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