Okay, what are our few ways that
you can obtain a metabolic alkalosis?
A few of them are,
if you had too much bicarb.
So you can have too much bicarb
if you overdose on an Antacid.
Another way you could get too much bicarb
is by losing too many hydrogen ions.
And this can happen in prolonged
vomiting over a number of days
or if you had a nasogastro tube and
you were suctioning out your stomach contents.
All of those would increase your pH
and increase your bicarb levels.
Okay, let's take a look at this on the diagram.
Again, we have pH, we have bicarb and
we have the isopleth on the PCO2 line.
If we have an increase in bicarb
and an increase in pH,
you know which directions you're going to travel.
In this case, we're going up the PCO2 line.
So, you're going from normal, and normal again is at pH of 7,4,
a bicarb level of 24, and PCO2 of 40.
You're travelling in the upward direction and
that gives you a higher bicarb level and a higher pH.
So, you want to think conditions
associated with this are either
ones that you gained too much bicarb or
lose too much hydrogen ions.
Either way you can get to the same point.
You may ask "Well, how would you know the difference"?
On a diagram you won't know, that's where you need
your patient history to get more information
about which one will be driving
this particular response.
Okay, let's now look at metabolic acidosis.
There are a lot of different
types of metabolic acidosis.
So, we have to go through
each one of them step by step.
You could have too much acid production,
through things like lactic acidosis,
this means you're gone through anaerobic metabolism
and you're producing too many hydrogen ions.
How do you do that' You go down glycolysis
to pyruvic acid. And then, from pyruvic acid,
instead of going through the Krebs cycle,
you go through Lactate dehydrogenase reaction,
and form lactic acid.
You do that when you need energy quickly.
You don't have time to wait to go through
the whole Krebs cycle.
You need to get energy right now,
to do that you might make lactic acid.
Another way is through ketoacidosis.
So, a diabetic often times you can't use glucose or
go through ketoacids to get enough metabolism.
What are other ways you can have a metabolic acidosis?
Well, some of them are related
to poisons that you might take in.
And this could be accidental or
this could be on purpose.
You could have propylene glycol being consumed.
A wood alcohol,
even overdose you know, on certain drugs like aspirin.
You could also have large amounts of bicarb loss.
And that would be something like losing
a lot of dietary contents such as in diarrhea.
So, in this case, you have a lot of bicarb that's
being pumped into the GI system from the pancreas.
If you keep losing that out of the body,
you will continually to dump a bicarb.
Type II - Renal Tubular Acidosis
also causes a bicarb loss.
The final way that you can have a metabolic acidosis
is either through a Type I or Type IV
Renal Tubular Acidosis.
These are both acid secretion issues.
So, knowing that there are four different mechanisms
that cause a metabolic acidosis,
we're going to have to try these through which is which.
and we have a couple of extra tools to do so.
But let's talk to those in just a minute.
First, let's go back to the diagram and figure out
how a metabolic acidosis looks
on one of these diagrams.
Again, we start off at normal. Normal as a PCO2 of 40,
a pH of 7,4 and a bicarb of 24.
In metabolic acidosis is traveling down the PCO2 line.
This causes a decrease in pH and
a decrease in bicarb always.
If you have a metabolic problem,
how do you respond to it?
Usually, respond with the opposite system
such as a respiratory compensation
to a metabolic problem.
Okay, let's go through these two problems
with their appropriate compensations.
A metabolic alkalosis is fixed
from a respiratory acidosis.
So, in this case you go from normal
up to PCO2 line to number one.
And then, from number one to number two.
Number two should bring pH back closer to normal.
If it fully compensates, if it brings it back
to the original pH or to within the original pH range,
This is a nice response.
So, you have a problem with the metabolic alkalosis
and how does the body respond to that?
It decreases alveolar ventilation which increases CO2.
If you have the opposite problem,
which is a metabolic acidosis,
you will travel down the PCO2 line.
So, this causes a lower pH and a lower bicarb.
How do you try to fix this problem?
By breathing more often.
You will now breathe out more CO2
and as you breathe out more CO2,
pH will start to return towards normal.
You noticed here that we are traveling along
kind of a linear sloped line
from one to two in both of this conditions.
That is because you always have to travel
between this isopleths along the blood-buffer line.