ABG Interpretation, part 10: Example problems 9-12

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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 9

A patient's arterial blood gas measurements read pH = 7.35, PaCO₂ = 30, HCO₃ = 19. 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. 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 30mm Hg, which is out of range on the alkalotic side, which is in the opposite direction as pH.
    2. Since the PaCO₂ is in the opposite direction as pH, we know it is not the respiratory system causing it.
    3. Therefore, the metabolic system is causing the acidosis and we have METABOLIC ACIDOSIS.
  3. Check if there is compensation. Because it's metabolic acidosis, it's the respiratory system that would be compensating. The respiratory system is represented by PaCO₂. So we'll check PaCO₂ again to check for compensation. Again, the normal range for PaCO₂ is 35 - 45 mmHg.
    1. The PaCO₂ here is 30 mmHg, which is out of range on the alkalotic side. This means there is respiratory compensation.
    2. To determine if the compensation is partial or full, we check the pH again. The pH was 7.35 which is normal but on the acidic side, so the respiratory system has succeeded in fully compensating.
    3. Therefore, we have FULLY COMPENSATED METABOLIC ACIDOSIS.
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ABG practice question 10

A patient's arterial blood gas measurements read pH = 7.48, PaCO₂ = 41, HCO₃ = 29. 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 7.48, which is out of range on the alkalotic side. Therefore, 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 41 mmHg, which is normal.
    2. Since the PaCO₂ is normal, we know it is not the respiratory system causing it.
    3. Therefore, the metabolic system is causing the alkalosis and we have METABOLIC ALKALOSIS.
  3. Check if there is compensation. Because it's metabolic alkalosis, it's the respiratory system that would be compensating. The respiratory system is represented by PaCO₂. So we'll check PaCO₂ again to check for compensation. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. Again, the PaCO₂ here is 41 mmHg, which is within the normal range. This means there is no compensation.
    2. Therefore, we have UNCOMPENSATED METABOLIC ALKALOSIS.

ABG practice question 11

A patient's arterial blood gas measurements read pH = 7.50, PaCO₂ = 50, HCO₃ = 30. 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 7.50, which is out of range on the alkalotic side. Therefore, 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 50 mmHg, which is out of range on the acidic side, which is in the opposite direction as pH.
    2. Since the PaCO₂ is in the opposite direction as pH, we know it is not the respiratory system causing it.
    3. Therefore, the metabolic system is causing the alkalosis and we have METABOLIC ALKALOSIS.
  3. Check if there is compensation. Because it's metabolic alkalosis, it's the respiratory system that would be compensating. The respiratory system is represented by PaCO₂. So we'll check PaCO₂ again to check for compensation. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. Again, the PaCO₂ here is 50 mmHg, which is out of range on the acidic side. This means there is respiratory compensation.
    2. To determine if the compensation is partial or full, we check the pH again. The pH was 7.50 which is out of range on the alkalotic side, so the respiratory system has not succeeded in fully compensating.
    3. Therefore, we have PARTIALLY COMPENSATED METABOLIC ALKALOSIS.

ABG practice question 12

A patient's arterial blood gas measurements read pH = 7.44, PaCO₂ = 49, HCO₃ = 28. 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 7.44, which is normal but on the alkalotic side. Therefore, we have probable 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 49 mmHg, which is out of range on the acidic side, which is in the opposite direction as pH.
    2. Since the PaCO₂ is in the opposite direction as pH, we know it is not the respiratory system causing it.
    3. Therefore, the metabolic system is causing the alkalosis and we have METABOLIC ALKALOSIS.
  3. Check if there is compensation. Because it's metabolic alkalosis, it's the respiratory system that would be compensating. The respiratory system is represented by PaCO₂. So we'll check PaCO₂ again to check for compensation. The normal range for PaCO₂ is 35 - 45 mmHg.
    1. Again, the PaCO₂ here is 49 mmHg, which is out of range on the acidic side. This means there is respiratory compensation.
    2. To determine if the compensation is partial or full, we check the pH again. The pH was 7.44 which is normal but on the alkalotic side, so the respiratory system has succeeded in fully compensating.
    3. Therefore, we have FULLY COMPENSATED METABOLIC ALKALOSIS.

