abg values

  1. I need some info on resp. acidosis, resp. alkalosis, metabolic acidosis, and metabolic alkalosis. I don't really understand it very well. I also need to know how you decide if it is compensated fully or partially. How do you know? Any information would be appreciated.
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  2. 24 Comments

  3. by   GingerSue
    here's a forum link:

    http://allnurses.com/forums/f205/hel...gs-228639.html

    From my manual:
    It is fully compensated if pH is normal

    It is partially compensated if pH is abnormal

    If pH is less than 7.4, then the client is acidotic
    If pH is greater than 7.4, then the client is alkalotic
    If pH and PCO2 are changing in opposite directions, then a respiratory disorder is present.
    If pH and PCO2 are changing in the same direction, then a metabolic disorder is present.
    If pCO2 and HCO3 are changing in the same direction, then the body is compensating for an imbalance.
    If PCO2 and HCO3 are changing in opposite directions then a mixed imbalance is present.

    Here's another link that might help:
    http://maagnursing.com/ABG/
    Last edit by GingerSue on Sep 28, '07
  4. by   deeDawntee
    This is one of those overwhelming subjects in nursing school. It is truly complicated at first and you are not alone to find the subject daunting. You will find charts where you go by arrows and if arrows both point one way then it is this etc. I would recommend that you do not use those charts as a way to learn ABG's, because you really aren't learning anything.

    1) the first thing you want to figure out is if the blood gas result is alkalosis or acidosis (or normal). Normal range is 7.35-7.45.

    2) the second thing is to figure out if the source of the abnormality is metabolic or respiratory. You do this by looking at the CO2 and the HCO3 levels.

    You really need to let yourself understand this. Let's start with Respiratory. If you were to hold your breath (or if you were being suffocated) your blood gases would become more and more acid because Carbon dioxide would build up in your blood and carbon dioxide is an acid. You would have respiratory acidosis.

    If you were really anxious and were hyperventilating and breathing really hard, you blood gases would become alkalotic, because you would be expelling more and more Carbon dioxide and you would lose that acid.

    Carbon dioxide is measured in the blood as PaCO2. The normal value is 35-45. It is very important that you remember that Carbon dioxide is an acid, so that a high PaCO2 equals acidosis. And that a low PaCO2 equals alkalosis. (I believe this point is counter-intuitive to a lot of people first learning to interpret blood gases...you MUST get that CO2 is an acid. Any level of PaCO2 (which is the measurement of CO2 in the blood that is above 45 is acidosis). Reiterate this to yourself, until you remember it..........CO2=acid.....

    The next thing to understand is the Metabolic side of blood gases. This is controlled by the kidneys. The kidneys produce bicarb (HCO3) which is the antacid....remember that bicarb=antacid.
    The normal range of HCO3= 22-26. (this result is intuitive, most students understand this level more easily.) A high bicarb (HCO3) >26 equals alkalosis and a low bicar (HCO3) <22 equals acidosis.

    Now you can easily interpret the straight forward ABG's (where no compensation has begun) I would practice the uncompensated blood gases until I had it down cold.

    For instance: pH 7.3, PaCO2 48 and HCO3 26. This is uncompensated Resp acidosis, because the pH and the CO2 are acidotic and the bicarb has not done anything out of the ordinary to compensate for it.
    If those blood gases were: pH 7.3, PaCO2 48 and HCO3 27, this is now partially compensated Resp acidosis because the kidneys have put out a little extra bicarb to compensate for the high PaCO2 (acid) but the pH is still abnormal.
    Now if those blood gases were pH 7.35, PaCO2 47 and HCO3 29, this is a fully compensated Resp acidosis.
    Lastly, if the blood gas were pH 7.39, PaCO2 45 and HCO3 26, this is a fully compensated as all values are normal.

    Now for metabolic distubances. If you were vomiting you will be losing acid and you would expect your blood gases to show metabolic alkalosis. If you had diarrhea you would expect your blood gases to shoe metabolic acidosis. (Also anything that causes anaerobic use of muscles or burns or massive lack of oxygenation to the muscles and tissues would cause metabolic acidosis).

