Continuous fetal heart rate monitoring is at its core an almost laughable idea.
We are checking a single vital sign and using that vital sign to extrapolate a host of ideas and meanings. OBs that have read strips for years can make some sense of them, but would we give so much meaning to any other single vital sign? Would we do it with an adult? Of course not, but there are people who do. In fact, there are entire countries where this is a major methodology for determining the etiology of illnesses.
But the people doing this are not physicians – they are the healers of various cultures. Throughout the world there are practitioners who claim to divinate illness through feeling a person’s pulse for several minutes. This is particularly prominent in Asia. They describe using the rate, strength, and character of the pulse to make all manner of determinations. This practice is fairly laughable to physicians, as it seems crazy to get so much meaning from feeling someone’s pulse.
But is this so much different than electronic fetal heart monitoring (EFM)? In fact its quite similar. Given that traditional healers are probably hit and miss with their diagnoses, its no surprise that EFM technology is similarly lacking.
Beyond the fundamental issues of divining information from a single vital sign, EFM also suffers from great interobserver variability. Just as a different mystic might think different things from feeling one’s pulse, different practitioners may interpret the same strip differently. In test performance terms, EFM has a small Kappa, where the larger a Kappa is the more the observers agree.
Not only do different practitioners interpret strips differently, they describe them differently as well. Some people call a late deceleration purely based on position relative to the contraction, while some consider a variable looking decel post contraction to still be a variable. Some people infer meaning from the variability during a deceleration, while others think this is inappropriate.
Recognizing these issues, the NICHD issued a new set of guidelines in 2008, defining how we should all describe our strips. Finally, we have a clear direction on how we should interpret strips! Or do we?
The NICHD guidelines categorizes strips into three categories, which basically boil down to:
Category I – strip’s fine
Category III – strip’s really really bad
Category II – everything else.
More specifically the categories (importantly, in the same order) are:
Late or variable decelerations: absent
Early decelerations: present or absent
Accelerations: present or absent.
and at least one of:
Late decelerations: present and recurrent
Variable decelerations: present and recurrent
Category II: everything that is not Cat 1 or Cat 3:
Rate: bradycardia but without absent variability OR tachycardia
Variability: Minimal, absent but without decelerations, or marked variability
Accelerations: Absence of induced accelerations after fetal stimulation
Recurrent variable decelerations accompanied by minimal or moderate variability
Prolonged deceleration >= 2 minutes but < 10 minutes
Recurrent late decelerations with moderate baseline variability
Variable decelerations with other characteristics, such as slow return to baseline, “overshoots” and “shoulders”
So how does this help us?
On the good side, it does help us to be more clear on our documentation, and helps us to be in more agreement on how we are going to categorize strips. We should all be able to agree what is a Cat 1, Cat 2, or Cat 3.
But other that that, its not terrible helpful. This is because Cat 1 is such a good strip that we all would have called it good, and Cat 3 is such a horrible strip that we all would have done an urgent cesarean delivery. The problems is that everything else is Cat 2.
Just about any strip can be Cat 2, from a baby that is just sleeping to one that is having recurrent hypoxic events that just haven’t decompensated yet. Ultimately, Cat 2 is just about any strip that we would disagree about. Some Cat 2s are clearly benign, and some are clearly precursors to Cat 3 strips, but most are somewhere in the middle.
So while the NICHD criteria makes it easier to document, it doesn’t really tell us what to do, because all the indecision is in that big category II.
So is there a better future to our electronic Indian Healer machine?
Probably, but its more likely to be a new technology than a new way to interpret what we have now. This new technology may be STAN monitoring, or ST segment interpretation of the fetal EKG. Like a full EKG, STAN not only looks at the heart rate but also at the movement of the electricity waveform in the fetal heart. STAN does computer analysis of the ST segment, in the same way that we look at ST segments in adults with concern for heart attacks. So far, the technology has been very promising in early trials in Europe, and in one study the center that implemented the technology cesarean rates for abnormal strips had decreased cesarean deliveries and a decreased number of infants born with cord pH < 7.05. However, the jury is still out, and there are a number of issues to still work out.
Like all things, the US is far behind in getting this technology. For better or for worse, the FDA requires a great deal more data than is required in Europe before this can be put into play. If STAN works out in Europe, likely we will see it in use in the US in the next 3-7 years. If STAN is a bust, as fetal pulse oximetry was in the 2000s, we may never see it here.
Either way, we’ll just keep reading the fetal heart rate tea leaves.
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