Hello and welcome to Nova Biomedical's educational webinar series. My name is Evan Andre Wala, and I'm the director of medical and scientific affairs at Nova Biomedical. Today we have a great pleasure to have Megan Brescher from Northwest Veterinary Specialists to talk about blood gas analysis and more particular how to understand and interpret blood gases using a tick tac toe method.
This is a brief biographical profile for Ms. Bresser. She is the specialty technician trainer at VCA in Northwest Veteran Specialists.
She graduated from Brigham Young University with a bachelor's degree in animal science with emphasis in veterinary technology. She earned her CVT degree at Oregon in 2000 and became a VTS in emergency and critical care in 2004. Brei has an extensive experience in critical care with over 16 years in the emergency department and ICU nursing and technician management.
During the presentation, she will review acid-based mechanisms including differentiation between metabolic and respiratory abnormalities. And she will also practise the simple tic tac toe method and how this can be utilised to interpret blood gas results. This webinar is approved for AAVSB race continuing education.
Upon completion of the webinar, you will receive an email with instructions on how to obtain these credits. Also, the speaker will address any questions that you may have at the end of the webinar. So without further ado, I would like to ask Ms.
Brescier to start the presentation. Thank you. Hi, everybody.
Thank you, Nova, for inviting me to do this webinar. I'm really excited to talk about, talk about acid base and tic tac toe. This is a topic that is really challenging, I think, for a lot of people to get all of the inverse relationships and and everything put together.
But I found a trick, this tic tac toe method, and it has really changed my life and my ability to understand acid base, and I find it kind of fun now. So, let's just jump right in and get started with this. .
What's important to know is just kind of the basic building blocks for what we're doing when we're talking about acid-base. And the first part is hydrogen. Hydrogen ions in the body are necessary for, pretty much all of the enzyme function that's happening, as well as keeping cell structure normal, So much relies on the hydrogen content of the blood being in this really narrow range of normal.
And so the body's goal is to just keep the hydrogen constant. And so, we're going to see compensation in order for the body to keep that number where it really wants it to be. PH is what we're using to measure the hydrogen content in the blood.
So that's what we're talking about when we say pH is high or low, we're really talking about the hydrogen concentration. Lastly, there are buffers in the body, and what these are doing, either donating or accepting hydrogen ions to kind of balance things out. I, I hated chemistry.
I did not do well in chemistry when I was in college, and so I'm not going to draw equations and balance. Not for you, but that is what's happening with buffers. The goal of a buffer is to minimise a pH change.
So whatever disease process is happening, the body is going to try to minimise any dramatic changes, and it will use buffers in order to do that. So, as relationships with acid base, and that's part of what makes it so confusing, but hydrogen and pH are the, the big ones that have this inverse relationship. So hydrogen is an acid.
And a low pH means a very acidic environment, and a high pH means very alkalotic or basic environment. And here's where things start to get confusing. The lower the pH, the more acidic.
That means there's more hydrogen because hydrogen is an acid. So low acidic pH means lots of hydrogen, a high or basic pH means not enough hydrogen, and that's our first inverse relationship when we're talking about acid base. Here's our bicarbonate, HCO3.
This is the main buffer of extracellular fluid in the body. There are quite a few buffers that are kind of rolling around, but, but bicarb is the main one that we're going to be measuring when we're doing our acid-based analysis and looking at our blood gas results. PH is going to follow bicarbonate.
So the more bicarb you have, the higher or more basic the pH of the body is going to be. The less bicarb that you have circulating around, the lower the pH is going to be. So, bicarb is a base, and it is kind of the opposite of hydrogen.
Bicarbonate is our metabolic indicator. So that's gonna make sense as we start to, to do our analysis, but just remember, bicarb metabolic. Then we got in our Venus blood gas measurements is our pH bicarbonate, and then CO2.
So carbon dioxide. The important thing to remember about carbon dioxide is that it is an acid. So if we think about bicarb being a base, carbon dioxide, when combined with water is going to make an acid in the body.
Here again, because carbon dioxide is an acid, it has an inverse relationship to the pH just Hydrogen does. So if we don't have enough CO2, we're going to have a more basic or increased pH. If we have a lot of CO2, we are going to have a decreased or acidic pH.
CO2 is our respiratory indicator, so bicarb is metabolic, CO2 is respiratory. Slow down the rabbit hole of, of not being able to relate this back to patients. And it's really important that we understand what this means for the animals in the hospital and why it's important that we notice what their acid-based status is and do something to correct it.
So, any changes in the acid-based system are going to cause compensation within the body. So we're, we're going to have a primary problem. Whatever illness is causing the primary change in the The body is going to go through some compensation again trying to minimise that pH change.
So as the team that is taking care of these animals, if, if we understand what their primary problem is, we can begin to anticipate problems that are going to happen with that primary problem, and we can also begin to anticipate the body's response to that and, and how the body is going to compensate for that change. We can by using the TH and, and how much that changes, we can start to determine the severity of the disease process in that patient. We can start to look at things like perfusion, how well is this animal moving blood around their body, how well are they delivering oxygen, how well are they expelling carbon dioxide, and it can also help just to guide our interventions with these patients.
There are two main organ systems that are dealing with the body's compensatory response, and that is the kidneys and the lungs. So the kidneys are regulating the excretion of hydrogen, they're regulating the uptake of bicarb, and what's important to understand about the kidneys is that they don't move very Quickly, so it can take hours to days for them to be able to make a significant change in the animal's pH just by, you know, kind of how they're functioning. So they're a little bit longer term fixing of any of these problems.
