Electronic Fetal Monitoring (EFM) Basics: External & Internal Methods Explained

Okay. Electronic fetal monitoring overview mini lecture. Um, EFM is sometimes a little bit confusing for

students to understand when we start to talk about it, but I promise the more we look at it and use it, it it gets easier

every time every time you experience it. So, we're going to start with the basics. We can do monitoring um a couple

of different ways. So we have external monitors and we have internal monitors. Externally we have one that monitors

baby's heart rate and one that monitors contractions. And then internally we have one that monitors baby's heart

rate, one that monitors contractions. So for your external monitors, these are the most common. Um the fetal heart rate

is assessed with an ultrasound transducer and it usually has a little US um stamp on it cuz these look very um

very similar. the the EFM and the contraction monitor, the TCO on the external ones look very similar, but one

does the heart rate and it has a little US. It uses ultrasound waves to capture the fetal heart rate and then puts that

data, that number onto the strip and that's what gives you the the fetal heart rate on um a monitoring uh

computer screen or paper if it's being printed. And then for contraction monitoring, it's uh we use a toco

dynamometer or we just call it toco for short. So, it looks very similar to the fetal heart rate monitor um except on

the side that is placed on the abdomen, it has a pressure sensor that detects changes in the uterine muscle and

abdominal tissue as contractions occur. And as that muscle tightens and as it the muscle tightens and it pushes on

that pressure sensor, that's what gives us the drawing of the contraction on either the computer screen or paper. For

internal monitoring, we don't use these as frequently. It does require that the patient have experienced rupture of

membranes in order to place internal monitoring. Therefore, one of the reasons we don't

use them, number one, internal monitoring is invasive. Number two, it requires the patient to be ruptured. And

then number three, every time we're placing something into patient, we know that that increases their risk for

infection. Um, so we only use internal monitoring if we have a really good rationale as to why we should do so. So

for internal monitoring, the FSE or fetal scalp electrode is this tiny little sensor with a little metal cork

screw on the very end and that this is um threaded through the vagina and cervix and attached directly to the

scalp of the fetus is the idea fetal scalp electrode by the healthcare provider or nurse midwife. Um and that

reads the fetal heart rate and puts it onto the tracing for us. And then an IUPC, an intrauterine pressure catheter,

is the internal monitoring for contractions. This is inserted much like the FSE except it's going beside of the

fetus into the uterine cavity where it detects pressure changes inside of the uterus um in millimeters of mercury and

that is what is printed on the strip. Um, an IUPPC can adequately assess

contraction strength with an objective measurement. A TOCO cannot adequately assess strength. So, our TOCO, our

external monitoring for our contractions is adequate for frequency of contractions and duration of

contractions, but not strength. For strength, we need to be asking the patient and palpating um with our hands.

The IUPC can give adequate data on the strength of contractions because it is an objective measurement. So that's

important to remember. So I mentioned a little bit in the last mini lecture when we are doing EFM

interpretation we are interpreting two different things separately and in relation to each other both the fetal

heart rate and the contraction pattern and each one have four categories. So for our fetal heart rate we looking at a

baseline variability axels and D cells and we usually do them in that order. And then for our contractions, we are

looking at frequency, duration, intensity, and then the resting tone. Also typically done in that order. So

four categories for each of the two items of importance. Um when you are looking

at a fetal monitoring strip, whether it be on the computer screen or on paper that is printed, um the fetal heart rate

is always on the top and the contractions are always on the bottom. This is a universal system. It would

never be flip-flopped. Um, so remember your heart rate's on the top and your contraction pattern is on the bottom.

So, what do we mean when we say fetal heart rate baseline? The baseline is essentially the average. If we were to

take an imaginary um pen and draw a mark through all of the points in the fetal heart rate that it could hit the most,

excluding the periodic and episodic changes, that is what we would get our baseline. The baseline is always rounded

to an increment of five for continuous monitoring. So even if it looks, you know, roughly something else, if it

looks roughly 143, we would round it to 145. The number is always going to end in a 0 or 5 if we're looking at

baseline. So you're going to round. For that reason, I might look at a fetal heart rate strip and say that the fetal

heart rate baseline is 145 and the nurse next to me might look at it and call it 150. And we're probably both right um

because we're rounding slightly. However, if I look at it and say it's 145 and she says it's 125, one of us is

clearly looking at something incorrectly. So, as long as as long as you're close to what that is, um usually

that is uh the most important piece. And then our baseline range that is considered normal for a fetal heart rate

is 110 to 160 beats per minute. So, that is drastically faster than the average adult or even

small child. fetal heart rate is a lot quicker um than what we would consider normal for anybody else. So 110 to 160

is the normal range. After we determine the fetal heart rate baseline, the next thing we look at is variability.