    For HCO3 levels less than 22= metabolic acidosis,
    and levels greater than 26 = metabolic alkalosis.

    OK, I'm going to stop now and wait for your feedback, if you would like me to take you through some problems or if you have some specific questions, please ask. But I won't write anymore until I hear from you if this is helpful or not.

    Don't give up, once your mind wraps itself around the whole respiratory aspect, it all will start to click.
    Last edit by deeDawntee on Sep 29, '07 : Reason: change in compensation explanation
  5. by   Daytonite
    you will find information on these subjects on this thread in the nursing student assistance forum
    i don't remember if these links are listed there, but here are some other good abg links for you:
  6. by   catzy5
    Quote from deeDawntee
    This is one of those overwhelming subjects in nursing school. It is truly complicated at first and you are not alone to find the subject daunting. You will find charts where you go by arrows and if arrows both point one way then it is this etc. I would recommend that you do not use those charts as a way to learn ABG's, because you really aren't learning anything.

    1) the first thing you want to figure out is if the blood gas result is alkalosis or acidosis (or normal). Normal range is 7.35-7.45.

    2) the second thing is to figure out if the source of the abnormality is metabolic or respiratory. You do this by looking at the CO2 and the HCO3 levels.

    You really need to let yourself understand this. Let's start with Respiratory. If you were to hold your breath (or if you were being suffocated) your blood gases would become more and more acid because Carbon dioxide would build up in your blood and carbon dioxide is an acid. You would have respiratory acidosis.

    If you were really anxious and were hyperventilating and breathing really hard, you blood gases would become alkalotic, because you would be expelling more and more Carbon dioxide and you would lose that acid.

    Carbon dioxide is measured in the blood as PaCO2. The normal value is 35-45. It is very important that you remember that Carbon dioxide is an acid, so that a high PaCO2 equals acidosis. And that a low PaCO2 equals alkalosis. (I believe this point is counter-intuitive to a lot of people first learning to interpret blood gases...you MUST get that CO2 is an acid. Any level of PaCO2 (which is the measurement of CO2 in the blood that is above 45 is acidosis). Reiterate this to yourself, until you remember it..........CO2=acid.....

    The next thing to understand is the Metabolic side of blood gases. This is controlled by the kidneys. The kidneys produce bicarb (HCO3) which is the antacid....remember that bicarb=antacid.
    The normal range of HCO3= 22-26. (this result is intuitive, most students understand this level more easily.) A high bicarb (HCO3) >26 equals alkalosis and a low bicar (HCO3) <22 equals acidosis.

    Now you can easily interpret the straight forward ABG's (where no compensation has begun) I would practice the uncompensated blood gases until I had it down cold.

    For instance: pH 7.3, PaCO2 48 and HCO3 26. This is uncompensated Resp acidosis, because the pH and the CO2 are acidotic and the bicarb has not done anything out of the ordinary to compensate for it.
    If those blood gases were: pH 7.3, PaCO2 48 and HCO3 27, this is now partially compensated Resp acidosis because the kidneys have put out a little extra bicarb to compensate for the high PaCO2 (acid) but the pH is still abnormal.
    Now if those blood gases were pH 7.35, PaCO2 47 and HCO3 29, this is a fully compensated Resp acidosis. It is fully compensated because the pH is normal, but the other levels are still abnormal.
    Lastly, if the blood gas were pH 7.39, PaCO2 45 and HCO3 26, this is a normal ABG as all values are normal. (no compensation seen)

    Now for metabolic distubances. If you were vomiting you will be losing acid and you would expect your blood gases to show metabolic alkalosis. If you had diarrhea you would expect your blood gases to shoe metabolic acidosis. (Also anything that causes anaerobic use of muscles or burns or massive lack of oxygenation to the muscles and tissues would cause metabolic acidosis).

    For HCO3 levels less than 22= metabolic acidosis,
    and levels greater than 26 = metabolic alkalosis.

    OK, I'm going to stop now and wait for your feedback, if you would like me to take you through some problems or if you have some specific questions, please ask. But I won't write anymore until I hear from you if this is helpful or not.

