welcome to Part 4 of Medical acid-base I wanted to just review what we had just
talked about before and that we've got two different types of metabolic
syndromes metabolic acidosis metabolic alkalosis and that we've got for
respiratory and the reason why there's twice as many respiratory's is because
you have to deal with the situation where respiratory has no compensation
from the kidney and then or very little compensation from the kidney and then
chronic compensation from the kidney same on the respiratory alkalosis side
as well and the key point that we discovered here is that when the pco2
and the pH are going in the same direction either up or down
the primary pathology is metabolic and then the opposite is true for
respiratory when we see the pco2 and the pH here for respiratory acidosis is
going up and the pH is going down and for respiratory alkalosis the pco2 is
going down the pH is going up again that's a respiratory process and what I
want to do is kind of put this together for you in a nice graph especially for
those people who are spatially inclined let's go ahead and clear this and I want
to kind of draw a graph for you and it's going to be a graph that hopefully
you'll take with you and you'll kind of see the utility in this so it's just a
regular graph with specifically pco2 on the y-axis and we'll put you know a
middle here which is about 40 and here pH with the middle of 7.40 okay and we
said that there were six different types of acid-base disorders so let's talk
about let's put some lines in here so we can kind of get an idea about what we're
talking about okay so that's that
and let's go ahead and put a line right about here and we'll put one more line
and right about here okay so here's our graph now we already said that if we had
a situation where the pco2 and the pH were going in the same direction that
had to be a metabolic and so let's go ahead and label these this one here
would have to be what well this line would have to represent that of a
metabolic process because the pco2 as it's going up so is the pH so we know
that this is down here in metabolic acidosis and why is it
acidosis because the pH is low so at metabolic acidosis tend to push things
down in this direction whereas this must be a metabolic alkalosis okay let's talk
about these other ones so these must be respiratory the question is which one is
a respiratory acidosis so which one's a respiratory alkalosis well we know that
these two up here must be acidosis because again they're lower than the pH
and are lower than pH of seven point four oh and these must be respiratory
alkalosis because they're higher than a pH of seven point four Oh notice though
that this one here has less play in terms of the pH and so if you were to
conclude that this must be a chronic line here and this must be the acute
you'll be right because again the chronic allows for kidney compensation
and there's less shift so this would be a chronic respiratory acidosis
and this would be a chronic respiratory alkalosis and if we go to this one this
would be acute respiratory acidosis and this one down here would be acute
respiratory alkalosis and you can kind of see what this is going to look like
now let's talk about this so as we go down here let's talk about the metabolic
acidosis first remember what's going on in metabolic acidosis bicarb is falling
and as the bicarb Falls the pco2 is go to also fall and when they both fall
remember the bicarb is going to fall further than the pco2 and you're going
to get a low pH so how do you know you're dealing with a metabolic acidosis
well we have something called winters formula or winters rules and let me put
this in terms of an equation and I'm going to be talking about these
equations so that you could figure this out now we all know that and I'm just
going to sort of right over here off to the side that we look at the
henderson-hasselbalch equation in terms of hco3 over co2 or the P co2 and we
know that things either go up or they go down or what-have-you and so what I'm
going to do is I'm going to tell you for every single point that one goes up what
does the other one do so we know that down here they're both going to be going
down okay they're both going to be going down how much does the bicarb go down
well I'll tell you for every one point that the bicarb goes down the pco2
should also go down by one point and that's how you can tell that what you're
dealing with there is a metabolic acidosis what about a metabolic
alkalosis well things up here are actually going
up and in fact the bicarb is going up the ratio for up here is for
every two points that the bicarb goes up the pco2 should go up by one point and
that's how you'll know so what do I mean remember everything starts off with a 24
and a 40 so here what would this speed if things were to drop by let's say four
points it would be 20 over 36 okay alternatively it could also be 14 over
30 so in other words for every point that the numerator drops the denominator
should also drop from this going to metabolic alkalosis for every two points
that the bicarb goes up so let's pick a number here let's say oh I don't know 30
it went out by 6 points and so the by the vco2 should go up by 3 points so
this would be 43 ok so let's go and look at the chronic respiratory situations
let's first of all look at acute respiratory acidosis so what's happening
in acute respiratory acidosis remember the lungs are not breathing the pco2
is going up if the pco2 is going up then here our fraction is going to start from
the bottom and here the pco2 is going up by a lot and we're not expecting a huge
increase in bicarb why is that because it's a cute we haven't had the kidneys
the chance to kick in so here the ratio is 10 for every 10 points that the pco2
goes up the bicarb only goes up by one point and so what would be a good
example here a good example here would be for instance if this was 50 on the
bottom and this would be 25 that would be acute respiratory acidosis what about
in chronic respite really dosis again same situation we
have a fraction however because the kidney is now kicking in we are
expecting to see less of an increase in co2 without the the kidney kicking in
and here it's for every three points that goes up on the pco2
the bicarb goes up by one point so something that we would see here let's
let's say we had the same kind of ratio let's say we had 49 okay that would be
nine increase for every three that would be three of those and so we would add
three to that that would be 27 okay because for 249 that's nine points 9
divided by 3 is 3 3 times 1 is 3 we add 3 to the 24 we get 27 and that would be
the new ratio and that's how we can tell let's go down to these again chronic
respiratory alkalosis here the ratio actually let's go to acute respiratory
as alkalosis remember here what's going on the lung is blowing off a tremendous
amount of co2 and the kidney has not had a chance to kick in so for every 5
points that the co2 drops by the pco2 drops by the bicarb is going to drop by
1 point and so let's look here let's say that a good example would be lets say
that the pco2 dropped to 30 okay that would mean that the bicarb would drop
down to 22 okay if you're doing your mouth right and then similarly over here
chronic respiratory alkalosis here the kidney has been allowed to kick in so
we're not going to get as much co2 drop per drop in bicarb and so here the co2
is dropping again but for every two points that it drops the bicarb goes
down by one point and so what would that would mean again if we had a ratio an
example where the pco2 had dropped down to 30 that's a
out going from 40 down to 30 for every two of those would be five so we drop by
five that means that our bicarb would then be about nineteen so again these
are ratios for every one that the the bicarb or sorry for every one of the
bicarb drops here are the pco2 drops by one and so these ratios here the ones
that I'm circling these here are ones to know for each of these different types
of categories because it will help us later identify if something else is
going on okay these are the characteristic signatures of these type
of processes and there are six processes these are sometimes known as winters
formula these are ones that I've kind of made up for the for the six here we got
metabolic acidosis metabolic alkalosis we've got acute respiratory acidosis
chronic respiratory acidosis chronic respiratory alkalosis and acute
respiratory alkalosis and so those are the rules
great so I think the basic points here were understood this is concludes part
four we're going to put everything to come together and show you how to attack
an acid-base problem and put it all together through a systematic step in
part five so please join me for part five and we'll kind of review everything
there Thanks