Need help with ABG Analysis

hypocaffeinemia, BSN, RN · Feb 1, 2009

This appears to be a compensated respiratory acidosis. Read up on compensatory mechanisms, but the clinical picture would likely be someone not exchanging gas well either due to depressed breathing, pulmonary edema, obstruction, or some other problem.

The "compensation" part is indicated by the high bicarb level. This is your body's attempt to neutralize the extra H+. It is considered fully compensated, because the pH has returned to a normal range (it's just inside normal).

Daytonite, BSN, RN · Feb 1, 2009

ph- 7.36 - normal

paco2-58-high

pao2-50- low

hco3-33- high

this is

compensated respiratory acidosis

.

what would the history and assessment of a patient with abgs like this look like and what is the treatment?

information on the weblinks of the thread i listed below will help you. you should be posting these kinds of questions on the student forums where we can help you understand the concepts behind what is going on.

what do i do when the ph is normal? since that is how we classify acidosis or alkalosis. is this where the compensated and uncompensated part comes in?

see post #45 on

https://allnurses.com/nursing-student-assistance/pathophysiology-p-microbiology-145201.html

-

pathophysiology/ a & p/ microbiology/ fluid & electrolyte resources

in the nursing student assistance forum for tutorials and weblinks to learn how to analyze abgs

nursej22, MSN, RN · Feb 1, 2009

Something that I've have found helpful to is to think of each value in terms of aicidotic, normal or alkalotic, instead of high or low. When i think of pH as high or low I tend to get it mixed up. I think this method makes it easier to to relate them to each other.

Like this:

pH -- 7.36 normal, but on the acidic end

PaCO2-- 58 acidotic (lungs aren't blowing off enough CO2)

PaHCO3--33 alkalotic

The 2 that are the same, tell you whether it's respiratory or metabolic, and the odd one out is the compensatory mechanism.

leslie :-D · Feb 1, 2009

Like this:
pH -- 7.36 normal, but on the acidic end

you mean on the alkalotic end?

leslie

hypocaffeinemia, BSN, RN · Feb 1, 2009

you mean on the alkalotic end?
leslie

I think Leslie needs some lunch.

leslie :-D · Feb 1, 2009

I think Leslie needs some lunch.

oh damn...

i'll be back.

leslie

leslie :-D · Feb 1, 2009

you mean on the alkalotic end?
leslie

don't listen to earle.

she's totally nuts!

I think Leslie needs some lunch.

:mad: ...

have no idea why, but the range of 7.32-7.36 was stuck in my head.

heh...

nevermind.:behindpc:

oh damn...
i'll be back.
leslie

yep, acidic.

my bad.

leslie

Daytonite, BSN, RN · Feb 1, 2009

Do the tutorials on the links of the student sticky thread. They are tried and true. We go through ABG discussions over on the student forums from time to time. It doesn't take much to get confused, especially with compensation. Who does this compensation stuff in actual practice, anyway? All we ever worried about was messed up pH and O2 and grabbed for the ET tubes for intubations.

FlyingScot, RN · Feb 1, 2009

Who does this compensation stuff in actual practice, anyway? All we ever worried about was messed up pH and O2 and grabbed for the ET tubes for intubations.

Well, in certain situations you might let this patient ride without a tube. Although this ABG puts them in what most ER nurses know as the "50-50 Club" if the patient is a chronic lunger or an asthmatic and not in profound respiratory distress you might want to think twice about jumping to intubation as they are indeed compensating and you could potentially make them worse. This might be a situation where a trial of Bi-Pap would be a good idea. This would be another situation where what the patient looks like is just as important as what the numbers are. Good question though.

chenoaspirit, ASN, RN · Feb 1, 2009

http://www.rnceus.com/abgs/abgmethod.html

http://www.scribd.com/doc/6442924/ABG-Interpretation

Than the following, I got from a website that I thought may help you understand better. I hope so anyway. :)

Normal ABG values are as follows:

pH (acid base balance) = 7.35 to 7.45
CO2 (carbon dioxice) = 35 to 45
HcO3 (bicarbonate) = 22 to 26

You also must note the following:

CO2 greater than 45 is acidotic

HcO3 less than 22 is acidotic
Co2 less than 35 is alkalotic
HcO3 greater than 26 is alkalotic

How to interpret ABGs:

All you have to do is memorize four basic questions and then answer them in order:

A. Is the ABG normal? If all of them are, then you have a normal ABG and you can stop here. If any one of the values is out of the normal range, then you must move on to the next question.

B. Is the pH Acidotic or Alkalotic?: To determine this you look only at the pH.

Alkalotic: If the pH is greater than 7.41 the patient is Alkalotic.
Acidotic: If the pH is below 7.39 the patient is acidotic.

C. Is the cause respiratory or metabolic?: To determine this, you look at pH and compare it with HcO3 and CO2. If the pH is acidotic, you look for whichever value (HcO3 or CO2) that is also acidotic. If the pH is alkalotic, you look for whichever value (HcO3 or CO2) is also alkalotic.

In this sence, you match the pH with HcO3 and CO2. If the pH matches with the CO2, you have respiratory. If the pH matches with the HcO3, you have metabolic.

