Birth Small Talk

Talking about birth

What is perinatal asphyxia? An analysis of how we construct meaning.

Photo by Jon Tyson on Unsplash

I’ll admit that this was not the sexiest idea for a blog post. Yet here we are! This is going to be a somewhat philosophical discussion about how we make sense of the world through language. It’s longish and detailed, so this one is more for the language enthusiasts, philosophers, or researchers among you.

There are entire library shelves packed with philosophical tomes that theorise the relationship between “the real world” and the way we represent it in art and language. I’m not going to go that deep – but let me start by saying that position that I take is that there are “real” things (objects, people, experiences) in a “real” world, but our ability to express their full reality through language is limited. These limits have been shaped by the frames that we use to experience and describe the world, and in turn they shape how we experience it.

As a researcher, I have developed skills in working backwards from a text to make the frame that sits between the “real” and the language we use visible. Let me step you through an example of that, as I show how what we think of as a concrete definition of perinatal asphyxia is really a rather slippery and vaguely defined idea. Again, I believe that there is a real experience going on for the fetus, but the way in which was can represent this in language doesn’t full capture it because it involves some assumptions and several choices.

Why is this important? Because the fetal distress meta-narrative that I have written about previously, requires that there is such a thing as perinatal asphyxia and that we agree on what it is, how it happens, and that we have things we can do to prevent, modify, or treat it. If the concept of perinatal asphyxia is itself not all that sound then neither is the fetal distress meta-narrative, and the entire way of thinking that makes CTGs seem logical dissolves into uncertainty.

Defining perinatal asphyxia

Let’s begin with a definition of perinatal asphyxia. Here’s one from a recent research paper on the topic:

Perinatal asphyxia was defined as pH ≤7.0 or BE ≤-12 mMol/L in UA or within 1 h, 10 min Apgar ≤5, or need for resuscitation > 10 min.

Locatelli, et al., 2020, p 2.

The authors didn’t just make this up. The definition comes from a professional society for neonatologists, so it is recognised as being a “fact” within that particular part of the scientific community. It is a standard definition, widely in use.

The first bit of the definition requires that blood has been collected from the umbilical artery (AU) in the first few minutes after birth, or from another artery in the baby in the first hour after birth. This must then be tested and the result show a higher level of acidity (a low pH) and a lower level of alkalinity (a low base excess). The second bit of the definition is about a score assigned by clinicians at 10 minutes of age. Scored out of ten the Apgar score gives points relating to the baby’s heart rate, breathing, tone, colour, and reflex movements. A score of 5 or less is low and indicates a baby that needs ongoing resuscitation. This is also captured by the final part of the definition. Resuscitation in this context means help with breathing or maintaining a normal heart rate and blood pressure.

Let’s start to dig into the assumptions that sit under the surface of this definition. For starters, it assumes that birth occurs in a facility with skilled birth attendants who can assign an Apgar score and resuscitate a baby, and probably has sufficient technology and resources to perform blood gas analysis. All the babies who have previously been tested and contributed to our knowledge about what blood gas results and Apgar scores mean were born in an environment where particular ways of knowing and working with birthing bodies and babies are taken for granted. That doesn’t make this “wrong”, it just means that extreme caution needs to be applied when assuming that ALL birthing bodies and babies behave the way they do in industrialised healthcare systems.

Measuring pH

Why measure acid levels? Metabolising sugars to produce energy is most efficient when there are adequate levels of oxygen in the cells. As oxygen levels fall, cells continue to generate energy, but they switch to a different chemical pathway to do so. This is called anaerobic metabolism and it generates lactic acid. It is really tricky to measure oxygen levels in the fetus directly, and easier to measure pH after birth and assume what this might have meant for the fetus an hour or so ago.

The physiology behind these tests and the significance of the results is well worked out in adults and in animal models, with less research directly addressing what they mean in the newborn. Assumptions are made that the tests have the same meaning in human newborn babies as they do in adults or in laboratory animals. While there is no doubt that low oxygen and pH levels over a prolonged period are harmful to the fetus / baby, less is known about what levels are abnormally low and over what time period low levels must be sustained to cause permanent damage. A range of other factors also impact on whether low oxygen causes damage (such as blood pressure and body temperature), and so the oxygen – pH – harm relationship is not straightforward as is often assumed.

All testing equipment requires calibration, and false positive (the result is abnormal but in reality there’s nothing wrong) or false negative (the result is normal but there is something actually wrong) are more common than we often consider. The definition assumes that a pH of 7.0 on machine A is the same as a pH of 7.0 on machine B – which may or may not be the case. Small portable point of care monitors are convenient but may be less accurate than large complex laboratory equipment. For lactate measurements, it has been demonstrated that different reference ranges are associated with different brands of test equipment (Wang, et al, 2017).

