Interpreting an arterial blood gas is a critical skill for nurses. It is more
than just simply looking at the pH value of our patients. it's about understanding
what's driving that imbalance and if, or how our body is able to compensate for
it. Today I'm going to teach you a four step process so that you can understand
what's happening with your patients acid-base balance, right after this.
Welcome back my name is Tammy and this is NurseMinder and on this channel we
do everything nursing so if you're new here consider subscribing below so that
you get the next video when it's released . Now before we can start into
how to interpret an arterial blood gas it's important to understand the factors
that were looking at. So there are three regulating systems in our body that help
us maintain that perfect environment for our cells to function normally. These are
called buffer systems. The first of the three buffer systems is the fastest to
react. We have the chemical, which is also known as plasma buffer system, and here
we see carbonic acid is the intermediary between hydrogen and bicarbonate and
water and carbon dioxide. Now carbon dioxide we know is excreted by the lungs
and so this leads to our second buffer system known as the respiratory system,
in which it will either retain or remove co2 to keep us balanced. The third system
is the kidneys which we call metabolic system. The metabolic system will retain
or remove hydrogen and bicarbonate to keep the acid-base balanced. Npw if any
one of these systems goes out of balance the other two will try to compensate to
maintain that acid-base balance so that our body can function at its maximal
capacity. Next we need to look at what our normal values are and what happens
when I'm outside of normal. We're going to start with pH. pH is just generally an
overall status of where our acidity is in the plasma. Now my normal range is
7.35 to 7.45, so if I am lower than that, I have an acidic environment and that
means I have too many positive ions in the blood and one of the biggest ones is
hydrogen. So there's an inverse relationship to
the number of hydrogen's and the pH value. Another way to think of this is I
have two little base - than I am acidic. Similarly if I am higher than 7.45 ,
it's considered to be an alkalotic environment. The second
category is CO2. This is our respiratory system. This is a direct measurement of
hydrogen ions and here - if I have too many hydrogen ions - I am greater than
that normal value of 45 and I'm considered to be acidic. if I have less
than 35, I'm considered to be alkalotic for CO2 levels. Now the last one is
bicarb HCO3. Bicarb is base, so if I have too much base I am alkalotic, if I have
too little base I am acidic. Now we're ready for the four step process. Simple
steps. First is to check each of those levels to determine if they're normal or
abnormal and if they're abnormal which direction are they going. From there we
can name the imbalance and determine if there's compensation. Let's work through
this with an example. So let's take this example here: a pH of 7.2 for CO2 of 48
and bicarb of 23. I'm gonna use my table here to help me out. The first thing I
want to do is check my pH. I see 7.24 is lower than the normal
range which means I have an acidotic environment. I'm gonna go ahead and label
this with a downward arrow and put the word acid beside it. So let's do the same
for our CO2 and bicarb levels CO2 48 is higher than the normal value, I put an
upward arrow and label it as acidotic; and bicarb 23 was in the normal range so
I'm just going to put the letter N. Now to name the imbalance. I know I have an
acidosis because my pH tells me there's an acidotic state. I need to identify is
it my respiratory system or my metabolic system that is driving this change. So
for that I look to see which value is also acidotic. My CO2 is acidotic which
means I now have a respiratory acidosis. Now the other question is - is there
compensation? To determine this, I need to look at the
opposite system, the bicarb - my metabolic system. Because the value is still normal
there hasn't been a shift yet in the kidneys to help support this imbalance,
so we would call this a non compensated respiratory acidosis. All right so let's
7.29 is low we're gonna put a downward
arrow and write acid. I now know I have an acidosis I'm gonna figure out which
one. CO2 level 35, that is normal so we're gonna put an N here. Bicarb 19, is
also low, downward arrow and I'm gonna put the word acid. This means my kidneys
are driving the imbalance so we call it a metabolic acidosis. Now to determine if
there's compensation, I'm going to look to see if the lungs are helping out.
Because it's a normal value, the lungs have not kicked in so metabolic acidosis
with no compensation. All right so you ready to try another one. Let's go. Go
ahead and work this one out for yourself and then come back for the answer. Okay
so 7.49 is elevated it is an alcolotic state. I know that I have
an alkalosis going on and I now need to determine which one. So go back and look
at your CO2 value. CO2 value is 28 that's pretty low - that's also an acidotic
state. My bicarb is 20 that's also low and that's an acidotic state. So here we
have no normal values within our arterial blood gas. Again look for the
one that is going in the same direction meaning is that alkalotic or acidotic.
Does it match my pH? My CO2 is also alkalotic so I have a respiratory
alkalosis. Now is there compensation? Have my kidneys
kicked in? My bicarb is off to the side and it is an acidotic state which is
what I would expect to kick in, but my pH is not normal yet. It's still working
together really hard. So this what we call a respiratory alkalosis with partial
compensation. Full compensation occurs when pH is returned to normal and our
CO2 and bicarb levels are still outside of normal.
Alright, time for one more. Go ahead pause this video, complete this on your own and
come back for the answer. So the pH 7.43 is within our normal range of 7.35
to 7.45 so we'll just put an N beside this value. CO2 at 34 is slightly low.
We're gonna put a downward arrow and identify that it is alkalotic.
Bicarb is 21 also slightly low, downward arrow and acidotic. So do i have
an imbalance? Well yes and no. Technically my pH is normalized so we can say that
there is no imbalance. However my respiratory system and my metabolic
system have been working pretty hard to keep it there. So now to determine what
imbalance my patient has just recovered from. We're gonna start with the pH - what
else? When we look at our pH 7.4 3 we can see that that is on the upper end of
normal range. If we use 7.40 as our mid range, anything above would be
considered alkalotic in terms of identifying the acid-base imbalance. Just
as with our previous steps, I now know I had an alkalotic state. I look for the
matching level which was my CO2 level and I can say I have a respiratory
alkalosis that is compensated. So there you have it. I hope you're still with me
because I want you to know that the best way to master this is to practice it,
every chance you get practice interpreting your arterial
blood gases. Until next time make it a great day :)