Metabolic/ respiratory acidosis and alkalosis

nursecompassion · Mar 20, 2005

RainDreamer said:
To tell whether it's a respiratory problem or a metabolic problem look at the CO2 and the bicarbonate (HCO3).
Normal CO2 is 35-45, look at it and see if it falls within that range, if it does NOT fall within that range then, it's abnormal and therefore the problem is respiratory acidosis/alkalosis.
Normal HCO3 is 22-26, look at it and see if it falls within that range, if it does NOT fall within that range, then it's abnormal and therefore the problem is metabolic acidosis/alkalosis.

I think for me your answer made the most sense and was the simplest.

Jules ?

Altra, BSN, RN · Mar 20, 2005

RainDreamer said:
To tell whether it's a respiratory problem or a metabolic problem look at the CO2 and the bicarbonate (HCO3).
Normal CO2 is 35-45, look at it and see if it falls within that range, if it does NOT fall within that range then, it's abnormal and therefore the problem is respiratory acidosis/alkalosis.
Normal HCO3 is 22-26, look at it and see if it falls within that range, if it does NOT fall within that range, then it's abnormal and therefore the problem is metabolic acidosis/alkalosis.

This is not necessarily true if one system is compensating for failure of the other, i.e., respiratory rate increasing to blow off CO2 (this lowers CO2 value to an alkalotic level, if you just looked at that value) in an effort to compensate for metabolic acidosis (as in DKA).

The compensation part is a little trickier. This is why it's crucial to see which of the 2 abnormal values (if CO2 and HCO3 are both out of range) match the abnormality of the pH.

HTH

RainDreamer, BSN, RN · Mar 20, 2005

I didn't mention anything about pH because she didn't ask about that, she said she understood the acidosis/alkalosis part. I only mentioned one step of the ABG analysis, you have to go through many steps to come to the conclusion of metabolic/respiratory, acidosis/alkalosis, uncompensated/compensated. If you look at the CO2 and the HCO3 and see which is abnormal, then you can go from there and look at the pH to see whether it's compensated for or not. Sorry if I confused anyone :)

UNFBSN2B · Mar 21, 2005

MLOS said:
Our critical care instructor is fantastic -- she just recently *refreshed* our memories from med-surg and drummed this into our heads ...
First, look at the pH: normal = 7.35-7.45. 7.35-7.39 has an "acidotic lean", 7.41-7.45 has an "alkalotic lean" and 7.40 is *perfect*.
Next look at the HCO3 (normal = 22-26) and the pCO2 (normal = 35-45). Which one "has the same name" as the pH (acidotic or alkalotic)? If it's the HCO3 then the problem is metabolic, and if it's the pCO2 then the problem is respiratory.
Example:
pH 7.33
pCO2 50
HCO3 26
The pH is acidemic, the pCO2 is high (CO2 is acid) and the HCO3 is OK. The pCO2 has the same "name" (problem) as the pH - this is respiratory acidosis.
Since either of these 2 systems (respiratory system & metabolic - kidneys) will try to compensate for failure of the other, the more complicated problems come in when there is full or partial compensation - the pH will return to normal (but w/the acidotic or alkalotic "lean") and the other value will also be out of whack - the key is to see which matches the "lean" of the pH.
We call this the who's your daddy method of ABGs ...
I have a packet with tons of these problems -- if anyone wants a sampler with the answers, just send me a PM.

Wow...we must have had similar teachers. My physiology professor gave us multiple scenarios until we had it drummed into our heads.

Nursekamala · Jun 23, 2008

Your information was quite helpful. Thanks a million. I have been struggling with how to make this info stick in my head. This is just what the Dr. Ordered. I would like to get that packet that you said you have to practice. **email address removed** Again, Thanks :loveya:

MLOS said:
Our critical care instructor is fantastic -- she just recently *refreshed* our memories from med-surg and drummed this into our heads ...
First, look at the pH: normal = 7.35-7.45. 7.35-7.39 has an "acidotic lean", 7.41-7.45 has an "alkalotic lean" and 7.40 is *perfect*.
Next look at the HCO3 (normal = 22-26) and the pCO2 (normal = 35-45). Which one "has the same name" as the pH (acidotic or alkalotic)? If it's the HCO3 then the problem is metabolic, and if it's the pCO2 then the problem is respiratory.
Example:
pH 7.33
pCO2 50
HCO3 26
The pH is acidemic, the pCO2 is high (CO2 is acid) and the HCO3 is OK. The pCO2 has the same "name" (problem) as the pH - this is respiratory acidosis.
Since either of these 2 systems (respiratory system & metabolic - kidneys) will try to compensate for failure of the other, the more complicated problems come in when there is full or partial compensation - the pH will return to normal (but w/the acidotic or alkalotic "lean") and the other value will also be out of whack - the key is to see which matches the "lean" of the pH.
We call this the who's your daddy method of ABGs ...
I have a packet with tons of these problems -- if anyone wants a sampler with the answers, just send me a PM.