The lungs, on the other hand, can increase or decrease CO2 levels, and they can do this almost immediately. So, by increasing respiratory rates, for example, an animal can exhale larger amounts of carbon dioxide. CO2 is an Acid, so they can exhale a lot of this acid and begin, we can begin to see changes in the animal's pH, almost immediately.
So, if, you know, we can start to see if we have a primary kidney problem, the animal is going to start to compensate by breathing. If they have a primary respiratory issue, their way to compensate is going to be, by their kidneys changing, hydrogen or bicarb. So, again, there's a lot of stuff that we're trying to pack in here and, and it can still be a challenge to, to see why this really matters in our patients.
Acidosis, and especially as, as we get lower and lower and lower on that pH and things get more extreme, we can see a decreased cardiac contractility. We can see the animals have a decreased response to catecholamines. So not only is our heart decreasing in its contraction strength, but we're also seeing a decrease in response to, vasoconstriction to help increase blood pressure, for example.
Antagonism of insulin. And hyperkalemia. So remember that, the, the body has a 1 to 1 exchange of hydrogen and potassium.
In alkalosis, we can see muscle spasms, we can see patients develop a really stuporous mentation, and we can see hypokalemia and hypocalcemia. So, as I mentioned, there's this 1 to 1 exchange hydrogen for potassium. So if we have an animal that, for example, has a really low pH is really acidic, that means there's too much hydrogen floating around.
The body is going to try to push that hydrogen into the intracellular space, so that it doesn't cause as much trouble out in the circulating blood. And so, the cells say, that's fine, I'll take your hydrogen into my intracellular space, but I'm going to want to exchange it for potassium. So with really, acidic patients, they're gonna drive that hydrogen intracellularly, but get potassium kicked out of the intracellular space and into the circulating volume.
So we may see patients have that potassium levels start to creep up if they're really, really acidic. The opposite happens for alkalosis. If the pH is really high, that means they don't have enough circulating hydrogen, so they're going to try to push hydrogen out of the intracellular space into the circulating volume, and they're going to need to push potassium intracellularly in order for that exchange to happen.
So, we may not notice this in mild pH changes, but when we start to see very, very dramatic, low pHs or very, very dramatic high pHs, we can start to see some of these potassium changes as well. It's good to keep in mind when you have a patient that already has potassium derangements for whatever reason, that if their pH is really out of whack, we're going to have a more difficult time getting those potassium levels back to a normal range because their acid-based status is so crazy. There are 4 main issues that we'll see, 4 main derangements with acid-base.
The first one, and, by far the most common derangement that we're going to see in our veterinary patients is metabolic acidosis. Listed here are a couple The reasons that we may see this, patients with low perfusion that have an increase in lactate, lactate is an acid, so these patients suffer from lactic acidosis, and we can see their pH start to go down just due to that increased level of lactate. Patients in kidney failure.
So whether that's acute kidney injury due to, you know, hypo perfusion, hypotension, whether it's chronic kidney failure patients, whether they're suffering from some sort of toxin, if the kidneys are not working, they're not able to balance that hydrogen and bicarbonate levels, and so we can see these guys in a metabolic acidosis. DKA, diabetic ketoacidosis. These guys are also suffering from a metabolic acidosis, and the, the acidosis is right in the title of the disease process.
So, you can start to see why we see so many of these metabolic acidosis patients, because these are fairly common disease processes that we're seeing in the hospital. We see the opposite, which is metabolic alkalosis. And these patients commonly present with a GI obstruction.
So they are doing a lot of vomiting, as you can see this little dog is here, and when they vomit, they're vomiting up that hydrochloric acid that's sitting in their. So they're getting rid of a lot of acid, driving their pH up, making them more basic due to that hydrogen loss. So if there's a patient that comes in and you do blood work and they have a metabolic alkalosis, start looking for why are they vomiting, where's that GI foreign body.
Respiratory, these patients are some of the most dangerously critical patients that we may see in the hospital, because they have a primary respiratory issue, and we all know that primary respiratory issues need to, we need to get on top of those as quickly as possible. These guys cannot, for whatever reason, eliminate carbon dioxide, so they're not able to appropriately ventilate off that CO2, and so they're TH drops because they've got all of that CO2, all of that acid hanging around. So, these can be patients that, are injured, so they've been hit by a car and they have, you know, fractured ribs and pulmonary contusions, and they just can't ventilate appropriately.
Patients with really severe pneumonia, patients with, cervical neurologic disease that prevents them from appropriate ventilation, we can see them in respiratory acidosis. Alkalosis is the last one that we'll, we can talk about. These are patients that have decreased carbon dioxide usually due to panting.
I have a picture of a greyhound here because greyhounds in the hospital. Pretty much pay the entire time they're there. They get really anxious and can, you know, kind of have a difficult time.
So we may see some respiratory alkalosis with them. Is it clinically significant? Most of the time it's not.
But it, it's just interesting that you may see this on your blood gas results, and you can say, great, now I know why, cause this patient is panting off a lot of their CO2, which is driving their pH up. Of what I think is the super cool part about acid-base is, is looking at how the body just naturally does what it's supposed to do in order to compensate for these problems. So, we'll first start with metabolic acidosis.
These guys have a decreased bicarb, so Bicarb and pH kind of follow each other, so not enough bicarb and a decreased pH, the patient is going to increase their ventilation. So they're going to breathe faster, breathe off that CO2, which is an acid, to try to bring that pH back up to a more normal level. I also have this in chart form in the next slide.
