Deciphering ABG's

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Specializes in Developmentally Disabled, LTC, Clinic, Hospital.

Does anyone have an easy, understandable way to decipher ABG's? Metabolic acidosis/alkalosis vs. Respiratory acidosis/alkalosis? This stuff is looking like a foriegn language to me!! Then they throw in this Compensated and uncompensated?? I'm totally lost. Any help would be appreciated.:banghead:

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Specializes in ICU.

ABG's are pretty easy to interpret. don't let them intimidate you. do it in steps.....Ph, acidotic or alkalotic

Co2, high or low or normal

O2, high or low or normal

HCO3, high or low or normal

BE, high or low or normal

the answer to these questions will tell you if it's acidosis or alkalosis. a normal Ph is compensated. the CO2/O2 will tell you if it's a respitory component. the HCO3/BE will tell you if it's metabolic. :smokin:

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Specializes in Med Surg, ER, OR.

if pH is low (

if pH is high (>7.4) it is alkalosis

CO2 and HCO3 will tell you whether it is a respiratory or metabolic problem. You breathe off CO2 (respiratory) and you need HCO3 for your stomach (metabolic)

If CO2 is elevated and pH is low...respiratory acidosis.

If CO2 is low and pH is elevated...respiratory alkalosis.

If HCO3 is elevated and pH is elevated...metabolic alkalosis.

If HCO3 is low and pH is low...metabolic acidosis.

Respiratory complications - CO2 and pH are in the opposite direction

Metabolic complications - HCO3 and pH are in the equal direction

Hope this helps a little bit when evaluating ABGs. I found them hard in school, but feel more comfortable now after finding tips!

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Specializes in CVICU.
Does anyone have an easy, understandable way to decipher ABG's? Metabolic acidosis/alkalosis vs. Respiratory acidosis/alkalosis? This stuff is looking like a foriegn language to me!! Then they throw in this Compensated and uncompensated?? I'm totally lost. Any help would be appreciated.:banghead:

What will make your pH change: Co2- if it is too high it will make your blood pH more acidotic. If it is too low it will make it more alkaline or basic. Normal pH is 7.35-7.45. Let's say your pH is 7.25 and your Co2 is 60 and everything els in the ABG is within normal range, then the problem is Co2 which means respiratory, because that is the only way Co2 is eliminated from the body via the lungs. This is respirtory acidosis. Well what if my pH is 7.50 and my Co2 is 30 and everything else is within normal range? Then it is still respiratory because the patient is eliminating a little too much Co2 by increasing the respiratory rate. This is respiratory alkalosis.

HCo3 (bicarb)- Using the same examples above, if you have a pH of 7.25, the other components are normal but your bicarb is low, this means that there is less base which in turn makes the blood more acidic, metabolic acidosis. With the second example of a pH of 7.50 and everything else being normal then your HCo3 would be higher, which means there is more base available and the blood will be more basic or alkaline. This is metabolic alkalosis.

Compensated vs Uncompensated: ph 7.20 Co2 25 HCo3 9 Be -17 In this example the pH is low (acidic) but the Co2 is low as well so this cannot be the problem. Looking at the HCo3, it is low, and a low HCo3 (bicarb) will make the pH low(acidic) so the problem is metabolic, but the Co2 has dropped to try and fix the mess that the bicarb is making, but it is unable to compensate. So this makes it an uncompensated metabolic acidosis because the HCo3 is the problem. Some might say that it is partially compensated because for a HCo3 that low the ph would be lower.

pH 7.36 Co2 25 HCo3 15 Be -15 Always look at the pH first and classify that regardless of the cause. This pH is normal but it is on the low side of normal Look at the Co2 is it high or low? It is low which means it is not the problem, but it has attempted to fix the problem by decreasing. The bicarb is really low which makes the blood pH low. So that is the problem. In this example the bicarb(metabolic) is causing the problem because it is too low and it has lowered the pH, but the respiratory system has compensated by lowering the Co2 which helps increase the pH to within the normal range. This patient is probably breathing very fast trying to blow off their Co2 but if the metabolic problem is not corrected, he will get tired of breathing so fast and start slowing the respirations, the C02 will increase and then it will be a metabolic and respiratory problem.

I hope this helps. If you have never been exposed to interpreting blood gases/ABGs they can be confusing but once you get the hang of it then you've got it.:up:

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Specializes in Emergency.

