Arterial Blood Gas (ABG) Interpretation, part 4: Example problems 9-12

by Cathy Parkes July 17, 2020

Full Transcript

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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