So, just depending on how you learn, this may make it a little bit easier for you this way or in chart form. But in metabolic alkalosis, these guys have too much bicarb, so their pH is too high, they're alkalotic. So these guys may actually decrease their ventilation.
They may want to hang on to more CO2, because CO2 is an acid, they're gonna try to bring that pH back down to normal. Respiratory acidosis, these guys have too much CO2. Again, here's that inverse relationship between carbon dioxide and pH.
So the kidneys are what's going to compensate for this primary respiratory acidosis. So the kidneys are gonna hang on to more bicarb, and they're going to try to excrete that acid since their pH is low, they're gonna try to hang on to that bicarb in order to bring that pH up to where it should be. Respiratory acidosis patients aren't going to compensate in an afternoon, right?
Because the kidneys take a little bit longer to change things than the lungs do. Respiratory alkalosis, these are our panting greyhounds. Their low CO2 means their pH is going to climb, and the kidneys are going to decrease the excretion of hydrogen.
So, here this is in chart form. Just a, a different way to look at it. You can see what the prime, and then what the compensatory mechanism is here.
So, if our primary issue is metabolic, the animal is going to compensate by changing respiration. If the primary disorder is respiratory, the animal's compensation is going to be through the kidneys, and we're going to be changing bicarb or changing CO2, whatever the opposite of the main problem is. So, anytime I do interpretation of blood gases, there's a lot of slowing down, stopping, and just going through methodically what's my primary problem.
What do I expect is that, how is that going to change the pH and then how is this animal going to be compensating? So, when you think about metabolic acidosis, which we see all the time, think about that DKA cat that comes in, it's collapsed, it's really dehydrated, pruned out, we do a blood gas, it's pH is very, very low. And its respiratory rate is really high.
A collapsed cat with a respiratory rate of 44 is not something you would expect to see. So you look at that cat and you say, oh, do we have a respiratory problem on top of everything else that's going on? But when you look at it, the cat's respiratory might be high because pH is so low, and that's how they're trying to compensate for that low pH.
So this is why I think this is so kind of nerdy fun, is that the body just knows what to do to try to fix these problems. And even before we can start any therapy on these guys, the body is already trying to fix the issue. There is a knowledge bomb that I like to remember.
Just looking at the relationships between pH, bicarb, and carbon dioxide, pH is going to follow your bicarb. So if you have high bicarb, you're gonna have a high pH. If you have low bicarb, you're gonna have a low pH.
And the pH is going to trend the opposite of your CO2. So if you have an animal that has a lot of carbon dioxide, their pH is going to be very low. High CO2, low pH, if they don't have enough CO2, so they're panting and breathing that off, so low CO2 is going to mean high pH.
Briefly mention the anion gap, as you get your printout, depending on what machine you're using to analyse your, your acid base and your blood gas results, you may have the anion gap on there, or this may be something that you want to calculate. The anion gap is a calculated difference between the body's major cat and and anions. Obviously, we're not going to put everything into this calculation.
We're just gonna look at sodium and potassium, and bicarbonate and chloride. So, there, there is a lot that electrolytes have to do with the pH and with the acid-based status. And when we're looking at just pH, bicarbonate, and carbon dioxide, we're not really taking into account some major electrolyte disturbances that these patients can have.
So that's why we might look at the anion gap because if we've got really crazy electrolytes, that can shift our pH a little bit and, and we may need to pay attention to that. The normal anion gap, whether your machine tells you what it is or whether you calculate it out, should be less than 20. If an animal's anion gap is greater than 20, we start to lean towards, hey, maybe this patient has a primary metabolic acidosis.
So, we're not gonna talk about this today, but mixed disorders, when animals have a bunch of different problems that can, that are all pushing their pH in all different directions. It can be challenging to figure out what the primary disorder is, so we may use the anion gap to help push us in the direction of saying, hey, this patient's anion gap is 27, I bet we're dealing with a primary metabolic acidosis. We all see the base excess that prints out on our results.
The base excess is just a measurement of treatment needed to correct a disturbance. So, again, how much acid do we need to add to a litre of blood to bring the pH to normal, or how much base do we need to return the pH to normal? That's what base excess is telling us.
Normal is -2 to 2, -4 to 4, depending on what reference you use, these numbers can be a little bit different. Again, base excess is not going to be the end all be all to interpreting what's going on with your patient, but it can help. In the right direction.
Now, because base base excess is only affected by fixed acids, it's, it's going to tell us if a patient has a metabolic disturbance, because carbon dioxide is what's known as a volatile acid, because when we combine it with water, that's when it becomes an acid. So, if a patient has a base excess that's really out of whack, again, that is going to push us to thinking, hey, perhaps this patient has a metabolic disturbance as a primary issue as opposed to a respiratory disturbance, as a primary issue. OK, so, finally, here we are.
How are we going to interpret these results? We know that our patient is sick. We know that their electrolytes might be out of control.
We know that they have weird breathing patterns. How are we going to figure out what our primary, what our compensatory issue is, and then work on fixing that. The first thing to do is determine what is the primary problem, cause we've got to figure that out so that we can start fixing it.
Determine if there is a compensatory change. Has the body realised that it needs to do something about this? And are we seeing, you know, major changes in our blood work results because there is a compensatory change, and we can't get away from at least posting normal close to your blood gas machine because we've got to know what's, what's out of whack in order to help us figure out what's going on.