    Don't give up, once your mind wraps itself around the whole respiratory aspect, it all will start to click.


    Thank you so much for taking the time to write this out!

    I am not in the nursing program yet (still waiting for my letter) but I remember going over this in AP, I also remember struggling with it, now reading your post though I have such a better understanding! I am printing this out and saving it for when I start (hopefully January). Also going back to my AP chapter and looking at it again to bring it all together. I love love love learning this stuff!

    Thanks again!
  7. by   fmrnicumom
    Great post! I'm not in yet either, but hopefully will be soon. This is great information and it makes much more sense now.

    Tiffany
  8. by   mickeyfan
    Thanks so much!! Awsome post! Quick question--pH-7.35, PaCO2-48, and HCO3-27. How do I figure this one? Thank you so much for all of your time! You are a life saver!!!!!
  9. by   deeDawntee
    Yaaayyy! I'm glad that first bit was helpful, so I will continue on a bit.

    Lets go on with more of an understanding of metabolic....(this point was confusing to me, because I didn't understand why they used the term metabolic...I thought it equaled metabolism which I thought had to do with the thyroid gland...but I was wrong...The term metabolic really has to do with any system in the body that is not the lungs (or the heart/lung partnership). So metabolic issues may show up with patients who have issues like, kidney failure, pancreatitis, GI bleeding, liver failure, diabetes (such as ketoacidosis) burns, trauma, electrolyte disturbances....see how broad metabolic issues are?....think outside the lungs...

    I add this here because in real practice, you will look at your patient's issues, as you interpret their blood gases....

    Now the body is amazing....it uses two mechanisms (and ONLY two mechanisms) to balance the pH of the entire body with only the respiratory rate and the bicarb put out by the kidneys....isn't that amazing??!!

    Here is an example: A patient will come in after several days of severe vomiting, their pH is sky high, because they have lost all that gastric acid...and their respiratory rate will be 8-10 bpm. The body is in severe metabolic alkalosis and the lungs are conserving CO2 (which is conserving acid) to keep the body's pH as close to normal as possible.

    The lungs will compensate for metabolic disorders, but they really don't do a very good job of compensating for their own disorders.
    The kidneys compensation of producing bicarb (or by absorbing bicarb and excreting it in the urine) is a slower process and much broader in its scope.

    One pathophysiology that we all run into all the time is the COPDers. These patients are chronic CO2 retainers....long term smoking severely impacts the lungs ability to expel all the CO2 out of the lungs, since cigarette smoke is mostly CO2. So CO2 builds up and has a huge impact on blood gases. Obviously their underlying problem will be Respiratory Acidosis....here is a typical blood gas:

    pH 7.35,
    PACO2 58
    HCO3 36

    This is a partially compensated respiratory acidosis. These people never reach normal levels of PACO2 so their kidneys are always compensating. God forbid, if these folks ever go into kidney failure and can no longer produce bicarb... not a good outcome....

    remember you have to come up with a first name, a middle name and a last name.

    The first name is one of three names: uncompensated, partially compensated or fully compensated.

    The middle name is either metabolic or respiratory.

    The last name is either acidosis or alkalosis.

    If the pH is normal, is it leaning? If so it is probably a compensated pH. Compensation causes a leaning pH, the pH leans towards the initial disorder. The body never overcompensates.

    OK, I will wait for more responses.
    Last edit by deeDawntee on Sep 29, '07
  10. by   deeDawntee
    Quote from itlpn
    Thanks so much!! Awsome post! Quick question--pH-7.35, PaCO2-48, and HCO3-27. How do I figure this one? Thank you so much for all of your time! You are a life saver!!!!!
    This is a partially compensated respiratory acidosis....

    The reason it is partially compensated is because both the PaCO2 and the bicarb are out of the normal range. But it is compensated because the pH is normal.

