# Medical Acid Base and ABGs Explained Clearly by MedCram.com | 2 of 8

thank you for joining me for part two of

medical acid/base time to review what we were talking about before we were

talking about the Henderson-Hasselbalch which I’ll go ahead and write for you

here in terms of what that was it was the pH is equal to the 6.1 plus the log

of this big equation the concentration of hco3 minus over the pco2 times 0.03

and we just got finished saying that we talked about the two issues here are the

two variables in the equation one was the bicarbonate which was primarily

dealing with metabolic processes and the other one was the pco2 and we said that

if the bicarb was changed that was a metabolic process and if the pco2 was

changed that was a respiratory process if the bicarb went down that was a

metabolic acidosis if the bicarb went up it was a metabolic

alkalosis if the pco2 were to go down that would

be a respiratory alkalosis at the pco2 were to go up it’ll be a respiratory

acidosis so respiratory here on the co2 metabolic on the bicarb and i found

those things change then that would be an acid emia or an alkyl emia so I want

to split this up here into two categories the hco3 minus and the pco2

and I kind of want to just tell you the differences between these two as we

talked about the bicarb is primarily made in the kidney okay where and it can

be excreted in the kidney and change and all that sort of stuff whereas the pco2

is primarily a lung situation so bicarb can have processes happening all over

the body and many different processes occurring all at once you can have a

several different metabolic acidosis for instance diarrhea can cause a

metabolic acidosis and vomiting can cause a metabolic alkalosis and both of

them can be occurring at the same time ironically they would cause cross cancel

out each other interestingly but both metabolic acidosis and alkalosis both

metabolic problems so you can have multiple happening at the same time

whereas you only have one one and it can either breathe on the either fast or

slow so there’s a single you can’t have a respiratory acidosis and a respiratory

alkalosis at the same time as I mentioned your lungs can only breathe

fast or slow so this can only happen once this in terms of the kidney

modifying bicarbonate takes a long time so like days for that to happen whereas

the lung can start to breathe quickly or slowly almost immediately so this is

like minutes in terms of how fast things can happen so there are definitely

differences here between bicarbonate it’s a metabolic situation it’s kidney

multiple can happen at the same time and it takes days for the kidney to ramp up

or to change when we talk about compensation pco2 on the other hand

primarily is governed by the lung there’s only one lung well there’s

actually two but there’s only one organ it can only breathe so fast either fast

or slow and that change can happen in minutes I want to explore a little bit

about bicarb because bicarb is kind of an unusual

situation here so let’s go ahead and put it up here so hco3 – okay so there’s

there’s kind of two ways in which you can lose bicarb or bicarb can go down

and that would be a metabolic acidosis you can lose it because you’re combining with a proton okay and in which case

