thanks for joining us again this is part three of Medical acid-base we've
talked about a number of things we've talked about acid-base bicarb and pco2
we've talked about the definitions of acidosis and acidemia and things of that
nature we've just briefly touched on the anion
gap and the non anion gap metabolic acidosis we've talked here about the the
ways that we can quantify the the degree of the acid-base disorder of an anion
gap I kind of want to review that so I'm going to throw up once again our
henderson hasselbalch equation so the pH is equal to six point one plus the log
of the bicarb concentration over the pco2
times zero point zero three and again we talked about anything that occurs up
here is a metabolic primarily anything that occurs down here is a respiratory
how they work out is going to determine how the pH has changed we talked about
how our different ways that we can lose bicarbonate we can lose bicarbonate with
two different ways one is by combining with a proton that comes from a
conjugate base if that occurs we're going to get an anion gap if we just
lose it it's not going to cause an anion gap because we're not getting any
negatively charged particles that are not in our chem seven and again anion
gap just to clarify again is equal to the sodium minus the addition of the
chloride plus the bicarb and that is normally twelve in a normal situation
and why is it that's the case because that is made up mostly of albumin and a
great way of calculating what the ni gap should be is just taking the albumin
concentration which is usually four and multiplying it by
factor of three to get it okay now I want to show you what the body does in
terms of trying to mitigate swings in pH we talked about that's very important
for the pH to stay in the same place and I'm going to simplify our henderson
hasselbalch equation here a little bit to kind of demonstrate what I'm talking
about let's just say the pH is basically proportional to the concentration of
bicarb okay over the pco2 because that's basically what's going on here is bicarb
over P co2 is going to work itself out into the pH so there's several different
possibilities of things that can happen let's remember again that the bicarb is
something that takes a long time for the body to adjust whereas the pco2 can
adjust itself almost immediately so let's let's talk about that let's talk
about a metabolic acidosis okay what's going to happen here in a metabolic
acidosis remember this bicarb is going to go down so bicarb or hco3 minus is
going to go down now if this if the numerator goes down what numerically
should the body do - pco2 to keep the pH in the same place this is called
compensation what what is the lung go to do to pco2 if the bicarb goes down well
you know that if the numerator goes down the denominator should also go down if
you're trying to keep the pH in the same place so P of co2 should go down how's
the body getting drop the pco2 it's going to breathe faster and so
you're going to get compensation by dropping the pco2 so in a metabolic
acidosis you're pco2 is also going to go down and it's going to go down
immediately because the lungs can work very fast and so it's almost going to be
seamless as this is going down in other words as the bicarb is going down the
pco2 is also going to be going down and that's what happens in a metabolic
acidosis all right what about a metabolic alkalosis well you know of
course that the bicarb concentration is going to go up and so if the metal if
the bicarb goes up what's the body go to do to the pco2
it's going to go up as well to keep the pH in the same place and so your pco2 is
going to go up and it's going to do it immediately it's going to happen very
fast because the lungs can adapt very quickly to the slow metabolic problem
the lungs are going to adapt very quickly and so metabolic acidosis you'll
see bicarb goes down pco2 goes down and a metabolic alkalosis bicarb goes up
pco2 goes up the key though is knowing that the thing that happens second never
happens to completion and so the bicarb will go down in a metabolic acidosis and
the pco2 will go down but it will not go down
enough to fully negate effects of the first thing that happened and so you'll
still get a acidemia in an acidosis so the acidosis is caused the compensation
is never fully complete causing you to have an acid emia here in a metabolic
alkalosis the bicarb goes up the pco2 doesn't go up enough to fully cover it
so you still have a alkyl emia let's talk about respiratory okay let's talk
about a respiratory acidosis and a respiratory acidosis what's going to
occur the pco2 is going to go up that's a respiratory acidosis so what's
going to happen to the bicarb this is the tricky point because there's
actually going to be two conditions because the pco2 can go up almost
immediately and specifically because the bicarb takes days to fully compensate
you're going to have two conditions you're going to have an early situation
where the by herb hasn't changed you're gonna have a
lake condition where the bicarb has change you're compensated and those are
broken down okay those are broken down into an acute and a chronic so there's
actually two types of respiratory acidosis there's an acute respiratory
acidosis where the bicarb hasn't had a chance to go up and you can have a
chronic respiratory acidosis where the bicarb
has had a chance to go up and that's why that's because the kidney takes time so
in an acute the bicarb goes up only a very tiny amount just a little little
arrow but a little arrow there okay whereas in a chronic the kidney has a
chance to compensate and so you're going to have the bicarb going up a lot any
venture as to guess which pH is going to be more normalized it's going to be more
normalized in the chronic why is that kidney azzam has more chance to retain
bicarb to compensate for the acidosis so you have two types of respiratory
acidosis again one because the kidney didn't have a chance to compensate and
another because the kidney does have a chance to compensate let's talk about
respiratory alkalosis okay here p co2 is going down now the pco2 is going down
guess what's going to the bicarb to keep the pH the same it's also going to go
down but again just like there was two different conditions in the first one
there's going to be two conditions in the second we're going to have a
situation where the kidney can't drop the co2 fast enough and that's going to
be an acute respiratory alkalosis so in that situation this hco3 is going to go
down only a little bit and in that situation you're going to have an alkyl
emia why is that because again the bicarb hasn't had a chance to drop and
then you could have a chronic condition where the hco3 goes down a lot has
chance has a chance to compensate so the
chronic condition allows the kidney to compensate the acute condition doesn't
allow the kidney to compensate and that's why you're going to have
different types of pH the pH swing is going to be much greater in the acute
situation so for instance in respiratory acidosis the pco2 goes up and that's
going to cause an acidosis a worse acidosis in the acute situation that in
the chronic why because the kidney has a chance to increase the bicarb in a
respiratory alkalosis the pco2 goes down so you're going to have a more Alcala
MEC state why because in the acute situation the bicarb doesn't have a
chance to dump that bicarb the al-khalili is going to become less
severe in the chronic state because the kidney then has a chance to dump the
pike are so actuality there are just six different acid-base disorders primarily
one metabolic acidosis two metabolic alkalosis three acute respiratory
acidosis for chronic respiratory acidosis five acute respiratory
alkalosis and finally six chronic respiratory alkalosis and there's
something I want to show you here let's take the metabolic acidosis here what's
the pH pH here in this situation is pH is down what about in the metabolic
alkalosis the pH is up what about here in the respiratory acidosis
well pH is down pH is down and here respiratory alkalosis pH is up and the
pH is up now I want you to notice something
whenever we have a metabolic process the pco2 and the pH are going in the same
direction in other words whenever the pH the pco2 are going in the same direction
you always have a metabolic process whenever in a respiratory however on the
other end the other hand the pco2 and the ph are going in opposite directions
okay so pH and pco2 always look at the pH and the pco2 remember those are the
first numbers on your blood gas the pH first and then the pco2 you'll see that
if they're going in the same direction it's a metabolic primarily process if
they're going in opposite directions then they are respiratory and this
concludes part three let's go to part four next and we'll develop this a
little bit more and make it a little bit more easy to understand thank you very
much