Metabolic/ respiratory acidosis and alkalosis

[jennielynn]

Call me stupid--but I'm having such a time with determining whether a person is in respiratory or metabolic acidosis/alkalosis based on the ABG levels. I know how to determine the acidosis/ alkalosis part---its the difference between metabolic and respiratory that screws me up. If anyone has any suggestions on how to tell the two apart--please share!!!!

[melmarie23, MSN, RN]

I didnt go through everyone else's response, but an easy way I remember it is that in relation to the pH, respiratory acidosis/alkalosis rides the seasaw, and in metabolic acidosis/alkalosis, it takes the elevator. In other words, respiratory goes the opposite direction, and metabolic same.

the values you just need to commit to memory.

compensation is another layer to the cake. Uncompensation occurs when there is a dysfunction (acidosis or alkalosis) but the compensating factor remains within the normal range.

eg) pH-7.17

PaCO2-65

HCO3- 23

The patient is in resp. acidosis (seasaw pattern) and HCO3 is within normal limits

Partially compensated is when there is a dysfunction and some compensation occurs

eg) pH-7.17

PaCO2-65

HCO3- 30

The patient is in resp. acidosis with partial compensation (follows seasaw pattern). The HCO3 is elevated, HOWEVER the pH doesn't rise (go on the elevator) with the bicarb, so this means that the metabolic function has started to compensate for the respiratory dysfunction

For full/complete compensation, the pH stays witin normal limits, but you need to look at which way its leaning (acidotic or alkalotic)

I hope this helps some!

[Sarah Hay]

This is not based on compensated or uncompensated because we haven't learned that...

With respiratory you look at pH and PC02 (pH and PCO2 will teeter-totter)

With metabolic you look at pH and HCO3- (pH and Bicarbonate will be on the same level plane - both up or down)

Respiratory ACIDOSIS

Lower pH (7.35-7.45)

Higher PCO2 (35-45)

Respiratory ALKALOSIS

Higher pH (7.35 - 7.45)

Lower PCO2 (35-45)

Metabolic ACIDOSIS

Low pH (7.35 - 7.45)

Low Bicarbonate (22-26)

Metabolic ALKALOSIS

High pH (7.35 - 7.45)

High Bicarbonate (22-26)

[allroses9]

I actually learned this today. If it's respiratory it's the lungs, if it's metabolic it's the liver and kidneys. We just started this today. Sorry if that doesn't help.

[NancyPoole]

I have a great audio program that explains it amazingly and will definetely help you understand it! I was lost until I found this program. Shoot me an email if you want me to send it to you! [email protected]

[JSlice., ASN, RN]

I need someone to help me understand the differences between the four Acid-Base balances.

How am I supposed to remember what the ph, co2, hco3, all do during these different conditions?

[polka-dot, RN]

The Basics (it can get much trickier than this!)

If the ph is acidic (below 7.35) and the bicarb level is low, then it's metabolic acidosis.

If the ph is alkalotic (above 7.45) and the bicarb level is high, then its metabolic alkalosis.

If the pH is acidic and the CO2 is high, then it's respiratory acidosis.

If the ph is alkalotic and the CO2 is low, then it's respiratory alkalosis.

Of course, you can have partially compensated versions of these plus combinations of acidosis and alkalosis, respiratory AND metabolic....but what I described above are the basics. Here are some more detailed steps from my notes on ABGs:

Step 1: Classify the pH

Normal = 7.35 - 7.45

Acidotic =

Alkalotic = > 7.45

Step 2: Assess PaCO2

Normal = 35-45 mm Hg

Acidotic = > 45 mm Hg

Alkalotic =

Step 3: Assess HCO3-

Normal = 22-26 mEq/L

Acidotic =

Alkalotic = > 26 mEq/L

Step 4: Determine presence of compensation (this is where it gets tricky!)

