Medical Acid Base and ABGs Explained Clearly by MedCram.com | 5 of 8


welcome to part 5 of Medical
acid-base this is where we want to kind of put everything together into one
complete package here and and then maybe do some questions here and some later
things let’s let’s kind of go back here and review remember we talked about
bicarbonate and the different types of bicarb waves of loss remember we said
one way of losing bicarb is if you combined it with a proton and that was
special because if you did you would have leave behind a conjugate acid or
conjugate base of that acid which is negatively charged and that would leave
you with a increased anion gap and that anion gap would for sure tell you that
you had some sort of a metabolic process going on the other way to lose
bicarbonate again is just simply losing it and you can do that that’s just a
simple metabolic acidosis so the first thing that you really need to do when
you’re doing this is to and we’ll get rid of all this here is to the first
rule whenever you want to do an acid-base problem and you can take this
to the bank is you need to calculate the anion gap anion gap remember how to do
that it is remember what the the anion gap is always the sodium minus the
chloride plus the bicarb and that should equal the anion gap so when you’ve
calculated the anion gap you need to figure out if it’s elevated and assuming
that the albumin is for it we’ll just assume that the albumin is for for this
discussion if the anion gap is greater than 12 if the anion gap is greater than
12 let’s just say for argument’s sake that the anion gap that we calculate is
20 that means we take the ni gap so anion gap minus 12
is going to give us something we call the Delta gap in that case it’s equal to
in this case it would be equal to 8 what does that mean what is a delta gap that
simply means there are 8 units of conjugate base negatively charged
particles out there more than there should be ok so what does that mean
again we got bicarb and we’ve got a acid with a proton attached to it and what
happened was eight of these released their protons bound with the bicarb and
that went off to form h2o plus CO 2 plus conjugate base negatively charged and
that’s then those eight of those is what we’re picking up here so if that’s the
case if our ni gap is 20 and that’s 8 more than it should be at 12 that means
we have anti Delta gap of 8 if that’s the case how many bicarbonate molecules
should we have lost we should have lost 8 the same amount
this tells us this Delta gap tells us how many bicarbonate molecules we should
have lost now let’s say we started off with 24 bicarbonate molecules that’s
normal if we calculate out a delta gap of 8 what should our new bicarbonate
level be it should be 16 it should have dropped so we had 24 bicarbonate
starting off and then we developed an anion gap metabolic acidosis and we
calculate our Delta gap to be 8 that means we took our anti gap which is 20
we subtracted out the normal anion gap that we should always be having which is
12 and we found that we were eight more than normal the body has to deal with
those eight more and the way it deals with that is by combining with bicarb so
if there’s eight things to deal with that means we should have lost eight
molecules of bicarb when we were gone from 24 down to 16 that’s what it should
have been another way of looking at this is saying that if we take our current
bicarbonate level and we add to it the Delta gap we should get back to 24 what
happens though if we do that and we end up with something like 16 or 17 then
what that means is that there must be another process that is causing us to
lose bicarbonate or let’s say we we do this calculation we take our current
bicarbonate level and we add our Delta gap to it and we come up with something
that’s greater than 24 let’s say it’s 30 that must mean that there’s another
process another metabolic process that’s occurring that’s causing us to gain
bicarbonate the reason why this is important is because we can tell if
multiple different metabolic processes are occurring at the same time so what I
want you to do on all these acid-base questions is calculate the anion gap
always do that and when you do that you simply subtract 12 from it assuming that
you have a normal albumin and you’ll get the Delta gap now that Delta gap tells
you specifically one thing or two things specifically if you have a delta gap
number one you can take it to the bank that you’ve got a anion gap metabolic
process there is only one thing that causes an anion gap and that is an anion
gap metabolic acidosis period so number one you already know if you’re n on gap
