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