If we want to go through buffers and
talk about them in more greater detail.
We have to spend a little bit of time going
through, what the power of the buffer is?
So different buffers will work at different pH’s.
and work at through a different level
or amount of buffering capability.
This strict definition of a buffer is anything
that consumes or releases a hydrogen ion (H+).
Again this helps to stabilizes pH.
The power of the buffer is related to the
quantity of hydrogen ions it can remove.
So we often times talk about the
blood is being a buffer itself.
And there are proteins in the blood
that will help buffer pH changes.
Hemoglobin is one.
Other proteins can be these
kind of buffers as well.
Cause remember a protein has a COON,
so it can bind the hydrogen
ion quite easily.
So the buffering power of whole blood is right
around 25 millimole per unit of pH (~25mM/pH).
And this is even without bicarb present.
So we always have to account for the
buffering capabilities of the blood,
when we are discussing
alkalemia’s and acidemia’s.
Now, let’s look at bicarbonate specifically.
So now we’re no longer talking about the
buffering capability of whole blood.
If we just look at bicarb, we can
develop what’s called a titration curve.
These titration curves are
ways that we can deal with,
how we change pH?
and then in what form you’re
going to have the buffer?
Is it more likely going to be as a base or is it
more likely going to be in a bound state?
So, if we look at the curve,
we have pH on the X-axis.
If we look at the other to Y-axis, it goes from
zero to a hundred. And then from a hundred to zero.
These two changes allow us to develop the
complete curve for this particular equation.
The blood is normally around 7,4.
The pK is a very important point. At this point,
you have 50% that is in this HCO3- state.
and 50% that’s in the bound state
which is the H2CO3.
This is the operating point in which
you could go upwards or downwards.
And so we’re gonna find out the each individual
buffer or titration curve that we look at
will have a slightly different pK.
And we’ll talk through why the
different pKs are important.
But for the blood and for bicarb,
the pK in this case is 6,1.
These allows us to develop an equation
to have a sol for what pH is it in the blood.
We can take 6,1, which is the pK,
plus the log of the bicarb over the PCO2.
Now, PCO2 we have to also
multiply it by a factor.
And that is to make sure it gets into solution
that it’s solubility coefficient.
So you just take the bicarb divided by the PCO2.
Take a log of that. add 6,1.
And that will be your pH.