So, Like these numbers can vary slightly depending on what reference you're using. These are the numbers that I use. This is, this is what our hospital uses.
It's fine if your hospital uses 18 to 24 as a normal, bicarb, for example, but just pick normals that everybody's going to use and post these close to your blood gas analyzer. So, I would recommend writing these down because we're gonna be doing a lot of practise blood gas analysis, and you're gonna need to know what your normal values are. 7.35 to 7.45 is your pH.
As you can see, that's a very, very narrow range of normal. CO2, 35 to 45, so that's the same that I use when monitoring and title CO2 under anaesthesia. So that's an easy one for me to remember.
And the normal bicarbonate is about 20 to 24. It's where the tic tac toe comes in. I, I wish that I had invented this because I find it so amazing, but I found this on a human nursing website called survivenursing.com.
You can go on there and find practise problems and kind of read more about how this works. But honestly, putting this tic tac toe into practise personally has just really changed my entire outlook and ability to interpret and understand acid base. So, It's very simple.
You're going to write your normals down, and you're going to put them in either a more acidic column or more basic. So, remember, the lower the pH, the more acidic it is. So 7.35 is on the acid side, 7.45 is on the basic side.
CO2, this is where you've got to make sure you put your numbers in the right spot, that because CO2 is an acid, 45 is on the acidic side because the higher our CO2 is, the more acidic, and the lower our CO2 is the more basic. So just make sure that the 45 goes in the acid column, the 35 goes in the basic column, and that little rest there means that CO2 is our respiratory indicator. So way back in like the second slide, when I was talking about CO2, it's a respiratory indicator.
And then bicarb with its 20 to 24, low bicarb is more acidic, high bicarb is more basic, that is our metabolic indicator. So write those numbers down at the top of your paper and then just write a tic tac toe grid and put acid, normal, and base across the top. So here is our first blood gas result.
We pulled this off the machine and the only three things that we care about right now are the pH, CO2, and HCO3. So let's look at that pH of 7.312.
Is that acidic, normal, or basic? When you go back to your normals up there and you say, OK, 7.312 is low, so that's on the acidic side.
So I'm just gonna write pH in my acid column. Next, I go to my CO2, and at 34.2, is that acid, normal, or base?
Because that is low, That is basic, because CO2 is an acid. So you're just gonna put CO2 in the base column, and then you're gonna look at your HCO3, your bicarb, 17.4.
Is that acidic, normal, or basic? That's low, that's acidic, so we're going to put that in our acid column. Right?
So now we look, where do we have 3 in a row, it's in our acid column, OK? So the pH bicarbon acid are all in a row there. Bicarb is our metabolic indicator.
So this patient has a primary metabolic acidosis. Because those three things are in the acid column, bicarb is in the same column as pH, bicarb is our metabolic indicator. This patient has a primary metabolic acidosis.
Now, we have to look at is this patient compensating or not. So we see that our CO2 is not normal. It is in the base column.
This animal has been ventilating more, breathing off that CO2. Pushing that CO2 outside of the normal range into the base column. So we say that this animal is at least attempting to compensate for this metabolic acidosis.
If my CO2 were normal, I would say this animal is not at all compensating, but because we've pushed it into the base column, that we are partially compensating. Again, it's partial because the pH is not yet normal. If this animal is able to breathe fast enough to drag that pH back to the normal column, we say, hey, they're compensating, not all is well, cause we still need to fix the primary problem.
But here is such an easy way to understand. Here's my primary disorder, and yes, this animal is attempting to compensate. So, practise makes, we're just gonna do a few of these to make sure that that everybody understands.
So again, here's our same normal box, here's our tic tac toe, and here are our blood gas results. We have a pH of 7.328.
Is that acidic, normal, or basic? I'm gonna put that in the acid column cause that's lower than the low end of my normal, which is 7.35.
A CO2 of 30.5, is that acidic, normal, or basic? That CO2 is low, CO2 is an acid, so if we don't have enough acid, that is in the base column.
And then my bicarb of 16.1, that is lower than normal, so that goes in the acid column. OK?
So I know that my primary disorder is an acidosis cause my pH is in the acid column. And then bicarb as my metabolic indicator, is in the same column as pH. So this patient has a primary metabolic acidosis.
And again, because that CO2 has been pushed out of the normal range, the body is breathing faster. It's hyperventilating, trying to breathe off that excess acid, push the CO2 outside of the normal range, so this patient is partially compensating or attempting to compensate for this primary disorder. Here's OK.
Here is another practise one for us. So here are our values, again, same tic tac toe, same normals, pH of 7.27.
And is that acidic, normal, or basic? And that is lower than what's normal, so that's an acid pH. A CO2 of 46, is that acidic, normal or basic?
It is higher than the normal range, and remember that CO2 is an acid. So we're going to put CO2 on our acid column. And then a bicarb of 34, and that is higher than normal, and bicarb.
Go in the base column. So we look at this. We have our pH and our CO2 all in the acid column.
So this patient has a primary respiratory acidosis, because CO2 is our respiratory indicator. And because the bicarb is outside of the normal range, it's way over in the base side there, this patient is attempting to compensate. Now, what that can tell us is because the kidneys take hours to days to, to be able to make any sort of significant change, I can tell that this patient has had this respiratory issue for longer than just a couple hours.
So this is not an acute problem, this is more of a chronic respiratory issue. So maybe this patient has some pneumonia that they've been working on for a couple of days, or they've got some You know, lung injury that they're kind of working through. So, so that's what we can kind of start to tell, as we're interpreting these blood gases.