My 1st step is to line everything up on my trusty paper towel:

pH 7.35-7.45

CO2 45-35

HCO3 22-26

I then put a dot in the respective place for each value (yes, the CO2 is flipped around, this puts acidosis on the left and alkalosis on the right for all values). I can then quickly figure out acidosis vs alkalosis, resp vs met vs mixed and comp vs uncomp. Then follow mcknis's rules and you should be good to go.

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Does anyone have an easy, understandable way to decipher ABG's? Metabolic acidosis/alkalosis vs. Respiratory acidosis/alkalosis? This stuff is looking like a foriegn language to me!! Then they throw in this Compensated and uncompensated?? I'm totally lost. Any help would be appreciated.:banghead:

What helps is to keep in mind how acid is produced in the body and how it's excreted, in relation to the patients clinical diagnosis. The lungs excrete approximately 150 mEq of acid per day in the form of carbonic acid.( Co2 + H20 ). The kidneys only excrete aout 50 mEq of acid per day.

Because the lungs excrete more acid when the respiratory system is compromised acidosis occurs more quickly.

Generally speaking there is usually little compensation for respiratory acidosis other than tachypnea and perhaps tachycardia if 02 is low., because the kidneys try to compensate but that compensation is slower and limited.

The lungs can compensate for metabolic acidosis by blowing of more C02 so, although the patient is acidotic the C02 will be low, hence a compensated metabolic acidosis.

There is a really good algorithm that I used to use when I was teaching Critical Care that you might find online. Unfortunately all my teaching info is packed away in boxes or I could send it.

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Specializes in premies, peds, adults.

remember "go to ROME" Respiratory opposite, metabolic equal"

but if you're in the baby land those numbers aren't quite the same. Acidotic numbers for adults are okay for premies! :nurse:

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Specializes in Med Surg, LTC, Home Health.

One of the greatest teacher i ever had taught it this way, and it is super-easy. Go over this a few times, and you will have a basic understanding:

First, you already know that the ph of blood is 7.35-7.45. Anything less than 7.35 will be acidosis, and anything above 7.45 will be alkalosis.

PaCO2 (parital pressure of carbon dioxide) 35-45-Think of CO2 as an acid. The higher it is, the more acidic. Since CO2 is removed by the lungs, it is the respiratory component.

HCO3 (bicarbonate) 22-26-Think of HCO3 as a base, or alkalotic. The higher the number, the more alkalotic, and the lower the number, the more acidotic. Since HCO3 is removed by the kidneys, it is the metabolic component.

ph- 7.49

PaCO2- 44

HCO3- 28

To get your answer, pick the component that matches the ph. Since the ph is akalotic, and the HCO3 is alkalotic, your answer is metabolic alkalosis.

ph- 7.32

PaCO2- 47

HCO3- 27

To get your answer, pick the component that matches the ph. Since the ph is acidotic, and the PaCO2 is acidotic, your answer is respiratory acidosis. Had the HCO3 been acidotic as well (

In the problem above notice that the HCO3 has risen above normal. It is adding more base to try and neutralize the acid. Since the ph is still abnormal, this is considered partially compensated respiratory acidosis.

If the HCO3 were normal (22-26), it would be uncompensated.

ph- 7.44

PaCO2- 48

HCO3- 29

The ph is normal, but since the others are not, you look at which way it is leaning. Since the ph is closer to an alkalotic state, and the HCO3 is high, there was initially metabolic alkalosis. PaCO2 has risen to compensate for this, bringing the ph back to normal. Thus you have fully compensated metabolic alkalosis.

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Specializes in med/surg, telemetry, IV therapy, mgmt.

the student help weblinks on how to read and interpret abgs are listed on poat #46 of the pathophysiology/ a & p/ microbiology/ fluid & electrolyte resources sticky thread in nursing student assistance forum. it includes tutorials on how to read and interpret abg results.

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R O M E

Respiratory Opposite Metabolic Equal

ROME

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Specializes in Developmentally Disabled, LTC, Clinic, Hospital.

Thank you, I started flipping the PaCO2 after I read this and it does make more sense to me by having them on the same sides. :bow:

My 1st step is to line everything up on my trusty paper towel:

pH 7.35-7.45

CO2 45-35

HCO3 22-26

I then put a dot in the respective place for each value (yes, the CO2 is flipped around, this puts acidosis on the left and alkalosis on the right for all values). I can then quickly figure out acidosis vs alkalosis, resp vs met vs mixed and comp vs uncomp. Then follow mcknis's rules and you should be good to go.

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