Hey everyone, I'm Brandon Odo.
And I'm Brian Bulling.
And this is Critical Care Scenarios, the podcast where we use clinical cases, narrative storytelling,
and expert guests to unpack how critical care is practiced in the real world.
Hey everyone, it is Brandon Beck with another Turbo topic today.
Ooh, double triggering on the ventilator.
You're watching a patient breathe during mechanical ventilation, and it looks like they are not
comfortable and synchronous.
Now vent synchrony is a big topic and we can spend a lot more time on it, and maybe we
will.
But let's just tackle today a pretty common form of dysynchrony.
And that is when you're standing there and watching the patient breathe, and you as you
watch your waveforms, instead of single breaths, you're seeing double breaths.
When the patient gets a breath, you're getting a double, one breath, and then another immediately
after.
Now you can recognize this by watching the patient clinically or by watching the scalars, the
waveforms on your ventilator, but it's pretty clear either way.
Now people will describe this using vague terminology, and that's one of the problems
with dysynchrony.
When people don't have a really robust understanding of what causes, what different types of phenomena,
they describe it with these rough bedside terms like, oh, the patient is stacking breaths,
bucking the ventilator, whatever.
So the first step is to elucidate what is actually happening clinically, and that'll
guide you to addressing it.
So when you see double breaths like this, there are generally two common causes.
Now in the setting of other disynchronies, it can be hard to tease some of this apart,
but let's say that is really the specific thing that you're seeing.
And the next step is to kind of bifurcate it into one of these two problems.
Now the more common problem and what you're likely to assume is that this is caused by
a patient who is more awake and has a stronger respiratory drive, and they are triggering
a spontaneous breath on a mode like assist control, which allows them to trigger or initiate
a ventilator breath.
They're getting the ventilator breath, and then as the vent breath ends, they're not
done yet.
They're still trying to inspire, and therefore they're triggering a second breath.
So understand that in your common controlled modes, pressure and volume control, the vent
decides when the breath ends.
Typically on pressure control, this is a time cycle.
You're just deciding the inspiratory time is 0.9 seconds, 1 second, something like that.
When that time runs out, inspiratory flow stops, the breath ends, expiration starts.
On volume control, usually this is driven by the flow you've determined and the volume.
So when the duration allotted for that flow to go in, the volume is delivered, the breath
ends, some vents let you set the inspiratory time on volume control to either way, whatever
the case.
The vent breath ends when it ends.
So if the patient triggered the breath, so they wanted it, the vent gives them a certain
amount of inspiratory time.
The vent breath ends, but the patient was still spontaneously inspiring.
Now you're in a disintegrate because they're trying to breathe in when the vent is no longer
giving them inspiratory flow.
The vent has switched to expiration, the expiratory valve is open, but the patient's still breathing
in.
So now we're in a pickle.
What happens when the two are fighting each other?
Well, as far as the vent is concerned, the breath is over.
Expiration is a passive process, so the patient can kind of do whatever they want during that
time.
It's not restricted the way inspiration is.
However, that also means that the same parameters that allow the patient to trigger a breath
are now in play again.
So of course our triggers on the ventilator are usually either a certain negative inspiratory
pressure or inspiratory flow.
Either way, if the patient is able to generate that by sucking at the ventilator, the ventilator
will trigger another ventilator breath.
So just like the first breath, we can trigger a second breath.
But we haven't fully expired yet.
That's how we're going to get a second vent breath.
It's occurring very shortly after the first breath finished before they've actually exhaled.
The ventilator allows them to trigger during this time, and therefore you get a second breath.
What this means is you'll stack it on top of the first one.
So if the volume you delivered, let's say we're in volume control, was 500ccs, now they've
only exhaled 50ccs of the last breath, but they're going to get a second 500 delivered.
And now they essentially have 1000ccs in their lungs.
They've stacked two breaths on top of each other and you got a doubled breath.
This is a common disinclin because in a patient who is active and breathing a lot spontaneously,
it's very possible they want bigger breaths.
And again, this functionally means a longer breath, but you can think of it easily as
a larger volume.
They're still trying to breathe in when the tiny controlled lung protective volume you
delivered to them has already ended.
These lung protective breaths that we're typically using are not what a lot of spontaneously
breathing patients want.
They're wanting 500 or more milliliters per breath.
