Hypoxemia Explained Clearly – Causes, Physiology, Hypoxia, Treatment
13
October

By Adem Lewis / in , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , /


welcome to another MedCram lecture
we’re going to talk about hypoxemia and its five physiological causes again
anything with the ending of a emia it’s going to have to be something
that’s related to the blood so hyponatremia hypokalemia hypercalcemia
again it’s referring to the amount in the blood this is as opposed to the term
that we use see a lot which is hypoxia the difference here is hypoxia has to do
with the amount of oxygen in the cells that’s the target area but how the
oxygen gets to those cells is in the blood and that’s what we’re going to
talk about today so what are the reasons why you might have a low oxygen
concentration in the blood well there’s five different mechanisms for that and
they lend themselves to five different answers on a test which is why this is
very highly testable stuff and we want to go over it so high altitude is one of
those reasons we’ll go over that today the other one is diffusion the next one
is hypo ventilation next is shunting and then finally we’re
going to go over VQ mismatch and this will take a number of lectures to go
over but we want to talk about where we’re going to go with this so these are
the five different reasons for low oxygen in the blood let’s go over those
now okay so we’re going to talk about high altitude this is exactly as it sounds as you go
up mountain the amount of oxygen in your blood at the top of that mountain is
less than at the bottom of that mountain that’s actually quite intuitive because
you know that as you go up in altitude it becomes harder and harder for you to
do things that you become more short of breath and this is something that we can
actually experience people who going up to Everest base camp notice that they
can’t breathe as well as they can when they’re down at sea level so what is the
reason for that well to find out we have to look at what is the equation that
gives us the amount of oxygen that dissolves into our blood and so the way
we look at that is by looking at the total barometric pressure total
barometric pressure in terms of millimeters of mercury is 760
millimeters of mercury this is the way we measure this is the air pressure at
sea level now we know that oxygen makes up about 21%
of that so what happens as you go up in altitude does the fractional or partial
pressure of oxygen go down no it doesn’t what actually happens is the total
barometric pressure goes down and as a result the 21% of that pressure becomes
smaller let me give you an example so at sea level again we’ve got 760
millimeters of mercury now as soon as you inspire this air at sea level into
your lungs it becomes humidified and this is kind
of a red herring we’re throwing into this but you should know that the
saturated vapor pressure is about 47 millimeters of mercury and so right off
the bat 760 – 47 times point two one is equal to 150 millimeters
of mercury so this is the pao2 available to us at sea level okay so this is at
sea level now at 19,000 feet which is approximately just above base camp for
Mount Everest the the total barometric pressure at that altitude is about 380 millimeters of mercury we subtract the
47 millimeters of mercury from the vapor pressure and what we come up with is
about 70 millimeters of mercury of pao2 and so here we clearly see that the
reason why the pao2 is going down in the blood is because the total barometric
pressure has dropped not because the fio2 which is this has changed in fact
it is the same it’s the same point to one so to review that high altitude what we see there is it’s
a result of a decrease in the total barometric pressure which is 760
millimeters of mercury at sea level what we see here is that if we put on 100%
oxygen the pao2 or the oxygen content in the
blood actually goes up so it responds which is good the other thing that we
see here is something called a normal a a gradient so what is an a a gradient
capital a stands for the alveolus if you note a cross-sectional area of a
alveolus looks like and there’s a blood vessel going by and a capillary the AAA
gradient this is the capital A this is the lowercase a it’s simply talking
about the difference in the o2 here in the alveolus versus here in the
capillary and so if there is a big difference between these two that must
be me and because there’s something going on here or there’s a barrier or
there’s something that’s preventing this oxygen from fully oxygenating the
capillary in this case there isn’t it’s simply a result of a low barometric
pressure and as a result of that the AAA gradient is normal so what does the body
do in the situation to counteract the low pao2 in the blood hyperventilation
and as a result of that what we see is the co2 levels or the P co2 levels the
partial pressure of carbon dioxide actually goes down and this allows more
room for the pao2 so again high altitude is a result of total barometric pressure
going down it responds to 100% oxygen the pao2 goes up when you put
someone on 100% oxygen in this case it does respond the a a gradient is normal
and the body’s response to this is to hyperventilate this is why you see
people hyperventilating at high altitude it’s to get their PA o2 up okay so we’re
going to talk more about these mechanisms these five physiological
causes of hypoxemia in the next lecture thanks very much you


38 thoughts on “Hypoxemia Explained Clearly – Causes, Physiology, Hypoxia, Treatment

  1. SHAVeD is the acronym I was taught to remember the 5 causes of hypoxemia:

    S hunt
    H ypoventilation
    A ltitude
    V /Q mismatch
    D iffusion

  2. We just had a lecture from Dr. Seheult today on pulmonary clinical correlates…really good stuff. Thanks for providing this videos!

  3. Truly enjoyed the altitude hypoxia videos for H.A.P.E. & H.A.C.E. Would it be possible to provide a physiology lecture on decompression sickness, oxygen toxicity, nitrogen narcosis that scuba divers experience? Thank you for these wonderful lectures which we use for our health care students. They are very well done!

  4. Thanks for the comment, will definitely take your lecture suggestions into consideration. Please visit the youtube channel called "MedWild" for some good information on HAPE and HACE.

  5. Thank you sir! That is a site I was unaware of for educational purposes. I have used MEDCRAM and Khan Academy Healthcare & Medicine as well because of the positive student feedback! Also, thank you for considering my suggestion.

  6. So wished i found your vids earlier in my nursing school journey. Better late, than never! Great job! Please keep them coming!

  7. Really enjoy these lecture! I am an LTAC nurse and all of this is great disease process review; Ispecially appreciate the lab value interpretation lectures.

  8. Thank you for the video.But how did u get those values????I got different values for sea level and mountain level.And u didn't add how AMS can be prevented or treated.

  9. Thanks for these! I am a veterinary technician studying to be board-certified in anesthesia and these are super helpful to me 🙂

  10. EMIA – I thought this was a song in the 70s.
    Seriously, there seems to be a basic solution for altitude oxygen depletion without the need for any medication and is touched upon in your description of hypoxemia.

  11. hello sir.. I am from india my dad is suffering from global hypoxic ischemic injury of brain since 29 dec,2017 due to cardiac arrest and his heart had stopped functioning for 40 minutes.
    Please suggest treatment or suggest any doctor who can help me. please contact on [email protected] or +91 8080292343

  12. hi i am still strugling with the difference between hypoxia and hypoxemia when you say hypoxia is a low amount of O2 in the cells, which cells are you talking about is it all the cells of the body or only the RBCs ? or else? please someone help me 🙂

  13. When I walk my oxygen level went from 100% to 85%. Went to ER and they tested my heart in one thousand ways and it's perfect. They didn't see anything in the lungs and they don't know why it happens. No I've never smoked anything and no history in my family. I have pain radiating down my right arm and pain in my hip and left calf. Gallbladder is clear and clean. Any guesses?

  14. I have found a 6 th: very low cardiac outputs in near arrest situation cause very low Sv02. They are hypoxic and refractory to low flow oxygen.

  15. You did a great job. I like in the beggining how you covered the root of the word. emia=blood.

    this could be very useful for my upcoming EMT exam. Do you have a video focusing on medical terminology? prefix/suffix/root? with greek/latin?

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