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. A lot of students come in or confused about
acid-base I've seen a lot of lectures on the internet about acid-base. Some get it
right some don't get it so right. I want to take acid base as a whole and
just start off in 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 the first
thing 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 a
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 in acidosis and acidemia in
fact what's the difference between an osis and anemia in terms of anything
that alkalosis alkalemia and the way I like to think about that is in terms of
a seesaw. imagine this big dichotomy in acid base you've got pH of
7.40 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 and you've got another metabolic acidosis occurring here but
over here you've got a you know a respiratory alkalosis or another
metabolic alkalosis these are processed 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 emia. so an emia
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
emia 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 gonna have
an acidemia if your pH is greater than 7 point 45 then you're gonna have an
alkelemia okay so what is an OSIS? an 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 alkelemic?
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 7 point
4 or 5 but you could have an acidosis so again basically line there is when
you're talking about the pH or 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 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 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 an equation water plus carbon dioxide is
equilibrated with carbonic acid which is h2co3 which equilibrate s--
with that 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 cuz
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 our
bicarb can be used up either because the acidosis is the loss of that bicarbonate
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 and carbon dioxide which the body can
breathe out so if we put that into an a new equation and if you're lost here so
far don't worry we're gonna 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 one 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 if we have this bicarb going down
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 P co2
what is P co2 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 into
two two carbon units goes through Krebs cycle or kreb cycle oxidizes that carbon
down to carbon dioxide and then it gets released and that co2 needs to be
released carbon dioxide is a Lewis acid this is
an acid this is produced in 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
in 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
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 regulated through the kidney whereas
pco2 is made when the bonding 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 so now since we've talked about by carbon pco2 let's go over 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 you kind of remember that because there's
similar numbers there so we kind of like 7.40 pco2 we kind of like 40 so 7.40 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 couple of definitional issues sometimes 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 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 it's really the same as bicarbonate okay it's
not the same as the pco2 that's different
pco2 is the partial pressure car the oxide 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 gone over the normals again this would be sodium up here potassium here
chloride here co2 there this would be something called the blood urea nitrogen
we'll get to that and different lecture this is cracking and that's glucose if
you've never seen this before you might as well get used to because it's kind of
standard this completes the first lecture of the basics where we go into a
lot more detail here in the next ensuing lectures thank you very much
you