ABG Interpretation, part 8: Example problems 1-4

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In this video, Cathy goes through four example ABG Interpretation problems and answers. You can download the questions and answers below to print out and follow along. We've also explained the steps for interpretation below.

Need help interpreting ABGs? Check out our Arterial Blood Gas Interpretation Flashcards for Nursing Students.

PRACTICE QUESTIONS
PRACTICE ANSWERS

ABG practice question 1

A patient's arterial blood gas measurements read pH = 7.29, PaCO₂ = 47 mmHg, and HCO₃ = 24 mEq/L. How would you interpret this?

Steps for interpretation

  1. Check the pH to determine if we have acidosis or alkalosis. The normal range for pH is 7.35 - 7.45.
    1. The pH here is 7.29, which is out of range on the acidic side. Therefore, we have ACIDOSIS.
  2. Determine which system, metabolic or respiratory, is causing the acidosis. Check the PaCO₂, which represents the respiratory system, first. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. The PaCO₂ here is 47 mmHg, which is out of range on the acidic side.
    2. Therefore, the respiratory system is causing the acidosis and we have RESPIRATORY ACIDOSIS.
  3. Check if there is compensation. Because it's respiratory acidosis, it's the metabolic system that would be compensating. The metabolic system is represented by HCO₃. So we'll check HCO₃ to check for compensation. The normal range for HCO₃ is 22 - 26 mEq/L.
    1. The HCO₃ here is 24 mEq/L, which is within normal range. There is no compensation.
    2. Therefore, we have UNCOMPENSATED RESPIRATORY ACIDOSIS
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ABG practice question 2

A patient's arterial blood gas measurements read pH = 7.31, PaCO₂ = 49 mmHg, HCO₃ = 30 mEq/L. How would you interpret this?

Steps for interpretation

  1. Check the pH to determine if we have acidosis or alkalosis. The normal range for pH is 7.35 - 7.45.
    1. The pH here is 7.31, which is out of range on the acidic side. Therefore, we have ACIDOSIS.
  2. Determine which system, metabolic or respiratory, is causing the acidosis. Check the PaCO₂, which represents the respiratory system, first. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. The PaCO₂ here is 49 mmHg, which is out of range on the acidic side.
    2. Therefore, the respiratory system is causing the acidosis and we have RESPIRATORY ACIDOSIS.
  3. Check if there is compensation. Because it's respiratory acidosis, it's the metabolic system that would be compensating. The metabolic system is represented by HCO₃. So we'll check HCO₃ to check for compensation. The normal range for HCO₃ is 22 - 26 mEq/L.
    1. The HCO₃ here is 30 mEq/L, which is out of range on the basic side. This means there is metabolic compensation.
    2. To determine if the compensation is partial or full, we check the pH again. The pH was 7.31 which is outside the normal range, so the metabolic system has not succeeded in fully compensating.
    3. Therefore, we have PARTIALLY COMPENSATED RESPIRATORY ACIDOSIS.

ABG practice question 3

A patient's arterial blood gas measurements read pH = 7.35, PaCO₂ = 48 mmHg, HCO₃ = 29 mEq/L. How would you interpret this?

Steps for interpretation

  1. Check the pH to determine if we have acidosis or alkalosis. The normal range for pH is 7.35 - 7.45.
    1. The pH here is 7.35, which is normal but on the acidic side. This might be acidosis.
  2. Determine which system, metabolic or respiratory, is causing the acidosis. Check the PaCO₂, which represents the respiratory system, first. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. The PaCO₂ here is 48 mmHg, which is out of range on the acidic side.
    2. Therefore, the respiratory system is causing the acidosis and we have RESPIRATORY ACIDOSIS.
  3. Check if there is compensation. Because it's respiratory acidosis, it's the metabolic system that would be compensating. The metabolic system is represented by HCO₃. So we'll check HCO₃ to check for compensation. The normal range for HCO₃ is 22 - 26 mEq/L.
    1. The HCO₃ here is 29 mEq/L, which is out of range on the basic side. This means there is metabolic compensation.
    2. To determine if the compensation is partial or full, we check the pH again. The pH was 7.35, which is within the normal range, so the metabolic system has succeeded in fully compensating.
    3. Therefore, we have FULLY COMPENSATED RESPIRATORY ACIDOSIS.

ABG practice question 4

A patient's arterial blood gas measurements read pH = 7.49, PaCO₂ = 33 mmHg, HCO₃ = 24 mEq/L. How would you interpret this?

Steps for interpretation

  1. Check the pH to determine if we have acidosis or alkalosis. The normal range for pH is 7.35 - 7.45.
    1. The pH here is 7.49, which is out of range on the basic side. So we have ALKALOSIS.
  2. Determine which system, metabolic or respiratory, is causing the alkalosis. Check the PaCO₂, which represents the respiratory system, first. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. The PaCO₂ here is 33 mmHg, which is out of range on the basic side.
    2. Therefore, the respiratory system is causing the alkalosis and we have RESPIRATORY ALKALOSIS.
  3. Check if there is compensation. Because it's respiratory alkalosis, it's the metabolic system that would be compensating. The metabolic system is represented by HCO₃. So we'll check HCO₃ to check for compensation. The normal range for HCO₃ is 22 - 26 mEq/L.
    1. The HCO₃ here is 24 mEq/L, which is within the normal range. There is no compensation.
    2. Therefore, we have UNCOMPENSATED RESPIRATORY ALKALOSIS.