    It is respiratory because, (the pH leans towards acidosis) and the value that is acidotic is the PaCO2.
    Last edit by deeDawntee on Sep 29, '07
  11. by   RRTM2
    This is just an easy way to put a name on it. You really need to know all the information previously mentioned to know what's going on with your patient... to know why their ABG looks this way and what to do about it.


    ex: pH-7.35, PaCO2-48, and HCO3-27


    Think of the mid ranges of normal.
    pH: 7.40
    PC02: 40
    HC03: 24

    which side of mid range is your ABG?

    pH moving alkalotic or acidic?
    PC02 moving alkalotic or acidic?
    HC03 moving alkalotic or acidic?

    Which one is moving in the same direction as the pH? That's your active mechanism.
    Which one is moving opposite of the matching ones? That's your compensatory mechanism.






    answer...
    pH: moving towards acidic range
    PC02: moving towards acidic range
    HC03: moving towards alkalotic range

    So respiratory acidosis, compensated
    (pH is at the lowest end of normal, so it's compensated, but barely. pH 7.34 would make it partially compensated)
  12. by   mickeyfan
    This is really helpful!!! I have a couple more problems. pH-7.48, PaCO2-32, and HCO3-24-is this metabolic alkalosis? Also, pH-7.45, PaCO2-47, and HCO3-29-is this Metabolic acidosis with partial compensation? Thanks!!!
  13. by   RRTM2
    Quote from itlpn
    this is really helpful!!! i have a couple more problems. ph-7.48, paco2-32, and hco3-24-is this metabolic alkalosis? also, ph-7.45, paco2-47, and hco3-29-is this metabolic acidosis with partial compensation? thanks!!!

    #1 – yes (edit: make that a no. daytonite is correct in her post below - it is respiratory alkalosis. sorry! and thanks daytonite!)

    #2 – no

    you are correct that it’s a metabolic mechanism, but if hc03 numbers are high is that acidosis or alkalosis?

    ph is within normal range. so if ph is within normal range then the compensatory mechanism has done its job and fixed the problem. it’s fully compensated.

    (again, this is just barely in range. ph of 7.46 would be technically out of normal range making it partially compensated.
    *this is just a technicality for test taking. a ph of 7.45 or 7.46 isn’t going to be much different for an actual pt)


    this is the mental tool that i keep in mind.

    alk / acid / alk
    ph / pc02 / hc03


    *ph numbers high = alkalotic
    pc02 numbers high = acidic
    hc03 numbers high = alkalotic
    Last edit by RRTM2 on Sep 29, '07 : Reason: error!
  14. by   Daytonite
    per post #25 on http://allnurses.com/forums/f205/pat...es-145201.html - the "pathophysiology/a & p/fluid & electrolyte resources" thread on the student nursing assistance forum:

    the mnemonic rome means the following:


    respiratory opposite
    • ph elevated pco2 diminished = respiratory alkalosis
    • ph diminished pco2 elevated = respiratory acidosis

    metabolic equal
    • ph elevated hco3 elevated = metabolic alkalosis
    • ph diminished hco3 diminished = metabolic acidosis
    normal levels of pco2 are: 35-45 mmhg
    normal levels of hco3 are: 21-28 mmhg
    normal ph is: 7.35-7.45

    i'm not real good at these so if i'm doing something wrong here, someone feel free to step in and correct me!
    ph-7.48, paco2-32, and hco3-24-is this metabolic alkalosis?
    ph 7.48 (elevated) - normal is 7.35 to 7.45
    pco2 32 (diminished) - normal is 35 to 45
    hco3 24 (diminished) - normal is 21 to 28
    what you have is the me part of the rome mnemonic, or ph elevated pco2 diminished = respiratory alkalosis, not metabolic acidosis.
    ph-7.45, paco2-47, and hco3-29-is this metabolic acidosis with partial compensation?
    ph 7.45 (normal) - normal is 7.35 to 7.45
    pco2 47 (elevated) - normal is 35 to 45
    hco3 29 (elevated) - normal is 21 to 28
    because the ph is normal, you have a compensated condition. however, you can also see that the pco2 is elevated above normal levels which would have made it respiratory acidosis or metabolic alkalosis. hard to tell without knowing which way the ph was before the compensation because the numbers are so close. so, i'm not sure about this one. someone feel free to step in and answer this one!

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