is greater than 12 and therefore you have a delta gap that’s positive that
you have an anion gap metabolic acidosis what you don’t know is if you have a non
anion gap metabolic acidosis that’s occurring what’s a non anion gap
metabolic acidosis it’s simply a process where you just lose bicarbonate or you
could have a a metabolic alkalosis that’s a process where you’re gaining
bicarbonate like vomiting or something like that how are you going to know if
that’s the case it’s very simple you simply take the gap the Delta gap I
should say you add it to your current bike
urban at level and if you got a number that’s abnormally high that must mean
you have an additional metabolic alkalosis occurring if you get a number
that’s low less than twenty two or twenty that means you have a non anion
gap metabolic acidosis that’s occurring simply meaning that you’re losing
bicarbonate through some other process something like diarrhea or something
where you’re not forming a conjugate base so getting back number one
calculate the anion gap and if there is a gap calculate the Delta gap okay if you do have an anti gap you’d by
definition have an anti gap metabolic acidosis then calculate the Delta gap
take the Delta gap and add to that the current bicarb okay if it is less than
22 as we’ve said before there are normals for our bicarbonates
and if it’s less than 22 then you must have a non anion gap metabolic acidosis okay if it however is greater than 26
then you have a metabolic alkalosis because you’ve basically factored in
this Delta gap and if you find that your bicarb is still high there must be
another process occurring and here when you factor in your Delta gap to your
current bicarb if it’s still low there must be in another metabolic acidosis
problem occurring the next thing to do is to look at your pH and your P co2 so
look at the pH and the pco2 if they’re going in the same direction then it’s
metabolic and I’m sure you can tell whether it’s an acidosis or an alkalosis
just look at the pH and tell if it’s going in different directions then it
must be our respiratory okay and then finally number four is apply winters
formula and I say that because if you apply
winters formula and the pco2 or the P the pco2 is either too high or too low
then there must be an additional respiratory process and we’ll go through
these the best way to do this is actually go through the questions and
see what they show so that’s the next step is to go through the questions but
before I do that I want to give you some examples about what things can cause
respiratory acidosis and metabolic acidosis etc and so let me go ahead and
do that now for you so again if we go to our graph that we had remember you had pco2 on the y-axis and
ph here on the X here we had metabolic acidosis now there’s two types of
metabolic acidosis there’s a mine gap and there’s non anion gap metabolic
acidosis these are the two processes that are occurring now anion gap you
should think about as mud piles em you D P I l II s and that’s the mnemonic these
are all the things that can cause an anion gap metabolic acidosis M stands
for methanol okay methanol is metabolized into formic acid formic acid
gives off a proton that proton is melded with the bicarbonate leaving formate in
this case the formate is causing the anion gap u stands for uremia uremia in
kidney failure there’s all sorts of acids and conjugate bases that can build
up there sulfates phosphates etc d stands for d ka diabetic ketoacidosis
but in fact all sorts of ketone ketone bodies can form anion gap and remember
you can get ketone bodies and diabetes diabetic ketoacidosis you can get
starvation ketosis you can even get alcoholic ketosis P is kind of a
placeholder paraldehyde can cause it i stands for iron isoniazid or i NH L
stands for lactic acidosis so you can get lactic acidosis in septicemia lactic
acidosis in ischemia and the lactic acid gives off the proton again it gets
buffered by the bicarbonate leaving lactate lactate is not in our chem 7
therefore causes an ni gap ye stands for ethylene glycol also alcohol so the metabolism of those
products can lead to negative anions which are not accounted for in the chem
7 that caused the anion gap and then s is salicylates salicylate it’s like
aspirin incidentally that can also cause an acute respiratory alkalosis and so
whenever you have an anion gap you got to think about the mud piles as the
reason for non Anna get metabolic acidosis just remember you’re not
getting the situation where bicarb is being lost because of its combining with
a proton with a conjugate base here you’re losing bicarb because you’re just
losing bicarb it’s not combining with anything you’re
