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