Full Transcript: ABG Interpretation, part 10: Example problems 9-12

We're back with more ABG interpretation problems. So we're on problem nine. The pH in this problem is 7.35, which we know is within range, right? Our range is 7.35 to 7.45. It's in range, but it's kind of on the acidic side. So let's just write that up. So we have a normal pH, but it's on the acidic side of things. So let's see who may be contributing to that acidosis. PaCO₂ is 30, which the PaCO₂ should be between 35 and 45, so it is low on the basic side. So we know that's not really responsible for the slight acidosis, right? So let's see what the metabolic system is doing. HCO₃ should be between 22 and 26, but it is low on the acidic side. So we know that we have metabolic acidosis that the respiratory system has fixed, and it has fully compensated for that metabolic acidosis because our pH is within normal range. So again, we've got acidosis that was caused by the metabolic system, which is represented by HCO₃. But the respiratory system has come in to save the day. It has become more basic to kind of counteract that acidosis, and it has brought the pH into a normal range. So in this case, we have fully compensated metabolic acidosis.

Alright. Number 10. We have a pH of 7.48. So our normal range is 7.35 to 7.45. It is out of range on the high side, so we have alkalosis here. Now we need to see who's to blame for this alkalosis. Is it the respiratory system, or is it the metabolic system? So with the respiratory system, we have a value of 41. So this is within the normal range - right? - which is between 35 and 45. So the respiratory system is normal. It's not acting up or doing anything; it's just chilling out.

Then we get the metabolic system. HCO₃ should be between 22 and 26. It is 29, so it is out of range on the basic side. So we have metabolic alkalosis so we know we have metabolic alkalosis because its HCO₃ is high on the basic side, and we know it is not compensated at all because the respiratory system, as represented by PaCO₂, isn't doing anything. It's just chilling out. So in this case, we have uncompensated metabolic alkalosis. So just to kind of reiterate, the metabolic system is acting up. It's causing the alkalosis, causing our pH to be too high and the respiratory system isn't doing anything about it. Okay? We'll do the next two problems next.

Alright. So these are the last two problems I'm going to go over. So number 11, the pH is 7.50. So it should be between 7.35 and 7.45, so it is out of range, on the high side which means we have alkalosis. So that's step one. Step two, who's to blame? Respiratory system or metabolic system? So if we look at the PaCO₂, it is out of range. It should be between 35 and 45. But it is 50, so it is out of range on the acidic side. So we know it's not causing the alkalosis, right, because it's acidic. So then, we look at the metabolic system, as represented by HCO₃. It should be between 22 and 26. It is out of range on the high side, so this is to blame. It is basic, or we have alkalosis, in other words. So we have metabolic alkalosis. It is out of range on the high side, causing the alkalosis. So we have metabolic alkalosis. Do we have compensation? So we have partial compensation because the respiratory system is becoming more acidic to help counteract this alkalosis, but it hasn't fully done the job because our pH is still out of range. So we have partially compensated metabolic alkalosis. So the respiratory system is trying, but it hasn't been fully successful because our pH is still out of range. So we have partially compensated metabolic alkalosis.

Alright. And now we got our last problem, number 12. pH is 7.44, which is within range right, it's within 7.35 to 7.45, it's a little bit on the basic side, so we have a normal pH that is a little bit on the alkalosis side. So let's see who might be causing that pH to be a little higher than we would expect. Let's look at the respiratory system first, as represented by PaCO₂. Should be between 35 and 45. It is 49, so it is out of range on the acidic side. So we know it's not causing this pH to be a little bit on the basic side, right, because this is acidic. We look at HCO₃. Should be between 22 and 26. It is out of range on the basic side, or alkalosis side. So we have metabolic alkalosis, because this HCO₃ is out of range on the basic side. We have metabolic alkalosis, and the respiratory system is coming in to save the day by becoming more acidic, and it has done such a good job that we've been able to bring the pH into a normal range. So we have fully compensated metabolic alkalosis.

So just to reiterate, the metabolic system is acting up, causing the alkalosis, but the respiratory system has become more acidic to help compensate, and it has done such a good job that the pH is in normal range. So we have full compensation.

Alright. So those are my 12 problems. Kind of a lot of the different variations you may run into on your test, and then as a nurse, when you are done with school. So hopefully that's helpful. Please leave comments, and let me know if there's any additional help you need. Thanks so much!

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4 comments

this breakdown was easy and so simple to understand thank you for being soo great

miriam

Thank you for this breakdown. If all teachers taught this way the world would be better. I now get it!

T. Fox

Thanks!!! Your videos have really helped me in understanding how to interpret ABG’s. We went through this so fast in the classroom that I was afraid I would forget a step on the test. So, again, THANKS!!!!!!

Roderick

Thanks so much for getting to the meat of the matter. This is nursing explain on level to grasp with all the fillers deleted.THANKS

Blondell Mcclendon

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