Tests for HIE
Hypoxic-ischemic encephalopathy (HIE) can be identified at different points. In many cases, parents first become suspicious that their child may have a developmental delay when their child starts missing developmental milestones. These parents can think back to their labor, wondering if something may have occurred during the process that may have caused the delay.
In other cases, medical professionals conduct tests immediately to determine if the baby has HIE. These tests occur if the medical staff suspect that HIE is possible, especially in cases of a difficult or prolonged labor, umbilical cord issues, and other events that they may suspect harbor a risk of causing oxygen deprivation-related brain damage, such as the need to resuscitate the baby after birth. This rapid diagnosis is absolutely critical for the baby, because the only current treatment for hypoxic-ischemic encephalopathy, hypothermia therapy, must be provided to the baby within 6 hours – the sooner, the better. Hypothermia therapy allows the baby’s brain to heal (to some degree) from hypoxic-ischemic injury, and it minimizes the severity of the baby’s disabilities. This treatment is critical to maximizing the baby’s functional abilities later in life. The tests that doctors prefer can vary, but they can include:
APGAR Scores and Hypoxic-Ischemic Encephalopathy
The APGAR test is a test administered to all babies when they are born. It evaluates the baby’s general health by looking at five key parameters:
- Appearance: What color is the baby? Blue or pale all over? Blue at the extremities? Pink all over? The letter “A” in “APGAR” stands for appearance.
- Pulse: Does the baby have no heart rate? Is its heart rate slow (under 100bpm)? Is the heart rate fast (over 100bpm)? The letter “P” in “APGAR” stands for pulse.
- Reflex irritability (grimace): Does the baby not respond to stimulation? Does it cry feebly and grimace? Does stimulation cause the baby to cry and pull away? The letter “G” in “APGAR” stands for reflex irritability, or grimace.
- Activity: Does the baby have no activity? Does it have some flexion (joint movement)? Does the baby have flexes arms and legs that resist extension? The second letter “A” in “APGAR” stands for activity.
- Respiratory effort: Is the baby not breathing? Is the baby’s breathing weak and irregular? Is the cry very strong? The letter “R” in “APGAR” stands for respiratory effort.
APGAR tests are performed at one minute after birth and five minutes after birth, and they are repeated if the score remains low afterward. Each of the five areas are evaluated on a 0-2 point scale, and the points are added up to provide a quick overall indicator of the baby’s general health.
The scores are broken down as follows:
- 1-3 points: critically low
- 4-6 points: below normal
- 7+ points: normal APGAR score
If the baby’s APGAR scores are low and remain low, this may indicate that the baby has a brain injury like hypoxic-ischemic encephalopathy (HIE). The lower the baby’s APGAR scores, the more likely it is that the baby will need doctors to provide medical intervention.
How Do You Pronounce “Apgar”?
Identifying HIE Through Brain Imaging
Brain Imaging: MRIs and CT Scans
MRIs and CT scans are two technologies that medical professionals can use to take pictures of your baby’s brain. These scans allow trained professionals to identify if your baby has been oxygen deprived and the extent of the injury. This is very important because brain injuries evolve over time. Medical professionals can request that the baby have multiple CT scans or MRIs, to make sure they can properly track what is going on in the baby’s brain.
MRI is the best imaging method of diagnosing babies with moderate to severe HIE. MRIs can be performed as early as 12-24 hours after birth. They accurately show injury patterns as early as 1 day after birth (sometimes sooner), and are especially useful after day 4. This method uses magnetic fields and a scanner to make a detailed image of the human brain. MRIs can identify brain lesions (regions where the brain has been damaged) and can also sometimes help doctors determine the time when a baby had a brain injury. MRIs do take longer than other imaging types, and there are some cases when babies can’t have an MRI (if they are unstable or are on machines that have metal in them). Some incubators and ventilators do not use metal parts, allowing some babies to have MRIs even if using a machine.
