Thank you for joining me today we’re
going to talk about Medical acid-base acid-base disturbances in patients and
the purpose of this lecture is to make acid-base demystified to a lot of
students come and are confused about acid-base I’ve seen a lot of lectures on
the internet about acid-base um get it right some don’t get it so right I want
to take acid base as a whole and just start off on the basics and go through
what you need to know and crack it down so that you can take a patient with an
acid-base problem and not only figure out what the patient has but also to be
able to talk intelligently to other people about what that patient has and
how you figured it out and do it in a systematic way so you could understand
so let’s demystify acid base so first I want to talk about is some of the
definitional things of acid base and that can sometimes be the most difficult
you know the way you talk to people is measure of how intelligent you are and
let’s get some definitions down because sometimes these are confused so there’s
two things that you’ll see a lot of in acid base and that is people talking
about an acidosis so acidosis versus acidemia what’s the
difference to an acidosis in acidemia in fact what’s the difference between a
gnosis and anemia in terms of anything alkalosis alkyl emia and the way I like
to think about that is in terms of a seesaw okay you can imagine this big
dichotomy in acid base you’ve got pH of seven point four zero which is kind of
where you want to keep things right in the middle and that’s a neutral pH and
you can go all the way up to seven point four five and all the way down to seven
point three five and and what happens is you get processes that occur in the body
so and so you’ve got a metabolic acidosis
here you’ve got another metabolic acidosis occurring here but over here
you’ve got a you know respiratory alkalosis or another metabolic alkalosis
these are processes that can occur and they’re all occurring at the same time
and depending on the balance of these because some of these could be big some
these can be small that’s when you get your amia so an emu is a state of being
you know you have hyponatremia hypokalemia these are all situations
that are occurring in the blood so the key point here is that an e mia is a
state of being and that’s basically completely determined on what your ph is
if your pH is less than seven point three five then you’re going to have an
acid emia if your pH is greater than 7 point four five then you’re going to
have an alkyl leimia okay so what is an OSIS and OSIS is a process it’s
something that’s actually occurring you could have many different processes
occurring at the same time so is it possible for you to have an acidosis but
be alkyl d’emic absolutely you can have something down here which is pushing
your which is trying to push your pH toward the acid side but if you have
something bigger up here that’s pulling it in the other direction and it’s
bigger you’ll still have a alkyl leimia because your pH is greater than seven
point four or five but you could have an acidosis so again basically line there
is when you’re talking about the pH is something make sure you use amia when
you’re talking about a process that’s occurring think of a metabolic or
respiratory acidosis that’s a process that’s occurring okay let’s clear the
screen here and sort of get back to some basics here I want to start off with a
little bit of equations it’ll tell us kind of the basics for where we want to
go so what is the pH well pH as some of you all know is equal to the negative
log of the concentration of protons so that’s important because as the number
of protons in the body goes up okay the pH is going to go down and so
we know that a low pH means more acid and then this in the body is sort of put
together in kind of a an equation where each or water plus carbon dioxide is
equilibrated with carbonic acid which is h2 co3 which equilibrate s’
with a proton plus hco3 – okay so why is this important well because everything
in the body sort of goes along with this equation and I think the big key here is
how the body deals with this player right here protons okay because protons
is acid as we just saw and how does the body deal with that acid well it deals
with it using bi carbonate bicarbonate is the body’s buffer that buffers
against protons so if extra protons are hanging around that could make the pH go
down away from where it should be of a pH of seven point four zero or 7.35 to
7.45 which is that normal range bicarb is used up a bicarb can be used up
either because the acidosis is the loss of that by carbonate or bicarbonate can
be used up because it’s having to buffer these protons and take these excess
protons away and so you can see what happens is the bicarb plus the proton
goes to carbonic acid carbonic acid freely diffuses into water which the
body could always use in carbon dioxide which the body can breathe out so if we
put that into anime new equation and if you if you’re lost here so far don’t
worry we’re going to get to the final equation that I want you to sort of