And then this carefully calculated 60ccs per kilo of ideal body weight, you gave them
as like 430ccs.
It's just small and they want more.
So that's a common disinclin.
Now the confusing part is that in a very opposite clinical scenario, you may see the other version
of these doubled triggers.
This is something called reverse triggering.
This is relatively recently described and this is my mean in the past 10, 15 years in
the literature and it's gotten a lot more attention recently in the way that many new
clinical phenomena do once you start looking for it, you start seeing it everywhere.
Now what happens here and this is key, usually the initial breath is ventilator triggered.
It occurs on the time trigger because the patient did not trigger a breath.
Now I suppose in theory it could be patient triggered but the reason you usually see it
happen this way is because this phenomenon tends to occur in patients who do not have
a strong respiratory drive.
They are sedated.
They have sedatives, perhaps opioids on board or maybe they have neurologic injuries, maybe
they're comatose.
Therefore the first breath is usually vent triggered.
However, when that breath ends, you get a second breath which is patient triggered.
So the vent gave them a breath and it caused the patient to breathe after that.
This is a phenomenon sometimes called entrainment but in a broad sense we're calling it reverse
triggering in the sense that the vent has triggered the patient to breathe rather than
the patient triggering the vent.
Why does happen, who knows, probably it's something like the inspiration delivered forced
to the patient's diaphragm causing some kind of a stretch reflex and stimulating them to
take a breath, something like that.
So that may explain why it tends to occur in patients who do not have a strong spontaneous
drive because if they do they would kind of take over control of their own diaphragm.
It's more like the vent is almost pacing their diaphragm for them.
And in fact we see this more in patients who are breathing less.
So one treatment is actually to let the patient do more of their own breathing, lighten their
sedation, perhaps put them in more of a spontaneous mode, perhaps decrease the respiratory rate
so they're able to trigger more of their own breaths, things like that.
But whatever the case, you see how this is very different from that double triggering
caused by strong spontaneous effort.
Usually that first breath is patient triggered then and so is the second breath.
With reverse triggering, typically the first breath is vent triggered but in every case
the second breath is patient triggered.
And again your treatments are going to be different.
When the patient is triggering these double triggers because of strong effort, you may
need to sedate them out of it.
You know that's often our first response to many disynchronies but if you truly have
to you do because they are getting very large tidal volumes, they're probably not lung protective.
So you know, when a patient with severe air, DS, you can't tolerate this.
But in a patient who is more well, maybe they're on the vent for other regions like neurologic
reasons, you may be able to go the other way and just liberalize them.
Put them on a very spontaneous mode like pressure support, let them do their own thing, and
then they don't have to fight the vent for the breaths they want and they can just breathe
normally.
The patient is reverse triggering, you're not going to get out of this by sedating them
more.
That may make it worse.
You have to either sedate them less or again liberalize them, let them kind of use their
own respiratory drive a little more so that it's not being stimulated by the vent so much.
So try to think of these options in these two categories.
And when you look at those double triggers, try to bifurcate it.
And the easiest way I think to do that is to look at that first breath and see how it's
triggered.
All the ventilators will tell you what triggered the breath.
They know what triggered it, whether they triggered it with a time trigger or the patient triggered
it with their own trigger.
You can look at the initial deflection to see if there's a little bit of negative pressure
as a classic way.
But you don't really have to.
The vent will tell you they give you a little light or a flag or a logo somewhere saying
what triggered it.
And I think that is often the easiest way to go about this.
Now you can have a reverse triggering that is not strong enough to actually trigger a
ventilator breath on that second breath.
And as you look at a lot of waveforms, you'll see smaller deflections sometimes occurring
at the first part of expiration.
Not strong enough that they're actually getting a second breath, but it's just causing aberrations
in the expiratory flow.
They're getting like a little bit of flow because they're breathing in a little and
it's probably caused by a weaker stimulation or entrainment of their diaphragm.
You can kind of do what you want with these things.
Again, it probably is some degree a disintegrate and may have implications on things like lung
protectiveness, but you don't necessarily have to do anything if it doesn't matter.
So that's how I want you to approach these double triggers.
Start to parse it out.
Don't just have these broad syndromic descriptions like, oh, they're stacking breaths.
They're getting two at once, whatever.
Understand what's happening and why.
And you start to make progress understanding disintegrate.
That's it for now.
Talk to you guys next time.
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