CT scans use X-rays to generate multiple ‘slices’ of images, which are ‘stacked’ together by a computer to form a 3D image of the brain’s structures. While it is not the preferred method of imaging a baby’s brain because it does use X-rays, CT scans are an alternative imaging method.
For more information about brain imaging and its role in detecting brain injury, please click through to the following page on brain imaging techniques [External Link].
Brain Imaging: Ultrasounds
Ultrasounds are another way of detecting hypoxic-ischemic encephalopathy, but this method has a lower sensitivity compared to other types of imaging. Ultrasound does not always image the outer parts of the cerebral cortex very well, and cannot always pick up on less-severe white matter abnormalities. It is, however, available at the baby’s bedside, and can show signs of hemorrhages (heavy bleeding) and abnormal ventricle sizes, as well as cerebral edema (swelling due to excess cerebrospinal fluid), increased echogenicity, and brain tissue necrosis (after 24 hours).
Identifying HIE Through Umbilical Cord Blood Gas Tests
Immediately after a baby is born (especially if the mother had a high-risk pregnancy), doctors collect an umbilical cord blood sample. Research shows that a blood sample that is taken properly can help determine whether the baby was in fetal distress (whether there was a period of time where the baby didn’t get enough oxygen).
The umbilical cord has one vein and two arteries. Blood drawn from a vein versus an artery will tell a different story; blood in the umbilical vein (which flows to the baby) reflects on oxygen flow in the uterus and placenta, while blood in the umbilical artery (which flows from the baby) reflects the fetus’ state along with the uterus and placenta.
The best way to test umbilical cord blood samples is from an artery. Medical staff clamp the cord and draw blood for testing. Once the sample is collected, there are numerous tests that can be performed. In order to determine whether the baby had a hypoxic-ischemic event, the blood’s pH is analyzed along with other factors such as PCO2, HCO3 levels, PO2 and base excess. These numbers describe the relative proportion of dissolved gases in the baby’s blood; if the arterial blood is acidotic (a condition called fetal acidosis), it means that the baby suffered an oxygen-depriving event.
Normal values differ significantly depending on whether the baby was born at term or preterm.
Umbilical cord blood gas tests can also help determine what kind of acidosis occurred. This can help pinpoint what the cause of the oxygen deprivation was. For example, if a baby has a high PCO2 (a high level of dissolved carbon dioxide in their blood), it means that more CO2 is being produced than the baby’s body can eliminate. This can, for example, occur in cases where the umbilical cord in compressed.
Sometimes, however, if PCO2 is very different from normal values, blood gas analyzers may not accurately calculate HCO3- levels. This can cause medical staff to calculate a different value (base excess or base deficit).
Umbilical cord blood gas testing isn’t always the best way to determine whether a baby likely had oxygen deprivation, however. Research has shown that some babies with HIE often have test results come back with a blood pH that is normal or very close to normal. This research also found that there can be catastrophic oxygen-depriving events that don’t show an acidic pH in the umbilical cord blood sample. If a baby has poor blood flow, it may develop acidic products in its blood, but those products won’t reach the sample site the blood was drawn from. This can also occur if the umbilical cord is occluded (blocked off completely) – if the umbilical cord is being sampled from a point downstream from an occlusion, the sample may not show any acidemia at all.
Almost all newborn babies with severe birth asphyxia have poor or no blood flow, which means that blood isn’t circulating well through the umbilical cord. This means that the acidic products that umbilical cord blood gas tests look for won’t be present in the sample. Functionally, this means that an umbilical cord blood gas test significantly underestimates how acidic the baby’s blood actually is.
Once the baby is resuscitated and their blood begins circulating better, the acidic products begin to clear their system via central circulation. Researchers found that analyzing a postnatal base deficit from a newborn within two hours of delivery is a more accurate measure of how acidic the baby’s blood was than the umbilical cord blood sample collected immediately after birth. This postnatal base deficit is a far more accurate predictor of neurological outcome than just umbilical cord blood gas testing alone.
