Can you help me to understand Acid- Base Balances?

itk3838 · Jul 19, 2012

Is it all depends on pH level? I don't see any good charts on this subject.

Anne36, LPN · Jul 19, 2012

Only thing I can remember from school is what you have posted. How to determine the type of acid-base imbalance.

chris1309 · Jul 19, 2012

Hello everyone!
It took me a while to understand Acid-Base Imbalances. I still don't understand how to figure out about compensation. Please help... after step 3, it' s all blurry.
Step 1:
Evaluate pH
pH
pH >7.45 - Alkalosis
Step 2:
Evaluate pCO2
>45 pCO2 - Respiratory Acidosis
Step3:
Evaluate HCO3
>26 - HCO3 - Metabolic Alkalosis
Step 4:
?
How do you determine compensation? If pH is within normal limits - compensation has occur but what happens if it's not?
Thank you!
ITK

Look at this site

http://www.ed4nurses.com/abgtoday.aspx

oluchika · Jul 19, 2012

This is the document my professor told us to download on ABGs last semester. I liked it because it breaks down each part.

http://orlandohealth.com/MediaBank/Docs/SLP/2010%20ABG%20SLP.pdf

BBRANRN2013, ASN, RN · Jul 19, 2012

If both HC03 and PC02 are abnormal then the body is compensating so then you look at pH again. If the pH is within normal limits then it is Fully compensating if it is not within normal limits then it is partially compensating:-)

itk3838 · Jul 19, 2012

Oluchika!!! I love your professor, he wrote very detailed explanation that even review books don't have!!! Priceless!!! Thank you so much!!! I finally got it!!! :bow:

itk3838 · Jul 19, 2012

SoonToBeRN2013 - in very short sentence you explained very easy way to remember. For me it was hard to understand what "compensation" stands for. Saunders has only 2 sentences that it is very confusing to apply in real problems. Thank you! :)

begosh · Jul 19, 2012

[color=#b22222]@oluchika[color=#b22222] - this is the best abg interpretation! thank you so much for sharing. i have read sooooo many books and online resources and still had difficulty understanding the breadth and depth of abgs. pdf file you posted was by far, very clear and easy to comprehend and absorb.

studentdrtobe · Jul 19, 2012

Use a systematic, step-wise approach to acid-base physiology:

1) What's the pH? If it's below 7.35, it's acidosis. If it's above 7.45, it alkalosis. Now, you've established whether the patient is within normal limits, acidotic, or alkalotic. Simple so far, right?

2) Next, you want to figure out whether that acid/base disturbance is metabolic in origin or respiratory in origin.

3) If it's metabolic in origin, you'll see changes in bicarb levels. If it's respiratory in origin, you'll see changes in pCO2. Decreases in bicarb would be mean metabolic acidosis, while increases in bicarb would mean metabolic alkalosis. Increased pCO2 means respiratory acidosis, while decreased pCO2 means respiratory alkalosis. Keeping up with me so far?

4) Now, to compensatory mechanisms. An easy way to remember this is that compensation will always be the opposite of what the primary disturbance is. For example, if the primary disturbance is metabolic acidosis (ex. DKA), the compensatory mechanism will be respiratory alkalosis -- what that means is that respiration rate is going to increase and because of increased ventilation rate, the pCO2 is also going to drop. Another example would be if a patient is in metabolic alkalosis, for example from excessive vomiting or something like that. In this case, the compensatory mechanism will be the opposite of metabolic alkalosis -- respiratory acidosis. So, you'll see decreased ventilation rate and an increase in pCO2.

This is the just basic gist of acid/base mechanisms. It gets a bit more complicated when you're dealing with mixed disorders, but the same basic principles still apply.

If you want to get a true, conceptual understanding of why all these things occur, all you need to understand, simply, is the carbonic anydrase mechanism and Le Chatelier's Principle from basic chemistry:

CO2 + H2O H2CO3 H+ + HCO3-

If you have metabolic acidosis, and HCO3- decreases, the reaction is going to be pushed to the right because of Le Chatelier's Principle (essentially to re-establish equilibrium). If the reaction is pushed to the right, we'll see a decrease in pCO2. So, what does that equation and concept tell us? With metabolic acidosis, we see a respiratory compensation where pCO2 drops -- respiratory alkalosis. Same idea with metabolic alkalosis -- HCO3- increases, so the reaction will be pushed to the left this time in order to re-establish equilibrium. What happens if the reaction is pushed to the left? There will be a rise in pCO2. And that's what the normal compensatory mechanism for metabolic alkalosis is -- respiratory acidosis! Same rules will apply when approaching disturbances due to respiratory issues.

Does all of that make sense? If you approach it with the above equation and concept in mind and go through each scenario in a systematic, step-wise fashion, you'll see that it's not so bad at all! Just remember back to what you learned in chemistry class! Hope this helps.

DocsWifey · Jul 19, 2012

The ph range is 7.35-7.45, so if the

ph is greater than 7.40 it's alkalosis

ph is less than 7.40 it's acidosis

Next, find out which organ has the problem: lungs or kidneys? pCO2 or HCO3 (Bicarb).

lungs: CO2 problem (respiratory)

kidneys: bicarb problem (metabolic)

If only one organ is the issue it's pretty easy, for example ph is in acidosis, CO2 is messed up -> respiratory acidosis

If both organs (lung and kidneys) have the problem (CO2 and HCO3 are messed up), you have to look which one matches the ph! If the ph is in acidosis and the bicarb is in acidosis too, then it's metabolic acidosis with partial compensation ( ph is trying to compensate, but is not fully there)

If both organs (lungs and kidneys) have a problem (CO2 and HCO3 are messed up), and the ph is within normal range (7.35-7.45), you have to look on which side (acidosis or alkalosis) within the normal range. Look up, I said the ph is greater or less of 7.40 -> alkalosis/acidosis. So let's say it's on the acid side but within normal range (7.35-7.40). Now check again which organ problem matches the ph. If it's the kidneys (bicarb), then it's a metabolic problem, therefore the patient is in metablic acidosis with fully compensation (fully comensated because the ph is normal)

itk3838 · Jul 20, 2012

The ph range is 7.35-7.45, so if the
ph is greater than 7.40 it's alkalosis
ph is less than 7.40 it's acidosis
Next, find out which organ has the problem: lungs or kidneys? pCO2 or HCO3 (Bicarb).
lungs: CO2 problem (respiratory)
kidneys: bicarb problem (metabolic)
If only one organ is the issue it's pretty easy, for example ph is in acidosis, CO2 is messed up -> respiratory acidosis
If both organs (lung and kidneys) have the problem (CO2 and HCO3 are messed up), you have to look which one matches the ph! If the ph is in acidosis and the bicarb is in acidosis too, then it's metabolic acidosis with partial compensation ( ph is trying to compensate, but is not fully there)
If both organs (lungs and kidneys) have a problem (CO2 and HCO3 are messed up), and the ph is within normal range (7.35-7.45), you have to look on which side (acidosis or alkalosis) within the normal range. Look up, I said the ph is greater or less of 7.40 -> alkalosis/acidosis. So let's say it's on the acid side but within normal range (7.35-7.40). Now check again which organ problem matches the ph. If it's the kidneys (bicarb), then it's a metabolic problem, therefore the patient is in metablic acidosis with fully compensation (fully comensated because the ph is normal)

Dear DocsWifey,

I would like to ask you, if pH is only one measurement to show compensation?