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