Hypoventilation and Hypoxemia Explained Clearly – Remastered

Hypoventilation and Hypoxemia Explained Clearly – Remastered


welcome to another MedCram lecture
we’re talking about hypoxemia and this time we’re talking about hypoventilation
we’ve already reviewed hypoxemia high altitude and also diffusion let’s talk
about hypoventilation so again let’s go back to our alveolus which we showed
here and our pulmonary vein pulmonary artery system okay so this is the
pulmonary artery which is deoxygenated and this is the pulmonary vein which
becomes oxygenated and you recall that we’ve got oxygen which goes in and
carbon dioxide which comes out so how is hypoventilation go to cause hypoxemia
well hypoventilation is simply when the lung or the respiratory rate or the
tidal volume goes down so that the amount of ventilation that’s occurring
the amount of air that’s going in and out of the lung is decreased now the
major consequence of hypoventilation is an increased co2 and basically that
increased co2 is gonna force the oxygen in the alveolus to go down and as a
result this is going to cause the amount of oxygen in the pulmonary vein or the
pulmonary artery to go down as well now remember there was a a gradient equation
and let’s go over what that a a grading equation was again and this is the a a
gradient equation and normally it equals about sixteen or twenty or so where in
the low numbers this factor right here dictates what the alveolar concentration
of oxygen is and of course this you can get from a blood gas is simply the
arterial or the pulmonary artery pulmonary vein concentration of oxygen
or partial pressure of oxygen you can see here if you have hypoventilation
you’re gonna have an increase in this factor here which is going to cause this
factor here to be bigger which subtracted from this factor is going to
make this whole a smaller and as a result the
is going to be smaller as well and your a a gradient actually in hypoventilation
stays about the same so what you see here is the a8 gradient in
hypoventilation actually does not change but what we do see is the alveolar
concentration of oxygen goes down and the arteriolar concentration of oxygen
goes down therefore we have hypoxemia so where do we see this we see this a lot
in patients who hyperventilate so why would patients be hypoventilating
narcotics and basically the example that I like to give is imagine that your
resident or a physician go up onto the wards and what do you see there if
you’ve got a orthopedic patient post-operative who got a lot of dilaudid
the patient is hypoventilating their respiratory rate is eight they’re in bed
they’re not responsive and yet let’s say they have a continuous pulse oximeter so
an S a o2 or an SP o2 and it says ninety two percent on four liters of oxygen so
the question is is this patient in respiratory failure and the answer is
yes they’re in respiratory failure because if you were to do a blood gas
you would see that their pH is like seven point one five they’re pco2 is
quite high let’s say it’s 60 or 70 and their po2 is let’s say about 70 and
their bicarb is still normal because this is acute what’s happened here is
you’ve got the pco2 going up the pH going down but because you’re on
supplemental oxygen you’re able to get a reasonable oxygen on your pulse oximeter
so this is another good reason why not to just look at the pulse oximeter when
you’re looking and seeing somebody to see if they’re in respiratory failure
because they could very well be in respiratory failure the other aspect of
this is that people who’ve got hyperventilation and hypoxemia can very
easily be fixed with supplemental oxygen and so that brings us to the other
characteristic of hyperventilation which is it responds to
oxygen very well so let’s review what we’ve already talked about so we’ve got
hypoxemia remember emia means in the blood and we’re talking about hypo
ventilation okay here are the key points about that number one it responds to supplemental Oh two we’ve noticed that
also in diffusion abnormalities and also in high altitude you’ve got a normal
capital a lowercase a gradient the other one that had a normal gradient so far is
the high altitude remember that diffusion had it increased a a gradient
and what are the some of the causes we’ll see we’ll have high co2 from
narcotics so that’s what you’ll see in hypoxemia secondary to hypoventilation
thanks very much

5 Replies to “Hypoventilation and Hypoxemia Explained Clearly – Remastered”

  1. Thanks for watching! See the rest of this course free: https://www.medcram.com/courses/hypoxemia-explained-clearly

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