Delivery of Oxygen | Hemodynamics (Part 2)


Alright everybody. Welcome back to our next lesson on hemodynamics. In this lesson we are going to talk about
the delivery of oxygen, which is ultimately the end goal of our hemodynamics. The goal is to delivery oxygen as well as
nutrients to perfuse our end tissues and also taking away any waste products that are a
result of metabolism. But ultimately the most important thing is
getting the oxygen to our tissues. In this lesson we are going to talk about,
and we are going to cover a few different equations that are used in understanding our
hemodynamics. I do want to preface this and say that the
point is not to have these as something that you guys need to memorize, but really just
to break it down and help you understand the components that all play a factor in the hemodynamics,
and ultimately the delivery of oxygen. So the first equation we are going to look
at is just that; our delivery of oxygen. So this is going to be our DO2. And the equation for our DO2 consists simply
of our cardiac output (“CO”) times the concentration of oxygen in the arteries (CaO2) times a factor
of 10. The 10 is really just there to get our units
of cardiac output and the concentration of oxygen all on the same page. Now you may look at this equation. It may seem a little scary or overwhelming
in trying to understand how this plays in to hemodynamics. Like I said, the goal is to understand the
components. Our end goal is delivery oxygen, and in this
case we can see that the components that make up our delivery of oxygen are “cardiac output
/ CO,” which is going to be how much blood we are circulating through our body, and our
‘concentration of arterial oxygen / CaO2″ which is basically how concentrated is the
oxygen in the blood that we are beating. So the concept is pretty simple, but I do
want to break this down a little further in order to better understand what is happening. The first one that I want to talk about is
our concentration of arterial oxygen, so that is going to be our CaO2. And big surprise, guess what, there is an
equation that we can use to determine what this concentration is. And this is going to consist of our hemoglobin
times 1.39, times our arterial oxygen saturation. Then we are going to add our partial pressure
of arterial oxygen and multiply that by 0.003. Now you’re probably looking back at the DO2
equation, and initially we were thinking that was kind of a complicated equation to look
at, and now you’re looking at this and you’re like “What the heck is going on here?” Again my point of this is that I don’t want
you to memorize this equation. There may come a point, later on in your nursing
career, as you become more advanced and more trained that this may play a role in some
of your practice. For the most part, the reason I’m explaining
this here is I want you to understand a couple key concepts that i want you to take away
from this. The first of these is that in order to determine
how concentrated our oxygen is in our blood, that there’s 3 factors that go in to that. We have our hemoglobin, we have our oxygen
saturation, and we have the partial pressure of oxygen, which is going to be our PaO2 off
our ABG. If you take a look and see where these components
play in to this equation, you can see that our PaO2 actually makes up a pretty insignificant
portion of our concentration of oxygen because we are going to multiply that by 0.003. Where as our hemoglobin and our oxygen saturation
we are multiplying by 1.39, so obviously we are going to end up with a larger number. So to really drive this point home, I do want
to give you some values so we can plug it in to the equation here and really see the
point that I”m trying to make. So let’s say we have a hemoglobin of 7. We would take that and multiply that by 1.39
then we would multiply by; lets say we have an oxygen saturation of 0.95. If we do the math on this, this give us a
grand total of roughly 9.24. Now if we move over to the other side of the
equation. Let’s say we have a partial pressure of oxygen
off our ABG that is 400. We’ll multiply that by 0.003 and that will
give us 1.2. So here you can see, even with very high partial
pressure of oxygen, it still only composing a tiny part of our total amount of concentrated
oxygen in our blood. And really the important takeaway from this
is, the two biggest factors in determining how much oxygen we are going to have in our
blood is going to be our hemoglobin and our oxygen saturation. Well hopefully that makes a little bit more
sense for you guys in understanding how we determine how much oxygen is going to be in
our blood. If we go back and look at our delivery of
oxygen equation, the other factor that is used in determining how much oxygen we are
delivery is going to be our cardiac output. And so our cardiac output, if we go ahead
and bring that down here… we do have another equation for this. And this is going to be “cardiac output / CO”
is equal to our “heart rate / HR” time our “stroke volume / SV.” And if we take a look at these components,
essentially what this is saying is, if we take how much blood is being ejected with
each beat, which is our stroke volume, and multiply that by how many beats per minute,
which is our heart rate, it’s going to tell us what our cardiac output is in liters per
minute. So just to give you some normals on some of
these numbers, our stroke volume is normally going to be 60-120 milliliters per beat. We should know our heart rate is normally
60-100 beats per minute. And our cardiac output is going to be 4-8
liters per minute. It is important to note that cardiac output
doesn’t take in to consideration the size of your patient. So if you have a small lady with 4 liters
of output, that’s going to be a big difference when we are comparing that to 4 liters of
output in, let’s say, a 350 pound man. So this is where there is another thing that
comes in to play that we call cardiac index. And essentially cardiac index is just going
to take your cardiac output and your body surface area and determine how that output
relates to the size of the person. And this way, no matter what the size the
person is, we can talk about the same numbers and have an idea of how sufficient or insufficient
that cardiac output is going to be for that patient. For our cardiac index, our normal numbers
are going to be 2.5 to 4, and this is actually in liters per minute per meter squared. Now finally from all of this we can break
things down one more time. And that’s if we take a look at our stroke
volume. There are three factors that go in to determining
what our stroke volume is going to be. That is going to be our preload, our contractility,
and our afterload. Now in a little bit we will get to talking
about these different components and what they mean and how they impact our stroke volume
and ultimately our cardiac output, but for now i just want you to understand how, if
we take a look at our hemodynamics, our ultimate goal is about delivery oxygen. And if we take that calculation and break
it down we can see how our cardiac output is composed as well as how the concentration
of oxygen in that blood is composed, and to give you a good understanding of those components,
why they are important, and ultimately how they effect our hemodynamics. And that’s going to conclude this lesson on
hemodynamics, talking about the delivery of oxygen. In our next lesson we are going to talk about
our cardiac output and all the different factors that play a role in determining what that
cardiac output is.

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