Daytonite, BSN, RN · Jun 23, 2008

nursekamala. . .there is information on respiratory and metabolic acidosis and alkalosis on this sticky thread in the nursing student assistance forum:

https://allnurses.com/forums/f205/pathophysiology-p-fluid-electrolyte-resources-145201.html - pathophysiology/ a & p/ microbiology/ fluid & electrolyte resources - look at posts #24 and #25.

Molly2008 · Feb 14, 2009

http://www.realnurseed.com/abg.htm

at the end of the web page there is a "cheat sheet". Has been very helpful for me.

shygoofyone · Feb 20, 2009

I use a tic-tac-toe method with my friends to help them.

1. Make a grid with three columns labeled "ACID, NORMAL, ALKALINE" and three rows labeled "PH, CO2, HCO3"

2. Write our your normal ranges:

PH______7.35-7.45

HCO3____ 20-26

CO2_____ 45-35 (if you put all the acidic values on the same side, it's easier!)

3. Plop in your numbers under the appropriate columns. Once you get two values in the same column you have your diagnosis! For example, with a PH 7.5, HCO3 30 and CO2 of 40, you see:

___________ACID_____NML_____ALK

PH__________________________7.5

HCO3________________________30

CO2_________________40

In this case, you have metabolic alkalosis (use your column heading as your third "tic-tac-toe" piece. Also....if you have anything in the "normal" column (besides ph), you know that it's uncompensated, because if the body were compensating, your third value would not be normal! :)

It's hard to explain on here. But, I hope this helps :) Good luck!

shorty3_31 · Feb 20, 2009

The simplest way to remember is to look at whichever value is the furthest off. For example, you can easily tell the difference between acidosis and alkalosis based off the pH, so let's make it 7.25. The next thing to look at would be PaCO2. Say it's 55 (just a number out of range). Then look at the bicarb (let's say it's 25). So PaCO2 is high whereas bicarb is normal and the pH is acidic. [Respiratory acidosis]

So, because the CO2 is off, it's respiratory. More often than not you can gauge it by which value is off. Usually if bicarb is off, it's metabolic, and if CO2 is off, it's respiratory.

Hope that helps.

1andrea1 · Feb 20, 2009

Our instructor taught us ROME

Respiratory

Opposite

Metabolic

Equal (not actuall equal, it would just be on the same end of the spectrum)

pH7.35 -------------------------------------------pH7.45

acidosis ------------------------------------------alkalosis

Basically if the pH is low (acidosis) and the CO2 is high it would be Respiratory Acidosis and if the pH is high and the CO2 is low it would be Respiratory Alkalosis (respiratory opposite)

If the pH is low (acidosis) and the bicarb is also low it would be Metabolic Acidosis and if the pH is high and the bicarb is high it would be Metabolic alkalosis. (metabolic equal)

This helped me in class but I know it confused some others, good luck!

hopeful234 · Sep 28, 2009

I would like the list of examples with answers. Thanks. Please send it to me via pm. Thanks

JomoNurse · Sep 28, 2009

I found a very simple way of figuring these types of questions out.

1. First, figure out if it's Acid or Alkalosis. Assign an arrow to it. (Acidosis is a BELOW average value, so the arrow would point down. Opposite for Alkalosis.)

2. Do the same thing for the other 2 values. That is, either put an arrow pointing upward, or downward, depending on if the value is low or high.

3. Here's where you determine if it's Respiratory or Metabolic:

If all of the arrows point in the saME direction, then it's MEtabolic in nature (see how I capitalized "ME" in both

of them?

If all of the arrows point in the diffeREnt cirections, then it's REspiratory in nature (see how I capitalized "RE"?)

Again, if all of the arrows point in the SAME direction (doesn't matter if they are all pointing up or all pointing down), then it's METABOLIC. If the arrows point in different directions (doens't matter which arrows are up or down, then it's RESPIRATORY).

I used this for my exams and once you have it down, you breeze through these problems like a charm. You better know this, you WILL be tested on these. A LOT of students don't understand them, instructors know it, and so they throw in a lot of these questions.