This is an NCLEX practice question on partially compensated vs fully compensated ABGs. This question provides a scenario about arterial blood gas results. As the nurse, you must determine if this is a respiratory or metabolic problem, alkalosis or acidosis along with if it is uncompensated, partially or fully compensated based on the results.
This question is one of the many questions we have practiced in our series called “Weekly NCLEX Question”.
To solve ABGs problems, I like to use the Tic Tac Toe method. If you are not familiar with this method, please watch my video on how to solve arterial blood gas problems with this method.
The Tic Tac Toe method makes solving ABG problems so EASY. However, if the ABG values are partially or fully compensated you must take it a step further by analyzing the blood pH level and which system is trying to compensate. My goal is to show you how to use the Tic Tac Toe method for partially and fully compensated interpretation.
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Lecture on Uncompensated and Compensated (Partial and Full) ABGs
NCLEX Practice Questions on Partially vs. Fully Compensated ABGs
Problem 1
A patient has the following arterial blood gas results: blood pH 7.43, PaCO2 28 mmHg, and HCO3 18 mEq/L. This is known as:
A. Partially compensated respiratory alkalosis
B. Fully compensated metabolic acidosis
C. Partially compensated respiratory acidosis
D. Fully compensated respiratory alkalosis
The first thing you want to do is to pull from your memory bank the normal values for arterial blood gases.
Normal ABG Values to Commit to Memory
<-Acid Base->
pH: 7.35-7.45 (less than 7.35 ACIDOTIC & greater than 7.45 ALKALOTIC)
PaCO2: 45-35 (greater than 45 ACIDOTIC & less than 35 ALKALOTIC)**
HCO3: 22-26 (less than 22 ACIDOTIC & greater than 26 ALKALOTIC)
**PaCO2 values are the opposite…so remember that
***Now when you are dealing with FULL compensation, you will have to further analyze the blood’s pH value to determine if it is a respiratory or metabolic problem. In full compensation, the blood pH will be NORMAL, but you must determine if the value is on the “acidotic” or “alkalotic” side.
How do you do this? Remember that the absolute normal for a blood pH is 7.40, and the normal range for a blood pH is 7.35-7.45. Therefore, if the blood pH falls between 7.35-7.40 it’s on the “acidotic” side and if the blood pH falls between 7.40-7.45 it’s on the “alkalotic” side. Look at the picture below for an illustration.
One thing to keep in mind when trying to understand ABG compensation, is that either the respiratory or metabolic system will always try to increase or decrease itself to help achieve a normal blood pH. For example, if the blood pH is acidic due to respiratory acidosis (a high PaCO2), the metabolic system will try to compensate by keeping bicarbonate (hence increasing the HCO3 level…therefore making itself “alkaline”) and this will help increase the blood pH.
Then ask yourself the following questions to help you start interpreting the values….
Question 1: Is this a respiratory or metabolic problem?
- PaCO2 represents a RESPIRATORY problem
- HCO3 represents a METABOLIC problem
Question 2: Is this acidosis or alkalosis?
- Remember the normal values for acidotic vs alkalotic.
Question 3: Is it uncompensated, partially, or fully compensated?
- Look at the pH: is it normal or abnormal?
- If the pH is ABNORMAL: it is either uncompensated or partially compensated…it will NEVER be fully compensated
- If the pH is NORMAL: it is fully compensated because the body has corrected the problem
Now set-up the problem using the Tic Tac Toe method:
pH: 7.43 (falls within 7.35-7.45) = NORMAL but is on the alkalotic side
PaCO2: 28 (less than 35) = ALKALOTIC
HCO3: 18 (less than 22) = ACIDOTIC
So, we don’t have a tic tac toe, therefore, the values are representing compensation (is it partial or full?).
To determine the type of compensation look at the pH…is it normal or abnormal? It’s NORMAL! Therefore, we have full compensation.
BUT is this a respiratory or metabolic problem (this is where students have trouble)?
To determine this, look at the blood pH:
The blood pH is normal, but it falls on the alkalotic side. Our respiratory system is also alkalotic but our metabolic system is acidotic. The problem is with the respiratory system and the metabolic system is trying to balance out the blood’s alkalotic state by decreasing the bicarb (HCO3) to make things more acidic, which will bring down the blood pH. The blood pH is now normal (so it’s fully compensated), but it’s still on the alkalotic side.
Our answer is: respiratory alkalosis, fully compensated by the means of metabolic acidosis.
Answer is: D
Problem 2
A patient has the following arterial blood gas results: blood pH 7.37, PaCO2 33 mmHg, and HCO3 17 mEq/L. This is known as:
A. Partially compensated respiratory alkalosis
B. Fully compensated metabolic acidosis
C. Partially compensated respiratory acidosis
D. Fully compensated respiratory alkalosis
Pull again for your memory bank to analyze the values. You should determine this:
pH: 7.37 (falls within 7.35-7.45) = NORMAL but it’s on the acidotic side
PaCO2: 33 (less than 35) = ALKALOTIC
HCO3: 17 (less than 22) = ACIDIC
So, we don’t have a tic tac toe, therefore, the values are representing compensation (is it partial or full?).
To determine the type of compensation look at the pH…is it normal or abnormal? It’s NORMAL! Therefore, we have full compensation.
BUT is this a respiratory or metabolic problem?
To determine this, look at the blood pH:
The blood pH is normal, but it falls on the acidotic side. Our metabolic system is also acidotic but our respiratory system is alkalotic. The problem is with the metabolic system and the respiratory system is trying to balance out the blood’s acidotic state by decreasing the carbon dioxide level (PaCO2) to make things more alkaline, which will help increase the blood’s pH from it’s acidotic state….which is has and this is why we have full compensation rather than partial. Note: If the pH was not normal and the HCO3 was still acidotic, it would be partial compensation. On the flip side, if the pH was not normal but the HCO3 was normal, it would be uncompensated.
Our answer is: metabolic acidosis, fully compensated by the means of respiratory alkalosis
Answer is: B
Problem 3
A patient has the following arterial blood gas results: blood pH 7.50, PaCO2 49, and HCO3 30 mEq/L. This is known as:
A. Fully compensated respiratory acidosis
B. Partially compensated metabolic alkalosis
C. Partially compensated metabolic acidosis
D. Fully compensated metabolic alkalosis
Again pull from your memory bank regarding normal values for ABGs as we did in the previous problem and set-up the problem using the Tic Tac Toe method:
pH: 7.50 (greater than 7.50) = Abnormal…ALKALOTIC
PaCO2: 49 (greater than 45) = ACIDIC
HCO3: 30 (greater than 26) = ALKALOTIC
There is a tic tac present: there is a three in a row with base, pH, HCO3 (as seen in the picture above).
We can see that this is a metabolic problem due to alkalosis. But now we must determine if this is uncompensated, partially, or fully compensated?
The pH is abnormal and this rules out full compensation, but is it uncompensated or partial?
To answer this you must look at the system that will attempt to correct the metabolic alkalosis, which would be the respiratory system, hence the PaCO2.
It is normal or abnormal? It is abnormal! Therefore, it is trying to correct the metabolic alkalosis that is presenting but it is unable to because the pH is still abnormal. If the pH was normal then full compensation has occurred.
Now you may be asking yourself what if the PaCO2 was normal? Then it would be uncompensated because the respiratory system isn’t attempting to correct the metabolic alkalosis.
Answer is: B
Need more practice: ABG Practice Questions