This lesson introduces basic ventilator modes, focusing on volume control, and explains key settings and monitoring parameters essential for understanding mechanical ventilation.
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all right you guys welcome back to
another video lesson in this lesson
we're gonna be taking a look at the
different basic ventilator modes that
you're commonly gonna come across these
are the modes that you're gonna see more
often than not and it's gonna be
imperative that you guys have a good
understanding of these so that in the
future when we talk about and you also
come across some other alternative modes
of ventilation you have this as a
baseline in which to understand some of
these other modes and my name is Eddie
Watson and I welcome you to ICU
advantage my goal here with ICU
advantage is to take these complex
critical care topics and really break
them down for you and make them easy to
understand for you guys I hope that I'm
able to do just that and perhaps by the
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with that said let's go ahead and get
started here and let's really start this
lesson off and begin with a quick
introduction to the topic of our basic
ventilator modes so in the previous
lesson which if you haven't watched it
yet I'm linking to it up above and down
in the description I provided you guys
with an introduction into the world of
invasive mechanical ventilation in that
lesson I talked about how pretty much
all of the ventilators that we use today
are all forms of a positive pressure
ventilator and within the world of
positive pressure ventilation there
really are many different types or modes
as we call them that our ventilators can
really operate in in this lesson here
I'm gonna be covering the basic vent
modes to try to really give you guys a
good understanding of the most common
modes that you're gonna come across in a
future lesson I am gonna take a look at
some of the more advanced modes that you
may very well come across now when we
take a look at our different vent modes
there's really two main categories that
you're really gonna come across the
first of these is something that we call
volume control and the other is
something that we call pressure control
so first let's take a look at volume
control here and I'm actually going to
take a look at some of these modes here
in just a minute but really the basis of
this category is that we're gonna be
setting and controlling the volume of
air that our patients get and the way
the vent does this is it delivers this
volume by providing pressurized air
causing it to move into the patient's
lungs now depending on many factors the
pressure that's required to deliver this
volume can and certainly will change
from patient to patient and from breath
to breath this right here is a very
important fact for you to remember so
now if we move over and quickly talk
about pressure control here the reverse
is taking place in pressure control
we're going to be controlling the
pressure that we deliver to our patients
and there are many benefits to pressure
control which we are going to discuss in
the next lesson on those advanced modes
but the thinking and understanding of
these modes is different than our
natural intuition now similar to like we
had just talked about with volume
control depending on many factors the
volume of air as opposed to the pressure
of air that is going to be delivered can
and will change from patient to patient
and breath to breath once again this is
going to be a very key point and this
really summarizes the main difference
between our volume control and our
pressure control as I mentioned here
volume control our volume is constant
and our pressure is the changing
variable whereas in pressure control
our pressure is constant and the volume
is our changing variable so a very key
important distinctive concept to know
now within each of these main categories
there really are many different modes
and even some that kind of cross in
between both of these modes here but for
the purpose of this lesson we're gonna
be sticking to just talking about volume
control so like I said the main
principle for volume control here is
that we want to ensure that our patients
are receiving a set volume of breath
each minute and like I said within this
category we have different modes that
are ultimately play a different role in
the impact on our patients work of
breathing in order to understand the
differences between these modes though
we really need to talk about some of the
settings and some of the things that
we're going to be looking at on our vent
alright so the first thing that we're
going to talk about in our settings is
something that we call our tidal volume
and this you'll see in the setting VT
and essentially our tidal volume is the
volume of air that set to be delivered
with each breath to our patient all
right the next setting that I want to
talk about is something that we call
frequency also known as our respiratory
rate and this will no usually find
abbreviated as either F or RR and this
one should be pretty self-explanatory
but it's how many breaths per minute are
being delivered to our patient now it's
important understand how this works and
how this triggers for a breath to be
given is it will actually take the
respiratory rate that you set and divide
that into 60 to figure out the amount of
time that we should have between each
individual breath and we'll talk about
it more here in a minute but when that
amount of time has elapsed then it
triggers another breath to be given all
right the next setting that we're going
to cover here is going to be our oxygen
concentration and this is what we refer
to as our fio2 and fio2 really means our
fraction of inspired oxygen this is
important to know because when we are
referring to our fio2 oftentimes we'll
say we're on 50% we're on 80% but really
