Alright, welcome everybody back to another video lesson from ICU Advantage. And this is going to be our third lesson in our series of lessons on arterial blood gases. And in this lesson, this is really going to be the...
meat and potatoes of what we've been trying to build up to at this point, which is our ABG interpretation. And my name is Eddie Watson and I'm gonna be your presenter for this series of lessons. And as always, in order to stay up to date with our lessons, make sure and subscribe to our channel below.
This way you'll be notified as soon as a new lesson is available. Alright, so to start this lesson off, we're gonna start with a little bit of an introduction. And this is going to be a primer of information that's going to become really important when we start looking at these ABGs and how we do our interpretation. And so the first of these is to know that the body has a normal pH value of 7.4.
And so our bodies, in order to maintain this normal pH, they'll use several mechanisms in order to keep that pH in that ideal normal range. And when we look at these different mechanisms, really the key component to maintaining that normal pH is going to be what we call the bicarbonate buffering system. And this system really involves the blood, lungs, and kidneys.
And we did talk about this bicarbonate buffering system in the previous lesson, which I'm going to link to up above. But we do have these two primary organs, which are going to respond to those changes to help correct any pH disturbances. And like I said, those are going to be the lungs and the kidneys. And so with our lungs, the first thing they can do is they can breathe faster or with a larger tidal volume. And what this is going to do is make the blood more alkaline in response to a state of acidosis.
And in contrast to that, we can breathe slower or with a reduced tidal volume to help lower the pH and create a more acidic environment. in response to a state of alkalosis. And one of the important things to know about this compensation mechanism is that this happens fast. We can quickly change our respiratory rate or that volume of inspired air, and we can pretty quickly make adjustments to our body's pH because of it.
And so when we look at our kidneys and how they're going to respond to these changes in pH, what we're going to see the kidney do is they can either reabsorb more or less bicarb depending on whatever the disturbance is that's going on inside of our body. And so if we absorb more bicarb, we're going to increase our pH, as opposed to if we absorb less bicarb, then we're going to see our pH fall. Now this compensation mechanism, unlike the process that's happening in the lungs, is actually a slow process. And so we're not often going to see these changes manifest themselves right away, but over time, over the course of many hours or sometimes even days. And so there are really a couple important things that I need to point out to you guys here.
And it really relates to the point that I just made about the lungs and the kidneys and how their different compensation mechanisms ultimately impact our body's pH. And the first of these is to know that carbon dioxide or CO2, as we had talked about in the previous lesson, is acidic and thus it's going to lower our pH. And changes in this CO2 are what we associate with a primary respiratory disorder. On the other hand, our bicarb, or HCO3 negative, as we talked about, is alkaline, and therefore it will actually raise our body's pH. And alterations in our bicarb are what we associate with primarily metabolic disorders. And so it's really important that you guys understand this because when you're looking at your ABGs and trying to determine what's going on and what sort of compensation mechanism is taking place, you really have to understand which direction our body's pH is going to adjust based on either our CO2 or our bicarb. All right, and so with that said, let's go ahead and talk about the primary alterations in our body's pH that we're going to see. And the first of these is going to be what we call respiratory acidosis.
And so with this one, we have a primarily respiratory dysfunction that has led us to be in a state of acidosis. And so really what this means for us is that we have an increased amount of CO2, and like we said, which is an acid, and therefore along with that, we're going to find ourselves with a decreased pH. And what this tells us is that the lungs are not sufficiently ventilating, and therefore that CO2 is going to be building up in our lungs. This leads to an... increase in those hydrogen ions within that blood lowers our pH and leads to a state of acidosis. So now on the other end of the spectrum, we're going to talk about respiratory alkalosis.
And so what's happening here is the lungs are actually overventilating or blowing off the CO2 from the blood. And this is going to, again, lead to a decrease in the hydrogen ions in the blood, leading to a higher pH and ultimately a state of alkalosis. And so essentially we have a decreased CO2, so less of an acid around, which is going to lead to an increase in our pH. Alright, and so moving on, the next of these that we're going to talk about is what we call metabolic acidosis. And so what's happening here is we actually have a decreased amount of bicarb within our blood, and thus less of an alkaline around. This is going to make us more acidic, and therefore lower our pH. And this can really be the result of many disorders, anything from within the GI system, endocrine, renal, nutrition, or other sorts of things.
