The Land of the ABG

Tzu911 · Apr 27, 2008

Correction: It was Co2 but not PaCo2 in the original questions. Trying to find the edit thread botton.....

hypocaffeinemia, BSN, RN · Apr 27, 2008

Hi all, based on a concept by Laura Gasparis Vonfrolio, RN, PHD, I find her story of "The Land of the ABG" a very effective learning tool to interpret the ABG values. However I'm having problem with the following 2 questions:
#5. pH 7.44, PaCo2 47, HCo3 28.
#6. pH 7.42, PaCo2 32, HCo3 27.
Since the pH is within normal range of 7.35 - 7.45, I understand these 2 are "compensated."

Because they are in the normal range, this means they are fully compensated. They can be partially compensated if there is evidence of compensation but the pH has not returned to normal.

I also understand these two are Alkalosis, based upon the increasing hco3 and ph values.

The HCO3 doesn't determine alkalinity. They are both on the alkalotic end of normal because the pH is between 7.4 and 7.45.

However I'm having difficulty with the "metabolic or respiratory" part.
For question #5:
co2 47 is greater than the normal range of 35 - 45 (could be a resp.)
hco3 28 is greater than the normal range of 22 - 26 (which means it can also be a met.)

For #5, it cannot be respiratory alkalosis. Remember ROME- Respiratory Opposite, Metabolic Equal. If you have an elevated pH as in the case of alkalosis, if it is respiratory in nature, the pCO2 will be lowered. Why? Hyperventilation is the cause here.

In #5, the pCO2 is slightly elevated. This isn't opposite of the direction the pH went. The HCO3, however, is also elevated- which is the same direction as the pH. This would be the "Metabolic Equal" part of ROME.

The elevated pCO2 is in fact the method of compensation for your metabolic alkalosis. You could expect their respirations to slow in order to build higher pCO2 levels to counteract the alkalosis.

For question #6:
co2 32 is less than 35 - 45 (could be a resp.)
hco3 27 is more than the 22 - 26 (could be a met also??!)
Help! Am I missing some tool set to distinguish these ambiguity?
TIA,
Mike.

#6 is a bit more difficult. I'd be hesitant to call it fully compensated anything. The bicarb, however, is just barely outside normal range (in fact, normal range according to my hospital is 22-28), so I'd be less inclined to believe that this is a metabolic alkalosis. The pCO2 is a bit lower than the bicarb is higher, all things considered, so I'd say this has a respiratory origin. Why the bicarb is on the way up, however, is beyond me. Improper compensation? I dunno, but all in all #6 is failry normal.

MayisontheWay · Apr 27, 2008

Hi all, based on a concept by Laura Gasparis Vonfrolio, RN, PHD, I find her story of "The Land of the ABG" a very effective learning tool to interpret the ABG values. However I'm having problem with the following 2 questions:
#5. pH 7.44, PaCo2 47, HCo3 28.
#6. pH 7.42, PaCo2 32, HCo3 27.
Since the pH is within normal range of 7.35 - 7.45, I understand these 2 are "compensated."
I also understand these two are Alkalosis, based upon the increasing hco3 and ph values.
However I'm having difficulty with the "metabolic or respiratory" part.
For question #5:
co2 47 is greater than the normal range of 35 - 45 (could be a resp.)
hco3 28 is greater than the normal range of 22 - 26 (which means it can also be a met.)
For question #6:
co2 32 is less than 35 - 45 (could be a resp.)
hco3 27 is more than the 22 - 26 (could be a met also??!)
Help! Am I missing some tool set to distinguish these ambiguity?
TIA,
Mike.

Mike,

Look at what is being compensated.

I can explain further if you need to, but that one sentence cleared it up for me! It will help you realize that there is no abiguity. Make sense?

May

hypocaffeinemia, BSN, RN · Apr 27, 2008

Correction: It was Co2 but not PaCo2 in the original questions. Trying to find the edit thread botton.....

The CO2 in an ABG is the PaCO2.

It stands for the partial pressure (arterial) of CO2.

Sometimes it's written pCO2 as well.

acerila · Apr 27, 2008

for #5

The ph is in the higher range of normal. So you have to look and see what can cause a high ph, is it your CO2 value or HCO3 value. Can your CO2 (of 47) cause a high PH? No. What about a high HCO3 (28) can that cause a high ph? Yes. So it is metabolic. The HCO3 increases causing a high PH so then the CO2 increases as well and brings the PH down.

#6 The CO2 is low and the HCO3 is high. When those two go the opposite way you have a mixed disorder. In compensated cases the CO2 and the HCO3 will always either both be increased or both be decreased.

Tzu911 · Apr 27, 2008

The CO2 in an ABG is the PaCO2.
It stands for the partial pressure (arterial) of CO2.
Sometimes it's written pCO2 as well.

You are right :redbeathe... I posted it too quickly and still can't find "edit thread" botton. :up:

EricJRN, MSN, RN · Apr 27, 2008

When you're making the distinction between a metabolic cause and a respiratory cause, I like to use the ROME method.

Respiratory Opposite, Metabolic Equal

To look for a respiratory cause, we're examining pH and pCO2. (Those would move in opposite directions, like a low pH and high CO2.)

If we suspect metabolic problems, we look at pH and HCO3. (Those would move in "equal"/the same directions.)

So, with #5 your pH is on the high side, but your pCO2 is also on the high side. That's not what we'd expect for a respiratory problem (we think "respiratory opposite"). However, the pH and HCO3 are moving in the same direction ("metabolic equal"), which clues us in to a metabolic issue.

Make any sense?

EricJRN, MSN, RN · Apr 27, 2008

The Edit button is at the bottom right of each post.

Tzu911 · Apr 27, 2008

Meth, May, and Acer, thank you guys so much. I'm going offline to study what you guys have explained. You guys are awesome thanks again!

Tzu911 · Apr 27, 2008

The Edit button is at the bottom right of each post.

Eric thank you for the answering my op and helping me with the technical question. It must have taken me longer than 5 minutes to realize that I needed to edit, AEB Brian's replied PM to me: "Registered members have a 5 minute window to perform an edit."

But thank you again Eric. :yeah:

Tzu911 · Apr 27, 2008

Mike,
Look at what is being compensated.
I can explain further if you need to, but that one sentence cleared it up for me! It will help you realize that there is no abiguity. Make sense?
May

Dear May:

I'm gonna give it a try here. Plz let me know if my rationale is floating to the right diretion. Sorry I'm such a noob.

To answer your question, the alkalosis needs to be compensated and restored back to near normal range.

For #5, The increased paco2 (47) is d/t hypoventilation. The increased PaCo2 level helps to lower the slightly higher bicarb level in the body.

For #6, Acer said this one is a mixed disorder so maybe the following explanation doesn't even apply. But here it goes: "compensated resp. alkalosis" is caused by the hyperventilation and results in decreased level of paCo2 = 32. The body tries to comensate or add more alkaline by having the kidney to hold onto bicarbonate a lil longer.

The ROME was really an effective short cut. With that, I prolly don't even need to look what's being compensated and still would be able to score. But that's not how I am. It bugs me not knowing the causes or the rationale behind it. So please bear with me if my attempts didn't make sense.