we need to understand that this number
is being expressed as a fraction or a
decimal so when we say we're on
fifty percent our fio2 setting is
actually going to be 0.5 if our patients
on a hundred percent fio2 then we have
an fio2 of 1.0 so the next setting that
I want to talk about in the world of
volume control is a setting called
positive end expiratory pressure this is
something that we more commonly referred
to as peep so thinking back to one of
our previous lessons where we covered
non-invasive ventilation think of peep
as being really similar to CPAP or BiPAP
on a BiPAP machine essentially this is a
constant pressure that's going to be
applied throughout expiration to really
help an open and keep open alveoli now
it's peep along with our fio2 which is
how we really help to improve our
patient's oxygenation and so for this
setting it's really important that we
maintain at least 5 centimeters of water
to help to provide what we call
physiological peep and the reason for
this is because of the ET tube that we
have in our patient that this can
actually allow the intrathoracic
pressure to fall to zero which would not
be a good thing now the range of
settings that will usually see for a
peep is typically in the range of 5 to
20 and since they didn't mention in a
minute ago for our fio2 we typically
aren't going to find that any lower than
35% or 0.35 and this can obviously go up
to a hundred percent alright and so the
final setting that i want to talk about
here in this world of volume control is
something that we call pressure support
this one you'll see abbreviated as PS
and the best analogy that I can really
give you for pressure support is if you
really think about this as a spotter at
the gym so this is really an extra push
of air to assist our patients when
they're taking spontaneous breaths so if
you think about that spotter is there to
kind of help provide a little bit of
pressure and support as you're going
through doing some sort of exercise
that's kind of the same thing that's
happening with our pressure support only
in this case we're helping our patients
take a breath so if you really think
about this the more pressure support
that we apply the larger the spontaneous
breath that a patient's going to be able
to take with Morris's
our settings usually for pressure
support you're gonna find in the range
of five to twenty typically though we're
gonna keep it at a minimum of anywhere
from eight to ten and this is really to
help overcome the resistance of having
to breathe through that ET tube actually
out there if you take the time to look
for it there is a chart that does a
breakdown based on the ET tube size and
how much pressure support it really
requires to overcome that resistance if
I happen to find it I'll link to it down
in the description but it's an
interesting chart and it really drives
home the point that just because of the
size and the resistance of that ET tube
we're already gonna have to give them
some sort of assistance because if we
gave them nothing breathing through that
ET tube would actually be harder to
breathe through than if they were
normally breathing alright so those are
all the settings that you're gonna need
to know when we're talking about these
different modes of volume control lastly
I do want to talk about a couple of the
different things that we're going to be
looking for in the monitoring of our
patients on the vent and I'm gonna go
through a couple different parameters
that you're gonna see on your vent but
just know that these parameters that I'm
listing here are far from all of the
parameters that are really important in
truly understanding how your patient is
tolerating being on the vent but again
this is where the respiratory therapist
comes in because this is their area of
expertise over time it certainly is
great to learn about a lot of these
different settings and different numbers
that you get on there but for a basic
understanding I'm gonna give you a
couple things that are going to be
really important the first of these is
going to be something that we call our
minute ventilation and this you'll see
abbreviated as ve now this one's
probably the most important one for you
to understand and that's because this is
a measure of the amount of air that's
being delivered to our patient per
minute so it's important to know how we
get this number and really in a perfect
world our minute ventilation would be
our tidal volume times our frequency and
if you really just kind of think about
that for a minute if we take the volume
of air that we're delivering with each
breath and then multiply that by how
many breaths were giving per minute
should tell us what our volume of air
that we delivered to our patient over
the course of a minute would be now as
we know we don't live in a perfect world
so we have to deal with things like
inefficiencies triggering pressure
limits and really the patient's own
response can and do impact the actual
delivery of air that they get but if you
do have to increase or decrease your
patients minute ventilation to do
something like let's say control our PA
co2 on an ABG then we're going to be
looking to adjust our patients minute
ventilation and again because we should
be keeping our tidal volume set based
off our patients ideal body weight then
really we know that if we need to be
making changes to our minute ventilation
we probably want to be adjusting our
respiratory rate the core concept here
is if we have more minute ventilation
we're gonna have more co2 clearance
hence less minute ventilation less co2
clearance and the goal for a patient's
minute ventilation is going to be from 5
to 10 liters per minute all right the
next thing I want to talk about it's
actually going to be the first of two
different pressures here it's gonna be
something that we call our peak
inspiratory pressure and this one you'll
see abbreviated as our pip now I'm not
