Arterial Blood Gas (ABG) Interpretation, part 3: Example problems 5-8

by Cathy Parkes July 17, 2020

Full Transcript

We're going to work through some more ABG problems. I have a new pen, so hopefully that'll work better.

Number five, we have a pH of 7.48, PaCO₂ of 31, HCO₃ of 20. First step, do we have acidosis or alkalosis, based on the pH? pH should be between 7.35 and 7.45. Because it is out of range on the high side, we know we have alkalosis. So that is step one. Step two, who's to blame? The respiratory system or the metabolic system? So let's look at PaCO₂ to see if it's the respiratory system acting up. So PaCO₂ should be between 35 and 45. 31 is out of range, and it's out of range on the basic side. So we know right away that we have respiratory alkalosis. So I'm going to write that down here. Now we need to see if the metabolic system is doing anything to compensate for this situation. So HCO₃ should be between 22 and 26. We have an HCO₃ of 20, which is out of range on the low side, so this is acidic so we have respiratory alkalosis. We have the metabolic system trying to compensate, but it is not fully compensated because our pH is out of that normal range. So in this case, we have partially compensated respiratory alkalosis. So write that up here, partially compensated respiratory alkalosis. So again, the metabolic system is trying to compensate. It's acidic, trying to compensate for the alkalosis, but it's not quite getting the job done, okay?

Number 6. pH is 7.45, which we know is actually within range - right? - because our range is 7.35 to 7.45. But it's kind of on the alkalosis side. So it's normal, but it's on the alkalosis side of things, okay? So see what's going on with respiratory system and the metabolic system. So PaCO₂ should be between 35 and 45. 30 is out of range, and it's out of range on the basic side. So we do have respiratory alkalosis going on and let's see what the metabolic system is doing. HCO₃ should be between 22 and 26. It's 19, which is on the low side on the acidic side. So in this case, we have respiratory alkalosis that the metabolic system has compensated for, and they were able to bring the pH up to a normal level. So we have fully compensated respiratory alkalosis in this case. So the respiratory system was acting out, causing this alkalosis, and the metabolic system came in, saved the day, became more acid to help compensate for that and was able to bring that pH into normal range. So again, we have fully compensated respiratory alkalosis. And that's problem six.

Alright. Number seven. We have a pH of 7.32, which is out of range, right? Our range is 7.35 to 7.45. It's out of range on the low side, so we know we have acidosis, so acidosis. Now we need to see who to blame, the respiratory system or the metabolic system. Let's first look at the respiratory system. PaCO₂ is 40 in the normal range because our normal range is 35 to 45, so we have normal respiratory. So we know this is not causing the acidosis. So let's go down here to HCO₃, or the metabolic system should be between 22 and 26. It is out of range on the low side, so it is causing the acidosis. So we have acidosis, and it is caused by the metabolic system. So we have metabolic acidosis. Is it compensated? Is the respiratory system trying to compensate for the issue the metabolic system has caused with metabolic acidosis? No. It's just chilling out in its normal range, right? It's 40. It's not trying to do anything. So in this case, we have uncompensated metabolic acidosis, uncompensated metabolic acidosis.

Alright. Let's do problem eight together. PH is 7.31. So, again, it's out of range, on the low side. So, again, we have acidosis. Let's see who to blame. Alright. So step two. Look at the respiratory system. PaCO₂ is 30 which is out of range, right? The range should be between 35 and 45. It's out of range on the low side, so it is basic-- or you could say alkalosis. Those are kind of interchangeable.

Now let's see what the metabolic system is doing. We should have somewhere in the range between 22 and 26. It is low. It is out of range on the low side, so we have acidosis here. So we know that the metabolic system is responsible for the acidosis. And we can also see that the respiratory system is trying to compensate, right? The respiratory system is becoming more basic, more alkaline, to try to compensate for this metabolic acidosis, but it has not been able to fully do the job because our pH is still out of range. So in this case, we have partially compensated metabolic acidosis-- so partially compensated metabolic acidosis. So the metabolic system is responsible for the acidosis. The respiratory system is trying to compensate by becoming more basic, but it has not fully done the job because our pH is still out of range. Okay. We'll pick it up with more problems soon!


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