Acid-Base Balance

Double-Helix, BSN, RN · Apr 6, 2012

Your normal pH range is 7.35-7.45. The median is 7.4

If your pH falls within the normal range (between 7.35 and 7.45) then it is compensated. For example, if your pH is 7.37 and your CO2 is 55, then it's compensated respiratory acidosis. If your pH is 7.31 and your CO2 is 55, then it's uncompensated respiratory acidosis.

ABG Interpretation Method

Arterial Blood Gases Made Easy

These might help. Also, feel free to PM me with other questions regarding ABG's. I had such a hard time understanding them in nursing school until one day it just clicked. I'd be happy to help.

SubSippi · Apr 6, 2012

This is my pharm teacher's step-by-step method for acid/base. First, list all the lab values, then:

1. Is the pH high, low, or normal?

-If it is > 7.4, write a "B" beside it for basic.

-If it is

*If the pH is normal (7.35 - 7.45), write an (N) beside the A or B. This will help determine if the disorder has been fully compensated.

2. Is the PaCO2 high, low, or normal?

-If it is > 45 mmHg, write a "A" beside it for basic.

-If it is

3. Is the HCO3 high, low, or normal?

-If it is > 27 mEq/L, write a "B" beside it for basic.

-If it is

Interpreting:

1. Two "As" = acidosis. If one of the "As" is CO2, then the disorder is respiratory. If one of the "As" is HCO3, then the disorder is metabolic. In both cases, the other A is the pH.

2. Two "Bs" = alkalosis. If one of the "Bs" is CO2, then the disorder is respiratory. If one of the "Bs" is HCO3, then the disorder is metabolic. In both cases, the other B is the pH.

3. Three "As" or "Bs" = a mixed disorder. All "As" indicates mixed respiratory and metabolic acidosis. All "Bs" indicates mixed respiratory and metabolic alkalosis.

Determine the compensation:

1. Uncompensated: the unpaired value is within normal limits. The fact that it has not changed means your body is not reacting, or "compensating," for the imbalance.

2. Partially compensated: the unpaired value is the opposite letter, of the pairs but the pH is still abnormal. This shows that your body is trying to compensate. But since the pH is still abnormal, the problem hasn't totally been fixed yet.

3. Fully compensated: the unpaired value is the opposite letter, and the pH is within normal limits. Since the pH is normal, your body has "compensated" for, or fixed, the problem.

I hope this can help!

KelRN215, BSN, RN · Apr 7, 2012

If the pH is in the normal range, it is always compensated. Think about what compensation means- one component is out of whack and the other component works to get the pH back to normal.

Both the PaCO2 and HCO3 are abnormal when it's "compensated" but the pH is within the normal range. One was abnormal to begin with and the other one became abnormal during the compensation process, which is what brought the pH back to normal.

Normal values are as follows:

pH: 7.35-7.45

PaCO2: 35-45

HCO3: 22-26

Say you have a patient who's pH is 7.32, CO2 49 and HCO3 24. What are you looking at? The pH is low, so it's some form of acidosis. Where is it coming from? CO2 is the acid and HCO3 is the base. Your CO2 is high, so you have too much acid. Your HCO3 is within the normal range and your pH is abnormal, so there's no compensation. So here, you're looking at uncompensated respiratory acidosis.

This may be a helpful website:

ABG interpreter - calculator