Here is another one, because I love to practise. So, here are the values for this blood gas. We have a pH of 7.385, so is that acid, normal, or base?
That is normal, so we can be done, right? This patient has normal pH, there's nothing wrong. Look at the rest of these values.
This is why it is so important to look at all of the numbers when we get these printouts, is that we can see that this patient has a CO2 of 60.7. That is way outside of the normal range.
60.7 is acidic. So this patient got a lot of CO2.
I'm very concerned about this patient's respiratory status, and then we go down and we look at the bicarb, and they have a bicarb of 36.7, which is also really high in the base column. So does this patient have a severe metabolic issue as well?
How, what do we do? So, what to do with this is just draw a line directly down the centre of your normal range of pH. So in the centre between 7.35 and 7.45 is 7.40000.
So look at the pH of this patient at 7.385. Does that fall to the acidic side of 7.4 or to the basic side of 7.4?
It falls to the acidic side. So what's in the acid column? CO2.
CO2 is our respiratory indicator. So this patient has a primary respiratory acidosis. Now, their bicarb is way over in the base column.
So that tells me that this patient is attempting to compensate for this respiratory acidosis, and because the pH has been pulled into the normal range, we may be able to say that this patient is compensating for this respiratory acidosis, or this patient is really, really sick and might have a mixed disorder. Mixed disorders, again, are, they get a little bit more complicated as, as we see these patients with, really dramatic illnesses. And it just really is saying that this patient might have two pretty severe disease processes going on, and we start to think mixed when we have dramatic changes in either our pH bicarb or CO2.
And then this patient has CO2 and bicarb. Are extremely elevated, so this guy might have a mixed disorder or might just be really dramatic in its compensation for its respiratory acidosis. Either way, we really need to intervene and get this patient's CO2 back closer to normal.
He All right, here is another practise one. Here are our values, pH of 7.35, acidic, normal, or basic.
It falls just right into that normal range. This guy's got a CO2 of 31. Is that acidic, normal, or basic?
And that is low, so we put this in the base column. And that bicarb is 16, acidic, normal, or basic, that bicarb is low, so that puts us in the acid column. So here we are again.
We have a normal pH, but obviously an abnormal CO2 and bicarbs. So how do we figure out what is going on with this patient? Draw our line.
Our centre of acidic and basic is 7.4 for our pH. So to 7.35 fall to the acidic or basic side of 7.4.
It's on the acid side, what's in the acid column, that's our bicarb, which is our metabolic indicator. So this patient has a primary metabolic acidosis, and they are compensating. So this is the cat that comes in with a respiratory rate of 44, 48 breaths per minute.
That's a DKA. They're really trying with their respiratory system to breathe off that excess CO2, to try to pull that pH back into the normal range, and they've been able To do that with a pH of 7.35 being just at normal, so we can say that this patient is compensating, but a normal pH does not mean a healthy patient.
We still need to get on top of this animal's disease process, figure out why they have a metabolic acidosis, and treat that. OK, you can see our pH here is 7.166, acidic, normal, or basic.
I'm gonna put that in the acid column. We have a CO2 of 43.7, acidic, normal, or basic, that is normal in that normal range, and then our bicarb of 15.8.
We're gonna put that in the acid column. Now, I've also put in this base excess, BEECF this base excess of extracellular fluid, that's all that that means. And with the number of -13, remember our normal was -2 to 2.
And so this is way outside of normal, and not just support. Remember, base excess is only fixed acids, and when your base excess is way out of whack, it points to a metabolic acidosis, which are tic tac. Supports.
So this patient has a primary metabolic acidosis, and our base excess helps us with that. And because the CO2 is in the normal range, we can say that this animal is not attempting to compensate for this metabolic acidosis. All right.
One more, pH of 7.565, acidic, normal, or basic. Put that in the base.
CO2 of 22.8, that is lower than normal, so that also goes in the base column, a bicarb of 20.6, that is normal.
And this patient has a normal base excess. You can see that of -1, and our anion gap is 11. And remember that normal anion gap is less than 20, so this patient has a normal anion gap.
Both base excess and anion gap point us in the direction of metabolic acidosis. And because those two things are normal, that is supporting the primary disorder of this patient being a respiratory alkalosis, and they Not compensating, which makes sense. Respiratory alkalosis is something that usually comes on pretty quickly as the animal is anxious and panting in the hospital, and the kidneys have not had any time to try to change that pH at all.
So you can see that the lungs will change things very quickly, but this is usually not anything that is clinically relevant, and so that pH is still pretty high, so we need to be hunting for some other issue going on with this patient. But respiratory alkalosis that is not compensating is what our tic tac toe is going to tell us. To another one.
I think practising is so important to really understand these things. I'm gonna let, you know, you guys kind of work through this one, so I'll give you a few seconds to kind of plug in your numbers. I'm looking at your pH of 7.18, a CO2 of 29, and an HCO3 of 13.
So plug those numbers in to the boxes where you think they go and come up with your primary disorder and whether or not this patient is compensating. So here we go. With our pH and bicarbon in the same column, this is a metabolic acidosis, the CO2 being in the base column, this patient is partially compensating.
All right, this is our last and then we'll move on and look at some arterial blood gas results, so we'll start looking at oxygenation. So again, here's our numbers. I just want you guys to get really comfortable drawing your tic tac toe column, plugging these things in where they go, and coming up with your primary in compensatory issues.
