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Mechanical Ventilation Explained - Ventilator Settings & Modes (Respiratory Failure) - YouTube
Channel: MedCram - Medical Lectures Explained CLEARLY
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Welcome to another MedCram lecture.
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We鈥檙e going to talk about mechanical ventilation.
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This is meant to be an introduction to mechanical
ventilation.
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If you鈥檝e never done mechanical ventilation
before we鈥檙e going to introduce you to the
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basics so you can go in and actually feel
competent about managing a patient on a ventilator.
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This is often a daunting task because typically
these patients are critical, but actually
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the basics are fairly graspable and we鈥檙e
going to go through those now.
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This is a series that鈥檚 going to actually
go through a number of different lectures.
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We鈥檙e going to start with the basics starting
right now.
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The first thing you鈥檝e got to know is you鈥檝e
got to know the definition of some of these
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things.
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You鈥檝e got the patient.
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That鈥檚 pretty easy.
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Then you鈥檝e got this thing coming out of
their mouth.
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That鈥檚 the endotracheal tube.
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We鈥檙e going to show this a little bit more
later.
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Then, you have it hooked up to a big machine
with a bunch of knobs on it, and dials and
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output.
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This is what we know as the ET tube.
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That鈥檚 the endotracheal tube.
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Then finally you鈥檝e got the actual ventilator.
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That鈥檚 important to know because sometimes
people are intubated.
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That means we put a tube down into their mouth
because they need airway protection.
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Sometimes we do it, in other words, because
they can鈥檛 protect their airway.
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They can鈥檛 protect stuff, liquids and solids,
from going down their airway where that stuff
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shouldn鈥檛 go.
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Needlessly because of this, it鈥檚 not too
comfortable.
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We鈥檝e got to sedate them and when we sedate
them, we鈥檝e got to put them on a ventilator.
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That might be one reason we would have to
do this.
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The other reason is because they can protect
their airway okay but they just can鈥檛 breathe
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on their own.
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They鈥檙e struggling to breathe so we help
them out with the mechanical portion of breathing
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and that鈥檚 where the ventilator comes in.
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The way we deliver that is through the endotracheal
tube.
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It鈥檚 kind of important to know what an endotracheal
tube looks like.
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The basic is pretty much the same all the
way around.
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It鈥檚 this long tube that kind of looks like
this.
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That鈥檚 the part that connects to the ventilator.
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This is the part that goes inside the patient.
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Actually, you鈥檒l see that there is a balloon
on the end of that endotracheal tube and the
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thing that allows you to blow it up is a little
thing that goes up, called the pilot balloon.
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It goes up.
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Actually, the pilot part comes out and it
looks like a little pilot balloon that you
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can kind of feel what the pressure is.
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Then there鈥檚 a little part where you can
inject air into it.
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When this goes down and you intubate somebody
it goes into their mouth past their vocal
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cord, specifically, and down into the trachea.
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The vocal cords usually end up about right
here so this is going down into somebody鈥檚
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trachea.
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Then usually it branches off.
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You鈥檝e got the left and the right main stem
bronchus.
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Here you have the endotracheal tube going
down.
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Now, this balloon gets inflated here so that
stuff that might make it down here doesn鈥檛
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go past and go into the lungs.
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It鈥檚 called airway protection.
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We blow up the balloon here after we intubate
them to make sure that happens.
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In some versions of this still have a little
device right here that also comes out.
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The purpose of that is to suck secretions
that might come up and go out and that鈥檚
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called subglottic suctioning.
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That鈥檚 kind of an option.
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This is the basic anatomy of an endotracheal
tube.
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Of course we just talked about the ventilator.
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That鈥檚 got a bunch of buttons and whistles
and things were going to talk about a little
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bit.
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Going back to our patient again.
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We鈥檝e got our endotracheal tube.
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We鈥檝e got our ventilator.
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What鈥檚 the purpose of this ventilator?
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The purpose of the ventilator is to maintain
homeostasis between the due gas concentrations
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that we鈥檙e talking about here, which is
carbon dioxide and oxygen.
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Oxygen is being put into the patient and carbon
dioxide is coming out.
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For the most part we want to keep those close
to normal.
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There鈥檚 some exceptions to that.
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Here鈥檚 the point though.
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There鈥檚 many different ways to put air into
somebody.
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We can say we鈥檙e going to put air into somebody
based on volume.
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We鈥檙e going to put a certain X amount of
volume into somebody and then let it come
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back out.
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That鈥檚 one way of doing it.
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Another way of ventilating somebody is saying
we鈥檙e going to inflate them to a certain
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pressure.
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We鈥檙e going to have this ventilator put
a certain amount of pressure into the patient
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and then when the pressure is released it鈥檚
going to come back out.
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We can do that.
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Now, we can do it at a certain rate.
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We can do this fast and we can do it slow
so in other words, how many breaths per minute.
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We can also adjust the flow rate.
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In other words, we can put a certain volume
in but we can get that volume slowly or we
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can give that volume very quickly.
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The other thing that we can do is we can decide
how much pressure to leave in there at the
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end of when we put the air in and then we
can decide how much pressure to leave in there
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after we鈥檙e done putting the air in.
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Finally, we can decide how much oxygen we
want to put in there.
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How much?
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We can put a lot or we can put a little.
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Now, just to further complicate this just
so you can kind of see where we鈥檙e going
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with this, we can have the ventilator be in
charge of when the patient gets a breath or
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we can have the patient be in charge of when
they want to get a breath.
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Think about all of these different variabilities.
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Now, you can quickly see how there are so
many different ways that you can ventilate
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somebody and each one of these ways is a different
mode of ventilation.