going to go too far into some ventilator
Theory here but essentially our pip is
the maximum pressure that's reached
during inspiration and the goal here for
our pip is to have this less than 35
with the goal of preventing lung injury
now the last setting and the last
pressure that I actually want to talk
about here is something that we call our
plateau pressure and this one's
abbreviated RP plat and when we talk
about some of these pressures and volume
control the plateau pressure is going to
be probably one of our most important
ones to keep an eye on because this
one's going to be an indication of our
lung compliance so we measure this one
at the end of inspiration with an
inspiratory hold or pause maneuver and
we really want to be shooting to have
our plateau pressure under 30 and this
is really to help prevent Barrow trauma
so important to know plateau pressure
means lung compliance if we see an
increasing plateau pressure this can
signal that there's some sort of problem
with our patient's lung compliance all
right so those are the settings and some
the major important things that we want
to be monitoring for in terms of numbers
on the ventilator and so now let's go
ahead and move on and talk about the
different volume control modes so I'm
going to go through and talk about a few
different modes that we're gonna see
here and it can really help to think
about these modes as being from the most
supportive to the least supportive in
terms of our patient's work of breathing
alright so the first of these modes that
I want to talk about is something that
we call assist control this is something
that you'll see abbreviated either AC or
VC for volume control now you may also
see people interchange this with CMV but
there actually is a very important
distinction and I'll kind of explain
that difference here in a minute when we
get to that so when we talk about assist
control there's a couple settings that
are going to be really important for
this mode obviously we're going to have
because it's a volume control we're
gonna have a predetermined volume set
for each breath so a VT or tidal volume
and we're also going to set the number
of breaths per minute or the frequency
for our patients in addition to that
we're also going to set an fio2 as well
as a peep important distinction here is
we are not going to have a pressure
support now let me try to explain why so
we know based on our tidal volume and
our frequency that every so often we're
gonna give the patient a set volume of
breath so if we had a tidal volume of
let's say 500 and a respiratory rate of
12 we know every five seconds we're
gonna give this patient a breath of 500
MLS and this is essentially what CMV or
control ventilation does whatever the
set number of breaths are and the volume
to be delivered the vent just continues
to pump that out one after another after
another and there is no derivation from
that no matter what the patient needs or
what they're trying to do they're just
going to continue to get at the same
frequency the same volume of breath
where assist control comes in is this
actually will take into account the
patient trying to take their own breath
so what happens here in assist control
is if a patient attempts to take their
own breath this is what we call
spontaneous breath that the ven is gonna
recognize this breath but it's going to
deliver the full set tidal volume so the
vent is either gonna deliver breath to
the patient when it's time or if the
patient tries to initiate their own
breath the vent is going to recognize it
but say I know you want a breath here
have the full breath and because of this
this is why we don't have a pressure
support because we're not gonna aid the
patient in taking a spontaneous breath
we're just going to detect that they
want a breath and then give them a full
breath so this sounds wonderful except
the fact that this can actually lead to
excessive ventilation especially if our
patients are too kipnuk for non
respiratory related reasons so here this
to Kipp Nia will lead to blowing off too
much co2 and ultimately lead our patient
into a respiratory alkalosis if you want
kind of a review on this I'm gonna link
to ABG lesson up above as well as down
in the description but here if you think
about if your patients in pain if they
have anxiety or even if they have some
sort of central nervous system
dysfunction causing them to have this
abnormal - Kipp Nia that this can
ultimately lead to blowing off too much
co2 when we physiologically normally
wouldn't want that now often times
though we will initially use AC when
we're intubating a patient as we really
have the full control over our patients
minute ventilation as well as fully
taking over their work of breathing
alright so because of some of these
problems that we just talked about with
assist control and also because of a
desire to want to be able to have a mode
that can really help with weaning our
patients down off the ventilator
another mode was developed and it's
something that we call synchronized
intermittent mandatory ventilation
something that goes by the name simv so
essentially with simv we're still going
to determine or mandate hence the name
mandatory that a patient gets at least a
set volume and a set number of breaths
per minute again for this we also will
set an fio2 and a peep so so far this is
looking just like a sis control
the big difference now when we compare
this to AC is what happens when a
patient takes their own spontaneous
breath in simv instead of delivering the
set volume of air the patient's actually
going to be allowed to take whatever
size breath they can and so now the
breaths that were delivering through the
vent are actually going to be
synchronized with the patient's own
spontaneous breaths to really help to
increase their vent compliance so
essentially as long as they take a
breath in a predefined window between
