welcome to another MedCram lecture
we’re going to talk about delivery of oxygen to the tissues and the pathway
that it gets to the tissues through the lung the bloodstream and then finally on
to the tissues and this is important because it involves a lot of physiology
it involves how oxygen diffuses into the blood and the equations that are used
and this is very easily testable because they can use equations to minimize the
answers and try to get you to think about these equations so let’s go
through this using the major equation which I’m going to write for you so the
delivery of oxygen which will abbreviate D o2 is equal to the cardiac output
which I’ll say is Co times the content of the arterial blood which I’ll
abbreviate cao2 so cardiac output is basically in liters per minute and the
concentration of oxygen in the arterial blood is basically units of millimeters
of oxygen and deciliters of blood so the basic equation here is again the
delivery of oxygen is the cardiac output how fast we can deliver oxygen in this
patient two times the content of that fluid and we can break this down even
further as we’ll see the cardiac output as you know is really the stroke M times
the heart rate and the content the oxygen content of the blood is actually
an equation that you should know which is one point three four which is a fudge
factor basically times the humid lobe and concentration times the saturation
of that hemoglobin molecule plus point zero zero three times the partial
pressure of oxygen in the blood now that sounds a little complicated but let’s
break this down okay so the cardiac output as you know
from any kind of a discussion in cardiology is simply the stroke volume
times health many times that stroke happens in a minute and that’ll tell you
what the cardiac output is so basically this is the how many liters per minute
you’re pumping and that many liters per minute times the amount of oxygen in
those leaders is going to tell you how much oxygen you’re going to be
delivering to the peripheral tissue well the content of blood the content of
oxygen in that blood is an interesting portion here there’s two components
notice there’s the first component and there’s the second component and that’s
very important here because you see when there is an oxygen molecule let’s take a
look here at the alveolus there’s the alveolus and the oxygen
molecule which diffuses into the goes into that alveolus is going to come in
contact with the pulmonary artery and then it’s because they’ve become
oxygenated and turn into the pulmonary vein now when that happens this oxygen
molecule is going to diffuse down into the plasma in the a pulmonary
circulation when that oxygen molecule is in solution we’ll say it’s dissolved in
the plasma we can detect that by measuring the partial pressure of oxygen
in the plasma this is known as the po2 the partial pressure of oxygen however
something happens as soon as that oxygen molecule goes into solution in that
plasma what happens is that a red blood cell comes by corpuscle there’s a side
view of it and it goes in to the bag of hemoglobin known as the red blood cell
and it binds to your hemoglobin molecule when it does that it essentially comes
out of solution and precipitates with that hemoglobin molecule the only way
you can detect that now is by detecting the saturation of this hemoglobin
molecule so there’s two forms of oxygen in the blood there’s the oxygen which is
dissolve solved in the plasma and then there’s
the oxygen molecules which are combined or connected or precipitated to the
hemoglobin molecule and that here is what is going on this part of the
equation in terms of oxygen in the blood is the part that represents that oxygen
which is bound to hemoglobin so you can see there’s a human globin concentration
factor and there’s a saturation factor so the amount of oxygen in the blood is
directly proportional to a fudge factor of 1.3 4 times the concentration of
hemoglobin that’s in the blood to begin with times the saturation of that
hemoglobin molecule in the blood and that tells you how much oxygen is there
the other portion of it which is this part down here tells you how much oxygen
is carried in the blood by simply the amount that is dissolved in the blood
and as you can see it’s a very small proportion so therefore the majority of
the oxygen which is carried in the blood is carried in the form of oxyhemoglobin
and not in the form of partial pressure of oxygen that is dissolved that’s a key
point here it’s a key point because they’re going to ask you where most of
this oxygen is coming from now let me rewrite that equation or that part of
the equation again we’ve said that the content of oxygen in the blood is equal
to one point three four times the hemoglobin concentration times the
saturation of o2 plus zero point zero zero three times the pao2