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You may have heard of these before, like AC
or SIMV or pressure support, or CPAP.
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These are all different modes and we鈥檙e
going to go through some of these modes and
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show you how it makes sense about how this
is working.
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Here鈥檚 our system.
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Over here, we鈥檝e got the ventilator.
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Here, we鈥檝e got the tubing that goes to
the endotracheal tube down into the lungs
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and we鈥檝e got our balloon here, filled with
air to make sure nothing else gets down there.
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We are ventilating our right lung and our
left lung.
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Let鈥檚 talk about the first mode of ventilation.
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This will become important later.
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The first mode that I want to talk about is
AC.
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The other way we call it is assist control.
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The other name for it also is continuous mandatory
ventilation or CMV.
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This is the most common mode of ventilation
that you鈥檒l see, especially on a medicine
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floor or medicine unit.
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The key here is that the patient triggers
the vent.
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How does that happen?
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Well, the patient takes a breath in and therefore
there is a negative pressure here, which causes
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a negative pressure to be sensed here, at
the ventilator.
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The other way you can sense it is by flow,
if there is a flow that actually goes through
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here by the negative pressure.
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As soon as the ventilator picks up on that
negative pressure, it鈥檚 going to deliver
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a specific volume.
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There is an actual dial on here where you
can actually turn the knob to a specific volume
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or you can enter it in.
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That volume can be anywhere from 500 CC鈥檚
all the way up to 600 CC鈥檚, usually.
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The ideal way of ventilating somebody would
be around eight milliliters per kilogram,
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ideal body weight.
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Anyway, whatever that volume is, it鈥檚 going
to deliver that specific volume in AC mode
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ventilation.
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Now, the patient can trigger it.
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You could also set up a backup mode or a rate.
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What does that mean?
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If I set the rate to, for instance, twelve
because there are twelve, five second intervals
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in one minute.
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That means every five seconds the ventilator
will give a breath to the patient of a specific
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volume, every five seconds only if the patient
does not take a breath.
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If the patient is breathing above twelve then
the ventilator will only give breaths when
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the patient triggers it by trying to take
a breath in.
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In other words, if you set the mode to AC,
set in a volume and set a rate of twelve,
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the patient can never breathe less than twelve
times per minute.
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Now there鈥檚 something you should understand
about this, which is very important.
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You may recall from chemistry and equation
that says PV equals nRT.
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In this system temperature is constant.
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R, of course, is always a constant and is
a constant.
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The thing that you must realize is that pressure
and volume are inverse in proportional to
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themselves.
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In other words, as the volume of the gas goes
up the pressure goes down, if you have the
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same amount of gas.
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However, the other way of looking at this
is compliance which I鈥檒l abbreviate as a
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C.
Compliance is equal to the change in volume
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over the change in pressure, which means to
say that if the pressure changes a little
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bit and the volume changes a lot, then you
have a very compliant lung.
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If you don鈥檛 have a very compliant lung,
it鈥檚 going to take a lot of pressure to
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make just a small amount of change.
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Here鈥檚 the point.
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The point is that these set of lungs have
a specific compliance and if you are delivering
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a specific volume into these lungs, you are
going to get a specific pressure after you
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deliver that volume.
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That pressure can change depending on the
compliance.
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The point of this is that you need to have
a readout that tells you what the pressure
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is in that lung so you can know what the compliance
is.
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In other words, in this mode of ventilation,
you set the title volume and the ventilator
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will tell you what the pressure is so you鈥檙e
setting the title volume.
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You鈥檙e setting how much volume of gas is
going to go into the lung and based on the
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compliance of the lung, it will tell you what
the pressure is.
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If the compliance of the lung goes down, then
typically you鈥檒l have higher pressures.
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If the compliance of the lung is very high,
in other words a very compliant lung, then
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your pressures are going to tend to be on
the lower side.
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Now, let鈥檚 make this converse to pressure
control.
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In pressure control what we鈥檙e doing is
we鈥檙e setting a pressure.
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In other words, we鈥檙e going to decide how
much pressure we鈥檙e going to ventilate this
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patient with.
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As you can imagine, if we鈥檙e setting a pressure,
there is a specific compliance to this lung,
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depending on what state it is in, and if we
set a certain pressure if the compliance of
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this lung is very low, then you can imagine
we鈥檙e going to have lower volumes.
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However, if the compliance of this lung is
very high, then we鈥檙e going to have higher
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volumes because remember compliance is equal
to the change in volume over the change in
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pressure.
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In pressure control, you can also have the
patient or time triggering a set change in
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pressure.
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Depending on the compliance, the volume can
change.
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The key here is that you have to have alarms
set up and you need to know and understand
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what those alarms mean.
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What could happen here, let鈥檚 for instance
say in a pressure control situation where
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you鈥檙e giving a specific pressure, if the
compliance of these lungs somehow drop precipitously
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all of a sudden because of some pathology,
which we鈥檒l get into, you will notice the
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volumes will drop.
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You would want to know that.
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You could set an alarm on the lower side of
the volume so that if the volumes did go down,
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an alarm would go off saying that you鈥檙e
not ventilating.
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Conversely, if you were back in our previous
mode which was assist control and you鈥檙e
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setting a certain volume, if the compliance
of the lung dropped in that situation then,
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as you would realize, the pressure would start
to go up because you鈥檙e trying to put a
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set amount of volume into a low compliant
lung.
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When that happens, the pressure goes up.
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The pressure would then trigger an alarm.
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The point here is in pressure control, you鈥檙e
setting a pressure and your output to read
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is your volume.
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In AC, it鈥檚 the flip of this.
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When we come back, we鈥檒l talk about the
pressure-volume relationship and a few more
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modes of mechanical ventilation.
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