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