Note that in this definition of perinatal asphyxia it is acceptable to either use results from blood from the umbilical artery collected at the time of birth, or those collected from the baby during the first hour of life. The later results will reflect the care of the baby during that hour, rather than providing a reliable indicator of whether the baby had been exposed to hypoxia in utero. They most definitely do not carry the same meaning as results collected at birth, yet in the definition they are treated as equivalent.

Apgar scores

Let’s move on to Apgar scores. The Apgar score was designed to provide a rapid indication of whether resuscitation efforts would be of benefit for a newborn baby (Calmes, 2015). Any clinician with some experience knows that they are highly subjective. Following a resuscitation, I have found it common to discover that midwife, obstetrician, and paediatrician have all documented a score, each different to the other. I also commonly see the Apgar assigned in retrospect after only a quick glance at the baby. While this might be sufficient to assess colour, breathing, and movement – heart rate and response to stimulation must be directly assessed by touching the baby, not assuming them on the basis that the other parts of the assessment are OK. 

The Apgar score is a product of knowledge developed in the industrialised maternity care system, in a time period where early cord clamping and removal of the baby from the mother were practiced. The lithotomy position, general anaesthesia or heavy sedation, and forceps assisted birth were also common at the time, each of these having an impact on how the baby transitions from life in utero. Apgar scores were not originally conceptualised as a proxy endpoint measure for hypoxia, despite this now being a common approach. Researchers who have examined the utility of Apgar scores for this purpose concluded:

Because Apgar scores are not clearly on any causal pathway of interest, we discourage researchers from using them unless the motivation for doing so is clear.

Bovberg, et al., 2019, p. 1695

The Apgar was designed to indicate need for resuscitation, and therefore a low score at ten minutes indicates a need for ongoing resuscitation, the definition of perinatal asphyxia uses the same set of phenomena twice. Note that continuing resuscitation is a clinical decision, and like the Apgars which inform this decision, there is a degree of subjectivity involved. In at least some instances, the decision to continue resuscitation beyond ten minutes may reflect skill of the clinician (who for example took several minutes to establish an airway and therefore didn’t deliver oxygen to the baby during that time), rather than the pre-resuscitation oxygenation status of the baby.

So what is perinatal asphyxia?

So what do we make from all of this? I have not doubt that there is an in utero event that the fetus experiences which conforms to what we think we are referring to when we talk about perinatal asphyxia. Because we can’t ask the fetus what this experience is like, we rely on other ways to define whether or not the fetus has experienced this state.

The measures we use are in large part related to choices that clinicians make and are not reliably measured by different people who are looking at the same baby, nor always reliably measured by the technology used for testing. They are based on assumptions that the physiology of the fetus that is measured when care is provided in industrialised obstetrics with the use of many non-physiological approached to birth is normal fetal physiology, and that these assumptions are true for all fetuses in all circumstances. With a bit of careful examination it becomes easy to see that the rock on which our knowledge is based turns out to be not all that solid after all.

Why does this matter? After all we’ve been getting along quite nicely with these definitions for decades, and their consistency means that when clinicians and researchers talk about perinatal asphyxia they are believe they talking about the same singular thing. It matters because in high income countries around the world we aren’t making substantial inroads in reducing the incidence of perinatal asphyxia leading to death or injury.

Rather than simply trying harder to do the same thing and hoping for a different outcome, I believe we need to go back to the fundamentals and ask ourselves whether the things we assume to factual, actually are. If we have these wrong, then we can’t make progress in addressing perinatal asphyxia.

Bovbjerg, M. L., Dissanayake, M. V., Cheyney, M., Brown, J., & Snowden, J. M. (2019, Sep 1). Utility of the 5-minute Apgar score as a research endpoint. American Journal of Epidemiology, 188(9), 1695-1704. https://doi.org/10.1093/aje/kwz132

Calmes, S. H. (2015, May). Dr. Virginia Apgar and the Apgar score. Anesthesia & Analgesia, 120(5), 1060-1064. https://doi.org/10.1213/ANE.0000000000000659

Wang, M., Chua, S. C., Bouhadir, L., Treadwell, E. L., Gibbs, E., & McGee, T. M. (2017, Jul 31). Point-of-care measurement of fetal blood lactate – Time to trust a new device. Australian and New Zealand Journal of Obstetrics and Gynaecology, 355, i6405-6407. https://doi.org/10.1111/ajo.12671

Categories: Basics, Language, Philosophy, Reflections

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