Interpreting ABG's

[Tarawr158]

Can someone please help me with this question.

ou are caring for a patient with a renal transplant who has come into the ED complaining of light-headedness and epigastric pain. The patient has a blood gas reading pH of 7.50, PaCO2 of 31mmHg, and a HCO3 of 20mmmol/L. The RN notifies the registrar because the patient is most likely experiencing:

a) uncompensated metabolic acidosis

b)uncompensated metabolic alkalosis

c)uncompensated respiratory acisosis

d)uncompensated respiratory alkalosis

For the answer I got compensated respiratory alkalosis.

This is how I figure it out:

pH 7.50- Alkalosis.

PaCO2 31mmHg- Alkalosis.

HCO3 20mmol/L- Acidosis.

pH and PaCO2 match (as in they are both alkalosis). This means it is respiratory relating.

And because the HC03 is acidic it is compensating.

BUT my lecturers answer to this is:

Just to clarify this question

pH 7.50 means it is uncompensated as patient is still in alkalosis

the cause is likely to be metabolic due to his kidney disease

and because the pH is above the reference range of 7.35-7.45 he is in alkalosis

The low pCO2 is due to the hydrogen ions being used up trying to compensate but the pH remains high so is not fully compensated as yet.

Hope that helps.

---- Now I am really confused. Am I working it out wrong?

[pmabraham, BSN, RN]

Good day, Tarawr158

Does Monster Method of ABG Interpretation | Mighty Nurse help?

Thank you.

[smf0903]

It should be respiratory alkalosis. Since you don't have the option of partial compensation, then it would be uncompensated respiratory alkalosis.

It can only be compensated if the pH is in normal range (7.35-7.45).

Think of CO2 as an acid: if it's high it's more acidic, if it's low it's more basic.

Think of HCO3 as a base: if it's high it's more basic (alkaline). if it's low it's more acidic.

I draw arrows first. This may be confusing at first but as soon as it clicks you'll never have another problem with ABGs

Whichever way your pH is going, match that to the CO2 or HCO3. In this case your pH is alkaline...CO2 is low which makes it more alkaline (see note above), therefore this is respiratory alkalosis. Since Co2 and HCO3 arrows are both pointing same direction (both are low) BUT the pH is still outside normal range, it's partially compensated (since there's no answer for partially compensated, then you just go with uncompensated).

I know people have other "systems" for doing ABGs, but I learned this way from a video a few years back. I have never been able to find the video again though!

[smf0903]

Sheesh, I don't know why my pictures always post so big on here Sorry about that!!

[dt70]

This is one of those thing where repetition is needed. Once you understand the pattern everything becomes simple.

For compensation, you should understand uncompensated, partial, and full compensation. For the primary problem the instructor most likely will just test your knowledge between respiratory and metabolic. Combined or mixed respiratory & metabolic is possible with critical injuries but unless the instructor mentioned that or is tough, you most likely do not need to go into that.

This site has a lot of practice with explanations: ABG Interpretation Quiz

[dt70]

Sheesh, I don't know why my pictures always post so big on here Sorry about that!!

I have had same problem. I think Full Editor has preview post now. Was not there before I think. I tried HTML tags to resize but that never worked for me.

[loveofrn, BSN, RN]

If you really want to practice go to this website and refresh the page everytime you want another series of question

Survivenursing.com/abg

[HouTx, BSN, MSN, EdD]

Also remember - the body never overcompensates.... will never over-shoot the homeostasis mark.

[pmabraham, BSN, RN]

Good day, Houston Texas:

"the body never overcompensates"

What about when a positive feedback mechanism gets out of control?

Thank you.

[dt70]

Good day, Houston Texas:

"the body never overcompensates"

What about when a positive feedback mechanism gets out of control?

Thank you.

pmabraham, Your comment interested me. I found a webpage you may be interested in reading.

It goes over questions you asked.

https://courses.washington.edu/med610/abg/abg_primer2.html

[psu_213, BSN, RN]

Just because the person has CKD you cannot make the assumption that this must be the cause of his acidosis. Sure, in a clinical setting, before you get ABG results, a metabolic derangement is high on the list because of the kidney issues. However, the facts "in evidence" (i.e., the ABG) tells you otherwise.

With the high pH, you know the person is alkalotic. Since it is not in the normal range, it must be uncompensated (I learned only compensated or uncompensated--no "partially" compensated). Your CO2 is low, this continues to alkalosis. The bicarb is also low--which would, otherwise, make a person acidotic. Since the person is alkalotic and the CO2 is in the "alkalosis range" and the bicarb is in the acidic range, it must be respiratory alkalosis.

Since the bicarb is low, the body is trying to compensate for it, but since the pH is still out of the normal range, it is still uncompensated.

[nurseprnRN, BSN, RN]

If it were a metabolic alkalosis, his bicarb would be in the higher-than-normal range, and he would be retaining CO2 to try to compensate. The bicarb is low, indicating that it's being eaten up by some sort of metabolic acids (like from the renal failure, which is famous for making people acidotic).

His CO2 is low, too. He might have been blowing off CO2 in another effort to get rid of acid when his acidosis developed, but is overdoing it -- is there another reason why he's still hyperventilating? (HINT: he's lightheaded! and in pain!) At pH = 7.50, he should be retaining CO2 to compensate and have a higher than normal CO2, right?

So my opinion is respiratory alkalosis, uncompensated, mixed with an underlying metabolic acidosis. Treatment of choice at this point would be giving him some pain med and a paper bag to rebreathe until he has a normal CO2, then reevaluate. (Remember the paper bag for hyperventilation-- you'll see it a lot!)

And this is a terrible scenario to give to a student because it doesn't lend itself to a clear answer without higher-order thinking about underlying physiology.

And there is that hint as broad as the side of a barn (hyperventilation!!) but because everyone focuses on the numbers they didn't look at the patient in the bed.