lack of spontaneous respiratory effort in the 20-30 minutes, without resuscitation, after birth almost always leads to death.
- Seizures are an ominous sign. Poor neurologic outcomes tend to be greater among infants who have seizures that are frequent or difficult to control.
- Abnormal clinical findings in the first 7-10 days of life often indicate a poor prognosis.
- Persistent difficulties with feeding or abnormal tone of the muscles required to suck and swallow may be a sign of damage to the central nervous system (CNS).
- Poor head growth during the postnatal period often is a predictor for neurologic deficits.
- An electroencephalogram (EEG) with normal background activity at around 7 days old is a positive prognostic sign.
Every child and birth injury are different. Talk to your child’s healthcare team about his or her prognosis. Find out as much as possible about your child’s overall health and medical conditions.
How to Optimize Your Child’s Prognosis
One of the best ways to optimize your child’s prognosis after an HIE diagnosis is to be informed. Be aware of what HIE is and how it affects your child. Be open-minded to treatment and therapy options that may help prevent further brain damage, such as cooling therapy. Work with your child’s healthcare team to create a plan for his or her treatment in both the short- and long-terms.