so if I wanted to increase the concentration or the carrying ability of
oxygen in the blood in general would it be more important for me to increase the
saturation or the pao2 and it would be more important for you
to increase the saturation just algebraically based on where this
equation is now how is that boiled down well there’s something called the
hemoglobin binding curve which I’m sure you’ve all heard of by this point okay
this describes the relationship between the po2 which is what we were just
talking about or the pao2 and the saturation percent saturation in the
blood okay so it kind of looks like this okay and this actually just keeps going
on and on and it kind of asymptotes with 100% and you’ve got 50% kind of in this
range right here the point of this is that once your saturation gets up high
enough into the 90s you can have so here’s 90% you can have increasing po2
levels which are only going to modestly increase your saturation levels so it
gets the point that increasing the PA o 2 will increase the oxygen content by a
very small amount and it will only increase this part by a very small
amount and why is that important that’s important to understand that
there is a diminishing marginal utility on increasing the amount of partial
pressure of oxygen that you’re delivering to patient because you’re not
going to get that much more saturation because of the hemoglobin binding curve
and that’s important because it’s the saturation which is part of the big part
of the equation which determines the content of oxygen in the blood okay so
let me show you where this would be practical on a test let me rewrite that
equation again so I can show you how this matters so going back to the first
equation the delivery of oxygen to the peripheral tissue generally speaking is
equal to the cardiac output times the oxygen content of the blood let’s expand
that once again we know that cardiac output is heart rate times stroke volume
and that the content of oxygen is equal to one point three four times the
haemoglobin times this essay o2 or the saturation plus zero point zero zero
three times the pao2 and then all of this is multiplied by itself okay so we
can come up with an equation here let’s say we’ve got a patients whose
saturation is let’s say it’s 92% here’s the question
the question is which of the following will increase the delivery of oxygen the
most and then here are the answer choices number one we can increase the
stroke volume by 10% number two we can increase the heart rate by five percent
number three we can increase the humid loeben by twelve percent number four we
could increase the SAO to the saturation by five percent or number five we can
increase the pao2 by thirty percent so which one of these is going to increase
oxygen delivery to the tissues now to those uninitiated or confused or didn’t
see this lecture you would be tempted to say if I increase the PA o two by thirty
percent just numerically that’s gonna improve my oxygen delivery obviously if
I give more oxygen I’m gonna be able to deliver more oxygen but however if you
look at this algebraic equation mathematically you can see that the
smallest component of this equation is this and so increasing this amount by
thirty percent is going to be multiplied by a very small number and you’re not
going to get the biggest bang for your buck in terms of delivery of oxygen so
that’s not the right answer the rest of these issues so stroke volume
heart rates hemoglobin and saturation are all pretty equivalent because we’re
multiplying all of these things together okay so all of this is multiplied
together so this going up by five percent times this going up by five
percent plus this going up by five percent or this going up by five percent
are all going to have pretty much the same equivalence in terms of the
improvement in the delivery of oxygen and so in that case you’d have to say
then that increase in the human and concentration by 12% will have a
greater effect on the delivery of oxygen than then the stroke volume going up by
10% or the heart rate going up by 5% now what about the saturation going up by 5%
yeah if this went up by 5% that would be nice but still not as good as increasing
the humor globin by 12% and this is the type of test question that you might see
and it has to do with the fact that you understand how most of the oxygen is
getting to the peripheral tissues and thanks for joining us

• November 26, 2019 at 4:34 pm

Thanks for watching. See the other video in this series free at our MedCram website: https://www.medcram.com/courses/oxygen-hemoglobin-dissociation-curve-explained-clearly

• November 26, 2019 at 5:40 pm

We can increase the amount of o2 in solution with hyperbarics! How could we use this equation to demonstrate this?

• November 26, 2019 at 7:29 pm

I was about to choose sv by 10% . But then realize then realize the fact you’ve explained