Full Transcript: ABG Interpretation, part 8: Example problems 1-4

Starting in this video, we are going to start going over some ABG interpretation problems. We're going to go through a lot of problems and try to hit all the different variations you may get. So let's start with problem number 1. And again, you can download these problems from our website, leveluprn.com, and kind of follow along with me. There is also an answer key on the website. So if you want to later work through these problems independently and check your answers, you can do that.

So problem number one, pH is 7.29, PaCO₂ is 47, HCO₃ is 24. So step one is figuring out if we have acidosis or alkalosis. So let's look at the pH for that. So pH should be between 7.35 and 7.45. But it is out of range on the low side, which means we have acidosis. So that's step one, all done, acidosis. Now, second step, we need to figure out who's to blame for that acidosis. Is it the respiratory system, or is it the metabolic system? Right? So the respiratory system, we're going to be looking at PaCO₂; metabolic system, we're going to be looking at HCO₃. So when we look at PaCO₂, we see we have 47. The normal range for PaCO₂ is between 35 and 45. If we are too high out of that range on the high side, then we have acidosis. So in this case, we know that the respiratory system is to blame for the acidosis, okay? So we have respiratory acidosis. Now we need to see if the metabolic system is trying to compensate for that. Are they trying to fix the problem? So our normal HCO₃ level should be between 22 and 26. And here we have 24, so it's totally within normal range. So the metabolic system is not doing anything to fix the situation. We have just kind of normal HCO₃ level. So in this case, we have uncompensated respiratory acidosis. So the respiratory system is causing the acidosis, and the metabolic system isn't doing anything to fix the situation, so uncompensated respiratory acidosis. Hopefully, you can read that okay.

Alright. Let's do another problem. Here, with problem two, we have a pH of 7.31. Again, this is out of range on the low side, which means again we have acidosis. So that's step one. Now we're going to figure out, is it the respiratory system to blame, or is it the metabolic system to blame? We look at the PaCO₂ to evaluate whether the respiratory system is to blame. PaCO₂ should be between 35 and 45. When it is high, when it is out of range on the high side, we have acidosis. So we know again in this situation that we have respiratory acidosis. Now let's look and see if the metabolic system is trying to fix the situation. HCO₃ should be between 22 and 26. In this case, it's 30, so it's on the basic side. So it is trying to compensate for this acidosis. Respiratory system is acting up, causing this acidosis. The metabolic system is basic, so it's trying to neutralize the situation. But does it fully compensate for the situation? No, because here you can see the pH is 7.31. It's not within normal range. So in this case, we have partially compensated respiratory acidosis. Metabolic system is trying to compensate but hasn't fully compensated so, again, partially compensated respiratory acidosis. okay! So that's problem two. And we will pick it up with more problem sets.

Okay, problem three. We have a pH of 7.35, PaCO₂ of 48, and HCO₃ of 29. So let's first look at the pH, see if we have acidosis or alkalosis. You'll notice that 7.35 is within the normal range for pH, but it is on the acidic side. So we have a normal pH, but we'll want to note that it is on the acidic side, okay? So let's see what's going on with the respiratory system. PaCO₂ is 48, which is out of range, on the acidic side. So we have some respiratory acidosis going on. Let's see what the metabolic system is doing about the situation. So the metabolic system is HCO₃, it should be between 22 and 26, and it is high, right? It's 29, which is out of range on the basic side. So the metabolic system is fixing the situation, right? We have respiratory acidosis, the metabolic system is making it more basic, and it is fully compensating for this because our pH is within normal range. So again, respiratory system is acting up, causing respiratory acidosis. Metabolic system saves the day by becoming more basic, and it basically fixes the situation because we have a pH that's within the normal range, 7.35 to 7.45. So in this case, we have fully compensated respiratory acidosis. Alright. That's problem three.

Let's do problem four. pH is 7.49. PaCO₂ is 33. HCO₃ is 24. So let's first determine do we have acidosis or alkalosis? It's always our first step. So in this case, our pH should be between 7.35 and 7.45. It is out of range on the high side, which means we have alkalosis. Now let's see who is to blame for the alkalosis, right? So our pH is alkalosis, which is like another word for being basic. So let's see if the respiratory system is to blame or the metabolic system is to blame. PaCO₂, again, represents the respiratory system, should be between 35 and 45. It is 33, so it is out of range on the low side, which means we have alkalosis and we have respiratory alkalosis. So right off the bat, we know that the respiratory system is to blame for the alkalosis. Now we need to check and see if the metabolic system is trying to compensate at all. If it is trying to compensate, then we'll see that it is acidic, okay? HCO₃ should be between 22 and 26. Our value is 24, so it's within normal range. So it's not basic; it's not trying to compensate. This is normal. So for this problem, we have uncompensated respiratory alkalosis, okay? Respiratory system is acting up, causing the alkalosis, and the metabolic system is not saving the day. They're not even trying because we have a normal HCO₃ level. So in this case, we have uncompensated respiratory alkalosis. Alright. That's problem four. We'll pick it up with more next!

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2 comments

This is so helpful, no need to know which arrow is moving in the same direction or opposite direction. Thank you.

JEM

I struggle with whether an ABG is compensated, uncompensated, or partially compensated. The interpretations here really helped. Thank you!

Tameasha

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