you’ll lose it because remember we talked about bicarbonate plus the proton

will turn into carbonic acid carbonic acid will then turn into a water

molecule and a co2 molecule which will breathe off and so bicarb can go down

because you’re combining with a proton and you’ll lose the bicarb molecule that

way or the other way you can lose bicarb is just simply loss and just lose the

bicarb so you’ll lose it because you pee it out

or you’ll lose it because you poop it out and so those are two different ways

now let’s talk about those two different ways of looking at this so if you lose

bicarb from simply just losing bicarb your bicarb will start to fall but what

will happen is because you’re actually losing negative charges okay so what

will happen is your chloride or your measure chloride will will go up in that

situation and why is that important well it’s important because all of the

positive charges in your body and all the negative charges in your body have

to remain the same maybe I can demonstrate here by drawing

a chem-7 okay you’ll see this over and over again in camp in medicine where we

have the sodium we have the potassium chloride

this says co2 but really it’s the bicarb okay this is the blood urea nitrogen

this is the crap name and this is glucose so I want you to notice this

because this is this will become important later is that the positive

charges are in the first column and the negative charges are in the second

column now why is this important well talk about this obviously the body has

as many positive charges in it as it does negative charges if you didn’t then

you would be statically electrically charged and the body can’t have that

so there are equal number of positive charges as our negative charges but the

problem with our little chem 7 as we call it here is that we’re not

accounting for all positive charges there’s calcium that we don’t have here

there is magnesium that we don’t have here and likewise we don’t have all the

negative charges here we don’t have phosphorus and sulfates and all sorts of

things that are negatively charged but we’ve got negatively charged chloride

item one got negative charge bicarbonate over here so if we were to add up in a

normal situation the sodium which is usually about 140 and the potassium

which is around 4 and the chloride which is you know around 100 or so and then

the co2 which is around 24 you can see very closely and very clearly here that

you your positive charges are going to outnumber your negative charges and when

that happens that’s a normal situation and in fact when we calculate this we

don’t even use the potassium in that calculation so what we’ve come up here

is with something called the anion gap now the anion gap is simply an

artificial measurement it’s artificial because we’ve chosen to include these

electrolytes in this chem-7 and what we’ve done is we’ve chosen to take the

chloride in the co2 and subtract it from the sodium and the normal anion gap is

and in a normal person 12:12 so that means that if we take the sodium and we

subtract out the total negative charges which is the chloride and the co2 we

will get an anion gap of 12 what does that mean that means there are 12

negatively charged units out there floating around in the body that we’re

not accounting for in our chem 7 and that’s normal that’s okay so what does

that mean that simply mean simply means that we can tell if there are other

negative particles that somehow come up all of a sudden and so what happens well

let’s go back to our bicarbonate thing again remember bicarbonate there’s two

different ways of losing bicarbonate one of the ways is if it combines with a

positively charged proton where is that proton going to be coming from well I

should recall from chemistry there is a negative a a negatively

or there’s a whenever there’s an acid okay

there’s always a proton and a conjugate base conjugate base and then when that

proton comes off the conjugate base becomes negatively charged and the

proton comes off and in this case it’s going to combine with the bicarb to make

co2 and h2o the key here however is this is that now we have a negatively charged

particle that is now floating around in the body so what is that going to do to

our anion gap it’s going to increase it and so your anion gap will increase

whenever you have a situation where bicarb is lost because it combined with

a proton that was attached to a conjugate base now what does that

conjugate base what could it be it could be anything it could in fact it’s it can

be anything any negatively charged particle that’s not either a chloride or

bicarbonate and that’s important to know because there are certain medical

conditions where you have these anion gaps that occur that tells you that’s

how the bicarb was lost okay so let’s talk a little bit more about the anion

gap we said before that the anti gap is usually 12 what does that mean what

makes up that what makes up the majority of that anion gap as it turns out the

molecule or protein albumin makes up the majority of that anion gap which is 12

what’s the normal what’s the body’s normal composition of

albumin how much albumin is there normally in the body well if you were to

measure in terms of milligrams per deciliter it would be four so four

causes you to have an eye gap of about 12

that’s a good way to calculate what the normal anti gap should be for somebody

because let’s say somebody had an albumin of two then what would their

normal anion gap be you can see that it would be about six that’s important to

note because if you know what somebody’s predicted anion gap is you’ll be able to

tell whether or not there’s an anion gap metabolic acidosis or something

occurring because if somebody has a process that is eating up bicarbonate

because there is an acid that’s giving off a protein and that bicarb is being

lost because it’s combining with the protein that was on a conjugate base as

we showed in the last slide that’s going to increase your anion gap so if you’re

if for instance somebody has an anion gap of 20 because we just calculate the

anti gap and remember what the anti gap is the NI gap is simply the sodium minus

the addition of the chloride plus the bicarb that will equal the NI gap okay

and if if it is 20 then we know that’s higher than what it should normally be

it should normally be about 12 okay if someone has an albumin of 4 that means

that there’s eight units there’s an eight unit jump that means

there’s eight units of conjugate base floating around that shouldn’t have been

there and it’s causing them it’s causing an acidosis and metabolic acidosis

however if we calculate anion gap in it’s 20 and our albumin is only two that

would mean our anti gap should be only about 6 and therefore the difference

between these two is actually 14 which means that there are 14 units of anion

gap that’s floating around that shouldn’t be there okay so let’s review again let’s go back

and talk about bicarbonate we said already that there’s two ways that you

can lose bicarbonate one is simply just loss of bicarbonate and the other one is

combining with a proton a proton that comes from a conjugate base if that

happens you’ll be left with the conjugate base that’s negatively charged

we can’t keep track of that negatively charged molecule in the chem 7 because

it’s not a chloride and bicarbonate therefore there’s going to be an

increase in something called the anion gap the anion gap is calculated by simply the equation of the sodium minus

the chloride plus the co2 or the bicarb hco3 minus so if you take the sodium and

you subtract the addition of the chloride plus the bicarb you’ll get the

anion gap the actual anion gap that actual anion gap if it’s greater than

what you would predict the anti gap to be and what is the predicted anion gap

we’ve predicted and I in gap should be the albumen times three normal albumin is 4 so 4 times 3 is 12 this whenever you get an increased anion

gap this is termed an anion gap metabolic acidosis it’s possible for you

to just lose bicarbonate through loss and not cause that in that situation

when you lose bicarbonate you will not be causing anion gap and this is

important because you’ll be able to tell the difference between an anion gap

metabolic acidosis in a non anion gap metabolic acidosis so now we’ll get into

a little bit more about the acid based disturbances and how to

calculate them in what’s compensation in our next part part 3 thanks for joining