each of the two mandatory breaths then
if they go to initiate that breath then
whatever breath they take the size the
volume that they get is what they get if
they happen to take that breath right
about the time that another mandatory
breath is going to come the vent is
going to recognize this but similar to
AC is it's then going to go ahead and
give that full set tidal volume this
ensures that we're maintaining at least
that mandatory minimum level of minute
ventilation so because the fact that our
patients are able to take their own
spontaneous breath that this is where we
actually are going to set a pressure
support here and again the point of this
pressure support is to assist them in
taking their spontaneous breath if we
notice that our patient is taking too
small of the spontaneous breath we can
increase this pressure support to really
help them achieve a larger spontaneous
breath so now a quick test of
understanding here let's say you have a
patient who has just been intubated and
they are currently sedated and paralyzed
still from the intubation if you were to
put this patient now in to assist
control or if you were to put this
patient into simv with all of the same
settings other than the pressure support
that you'd set in simv
what would be the difference that you
would see in your patient on the vent
now well hopefully you realize that that
was a trick question
because there's going to be no
difference between these two so if a
patient is taking no spontaneous breaths
simv is going to be indistinguishable
from AC and if you really kind of think
this one through if they're paralyzed
and they're not taking their own
spontaneous breaths we do have a
frequency and a tidal volume set
so again if we think of that example of
a volume of 500 and a frequency at 12
every five seconds we're gonna give this
patient 500 tidal volume and this is
just gonna go over and over and the
patient doesn't take any spontaneous
breath that's all that they're gonna get
well if they were an AC again they're
gonna still be getting every five
seconds of volume of 500 and again
they're not taking any spontaneous
breaths so that's all that they're gonna
get as well and these two modes are
going to be completely indistinguishable
from one another now simv is really good
because it can actually allow patients
to gradually take back over their work
of breathing over time and so the less
support that we give them with the
mandatory breaths the more work of
breathing that the patient is going to
need to take on on their own and so like
I said simv was initially developed with
the help of really weaning patients from
the vent but often we find it as one of
our primary modes of ventilation because
of the fact that some of the work of
breathing is on the patient it really
requires close observation of our
patients physiologically as well as
psychologically to see how they're
responding to this work of breathing now
our patients may be at risk of becoming
tachypneic hyperventilating and leading
themselves into a respiratory alkalosis
but again because we're relying on them
for some of the work of breathing if
they're minute ventilation just isn't
sufficient for what they need they're
not taking enough breaths or large
enough breaths then we can go to the
other side of things and be retaining
co2 leading to a respiratory acidosis
all right so the last mode that i want
to talk about here is something that we
call pressure support now oftentimes
you'll hear this referred to as CPAP let
me tell you this is not CPAP please
don't call it that and in talking about
pressure support this actually
technically isn't a volume control mode
of ventilation because in volume control
we are setting and controlling the
volume that our patient is getting and
pressure support is a form of
spontaneous breathing so for patients in
this mode we're only going to set an
fio2 a peep and a pressure support so
there's not going to be a tidal volume
or a rate set for the
patience although that said most vents
do have a safety mechanism in place
something that we call backup rate so in
the event that our patient goes APNIC
this backup rate is gonna kick in and
take over until we reset it now here in
pressure support minute ventilation and
thus our patients work of breathing will
be almost entirely dependent on the
patient's effort with the assistance of
whatever we set our pressure support at
so oftentimes you'll see this used as
our last step or trial before excavating
patients typically if we do have our
patients and pressure support and we are
doing this spontaneous breathing trial
we usually have them set at 10 over 5
which is 10 of pressure support and five
of PEEP or for a very short run
sometimes we will run them 5 over 5 and
again this is going to be a short run
just prior to excavating all right so
that finishes up our discussion here
talking about the different vent modes
hopefully these modes make sense you can
see that we're looking at some of the
same settings were functioning very
similar in terms of volumes that were
being delivered but where some of the
key differences come in is how we handle
a patient's spontaneous breath from CMV
or control ventilation where we pretty
much don't acknowledge that at all
down through recognizing those breaths
but giving the full breath an AC to simv
where the patient will determine the
size of their breath all the way down to
pressure support where the patient's not
going to get any mandatory breaths and
everything's going to be based on their
own work of breathing like I said it's
sort of this progression from the most
amount of support and the most effort
and the most coverage taking over of our
patients work of breathing down to the
least amount all right and with that
said I do want to thank you guys so much
for watching if you found this lesson
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