And now again, on the opposite end of this, we have what we call metabolic alkalosis. And here, when the bicarb level is raised in the blood, we're going to have more of that alkaline around, leading to an increase in our pH. And again, this can really be caused by a whole host of different things. And so really the last thing that I want to cover within this introduction here is I want to list out across the bottom here what our normal values for an ABG are.
Because in order to successfully be able to interpret your ABGs, you're going to have to memorize and know what these normal values are. So the first of the values that we're going to see on our ABG is going to be our pH. And this is going to be with a normal value of 7.35 to 7.45. The next value we're going to see is the partial pressure of the arterial oxygen or the PaO2, and this is going to have a normal value between 80 and 100. From there the next value that we're going to look at is the partial pressure of the arterial CO2 or the PaCO2, and this one's really easy to remember because it goes right along with our pH, and this is going to be a normal value of 35 to 45. And finally, the last value that we're going to look at here is going to be our bicarb or HCO3 negative. And again, our normal value for this is going to be 22 to 26. Now, there are going to oftentimes be other numbers that you get with your ABG results.
And those certainly are important to know and understand what's going on. But for the purpose of this lesson and this ABG interpretation, we're not going to be looking at these other values. Alright, so with that out of the way, let's go ahead and move on to the steps for basic interpretation.
And so for this, we're going to be looking at performing our basic ABG interpretation. No matter what's going on with your ABG and with your patient, you're always going to start with these first four steps in order to begin to analyze what's happening. Now, one thing that's really important here is you're going to get a lot of information on those ABG results.
And a couple big things that we often care a lot about are going to be the partial pressure of the arterial oxygen and the oxygen saturation. And these absolutely are important for assessing our patient's oxygenation status, but they really play no part in our interpretation of the ABG. And so moving forward, you're going to see these numbers here, but we're often going to just disregard those for the purpose of this ABG interpretation.
And I know that sounds a little funny. And again, I don't mean to... diminish their importance because, again, they play a vital role in determining how our patient's oxygenation is going. But again, for those steps in determining are we in a respiratory acidosis or metabolic alkalosis or what's going on with our patient, they're not going to have any part in that.
And so when we go to go through these steps of this basic interpretation, there's really four main steps that we're going to go through. One, two, three, and four. And so for our first step, we actually want to look at the pH and determine is it normal, acidic, or alkalotic.
And so if we find we have a pH that's less than 7.35, then this is going to mean we have an acidosis. Whereas if we find that we have a pH that's greater than 7.45, then this means we have alkalosis. Now for step two, what we're going to want to do is assess our CO2.
So again, if we think about those normal values, 35 to 45, if we're greater than 45, we're going to be high. And if we're less than 35, we're going to be low. Now for step three, we're going to do the same thing, but this time assessing our bicarb. So again, we know the normal range 22 to 26. So if we're less than 22, then we're going to be low.
And if we're greater than 26, then we're going to be high. Now finally here for step four, we want to determine is this respiratory or metabolic. And so in the presence of an abnormal pH, we want to look and see which of our values is abnormal.
Is it the CO2 or is it the bicarb? And so if it's the CO2 value that's abnormal, like we had talked about, this means that we have a primarily respiratory-driven problem. On the other hand, if it's the bicarb that's the abnormal value, and again, we have a pH that's outside that normal range, we know that it's a metabolic process that's driving things.
And so there is actually a pretty popular acronym that really can help you to memorize, is this a respiratory or metabolic issue? And it's something that we call ROAM. And what this stands for is respiratory opposite, metabolic equal. And what this really is trying to tell us is how is the pH going to respond in response to whichever one of our two molecules is the one that's in an abnormal range.
And so what will happen is the pH will rise in the opposite direction of CO2. So if our CO2 is high, think more of an acid, the pH is going to lower. And vice versa, if our CO2 is low, we have less of an acid, so our pH is going to rise.