Are PaCO2 and HCO3- abnormal (or almost so?) in opposite directions (one acidotic, the other alkalotic)? If yes, then compensation is PRESENT.

Is one component normal and the other abnormal? If yes, compensation is ABSENT and the problem is likely acute.

Step 5: Identify the primary disorder, if possible

-If pH is clearly abnormal, then the acid-base component most consistent with the pH disturbance is the primary disorder (see "basics" up above)

-If pH is normal or near-normal, the more deviant component is the probable primary (also...note whehter pH is on the acidotic or alkalotic side of 7.4. the more deviant component should be consistent with this pH.)

Step 6: Classify degree of compensation, if present

Metabolic acidosis: the decrease in PaCO2 is approximately equal to the last two digits of the pH.

Metabolic alkalosis: The PaCO2 is approximately equal to 0.6 x the increase in HCO3- level.

Respiratory acidosis: For every 10 mm Hg increase in PaCO2, the HCO3- level is increased by 1 mEq/L (in acute

acidosis) or 4 mEq/L (in chronic acidosis)

Respiratory alkalosis: For every 10 mm Hg decrease in PaCO2, the HCO3- level is decreased by 2 mEq/L (in acute

alkalosis) or 5 mEq/L (in chronic alkalosis)

COMPENSATION BEYOND THESE LIMITS SUGGESTS THE PRESENCE OF A COMPLEX DISORDER!!!

[~Mi Vida Loca~RN, ASN, RN]

ROME= Respiratory opposite and Metabolic Equal, if the values are opposite your talking about Respiratory and you will know if it's alkalosis or acidosis by the PH (low is acidosis and high is alkalosis)

If the values are equal then it's metabolic and you know which same way.

So if PH is high and so is BiCarb then it's Metabolic Alkalosis.

If PH is low and the CO2 is high then it's Respiratory Acidosis

Hopefully I said all that right I am tired and to lazy to go double check I said that right and my brain is officially closed down from school mode for a while LOL

[Intern67]

'

JSlice. said:

I need someone to help me understand the differences between the four Acid-Base balances.

How am I supposed to remember what the ph, co2, hco3, all do during these different conditions?

By not remembering them, but *understanding* them. The book "Fluid and Electrolytes Made Easy" has a great ABG tutorial and very easy to understand acid base discussions. Honestly though your Med-Surg book probably has a good step by step discussion of analysis.

Once again, do not try to memorize nonsense like "When this goes up that goes down" or "When these two are high and that one is low then it's acidosis/alkolosis with/without/partial compensation.

My classmates who do this almost universally throw up on themselves on these questions during exams.

Start with pH. What is pH? You know the normal range is 7.35 to 7.45, but WHAT is happening to push it outside that range? Which way is more acidic and which way is more alkaline?

Move on to PaCO2. Sure you know normal levels are 35 to 45 mm Hg, but what does that mean? How is the partial pressure of CO2 related to acidity? What is carbonic acid anyway? If someone's respiration rate increases, are they getting rid of more CO2 or keeping more? What is the effect of increased PaCO2 on serum pH? WHY? If a patient's pH changes in response to respiratory rate is that a respiratory response or a metabolic response?

Then go to bicarbonate. Again, you know the number 22-26 mEq/L but how does it go higher or lower? How does bicarb interact with acids? How does the body control the serum bicarb levels? Why does the body react to more acidic pH by conserving bicarb and is that a metabolic or respiratory response? If someone is vomiting acidic stomach contents which direction is their pH going to go? What will their body do in response? Increase respirations or decrease?

Now I know I have not helped you much here. But if you can know the answer to the above questions and understand why those answers are correct, you simply will never ever get an ABG or acid base balance question wrong.

Good luck!

[~Mi Vida Loca~RN, ASN, RN]

Intern67 said:

'

By not remembering them, but *understanding* them. The book "Fluid and Electrolytes Made Easy" has a great ABG tutorial and very easy to understand acid base discussions. Honestly though your Med-Surg book probably has a good step by step discussion of analysis.