commit to memory and that’s this henderson hasselbalch equation which the
body is governed by which is the pH of the body is equal to six point
plus the log of the concentration of bicarb over the pco2 times 0.03
okay now this looks like a daunting equation but let’s go over it there are
two factors here that you need to be very cognizant of number one is the
bicarbonate okay bicarbonate is a substance that is a base okay so it’s an
antacid it’s primarily made in the kidney and it takes a few days for that
production to either go up or to go down it could also be made anywhere acid is
lost in the body through some metabolic process and it can be used anywhere in
the body to buffer acid at the same time so anything that happens with
bicarbonate by definition is a metabolic process so if we have them if we have
this bicarb going down okay then that would be a metabolic acidosis if we have
this bicarb going up that is a metabolic alkalosis that is a process that is
occurring it may translate into a pH but we have to look at the other factor the
other factor here is pco2 what is pco2 pco2 is the partial pressure of carbon
dioxide in the blood where does this carbon dioxide come from well you know
where this comes from it comes from cellular respiration okay so remember
glucose gets broken down into two three carbon units and those two three carbon
units get broken down to two two carbon units goes through krebs cycle kreb
cycle oxidizes that carbon down to carbon dioxide and then it gets released
annex co2 needs to be released carbon dioxide is a Lewis acid this is
an acid and there’s this is than almost every single cell of the
body and only has one way of getting out and that is through the lungs so if this
is going up that means the lungs are not getting rid of them and that means this
is accumulating the body and that would be a if this is going up therefore this
would be a respiratory acidosis so everything having to do a co2 is
respiratory if this is going down that means the lungs are getting rid of co2
more that would be hyperventilation for instance that would be a respiratory
that would be a respiratory alkalosis and so what we see here is a balance we
see bicarbonate which is produced mainly in the kidney and can be lost anywhere
in the body so it’s produced everywhere in the body and Purdue and and regulated
through the kidney whereas pco2 is made everywhere in the
body and is regulated through the lungs if bicarb goes up that’s a metabolic
alkalosis bicarb goes primarily down that’s metabolic acidosis if co2 goes up
that’s a respiratory acidosis and if co2 goes down that’s a respiratory alkalosis
okay okay so now since we’ve talked about by carbon pco2 let’s go over some
of the some of the normal values for these things so pH as we said is equal
to 7.35 to 7.45 and that’s the normal range and what happens if things go out
of this range well the body doesn’t work so well
proteins start to denature and that’s why the body wants to keep things
between that range and we’ll see how it does that
pco2 okay is equal to about 35 to 45 kind of remember that because they’re
similar numbers there so we kind of like 7.40 pco2 we kind of like 40 so 7.4
oh is kind of the normal 40 is kind of middle and finally for the bicarb here
the range there is 22 to 26 with the normal being about 24 okay so that is
the the middle of the range now a couple of definitional issues sometimes you’ll
see you’ll see bicarb also listed as co2 okay you’ll see that on what we call the
chem 7 or something like that or like a little graphic here that kind of looks
like this you’ll see it like that where you’ll have the sodium and we’ll talk
about this you’ll have the sodium up here at the potassium here the chloride
and they’ll say co2 down here okay that’s co2 in that chem 7 is really the
same as bicarbonate okay it’s not the same as the pco2 that’s different
pco2 is the partial pressure carbon dioxide here this is the total dissolved
co2 synonymous with bicarb so if you see co2 it’s the same as hco3 – just be
aware that those are the same numbers but that’s different than the pco2 which
has a normal of about 40 okay the other thing that you’ll see is a blood gas
sometimes you’ll see an ABG and the form for that is you’ll have the pH listed
first then you’ll have the pco2 second and the po2 third and then you’ll
finally have the bicarbonate last so a normal would be for instance seven point
four zero / 40 / 90 / 24 that would be a normal blood gas okay so we’ve got a
common gone over the normals again this would be sodium up here potassium here
chloride here co2 there this would be something called
blood urea nitrogen we’ll get to that and different lecture this is creatinine
and that’s glucose if you’ve never seen this before you might as well get used
to because it’s kind of standard and this completes this completes the first
lecture of the basics we would go into a lot more detail err on the next and next
ensuing lectures thank you very much

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