Medical Acid Base and ABGs Explained Clearly by MedCram.com | 6 of 8


so welcome to part 6 of acid-base
disorders and this is where it all sort of comes together at this point where
we’re looking at the questions and we’re going to go through a specific order and
hopefully we stick to that order we’ll be able to figure out any acid-base
question they’ll throw at us remember the form that we’re going to follow is
for the ABG okay we’re going to have the pH first okay then the pco2 second
followed by the po2 and then the bicarb I’ll last there and for the chem seven
remember we’re always going to have this sort of a pattern we’ll see that over
and over again with the sodium potassium chloride and the hco3 – we’re not really
going to be talking about the blood urea nitrogen the Kratt Neen or the glucose
so we’ll just focus on these areas right there okay so let’s throw the screen and
let’s go ahead with our first question so first hand the someone gives you a
blood gas and the pH is 7 point 4 7 / 29 / 94 okay
and the bicarb in this case is 22 we can also pick that on the chem 7 let’s go
ahead and give you the chem 7 and the chem 7 is 1:40 and the potassium is 4.0 the
chloride is 106 and against a winch and the bicarb is 22 so what’s the very
first step that you need to do very first step that you need to do is number
one calculate the anion gap this is always going to be the first step the
reason why this is the first step is because remember if you have an anion
gap then you always have an anti gap metabolic acidosis so that will tell you
first off so what is the anion gap it’s going to be 140 minus the addition of
these two so 106 plus 22 is 128 so 140 minus 128 is equal to 12 now we’re going
to assume here for all of these answers that everyone has a normal albumin
remember that you could calculate what someone’s out anion gap should be based
on their albumin simply by multiplying their albumin times three
normal albumin is 4 so 3 times 4 is 12 and so we’ll always assume that the
normal ni gap should be equal to 12 so the patient has an anti gap of 12
therefore the Delta gap which is the second thing that we calculate or the
next thing the Delta gap is simply the anion gap which is 12 minus 12 always
okay so we always take 12 away from the NI gap and our Delta gap is zero that
means that there is no anion gap metabolic acidosis is occurring none
that’s very important okay all right so next next step is number two okay with
number two we look to second rule which is look at the pH and the pco2
and if they’re going in the same direction it’s a metabolic process and
if they’re going in different directions it’s a respiratory process here the pH
is going up from seven point four zero and here the pco2 is going down from a
PCO to of 40 they’re going in different directions
therefore we know this must be a respiratory problem and is it a
respiratory alkalosis or respiratory acidosis well it must be a respiratory
alkalosis because the pH is greater than seven point four five
it’s higher than seven point four zero so it’s a respiratory alkalosis now
there’s two types of respiratory alkalosis there’s a chronic and there is
an acute okay chronic and acute so the question is
which one of these two are we dealing with for that we need to use winters
formula remember if you look back at our previous lectures in a chronic
respiratory alkalosis in a chronic respiratory alkalosis the bicarbonate
will drop hco3 one unit for every two units that the pco2 drops okay in an
acute respiratory alkalosis remember that for every drop that the
pco2 does or specifically for every five units that the pco2 drops the bicarb is
only going to drop by one point and why is that because this is an acute
respiratory alkalosis so it’s going to drop more before the bicarb kicks in
because it’s acute the kidney doesn’t have a chance to kick in whereas in a
chronic state the pco2 is going to drop by less before the pco2 goes down so
let’s look and see in terms of bicarb and pco2 where we are you’ll see here
that the pco2 went from 40 down to 29 now that is a drop of about 11 so the
pco2 actually dropped by 11 points how much did the bicarb drop by normal is 24
so it dropped by about two points so which one of these ratios does this fit
better does it fit better under the chronic or does it fit better under the
acute you can see that it fits better under the acute because it follows that
ratio more carefully a two over eleven is very similar to one over five
therefore the answer is that this is an acute respiratory alkalosis okay let’s go on to the next question
suppose we have a pH of seven point four to twenty nine 94 and bicarb of nineteen
and we have a chem-7 here which is 140 over four point zero one ten over
nineteen let’s go ahead and do it our first step which is to calculate the
anion gap okay so remember we’re going to add up these two numbers here which
is the chloride and the bicarbonate which in this case is 129 and subtract