Identifying HIE Through Developmental Screening
One of the most common ways that parents obtain a diagnosis of HIE for their child is when the child begins to miss key developmental milestones. At each month and year of a baby’s life, there are certain developmental items they are generally expected to be able to do. If (barring genetic anomalies) a child misses a particular developmental milestone, or if a pattern of developmental delays persists, it may mean that the baby had HIE. Sometimes, a baby or child may be diagnosed with cerebral palsy; the underlying cause of cerebral palsy is sometimes HIE.
The CDC has a collection of milestone checklists for new parents:
- Developmental milestones at 2 months
- Developmental milestones at 4 months
- Developmental milestones at 6 months
- Developmental milestones at 9 months
- Developmental milestones at 1 year
- Developmental milestones at 18 months
- Developmental milestones at 2 years
- Developmental milestones at 3 years
- Developmental milestones at 4 years
- Developmental milestones at 5 years
These checklists can also be found in a single convenient packet here.
To learn more about developmental milestones and birth asphyxia, visit the HIE Help Center’s page the topic here.
Sometimes developmental difficulties are caught early. This can happen if a baby had difficulty with feeding (latching, sucking or swallowing). It can also occur if certain developmental reflexes don’t go away when generally expected, or if they are exaggerated.
Screening generally occurs in conjunction with multiple medical and therapeutic specialists. Parents of children with HIE commonly consult pediatric neurologists, pediatricians, orthopedic surgeons, ophthalmologists, psychologists, and numerous other specialists in order to secure a diagnosis. Early diagnosis is critical for improving a child’s outcomes – the earlier a child starts therapy, the likelier it is that outcomes will be better for the child.
Tests for Common Concurrent Diagnoses
HIE does not usually come as a single diagnosis; there can often be multiple diagnoses that a child may have. Some of the most common are intellectual and developmental delays or disabilities, as well as cerebral palsy. Sometimes children with HIE can have speech delays, motor disorders, or seizure disorders that are diagnosed first. In other cases, the baby may be diagnosed with intracranial hemorrhages (brain bleeds) or fetal stroke. In other cases, when the HIE is mild and the baby is treated with hypothermia therapy in a timely fashion, the baby may have very few to no impairments. In many cases, medical professionals run evaluations of a child once a parent has brought up developmental concerns.
Children with HIE are sometimes diagnosed with cerebral palsy. This is usually a clinical diagnosis made when a baby or child has muscle spasticity. Sometimes this is seen when a baby begins missing developmental milestones. There are two additional tests that may be helpful. About 45% of children with cerebral palsy have seizures. EEG testing can be used to determine if a child has seizures or epilepsy, which is critical to preventing further brain damage. Another test that screens for coagulation problems is performed in children with hemiplegic CP or in children that show evidence of cerebral infarction (stroke) caused by HIE. This test determines if the child has a blood clotting disorder called prothrombotic coagulation disorder. Children with hemiparesis (weakness on one side of the body) should be tested for HIE.
- Laptook, AR, et al. Prediction of Early Childhood Outcome of Term Infants using Apgar Scores at 10 Minutes following Hypoxic-Ischemic Encephalopathy. Pediatrics. 2009 Dec; 124(6): 1619. doi: 10.1542/peds.2009-0934.
- de Vries, LS, et al. Patterns of Neonatal Hypoxic-Ischaemic Brain Injury. Neuroradiology. 2010 Jun; 52(6): 555–566. doi: 10.1007/s00234-010-0674-9.
- Heinz, ER et al. Imaging Findings in Neonatal Hypoxia: A Practical Review. American Journal of Roentgenology. 2009;192: 41-47. doi: 10.2214/AJR.08.1321.
- [For Parents] Plain Language: HIE Radiology and Patterns of Neonatal HI Brain Injury
- Rutherford, MA, ed. MRI of the Neonatal Brain. ISBN 0 7020 2534 8. Available online.