And that's where we get the respiratory opposite from. But in contrast to that, the pH is actually going to go in the same direction as the change in our bicarb. So again, think if you have more bicarb around, you have more of an alkaline, therefore leading to a rise in our pH. But on the other hand, if you have less bicarb around, you're going to have you're going to have less of an alkaline around, and therefore you're going to see a lower pH. And so again, the pH is going to move equal to or in the same direction as a metabolic problem.
And hopefully that makes sense with that acronym, because we are going to be using that moving forward. And so let's do that now. Let's go ahead and move on with some examples to really help solidify those four steps for you. And so in each of these examples, we're going to be looking at our pH. our PaO2, our PaCO2, our bicarb, and our oxygen saturation. All right, so for this first example, we're going to walk through it slowly and go through each of these steps one by one and really show you how we're doing this.
So for this example, we're going to have a pH of 7.38, a PaO2 of 110, a PaCO2 of 42, a bicarb of 23, and oxygen saturation of 98%. Now, as we talked about, for the purpose of this ABG interpretation, we're not going to pay much attention in these steps to our PaO2 and our oxygen saturation, but we will look at and analyze these other values here. So for step one, if you remember, we're going to take a look at our pH and determine is this acidosis or alkalosis. So in this case, we have a pH of 7.38.
And if you remember or look down here at the bottom, you see our normal value is 7.35 to 7.45. You actually can see that this pH value is normal. So now moving on to step two, we're going to want to assess our carbon dioxide.
And here we have a value of 42. So again, if you remember or look down at the bottom, you see our normal value is 35 to 45. Well, once again... this value is going to be within that normal range. And so now moving on to step three, we're going to assess our bicarb.
And so here we have a bicarb of 23. And so again, if you remember or referencing down below, our normal bicarb is 22 to 26. Well, once again, this value falls within that range, and therefore it's a normal value. And this brings us to a point, which is something that we hadn't talked about yet. But if you reach step three and you have... A normal pH, a normal CO2, and a normal bicarb? Well, guess what?
You've got a normal ABG. All right, so let's go ahead and move on to another example here. So here we're going to have a pH of 7.27, a PaO2 of 80. a PaCO2 of 53, a bicarb of 24, and an oxygen saturation of 94%. So again, for the purpose of this interpretation, we're going to go ahead and ignore our PaO2 and our oxygen sat. And so to start with step one, we're going to look at our pH and determine is this acidosis or alkalosis.
Here we have a pH of 7.27. Again, we know our normal value is... 7.35 to 7.45, and so this time our value is actually lower than the normal values, therefore meaning that this is a more acidic environment, therefore we have a state of acidosis.
So now on to step two, we're going to assess our CO2. Here we have a CO2 of 53, and again we know our normal value is 35 to 45, so at this point we see that our CO2 is higher than the normal range. Perhaps that might mean something. Now, moving on to step three, we're going to assess our bicarb.
And in this case, we have a bicarb of 24. Again, we know our normal bicarb is 22 to 26. Therefore, this bicarb is actually normal. So now at this point, we don't have a normal ABG. And so we're going to move on to step four, which is determining, is this a primarily respiratory or metabolic disturbance?
And so if you remember, we want to look and find out which value is abnormal in the presence of an abnormal pH. So now in this example, I think it's pretty clear. We do have an abnormal pH, and the value that's abnormal is going to be our CO2. And if you remember, we said that CO2 is a primarily respiratory disturbance. And so based on that, we can actually make a determination of what this ABG interpretation would be.
But again, we also can use the acronym ROAM. R-O-M-E, respiratory opposite metabolic equal. And here we can see that we have a decrease in our pH, but an increase in our CO2 going the opposite direction. Therefore, this must be a respiratory problem.
And so putting all that together, we then can determine that in this case, our patient has a respiratory acidosis. All right, hopefully that made sense of what we did there as we went through those steps. But we are going to go through some more examples to help solidify that for you. So for this next example, we're going to have a pH of 7.51, a O2 of 95, a CO2 of 29, a bicarb of 22, and an oxygen saturation of 97%.