PH of 7.346 puts that just barely acid. Remember, we don't round with pH, so 346 is still acid.
CO2 of 22.7, that's really low, so that goes in the base column, and a bicarb of 12.6 is extremely low.
So this patient has a primary metabolic acidosis, and they are making an attempt to compensate by blowing off all of that excess CO2. So, hopefully, you're feeling really comfortable with just the basic tic tac toe method to look at your venous blood gas results. We are also going to use the same tic tac toe method when we're looking at arterial blood gas results, but we're going a piece of oxygenation.
So when we're looking at an arterial blood gas result, we are all, we're going to still look at pHCO2 and HCO3, but we're also going to add the PAO2 levels. So the PA means we're looking at the pressure of dissolved oxygen in the artery, so arterial oxygenation. If we look at P little ACO2, that's measuring arterial CO2, the nice thing about carbon dioxide is that the numbers are pretty close in both Venus and arterial samples, and so our normal values are the same.
I'm also gonna add the PAO2 to FIO2 ratio if the patient is on supplemental oxygen. So important to remember that if we're giving an animal extra oxygen to help them, that we should see higher than normal levels of oxygen dissolved in arterial blood. So that FIO2 is a fraction of inspired oxygen.
So, again, if my patient is on supplemental oxygen, I need to take that into account when I am interpreting their PAO2 levels. 2 is the oxygen content of arterial blood, and what we're doing with that is really measuring how well our lungs are functioning and how well the body is able to get blood to the lungs. So, can the animal take in oxygen, but then is there blood getting to those alveoli that can pick up that oxygen and take it out to the rest of the body?
Normal values on room air are about 85 to 110 millimetres of mercury. This number again, is going to vary depending on the reference that you use. But supplemental oxygen should increase the result.
So if I'm breathing instead of room air, which is 21% oxygen, if I'm breathing 100% oxygen, my PAO2 should be much higher than 85 to 110. So kind of a quick way that you can determine what an animal's PAO2 should be if they're breathing supplemental oxygen, is that PAO2 should be 5 times their FIO2. So if an animal is under anaesthesia, intubated, breathing 100% oxygen, and you draw an arterial blood gas on that dog, your PAO2 should be 500.
So on room air, normal is 85 to 110, but when that animal is breathing 100% oxygen, their PAO2 should be about 500. So when you pull that blood gas result off the machine, you know, if that animal has a PAO2 of 200, but they're breathing 100% oxygen, they're not doing well. So 5 times the FIO2 is roughly what the animal's PAO2 should be.
Again, here's kind of what we're saying with that. So when we look at this PAO 2 divided by FIO2, that's exactly what we're doing. We're taking the number that the blood gas analyzer gives us for PAO2, and we're dividing it by SIO2 as a decimal.
So usually we say, you know, if an animal's breathing, You know, an FIO2 of 50%, that is 0.5. So normal when you take the animal's PAO2, divided by their FIO2 as the decimal, that number should be 3 to 500, OK?
So when just your, you know, quick way to determine if they're oxygenating OK is to take 5 times their FIO2 should be their PAO2, and then PAO2 divided by FIO2 is a decimal, should be 300 to 500. If the animal has that number as less than 300, we can say, well, this animal's got some pretty significant pulmonary disease. If it's less than 200, we start wondering, are we getting into ARDS or acute respiratory distress syndrome, territory with that.
We don't know, there isn't like a cutoff that says, yes, this patient has ARDS, but if your PAO2 divided by FIO2 is less than 200, that patient is in some significant trouble. Our arterial blood gas normal. So, the good news about this is the first, the top three numbers, your PH, PACO2, HCO3, those numbers don't change.
We're just adding our PAO2, 85 to 110 on room air, remember. And our PAO2 divided by fraction of inspired oxygen should be 300 to 500. So, just add that to your list of normals that you're gonna post on your blood gas analyzer, so that you can really tell how well your patient is doing.
All right, here are his numbers. So, he has a pH of 7.288.
So is that acidic, normal, or basic? Definitely goes into the acid column, so we put our pH in acid. Our CO2 is 80.1, whew, this dog is not doing well.
That is definitely a very acidic CO2. We have a PAO2 of 126. Just hang on to that number, because in order to complete our tic tac toe, we need to look at his bicarb of 31.7, and we can see that that is in the base column.
Now, his fraction of inspired oxygen is 100%. This is a dog that needed mechanical ventilation, so scarily enough, his CO2 is 80.1 as we started him on the ventilator.
So just looking at our basic tic tac toe. This patient, a primary respiratory acidosis, and he's been struggling to breathe for so long because he's a bulldog, that he has already started to partially compensate, so his kidneys have been able to push that bicarb outside of the normal range, just trying to compensate for his respiratory acidosis. So, Now, we're gonna go look at that PAO2, and you can see that the normal values for PAO2 are 85 to 110, but this is where you are smarter than just looking at the number and saying, oh, that's normal, he's fine, because this dog is breathing 100% oxygen, so a PAO2 of 126 is nowhere near normal.
So if we take this animal's PAO2, which is 126, and we divide it by his FIO2, which is 1, We get 126. And remember what the normal values for this were, 300 to 500. So this patient has a pretty severe oxygenation issue.
He definitely needs to be on the ventilator and we have some work to do. Here's the same bulldog. He's now been ventilated for a few hours, and this is our repeat blood gas that we did on him, just to kind of see how we're doing.
So these numbers, just looking at them, are much, much better than they were before. So we have our pH of 7.42.
