Could my baby have HIE even if the umbilical cord blood gas test shows normal pH?

It is possible that an umbilical cord blood gas test can come back normal, even when a baby does have a hypoxic-ischemic injury like hypoxic ischemic encephalopathy (HIE), which can lead to cerebral palsy (CP) and other disorders.

What considerations should be taken into account when analyzing umbilical cord blood gas test results?

What parameters are being measured?

In many cases, if a baby is oxygen-deprived from an anoxic or hypoxic-ischemic issue, their blood will be acidic, because the body will attempt to compensate for a lack of oxygen by switching to anaerobic respiration. Trained staff can use umbilical cord blood gas tests to see whether the blood’s pH is within normal ranges. The problem with these tests, however, is that the equipment used to analyze the samples doesn’t necessarily properly calculate the levels of certain substances (like bicarbonate) when the PCO2 (a measure of how well circulation is working) deviates too far from the norm. This means that staff should be measuring ‘base deficit’ (or ‘base excess’) rather than bicarbonate levels if PCO2 is particularly abnormal.  Babies with severe acidosis usually have a base deficit of 12 or more.

Judgement criteria that are too narrow to be medically accurate

The American College of Obstetricians and Gynecologists (the organization that sets policy for OB/GYNs in the U.S.) says that arterial cord blood pH has to be less than 7.0 for it to be used as a link between birth asphyxia and neurologic injury. The problem with this definition is that recent research shows that birth asphyxia causes brain injury even at pHs higher than 7.0. This means that a significant number of babies with birth-asphyxia-related injuries, if evaluated on the basis of this testing criteria, won’t be classified as having birth asphyxia-caused brain injury.

One particular landmark study found that between 10-15% of babies with adverse neurological outcomes had a blood pH of 7.10-7.11, and at least half of those that had seizures and encephalopathy (which are markers of brain injury in many cases) within 24 hours of birth had a pH of more than 7.10. This means that babies with birth asphyxia often have a normal pH.

Assumptions that umbilical cord blood gas samples are accurate reflections of a baby’s pH

If a baby’s circulation and blood flow are poor, the chemical markers used to determine whether the baby is acidemic may not reach the sample site. This means that arterial cord blood samples can severely underestimate a baby’s acidemia in certain cases.

When a baby is resuscitated, their circulation can improve, restoring the flow of blood around their body. This means that the anaerobic respiration products in their blood clear to central circulation. Because the base deficit from samples from the first hour of delivery is often worse than the values found in umbilical cord blood samples, this can also demonstrate what degree of injury the baby had. These samples can help predict neurological outcomes.

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Legal help for birth injuries and birth asphyxia

B JESSE AND REBECCA1 If your child had cognitive delays, cerebral palsy, or other developmental difficulties stemming from a difficult or mismanaged birth, please consider reaching out to the birth injury lawyers at Reiter & Walsh, P.C. We are one of the few firms nationwide that exclusively handle birth injury cases, and the bulk of our cases relate to hypoxic-ischemic encephalopathy (HIE) and cerebral palsy. Firm owner, Jesse Reiter, has practiced birth injury law since the beginning of his career in 1987; attorneys Jesse Reiter and Rebecca Walsh are both recognized as two of the best medical malpractice lawyers in the United States by U.S. News and World Report. The publication also named Reiter & Walsh ABC Law Centers as one of the best medical malpractice law firms in the nation.

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Related Resources | Birth Injury & HIE