Hypoxic ischaemic encephalopathy (or HIE) is a condition affecting newborn infants. As the name suggests, it relates to low oxygen supply (hypoxia), and / or reduced blood flow (ischaemia) causing damage (-pathy) to the brain (encephalo-). Other parts of the body might also show signs of damage from low oxygen, like the kidneys or the gut. It is diagnosed when there is a combination of high acid levels in umbilical cord blood plus symptoms suggesting brain injury (like seizures, being difficult to wake, pauses in breathing, and being floppy).
Some infants with HIE make a full recovery, while others experience longstanding brain problems (Pappas, Milano, & Chalak, 2023). Without the use of therapeutic hypothermia (more on that in a moment), between 28 to 48% of infants who survive HIE develop cerebral palsy, 50% have low IQ scores, 4-6% are deaf, and 6-14% are vision impaired. Prevention of longterm damage among infants with HIE is an important goal.
After birth, therapeutic cooling or hypothermia is commonly used. Either the head alone, or the infant’s entire body is deliberately cooled, dropping the temperature by a few degrees. This reduces the oxygen requirement of the brain, reducing the potential for further damage to the cells. There’s sound evidence this approach reduces (but doesn’t eliminate) death and disability (Jacobs et al., 2013). But stopping HIE from happening in the first place would be an even better idea.
CTG use and HIE
HIE is one of the things CTG monitoring is meant to be useful at preventing. However, there is very little evidence to back this up. Only one randomised controlled trial has measured the impact of CTG use (rather than intermittent auscultation) on rates of HIE. That’s the 1993 Athens based trial by Vintzileos and colleagues (criticised for an apparent breach in randomisation – see Keirse, 1994). One of 746 infants exposed to CTG monitoring and two of 682 infants exposed to intermittent auscultation developed HIE, with no statistically significant difference.
That’s it. That’s the entirety of the evidence base from randomised controlled trials looking at whether CTGs are useful for preventing HIE.
Changes in HIE rates over time
Researchers from the USA have sought to answer the question of whether attempts at preventing HIE are working or not (Cornet, et al., 2023). They gathered data from 15 hospitals in Northern California owned by the one company (Kaiser Permanente), with 289,783 births between 2012 and 2019. First, they identified a sample of infants with acidosis (high blood acid levels at birth) – 4,370 of the total population, or 15.1 per 1000 births. Then, charts of a random selection of 1,200 of these infants were reviewed, looking for evidence of a diagnosis of HIE.
1.7 per 1000 infants fit the diagnostic criteria for HIE, with 1.6 per 1000 having this diagnosis listed on their hospital discharge form. 1.4 per 1000 were treated with therapeutic cooling. There was no change at all in the incidence of a diagnosis of HIE over time. There were increases over time in both having a diagnosis of HIE on the discharge form (from 1.4 to 1.8 per 1000), and the use of therapeutic cooling (from 1.2 to 1.7 per 1000). These findings remained true after adjusting for changes in confounding variables.
There are two possible explanations for the rise in discharge diagnosis and the use of cooling. First, you could argue (and the authors do) that this shows people were simply better at written accurate discharge summaries, and therapeutic cooling became a more popular treatment option. Second, you could argue that more babies had injury due to low oxygen levels. There is a clue in their data suggesting that this second one might have been the case. The incidence of neonatal acidosis increased significantly from 13 to 17 per 1000 during the study period. With more babies exposed to low oxygen levels causing acidosis, you would expect more cases of HIE.
In summary…
In this large US based population, there were no signs HIE rates were falling over time, and maybe a hint of a suggestion they were rising. It is difficult to determine rates of CTG use in the USA as this data is not typically collected or reported, but they are high. While the authors mentioned how new computerised approaches to CTG monitoring might have better capacity to identify fetuses at risk for HIE, I was pleased to see they did not make a recommendation for more intense and higher technology fetal surveillance approaches as a means to modify the rate of HIE.
I’ve said it before and I’ll say it again – it’s well past time to stop pretending CTG monitoring is working and start developing an approach that actually works to prevent harm from low oxygen levels during labour. Can we get on with it now?
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References
Cornet, M.-C., Kuzniewicz, M., Scheffler, A., Forquer, H., Hamilton, E., Newman, T. B., & Wu, Y. W. (2023). Perinatal Hypoxic-Ischemic Encephalopathy: Incidence over time within a modern US birth cohort. Pediatric Neurology, in press. https://doi.org/10.1016/j.pediatrneurol.2023.08.037
Jacobs, S., Berg, M., Hun,t R., Tarnow‐Mordi, W., Inder, T., & Davis, P. (2013). Cooling for newborns with hypoxic ischaemic encephalopathy. Cochrane Database of Systematic Reviews, 1, CD003311. DOI: 10.1002/14651858.CD003311.pub3.
Keirse, M. (1994, Jun 01). Electronic monitoring: Who needs a Trojan horse? Birth, 21(2), 111-113.
Pappas, A., Milano, G., & Chalak, L. F. (2023, Mar). Hypoxic-Ischemic Encephalopathy: Changing outcomes across the spectrum. Clinics in Perinatology, 50(1), 31-52. https://doi.org/10.1016/j.clp.2022.11.007
Vintzileos, A. M., Antsaklis, A., Varvarigos, I., Papas, C., Sofatzis, I., & Montgomery, J. T. (1993, Jun 01). A randomized trial of intrapartum electronic fetal heart rate monitoring versus intermittent auscultation. Obstetrics & Gynecology, 81(6), 899-907. https://www.ncbi.nlm.nih.gov/pubmed/8497353
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Categories: CTG, EFM, New research, Perinatal brain injury
Tags: HIE, Therapeutic cooling
Birth Small Talk 
Historically, CTG interpretation has been based on pattern recognition of CTG features. I wonder if we will find any difference / reduction in HIE if we look for outcomes in hospitals where Physiological interpretation of CTG is used.
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I look forward to seeing some research evidence evaluating the effectiveness of the Physiological interpretation guideline.
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What is “physiological interpretation”?
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It’s a particular guideline, developed in the UK.
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