Hey, look at that. We've pulled that into the normal range because we've gotten his CO2 down from 80 to 46.9.
So we have done a really good job with our ventilator. CO2 is not quite normal, but it's really close, it still falls in the acid column. And then if we'll skip our PA02 for a second and look at our bicarb of 28.6, that is still increased, so it's still in the base column.
Now, what's really interesting about this patient, and this really illustrates the time that it takes the kidneys to do any sort of compensation, is that if we draw our line at 7.4, our pH on this patient falls to the base side of 7.4, and what's in the base column is our bicarbs.
So we, if we didn't know anything about this dog, we would say that this patient has a primary metabolic alkalosis. And he's compensating. Now, we know that because this dog is on the ventilator and he came in with a CO2 of 80, he still is dealing with his respiratory issues, but because the kidneys take so much longer to kind of catch up to what the lungs are doing, we, we can be tricked into thinking that this patient Has a metabolic alkalosis.
So, just a little nerdy thing about this compensatory, system that the body has in place. So, we can say he has a metabolic alkalosis just because that's what our tic tac toe tells us, but we know more information about this dog, and he still has this respiratory issue. So let's move on and look at his oxygenation.
So his PAO2 is 163.4, which is improved, but again, look at our FIO2, 60%, he's still breathing a significant amount of oxygen. That PAO2 of 163.4 is not normal.
So we need to take our PAO2 of 163.4 and divide it by 0.6, because that is our FIO2 as a decimal, and we get 272.
That is so much better than 126. It's still less than 300, it's still less than ideal, but we are getting a lot better. We're making some significant progress with this dog, and that's what our blood gas really tells us.
What do we want to do with our FIO2 at this point? Do we want to keep turning him down because we're concerned about oxygen toxicity? Looking at these numbers, I would say he's responding positively, and we may be able to kick his FIO2 down to maybe 55% and kind of see how he does and get that all those numbers back up to as close to normal as possible.
But that's just an example of how we use these blood gas results to help us determine what the patient needs next. Another example for an arterial blood gas. This is a 9 year old female spayed Labrador.
She comes into the hospital for increased respiratory rate and increased respiratory effort, according to the owners. Because she was a really nice dog, we decided to do an arterial blood gas on room air, just to kind of determine, you know, what, what's going on. Is she breathing faster because she's painful, does she have another disease process going on?
And these are the numbers we get from her. So, again, we're gonna plug these into our tic tac toe, and see if we can figure out what's going on with this dog. So, our PHS 7.46 is basic.
The CO2 of 44.9 is normal, so this patient doesn't have a CO2 issue, which is interesting cause she presented initially for what the owners thought was a respiratory problem. And we look at a bicarb here of 32.5, so that is definitely increased.
So what's going on with this patient? We'll look at our oxygenation in just a second, but this animal has a primary metabolic alkalosis. And she is not compensating because her CO2 is normal.
Interestingly enough, if we go all the way back to the beginning of this presentation, what did I say about metabolic alkalosis? Is that with those patients, you're looking for a GI foreign body. What is causing the problem with this patient?
So, what we think may be going on with this dog is that she's been potentially doing some regurgitating at home that the owners may not have noticed. So she's regurgitating and getting that acid out of her stomach, and probably aspirating some of that down into her lungs, which has given her a little bit of pneumonia, which is why we're seeing her increased respiratory rate and effort. So, let's look At our respiratory values and see if that supports what we think is going on with this dog.
PAO2 is 76%, definitely lower than normal, the low end of normal is 85%, and we look at our FIO2 of 21%, If we take our PAO2 and we divide it by our FIO2, we get 361.9, which is 3 to 500. So she's doing OK with her oxygenation.
Her PAO2 is low. This dog would probably benefit from maybe some flow by oxygen, maybe a nasal cannula, to help her with her pneumonia. But looking at all of this, we should probably take some abdominal rods of this dog too, and see what's going on.
And this is where, again, our blood gas analysis can really help point us in what's happening with this patient. We need to chase down her metabolic alkalosis in order to get this dog fixed. All right, that's true.
Here's a 2 year old border collie. She presented to the hospital for partial drowning. So here are her numbers.
PH of 7.326 puts us in the acid column, a CO2 of 52.1, that's elevated, so that's also in the acid column.
And then our bicarb of 27.4, that is in the base column. So, we look at this patient, and that's surprising because of our partial drowning, this animal has a respiratory acidosis.
Trying to partially compensate for that. OK. So now let's look at our oxygenation numbers.
Our PAO2 is 94.7. That's good, right?
No, let's look at our FIO2 of 100%. That PAO2 is really terrible. So, 94.7 divided by 1 gives us a PAO2 divided by FIO2 of 94.7.
That is terrible. So, this dog was also on the ventilator, and we were really trying hard to help this dog get her CO2 levels down, so that she could blow off that excess CO2 and get her pH back to normal and get those lungs under control. Here is a 2 year old French bulldog who was attacked by a dog, was under anaesthesia for exploratory surgery, and these numbers are really scary.
This dog has a pH of 7.089, which is really, really, really acidic. And why is that really, really, really acidic when we look at that CO2 of 101.8, that is not really life sustaining.
This dog needs a lot of help in a very short period of time. Let's look at our bicarb of 30.1, that is in the base column.
This dog had some significant pulmonary injury and, you know, rib injury and inability to appropriately ventilate on her own, and you can see that that this dog has just a really signatory acidosis. It's been going on long enough that the body is partially compensating for it, but we really need to get this under control. If we look at our oxygenation numbers with our PAO2 of 57, that is terrible whether this dog is breathing room air or not.