Variability is the beattobe changes in the fetal heart rate. So this is something that's very different um for

the fetus in uterero than it is in a newborn once they're born, for an older child, for an adult. And the reason that

fetal heart rate has such variability um is related to the sympathetic and parasympathetic nervous system working

to regulate the heart rate simultaneously. One is pulling the heart rate up, one is pulling the heart rate

down. Um and that's what gives us these beatto beat changes over seconds instead of a longer time frame than if we were

looking at an older child or an adult. Therefore, the variability speaks to the central nervous system function of the

fetus and the oxygenation status of the fetus. So those are the two things that we can tell based on fetal heart rate

variability. And when we look at variability, we have four categories that we identify. So we either have

absent variability, minimal, moderate or marked. So this picture here shows the difference of those four categories.

Now, this is a handdrawn strip. This is not a fetal heart rate strip because there are four um fetal heart rates on

here. I guess it could be if we were going to have quadruplets, but um we would be delivering them very very

quickly cuz some of these are not good. So, your your absent variability, that's the one on the very bottom you see. Um

it the B2B variability is zero. It is looks like somebody took a pen and drew a mark straight across the paper. There

is no B2B change. That is absent variability. Minimal is the next category that is between one but less

than five five or less beats per minute variability change. So you can see in regards to the bottom two lines, absent

is very flat. There's next to nothing. Minimal, we have a little bit of variability, but it's far less than what

you see when you look at the two categories above. So it's less than five beats per minute.

Moderate variability is our largest category as far as range. It's 6 to 25 beats per minute and that is the one we

like to see. So that is um reassuring on a fetal heart rate strip if we have moderate variability.

And then marked variability is more than 25 beats per minute beatto beat change. So that is our top line on the fetal

heart rate strip. And a good uh set of checks and balance for yourself is that if you can look at a fetal heart rate

strip and identify a baseline, then you can kind of rule out that you have marked variability. Because if you look

at the the fetal heart rate strip on this one that is that is categorized as marked, it would be almost impossible to

pick one number that would be an average for that strip because it is so um greatly varied B2B. So if you can look

at the fetal heart rate and say, "Oh, this is what I would call that baby's baseline, then you can kind of check off

that it's not marked variability. It's probably within at least moderate." And that's what we're shooting for anyway.

So if we had minimal or absent variability, that usually speaks to a central nervous system issue or poor

oxygenation of the fetus. um we can have periods of minimal variability during fetal sleep cycles which again that is

when their central nervous system is um not necessarily depressed but less active and so that's why we can see that

and that's for a short amount of time. We have certain medications that when we give to patients in labor or when

they're antipartum will cause a decrease in fetal heart rate variability and we know that that happens. Marked

variability is definitely the least commonly um seen category of variability in fetal heart rate monitoring. And the

the times that I have seen true marked variability in my career has been related to some type of fetal heart um

defect or disorder, cardiac issue that usually we already knew existed that had been diagnosed on ultrasound or

something um of that nature prior to us putting baby on the monitor. So it was a known issue and that's the only time

I've seen true marked variability um in a fetus. So after we determine our baseline and

our variability then we look for accelerations. Now accelerate means to speed up. So when we are looking at this

this is an increase in the fetal heart rate from the baseline for a period of time. Um that period of time is usually

looked at for 15 seconds. So as long as it increases for 15 seconds um by more than 15 beats a minute that is

reassuring in ways of accelerations. Uh that number can go down to 10 by 10 if the fetus is less than 32 weeks

gestation. But for our sake we're taking care of all full fullterm ones in our normal inpartum. So we are going to look

for 15 by 15s. If an acceleration lasted longer than 2 minutes it would be considered a prolonged acceleration. Um,

anything longer than 2 minutes but less than 10 gets the name prolonged whether it's accelerations or decelerations. Um,

more than 10 minutes is a baseline because we look at at least 10 minutes of strip to determine the baseline. So

if something changes for more than 10 minutes and considered a baseline change but accelerations are related to

oxygenation or the absence of hypoxia, which is a good thing. And often they're associated with fetal movement. They

don't have to be. It doesn't have to have an acceleration when baby moves to be reassuring. The presence of

accelerations is reassuring overall. So this is one of the things we look at at fetal murdering that is always a good

thing. It's always great to have accelerations means the the baby is well oxygenated or isn't hypoxic which is

ideal. Decelerations therefore decelerate means to slow down. So these are decreases in the fetal heart rate

for a period of time. Um there are different types of decelerations. We actually have four types. um and what

type of deceleration it is tells us what is causing it to occur. So if we identify the type of

deceleration, we know what the cause is and therefore if it's a deceleration that we need to be concerned about, we

will know what to do to fix it. So I said we have four types and we have three categories here. So, we've got

like the always okay kind of deceleration, the always bad, we need to do something about it decelerations, and

then one that kind of depends on how frequent they're occurring and how deep they are. So, these are our four types.

