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acid/base imbalances


I have a final on Wed. and on our final is the electrolyte and acid base imbalances. I know about the electrolytes but I'm still having trouble determining if the imbalances are compensated or not. I fanyone knows how to do this wouldn't care to explain it to me I'd really appreciate it. Thanks

Daytonite, BSN, RN

Specializes in med/surg, telemetry, IV therapy, mgmt. Has 40 years experience.

you are talking about abgs. to determine if acidosis or alkalosis is compensated there is a sequence to follow:

  1. check the ph. if compensation has occurred the ph will be in normal range of 7.35-7.45
  2. check the co2 and hco3. if one is normal, look at the other and that is your culprit. co2 is the respiratory one and hco3 is the metabolic one. depending on if it is elevated or depressed tells you if it is acid or base.
  3. if both ions are out of whack, it is usually a respiratory alkalkosis that is being compensated.

there are some practice problems on https://allnurses.com/forums/2488838-post46.html

also see this recent thread: https://allnurses.com/forums/f50/abg-help-349441.html

CO2 is a negative ion so it is basic; HCO3 is positive so it is alkalinic.

I thought CO2 was a volatile acid, while HCO3 is the base in the buffer pair.

I have my final tomorrow, so I better just go check!

Daytonite, BSN, RN

Specializes in med/surg, telemetry, IV therapy, mgmt. Has 40 years experience.

i thought co2 was a volatile acid, while hco3 is the base in the buffer pair.

i have my final tomorrow, so i better just go check!

i am sorry. i was trying to explain how to assess compensation and didn't do a very good job of it. your information about hco3 being a base is correct.

for the rules of diagnosing abgs and determining acidosis or alkalinity of a compensated sample, see the really nice table at the end of this paper that was posted on allnurses by another student: arterial blood gases basic principles.doc - guide to assessing blood gasses

as far as interpreting abgs and compensation. . .

- interpreting abgs

- there are types of compensation


  • if ph is normal but pco2 and hco3 are abnormal this is fully compensated

  • if ph, pco2, & hco3 are all abnormal this is partially compensated

  • if ph is abnormal and either pco2 or hco3 are abnormal, but pco2 or hco3 are normal this is totally uncompensated.


the body will compensate in an attempt to keep the ph within normal limits

  • if the disorder is metabolic, compensation is achieved by altering respirations-increasing or decreasing pco2 to bring ph to normal

  • if the disorder is respiratory, compensation achieved by retaining or increasing excretion of bicarbonate

pco2 forms carbonic acid so is considered an acid

  • high pco2 causes ph to drop (toward acidosis)

  • low pco2 causes ph to climb (toward alkalosis)

hco3 (bicarbonate) is considered a base

  • high hco3 causes ph to climb (toward alkalosis)

  • low hco3 causes ph to drop (toward acidosis)

http://www.rnceus.com/course_frame.asp?exam_id=18&directory=abgs - "interpretation of abgs: a four step method". at the left side of the page, click on "four steps of abg interpretation".

  • look at the ph to determine:
    • acidosis (below 7.35)
    • normal or compensated (7.35 to 7.45)
    • alkalosis (over 7.45)

    [*]what is pa co2 doing? this is the respiratory effect.

    • alkalosis, causes high ph or normal low end ph (below 35)
    • normal or compensated (35 to 45)
    • acidosis, causes low ph, normal high end ph (over 45)
    • if a respiratory cause is ruled out, then move on to the next step

    [*]what is the pahco3 doing (normal hco3- is 22-26)? this is the metabolic effect.

    • high ph is alkalosis
      • if the paco2 is high it is metabolic; if it is low it is respiratory

      [*]low ph is acidosis

      • if the paco2 is high it is respiratory; if it is low it is metabolic

    [*]if paco2 is abnormal and ph is normal, it indicates compensation.

    • ph > 7.4 would be a compensated alkalosis.
    • ph

Here's a website that makes ABG's fun. just note that they may have different values than what your instructor tells you. In my school we go by PaCo2 of 35-45 and HCO3 of 22-26.

I agree with Daytonite on how it works.


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