Once again, do not try to memorize nonsense like "When this goes up that goes down" or "When these two are high and that one is low then it's acidosis/alkolosis with/without/partial compensation.

My classmates who do this almost universally throw up on themselves on these questions during exams.

Start with pH. What is pH? You know the normal range is 7.35 to 7.45, but WHAT is happening to push it outside that range? Which way is more acidic and which way is more alkaline?

Move on to PaCO2. Sure you know normal levels are 35 to 45 mm Hg, but what does that mean? How is the partial pressure of CO2 related to acidity? What is carbonic acid anyway? If someone's respiration rate increases, are they getting rid of more CO2 or keeping more? What is the effect of increased PaCO2 on serum pH? WHY? If a patient's pH changes in response to respiratory rate is that a respiratory response or a metabolic response?

Then go to bicarbonate. Again, you know the number 22-26 mEq/L but how does it go higher or lower? How does bicarb interact with acids? How does the body control the serum bicarb levels? Why does the body react to more acidic pH by conserving bicarb and is that a metabolic or respiratory response? If someone is vomiting acidic stomach contents which direction is their pH going to go? What will their body do in response? Increase respirations or decrease?

Now I know I have not helped you much here. But if you can know the answer to the above questions and understand why those answers are correct, you simply will never ever get an ABG or acid base balance question wrong.

Good luck!

I have remembered the *nonsense* like the ROME mnemonic and it has saved me on many tests. I see the values, that saying pops in my head and I figure it out real quick and move on.

[Intern67]

Note to Vida Loca and everyone,

I posted my response to the OP before seeing the previous responses. My characterization of the use of memory tools as "nonsense" was in no way a response to your posts (as I had not seen them). I was trying to reinforce the idea that knowing the underlying processes was very beneficial.

In reading the thread, it looks like I am responding to your posts, but I was not. Of course I use mnemonics as much as any other nursing student, but in the case of ABGs, my personal experience with other students is that they should be used after the basics are understood.

Thanks!

[~Mi Vida Loca~RN, ASN, RN]

Intern67 said:

Note to Vida Loca and everyone,

I posted my response to the OP before seeing the previous responses. My characterization of the use of memory tools as "nonsense" was in no way a response to your posts (as I had not seen them). I was trying to reinforce the idea that knowing the underlying processes was very beneficial.

In reading the thread, it looks like I am responding to your posts, but I was not. Of course I use mnemonics as much as any other nursing student, but in the case of ABGs, my personal experience with other students is that they should be used after the basics are understood.

Thanks!

It did look like that, thanks for clearing that up. I do agree you need to know the why's, but I also think when you're in your timed test and you see a question like "The values on the patient are XXXX are they in Resp. Alkalosis, Resp. Acidosis, Metabolic Acidosis or Metabolic alkalosis. It's a great tool to think of real quick put the right answer and move on.

Sometimes you might have a question asking what the patient would be in if they were hyperventilating and for that, you need to understand the process to figure it out.

In the real world and cliniclals you absolutely need to know the WHY's as well. What I posted for a quick and easy reference to figure it out on a test when only looking at the values.

[Intern67]

~Mi Vida Loca~ said:

I do agree you need to know the why's, but I also think when you're in your timed test and you see a question like "The values on the patient are XXXX are they in Resp. Alkalosis, Resp. Acidosis, Metabolic Acidosis or Metabolic alkalosis. It's a great tool to think of real quick put the right answer and move on.

Just yesterday, I was in a study group where we reviewed ABG analysis for the final exam. The students who relied on memorization had almost no clue where to even start. The ones who understood the underlying mechanisms had nothing to remember and were able to address the questions without difficulty.

Now, when the test is tomorrow or in a couple hours, you do what you have to do. But if you are just learning, take the long road, it means less studying in the future!