Arterial Blood Gas (ABG) Interpretation, part 1: Introduction, Normal Ranges, Steps in Interpretation

by Cathy Parkes July 17, 2020

Full Transcript

In this video series, I'm going to go over ABG interpretation or arterial blood gas interpretation. So this is a topic that all nursing students will definitely need to know. And my goal is to help you feel very comfortable solving these problems and getting them right on all your exams. So I have a number of resources available on my website to help you. If you can use some extra help with ABG interpretation, I have an ABG interpretation guideline which has all the normal ranges and what it means when things are not in the normal range and how to go about interpreting the ABGs. I also have practice questions on my website that you can work through independently. I have an answer key there as well so you can check your answers. Or you can work through those problems with me because I will be working through all of those problems, one by one, in this video series to make sure everybody is really comfortable with ABGs.

So before I get into specific practice problems, I want to go over some foundational information that's going to be really important for you to know before you get into those practice problems. So let's talk about the three important components of an ABG result that you need to really pay attention to. The first is the pH, and the normal range for pH should be between 7.35 and 7.45. Then we have PaCO₂, which when you see this, I want you to think about the respiratory system. PaCO₂ should be between 35 and 45. And then, lastly, we have bicarb, which is HCO₃. When you see HCO₃, I want you to think about the metabolic system. HCO₃ should be between 22 and 26, okay? So these are the three values that you're going to pay attention to, and you definitely need to know those normal ranges. So what does it mean when these are not within the normal range? Let's talk about that now.

So with pH, if pH is less than 7.35, that is indicative of acidosis in the body, okay? And if pH is over 7.45, that is indicative of alkalosis being present in the body. With just looking at the pH, we don't know who the culprit is. We don't know if it's the respiratory system or the metabolic system. All we know is that we either have acidosis or alkalosis. Then we can read these values to really figure out whether we're dealing with respiratory or metabolic acidosis or respiratory or metabolic alkalosis. So with PaCO₂, if it is under 35, that is indicative of alkalosis. If it is over 45, that is indicative of acidosis. And again, when we're talking PaCO₂, think the respiratory system. For HCO₃, our bicarb, if it is under 22, that is indicative of acidosis. And if it is over 26, that is indicative of alkalosis. And again, when you see HCO₃, I want you to think about the metabolic system. So you have to know this information before you can effectively work on those practice problems and interpret the ABGs.

So I handle ABGs in three steps when I do it. The first step is to determine, based on the pH, whether I'm dealing with acidosis or alkalosis, okay? So I look at the pH, and I determine where are we? Do we have acidosis, or do we have alkalosis? And then the second step is figuring out who's to blame for that acidosis or alkalosis. Is it the respiratory system, or is it the metabolic system? Okay? So if I find out I have acidosis up here from looking at the pH, I need to figure out, is it the respiratory system or the metabolic system to blame? If I find that PaCO₂ is over 45, I've found my culprit, okay? Because if I have a PaCO₂ over 45, that indicates acidosis, and I know the respiratory system is to blame. On the other hand, let's say this is normal, okay? This PaCO₂ level is normal. And down here with bicarb, I have a bicarb that is less than 22. Well, then the metabolic system is my culprit and what is causing my acidosis. So again, first step, do I have acidosis or alkalosis? Second step, who's to blame? Who's acting up? Okay?

So let's say, in our hypothetical example, we have acidosis and the respiratory system is to blame, okay? Sorry, right here. PaCO₂ is over 45. We have respiratory acidosis. The third step in the process is to figure out if we have compensation. So if the respiratory system is acting up and giving us respiratory acidosis, the third step is figuring out if the metabolic system is trying to compensate, is trying to fix the problem. Is the metabolic system just chilling out and not doing anything? Are they trying to compensate, or have they fully compensated for respiratory acidosis acting out? So that will be the third step. So these will become more obvious, and you'll be able to work through these three steps as I work through the practice problems. So I just wanted to share this general information and just my three steps, and we'll go through specific practice problems in my next video. Thanks so much for watching.


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