Or, put more simply:

Metabolic Alkalosis: If the pH is alkatotic and the HcO3 alkalotic.
Respiratory Alkalosis: If the pH is alkalotic and the HcO3 is alkalotic
Metabolic Acidosis: If the pH is acidotic and the HcO3 acidotic.
Respiratory Acidisis: If the pH is acidotic and the CO2 is acidotic.

D. Is the cause compensated or uncompensated?

Uncompensated: if the pH is anywhere outside the normal ranges (greater than 7.35 or less than 7.45)
Compensated: pH is anywhere inside the normal ranges (Anything between 7.35 to 7.45)

So, here are some examples:

1. Ph 7.40, CO2 37, HcO3 23

What do you have here? All the number are within normal range, so you have a normal ABG.

That was easy enough. You need to go no further in analyzing this ABG.

2. ph 7.23, CO2 50, HcO3 24

What do you have here?

A. Is the ABG normal? You can see right away that all the values are out of the normal range, so you must move on to the next question.

B. Is the pH acidotic or alkalotic? Since the pH is less than 7.39 it is acidotic.

C. Is is metabolic or respiratory? Since the pH is acidotic and the CO2 also acidotic, then you have respiratory acidosis.

D. Is it compensated or uncompensated? Well, the pH is outside the normal range of 7.35 to 7.45, so it is uncompensated. You don't have to look at any other values. You are done.

The ABG is uncompensated respiratory acidosis

2. pH 7.36, CO2 50, HcO3 29,

A. Is the ABG normal? You can see right away that both CO2 and HcO3 are out of the normal range, so you move on to the next question.

B. Is is acidotic or alkalotic: The pH is less than 7.39, so it is acidotic

C. Is the cause respiratory or metabolic?: The pH is acidotic and the CO2 is also acidotic, so you have respiratory acidosis.

D. Is it compensated or uncompensated? Since the pH is within normal limits, it is compensated.

In this example you have compensated respiratory acidosis.

3. pH 7.50, CO2 42, HcO3 33

A. Is the ABG normal? No. Some of the values are outside the normal ranges.

B. Is it acidotic or alkalotic? The pH is greater than 7.41, so it is alkalotic.

C. Is the cause respiratory or metabolic?: You know the pH is alkalotic, so you look for the matching value. The HcO3 is alkalotic, so it matches the pH. So, what you have is a metabolic problem.

D. Is it compensated or uncompensated? Since the pH is outside the normal range of 7.35 to 7.45, it is uncompensated.

Thus, you have uncompensated metabolic alkalosis.

4. pH 7.50, CO2 18, HcO3 24

A. Is the ABG normal? No, pH and CO2 are both out of the normal range.

B. Is it acidosis or alkalosis? Since the pH is greater than 7.41 it is alkalosis

C. Is is respiratory or metabolic? Since the pH is alkalotic and the CO2 is also alkalotic, you have a respiratory problem

D. Is is compensated or uncompensated: It is uncompensated because the pH is outside the normal range of 7.35 to 7.45.

What you have here is uncompensated respiratory alkalosis.

People tend to get confused on the difference between CO2 and HCO3-. Remember that the job of the lungs is to expel the gas carbon dioxide (CO2) and bring in O2, and that bicarbonate (HCO3-) is an alkaline agent (sodium bicarbonate is regularly used in the hospital to raise patients' pH).

The trick seems to be to think of CO2 as an acid. In looking at the above equation, you can see that if you were to increase CO2, (by hypoventilating, for example), you would drive the equation towards carbonic acid. Obviously, this increases the acidity of the blood (lowers the pH).

The carbonic acid dissociates into a strong acid (H+) and a weak base (HCO3-).

Similarly, if you were to hyperventilate and blow off lots of CO2, you would drive the equation to the left, using up acidic molecules, and thereby raising the pH.

So the lungs can control pH by controlling CO2 - they retain it to lower pH and make blood more acidic, and they expel CO2 to raise pH and make the blood alkaline. Those are the fundamental points to remember about respiratory disorders.

The kidneys have different mechanisms. They control the excretion of the ions on the RIGHT side of the equation - H+ and HCO3-.

Obviously, excreting H+ raises the pH (less acid - more alkaline blood) and retaining H+ lowers the pH (more acid = more acidid blood).

Similarly, excreting HCO3- lowers the pH (less base = more acidic blood), and retaining HCO3- raises the pH (more base = more alkaline blood).

That's it for the basics of metabolic disorders - the kidney modifies the concentrations of H+ and HCO3-. There are many other metabolic reasons why the blood becomes alkaline or acidic, but always keep these basics in mind.

The final thing to consider is that when one system (say the lungs) tips the balance, the other system (say the kidneys) tries to compensate. A good rule of thumb is that the second system can NEVER overcompensate. In simple acid-base disorders, you can assume that if the blood is acidic, the primary disorder is an acidosis (DON'T assume, therefore, that the primary disorder is an alkalosis that has overcompensated).

hypocaffeinemia, BSN, RN · Feb 1, 2009

chenoaspirit,

Compensation does not necessarily mean that the pH has returned to it's normal range. You can have partial compensation, where the pH has is still outside its normal range, however, compensatory mechanisms are evident.