just losing it the biggest thing here that you would need to know is diarrhea okay diarrhea also something called
renal tubular acidosis especially type 1 and the other thing here that can cause
a metabolic acidosis is carbonic anhydrase inhibitors or CA this would be
like medications that block bicarbonate reabsorption in the in the proximal
convoluted tubule as soon as Olamide is an example of a
carbonic anhydrase inhibitor and it causes diuresis which is bicarbonate
rich the other thing that can also cause this is Addison’s disease okay but
Addison’s disease is kind of in it is placed by itself these three here can
cause hypokalemia Addison’s can cause hyperkalemia so these three here would
actually be considered a hypokalemic hyperchloremia we would call it our high
chloride metabolic acidosis whereas Addison’s disease this is where
you have adrenal insufficiency would cause a hyperkalemic metabolic acidosis
and remember I don’t want to get into too much detail but if you lose the
function of the adrenal gland you can you don’t get aldosterone which is
secreted from the zona glomerulosa and that doesn’t work well the distal
convoluted tubules and when that’s not working you’re not getting potassium and
proton excretion and therefore you’re you’re losing bicarbonate because it has
to buffer that that proton there so anyway that’s a non Ana got metabolic
acidosis so what can cause a metabolic alkalosis metabolic alkalosis can be
caused by vomiting okay so you’re losing chloride and the other thing that can
cause a metabolic alkalosis that you should remember here is added as
actually Cushing’s disease so too much adrenal cortical hormones the difference
between these two however is that vomiting will respond to saline or
sodium chloride and that’s known as chloride responsive
whereas Cushing’s where you have too much adrenal is chloride insensitive so
it won’t respond to sodium chloride in terms of the respiratory components
these are set these are pretty obvious so what could cause a an acute
respiratory acidosis Q respiratory acidosis would be something like a COPD
exacerbation okay so something that happens acutely or too much drugs
narcotics so basically the lungs stop working pretty quickly and there’s no
chance for the kidney to compensate what we call is a chronic respiratory
acidosis just compensated COPD we see this all the time how do you know for
patients with chronic co2 retainer when they come in what we know they got high
bicarb that means their kidneys had a long time to compensate for that high
co2 they still have an acidosis though so what could cause an acute respiratory
alkalosis hyperventilation anxiety disorder asthma exacerbation can also do
it in the early stages asthma and then what about in the chronic chronic
respiratory alkalosis so when breathing fast for a long time
the one that that’s probably the most common is actually pregnancy so in
pregnancy of progesterone progesterone is a respiratory stimulant and that
people could be breathing fast for time and that would cause that type of a
picture so here are the examples I think in the next section we’re going to go
actually over questions and we’re gonna go in the order that we talked about and
we’ll come up with blood gases and chem 7 s and figure out exactly what is going
on with the patient and and I think if we go through things step by step you’ll
start to understand why we’re doing things the way we are so join me for
part six thanks

27 thoughts on “Medical Acid Base and ABGs Explained Clearly by MedCram.com | 5 of 8

  1. if you mean what if the delta gap and bicarb added is between 22 and 26? Then the answer is that there is no other metabolic acid base problem going on or, if there is, then it is a non anion gap metabolic acidosis and a metabolic alkalosis of equal magnitude canceling each other out as far as bicarb is concerned.

  2. "If you have a delta gap, number one, you can take it to the bank that you've got a anion gap metabolic process.
    There is only one thing that causes an anion gap, and that is an anion gap metabolic acidosis, period."
    Should it be, "There is only one thing that causes a delta gap, and that is an anion gap metabolic acidosis, period?"
    I believe the anion gap caused by albumin is normal, right?

  3. The two types of metabolic acidosis should be "delta gap metabolic acidosis" and "non-delta gap metabolic acidosis". The delta gap defines them, not the anion gap!

  4. Did you mean Conn's Syndrome (primary hyperaldosteronism) causes metabolic alkalosis vs. Cushing's Disease ( Pituitary adenoma = release of excess ACTH)?

    Or does increased ACTH also affect aldosterone production?

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