it from 140 so we get an anion gap of 11 which is about 12 which is normal so our
Delta gap is actually negative one in this case which is close to zero so
there’s no anion gap metabolic acidosis number two we look at the pH and the
pco2 and remember if they’re going in the same direction its metabolic if
they’re going in different directions its respiratory here the pH is going up
from seven point four zero the pco2 is going down to going in opposite
directions it must be respiratory and in this case it must be a respiratory
alkalosis since the pH is alkyl emic slightly so it’s a respiratory alkalosis
again is it an acute or is it chronic respiratory alkalosis and for that we
need to look at winters formulas once again remember in in the alcohol in the
respiratory alkalosis acute for every drop
in the pco2 of five there was a drop in the bicarb of one and then for chronic
the ratio was for every two that dropped in the pco2 the bicarb dropped one okay
so let’s take a look here and see how much did our bicarb draw our bicarb
dropped by about five points I went from normal of twenty four down
to nineteen so a ratio is a five on the top that it dropped how much that our
pco2 drop well it dropped by about eleven points because it went from about
a forty which is normal down to a twenty-nine so that’s our ratio now
which one does that most look like does it look like the acute or does it look
like the chronic you can see here that that looks more like the chronic and so
this is a chronic respiratory alkalosis let’s go into the next question
pH of seven point two six sixty fifty-five and a bicarb of twenty six
again let’s do our little chem seven sodium here one forty potassium 4.0
chloride is 110 I’m sorry let’s do let’s make it 104 and the bicarb is again
twenty-six what’s our first step that we need to do you’ve got it got to
calculate the anion gap and I gap here 104 plus 126 is 130 and 131 40 is 10 so
the anion gap is equal to 10 which again is
essentially normal there’s no increase ni gap Delta gap if you want to
calculate it would be around negative two anyway for the most part there is no
anion gap metabolic acidosis so we go on to number two
and that’s when we look at the pH and the pco2
here the pH is definitely going down and here the PA or the pco2 is definitely
going up again we’ve got opposite problems opposite directions and so what
we have here is a respiratory acidosis no question about that but you’ll
remember there’s two types of respiratory acidosis there’s an acute
respiratory acidosis and a chronic respiratory acidosis and you’re
recalling the acute respiratory acidosis for every increase in the pco2 by 10 the
bicarb goes up by 1 and in the chronic respiratory acidosis for every increase
in the pco2 that goes up by 3 the bicarb goes up by 1 why is that again because
in the acute remember the kidney doesn’t have a chance to compensate so you’re
going to have a much higher rise in co2 before the kidney kicks in then you will
in the chronic so let’s put that to the test here with our specific question how
much of the bicarb go up by well we see here
normal is 24 it went up by 2 points so we’ll put a 2 there and how much that RP
co2 go up well it went up by about 20 because normal is 40 so the question is
what ratio does this most look like and you can see 2 over 20 is most like 1
over 10 therefore this must be an acute respiratory acidosis okay let’s go
through it again let’s do another question here we have a pH as equal to
27.3 460 55 and a bicarb of 30 got a chem-7 going on here and the sodium is
140 the bike sorry the potassium is 4.0 the chloride is a hundred and as we
mentioned the bicarb is thirty okay so what’s our first step again calculate
the anion gap of course here we have 100 plus 30 which is 130 minus one from 140
is 10 so the Delta gap is negative 2 essentially we have no anion gap
metabolic acidosis go into number two the pH and the pco2
here pH definitely going down pco2 definitely going up okay
so again it must be a respiratory component and it must be an acidosis but
again the question is is it an acute or is it a chronic and let’s review those
again remember for acute and for chronic for acute respiratory acidosis the ratio
is 1 over 10 and for a chronic respiratory acidosis is 1 over 3 and
we’re simply talking about the increase in hco3 – over the increase in p co2
increase in hco3 – over the increase in pco2 so let’s do our ratio here again
how much did the bicarb go up by bicarb is 30 from 24 that would be an increase
of 6 and how much did our pco2 go up by it went up by 20 because 40 is normal
and it’s 60 so that would be 20 so which one does
this look most like does this ratio here look more like this or like this and you
can see it looks more like the 1 over 3 therefore this is a chronic respiratory
acidosis good well join me for part 7 for more questions

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