Once again, we're going to go ahead and disregard our PaO2 and our oxygen saturation. And so again, back to step one, we're going to look at our pH of 7.51. We know our normal value is 7.35 to 7.45.
Therefore, in this case, our pH is high, meaning we have an alkalosis. For step two, we're going to assess our CO2. And here we have a CO2 of 29. Again, knowing our normal CO2 is 35 to 45, we can then determine that this CO2 value is actually low. And finally, for step three, we're going to look at our bicarb, see that our bicarb is 22. Again, our normal is 22 to 26. Therefore, in this example, while we're... close to being out of range, our bicarb is actually still normal.
And so now at this point, we don't have a normal ABG. So we're going to go on to step four and determine is this respiratory or metabolic. So now again, here in this example, we have an abnormal pH. And the value that's abnormal here is again our CO2. And so we should know that this is going to be a respiratory problem.
But again, if we think Rome, respiratory opposite, metabolic equal, here we have a high pH. and a low CO2 going in the opposite direction. So again, we can conclude that this is a respiratory problem. And therefore, we can come to the conclusion that this patient has a respiratory alkalosis.
All right, so we're gonna do a couple more examples here real quick. Hopefully at this point, you guys are starting to get these. And so we're gonna roll through these a little bit quicker just to make sure that we do have that understanding.
All right. The next example, we're going to have a pH of 7.30, a PaO2 of 87, a PaCO2 of 37, a bicarb of 20, and an oxygen saturation of 95%. Once again, we'll go ahead and disregard these here. And so for step one, we're going to look at our pH, and we can see this value of 7.3 is actually going to be lower than our normal value.
Therefore, we have an acidosis. Next, we're going to assess our CO2. which is 37, which is actually within our normal range of 35 to 45. And then for step three, we're going to assess our bicarb. And here we know that the value of 20 is actually low when compared to our normal of 22 to 26. So again, we don't have a normal ABG, so we want to determine is this respiratory or metabolic.
And so in this example, we have an abnormal bicarb with an abnormal pH. But here you can see that our pH is low and our bicarb is low. And since we know that it's the bicarb that's the abnormal value here, we can tell that this is a metabolic disturbance. But once again, if we utilize the acronym ROAM, here we can see these values are moving equal or within the same direction. Therefore, we can tell that this is a metabolic problem, and thus this patient has a metabolic acidosis. Alright, one last example for you guys here.
For this example, we're going to have a pH of 7.49, a PaO2 of 100, a PaCO2 of 42, a bicarb of 29, and an oxygen saturation of 100%. And once again, let's go ahead and disregard these values here. And so first let's look at our pH, 7.49. We know that this value is high, meaning we have an alkalosis. Step 2, we're going to assess our CO2.
Here this value of 42 is actually going to be normal. And then for step 3, we're going to assess our bicarb. Here our bicarb is 29, and therefore we know that this is high. So once again, we don't have a normal ABG, and our abnormal value in this case is the bicarb again, again telling us that this must be a metabolic disturbance.
And just to verify using Rome, we have a high pH in the presence of a high bicarb. Therefore, they're moving equal or in the same direction. Therefore, again, we can confirm this as a metabolic disturbance, meaning that our patient has a metabolic alkalosis. All right, well, hopefully you guys were able to follow along with that and you could kind of see what was happening and the thought process that goes into evaluating those basic ABGs. But really, that's only the...
first step in what we want to do. And so in our next lesson, we're going to take a look at the compensation mechanisms, how those work in the body, as well as how we analyze these ABGs to determine what kind of compensation or lack thereof is going on inside our patient's body. And so with that said, I do want to thank you guys for watching this video. I really hope that you guys found this information useful. If you did, please hit that like button down below as it really does help to spread the word about our channel.
And as always, we do invite you to subscribe to our channel, which you can do down below. Make sure and turn on all notifications, as well as if you found this useful, do share the video as well so other people can find it helpful too. As well as make sure and check out the next lesson in this series, which is going to be part four, in which we talk about compensation and what's going on and how we analyze that. As well as feel free to check out another one of our great series of lessons that we have on Shock. And as always, you guys have a great day and we'll see you in the next lesson.