We have early decelerations, which if we note them on the fetal monitor, we document that they're there and we move

on with life. They are always okay. Um, late decelerations and prolonged decelerations are always bad. We need to

be intervening. We need to be evaluating whether our interventions are effective. We need to be notifying um the

healthcare provider that these things are occurring. Um we need to do something about both of those. Variable

decelerations um are the one that's in the in the kind of gray area category. So if you if you always had or um my

kids like a stop light method, early D cells are green light, late and prolongs, red light, hard stop,

variables are your yellow. So if a fetus has shallow infrequent variables occasionally, usually nobody gets bent

out of shape about those, but if a fetus is having a variable D cell that lasts for a minute and drops 60 beats below

baseline every contraction and the patient is contracting every 3 minutes, that is

going to be when we we feel like we need to do something to try to prevent or lessen the severity of those variable D

cells because over time if baby is experiencing using those for an extended period of time, they will run out of

reserves and they will become more hypoxic and then we will start to see more of our late andor prolonged D

cells. So always okay is your earliest always bad or late and prolonged and then depending on their frequency and

how deep they are variable D cells are the are the yellow category. So we said those are our four categories

for fetal heart rate. And now we're going to talk about the four things that we look at for contraction patterns. So

frequency means how much how often the contractions are occurring. So we count this from the start of one contraction

to the start of the next contraction. Duration is how long the contractions last. So the start of a contraction to

the end of a contraction. And for both of those items, it can be a range. Sometimes the frequency of contractions

is every 3 to 7 minutes. Sometimes it's every 10 to 15 minutes. Sometimes it's every 1 and a half to two minutes. Um

but it's okay if there is a range for those. Same thing with duration. Um I always like to reiterate that the muscle

is a or the uterus is a muscle, not a machine. So it's not always rhythmic down to the second. It's not always

exactly the same time between contractions. And contractions don't always last the exact amount of time as

the last one. So just like frequency for duration, usually we will say the contractions are lasting 60 to 80

seconds or they're lasting 30 to 45 seconds or whatever that might be. We are looking at the contractions over a

period of time and if the shortest one was 30 seconds long and the longest one was a minute long, then it's 30 to 60

seconds and that's the range for the the portion of the strip that we're looking at. And that's okay.

intensity we talked about a little bit in the last mini lecture. So we have that mild, moderate, strong nose, chin,

forehead um feeling and that is when we're palpating the abdomen during contractions. Uh and then we also are

going to obviously ask the patient about the intensity of their contractions. And then our fourth item to look at is the

resting tone. So that's the relaxation of the uterine muscle in between contractions. And that's when ideally

the abdomen feels soft um to palpation. If it was for more rigid then that tells us that we are losing our resting tone

and we need to identify why that might be. If that is a complication that is starting to occur. If it is um an error,

not necessarily an error but an indication that we might be if we're inducing a patient where we have them on

ptocin for augmentation and we're making our body boom out these contractions. If we start to lose our resting tone, maybe

that's an indication to us that we need to slow up on the ptocin, that we're we're doing too much.

So, when we look at the contractions on an electronic fetal monitor, this is

in a nutshell what you're looking at. So, all the different pieces we just talked about. So, frequency, start of

one contraction to the start of the next contraction. Duration, start of one to the end of one. So this would also be a

duration between here and here. And intensity is how strong. Now important to remember I said intensity is only

accurate on the monitor if we are using internal monitoring that IUPC and that's when that millimeters of mercury would

come in right here for our numbers for this this number to mean something. If we are using external monitors we still

can monitor our frequency. We still can monitor duration and those are accurate. How high the contraction goes on the on

the strip if we are using external monitoring is completely useless information to us. These numbers mean

nothing for strength. If we are using external monitoring that is when our palpation comes into play. That is how

we adequately assess strength of contractions with external monitoring is to palpate. And then resting tone is

that in between and we're going to palpate then as well if we're using external monitors. Again, if we have

internal monitors, then we can use our numbers. Otherwise, we are palpating during the intensity of the or the peak

of the contraction for intensity and then during the resting tone between contractions to make sure that it's

adequate. So, that's a little overview and we're going to talk more in depth about the

different pieces of of fetal monitoring and then what we use this information for in class, but this is a good um kind

of broad lens overview to get you started and really familiar with what we're looking for.