abg values - page 2

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... Read More

  1. by   deeDawntee
    hi, i've added some corrections to daytonites post: my editions are in green: 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 (elevated) - normal is 7.35 to 7.45
    pco2 32 (diminished) - normal is 35 to 45
    hco3 24 (normal value) - normal is 22-26
    what you have is the me part of the rome mnemonic, or ph elevated pco2 diminished = respiratory alkalosis, not metabolic acidosis.

    this is a respiratory alkalosis because of the alkalotic ph and the alkalotic paco2. you have to remember that the body never over compensates, so the ph being alkalotic would be a alkolotic condition.
    ph 7.45 (normal) - normal is 7.35 to 7.45
    pco2 47 (elevated) - normal is 35 to 45
    hco3 29 (elevated) - normal is 22-26
    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!

    the reason you know this is metabolic alkalosis is because, as you can see the ph is leaning towards alkalosis....it is on the alkalotic side of normal...


    if the ph is normal, is it leaning? if so, consider compensation,
    (1) compensation causes a leaning ph, the ph leans toward the initial disorder.
    a. the body never over compensates. a normal non-leaning ph (7.40) with two abnormal indicators suggests a mixed disorder.
    (2) for compensation to be occurring. one parameter change must help the other.

    i am looking around and am finding a discrepancy between definitions of uncompensated, partially compensated and fully compensated abg's, (hence my confusion on my first post)...i am doing more research and will post information as i find it....

  2. by   deeDawntee
    http://www.wisc-online.com/objects/i...?objID=NUR6906

    Hey, check out this explanation and quiz....this is consistent with my first explanation on compensation....this is very good....
  3. by   Daytonite
    Quote from deeDawntee
    http://www.wisc-online.com/objects/i...?objID=NUR6906

    Hey, check out this explanation and quiz....this is consistent with my first explanation on compensation....this is very good....
    Excellent tutorial!
  4. by   frez
    thank you thank you thank you and did i say thank you! I am learning this again in my third semester nursing and i was having a problem understanding how you tell whether it was metabolic or respirtory after being fully compensated. I think i get it now!!

    Frez
  5. by   deeDawntee
    ok i have researched around and i believe this is the bottom line in the compensation definitions:

    uncompensated: ph abnormal and no change in secondary value
    partially compensated: ph is still abnormal, but the secondary value has begun to change in the direction to correct initial disturbance
    fully compensated: the ph is normal, the compensation mechanism has been successful, however is still out of range.

    in practice, i am watching abg's all the time. what is really important is if you can tell if it is respiratory or metabolic/acidosis or alkalosis and if the body is doing something to help it.
    also, remember that you will have your patient as the basis of your evaluation, not some obscure numbers....what is important as well is the trending in abg's...is there an overall improvement? (the same as any other lab values).
  6. by   deeDawntee
    Here is a quiz for anyone interested!!
    1. pH 7.28, PCO2 60, HCO3 24
    2. pH 7.36, PCO2 62, HCO3 35
    3. pH 7.6, PCO2 40, HCO3 40
    4. pH 7.6, PCO2 16, HCO3 24
    5. pH 7.41, PCO2 49, HCO3 30
  7. by   frez
    Quote from deeDawntee
    Here is a quiz for anyone interested!!
    1. pH 7.28, PCO2 60, HCO3 24
    2. pH 7.36, PCO2 62, HCO3 35
    3. pH 7.6, PCO2 40, HCO3 40
    4. pH 7.6, PCO2 16, HCO3 24
    5. pH 7.41, PCO2 49, HCO3 30

    ill give it a shot
    1--respiratory acidosis-uncompansated
    2--respiratory acidosis fully compansated
    3--metabolic alkalosis partailly compensated
    4--respiratory alkalosis--uncompensated
    5--metabolic alkalosis-partially compensated
  8. by   deeDawntee
    1--respiratory acidosis-uncompansated yes
    2--respiratory acidosis fully compansated yes
    3--metabolic alkalosis partailly compensated yes
    4--respiratory alkalosis--uncompensated yes
    5--metabolic alkalosis-partially compensated -or fully compensated because the ph is normal-depending on the definition of fully compensated your are going by--this is where the discrepancy is in various references....clinically makes no difference...because you do know your abgs....great job!


  9. by   jcarabal
    Thank you so much for explaining the abg's values. I understand it much clearer now. Can you please continue explaining. You are great at it. Can you please continue.
  10. by   Daytonite
    Quote from jcarabal
    Thank you so much for explaining the abg's values. I understand it much clearer now. Can you please continue explaining. You are great at it. Can you please continue.
    Who are you directing your comments to and what else is it that you need explained?
  11. by   tonidelagarza
    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.
    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.
    JUST WANTED TO SAY THANK YOU! I ALWAYS STRUGGLE WITH THIS TOPIC IN NSG SCHOOL. IM AN LPN FINISHING MY RN IN MAY AND I KNEW THIS DREADED TOPIC WOULD COME UP AGAIN! BUT YOUR EXPLAINATION WAS GREAT! THANKS AGAIN!
  12. by   Jonathank
    Just to nitpick: CO2 is NOT an acid. It's just easily transformed into H2CO3 (carbonic acid). One of my instructors referred to it as an electrolyte. It's not that, either. It's just also easily transformed into HCO3- (bicarbonate).

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