You can see that they're on 100% oxygen, so our PAO2 divided by FIO2 is awful. That PAO2 should be 57, not 100.4.
I don't know where that number came from, but you do 57 divided by 1, gives you 57. So this is really Really awful oxygenation. This dog needs manual ventilation immediately to try to help that.
Hopefully, you're going to see that in cyanotic gums. If it's an open chest procedure, you can see that the lungs are not inflating, and that's how we get this dog to these awful numbers, but we need to do some intervention right away because with a pH of 7.089, this little dog is not going to be with us very much longer if we don't step in and help.
She made it to the end. Remember that there are these confusing inverse relationships with pH and CO2, and bicarb and which is gonna pull it in which direction, and just slow down. Remember that pH trends with your bicarb, it trends opposite of CO2.
Remember compensation. Remember that it's not just as simple as looking at one thing, that these patients are going to, potentially change their respiratory, effort to change their respiratory rate in order to compensate for what's going on. Remember, it is as simple as Tic Tac.
To and always relate your results back to your patient. What does this mean for my patient? What do we need to be doing?
How can I help, how can I further monitor this patient? What do I anticipate these changes being, due to the, acid-based status of this animal? I really for time.
If you have any further questions, if you want, any more, you know, acid-based problems, or you wanna share any really cool examples that you have, don't hesitate to shoot me an email, but I really appreciate all of your time, all of your efforts, and good luck interpreting acid-base and blood gas in the future. Great, thank you very much, Megan, for this amazing presentation. That was very, very nice.
Who would have thought that, you know, the symbol tic tac toe that we play with our kids to keep them busy in the restaurant will be used for interpreting blood gas analysis. So it was a very nice presentation, and we'll wait a little bit, you know, for questions from the audience, by the way. OK.
You can, you can type your questions, you know, on the Q&A session. And obviously Megan will answer them, but until we get like the questions, can I ask, is there any, I know you presented like a lot of information. Is there any golden rule, you know, how do you remember?
I mean, you've done it like a million times, I'm pretty sure you memorised all of this, but how do you memorise? How do you remember this? Do you use like flashcards maybe.
My favourite thing to do with any memorising anything is to write just a couple things down on an index card, and I tape it to my bathroom mirror and I stare at it when I brush my teeth. So it's a couple times a day, and it may just be like pH and you put it up there for 3 or 4 days and you just look at it, 7.35 to 7.45 and then put your CO2 and it kind of settles into your head.
I know. Well, I guess that will be also very interesting, you know, for residents and even medical students, you know, to memorise this and play the Tiktok. It was really nice.
And if I may, like another question a scientific question you did talk about the an eye on gap, which is a very valid concept for blood. I'm sorry, for acid-bas balances. We know that there is also another concept out there.
Strong iron gap that utilises a couple of extra electrolytes, negative charged electrolytes like ionised magnesium ionised calcium, lactate. So that's also another approach that has been used also in veterinary medicine. So I was wondering if you heard about that or Yes, there's, there's a a lot written about the kind of the strong ion difference and looking at more than just the very basics to kind of look, especially when we get into the more complicated mixed disorders, .
So, yes, if, you know, once you get this really good base, of really, really understanding how the tic tac toe works. And, you know, once you get these patients with very complicated, you know, multifaceted disorders, looking at the strong ion difference, looking at how electrolytes are pulling things, looking, you know, taking lactate more into consideration. And that's A lot more complicated.
It's less straightforward. I don't know that I have a really good grasp of it, but at least just being aware of, you know, other things that are out there. Absolutely, absolutely, thank you very much.
You're absolutely right. It's only in specific medical conditions, for example, sepsis, and we know that lactate is elevated sepsis over there. They put like the lactate in the strong iron gap makes a little bit of a difference.
I see a question about, obviously, you know, can you make the PowerPoint slides available? I guess I can also answer this question at the end of the presentation you guys will receive like a link so you can. Download the certificate, the continuing education certificate, but I'll have to check with the administrator if the slides will be available for downloading.
But if some individuals, you know, want the slides, the PowerPoint slides. Are they available on your behalf, Megan? Yes, if they, if they want to email me, I have turned this presentation just into a PowerPoint, so yeah, I, I'm OK with that.
Absolutely. Again, it was an amazing presentation and you have like so much information there that I guess people, you know, like to take advantage of that. All right, we'll wait a few more minutes for, yeah, go.
OK, go ahead. No, I was just gonna say it's a lot of information. And so not many people have questions till a couple days later.
I know, I know, I know, I know, I know. And by the way, again, your, your email was at the end of the presentation and they will get it also so they can ask you questions. If they if they have.
All right, let's wait a few more minutes for a couple of other questions. OK. How, how, how many years are you doing this?
I've, I've been lecturing, for about 5 years, and I've been doing acid-base for maybe 2. So this, this is something I waited a long time to tackle because it is so, there's just so much involved with it, and I think so many of us get intimidated by this early on and just say that's too hard, I'm never gonna learn it. And so it's just been the last couple of years that I found this tic tac toe method and that everything really started to make a lot of sense to me.
Absolutely. No, it was amazing and as you said, obviously, you know, at some point you need to read again the slides again and to say listen to your presentation again because my slide, let's say 40, I forgot what you said the slide 2. So I kept your advice and I wrote down, you know.
The normal range is, but you know, you know. Yeah, it does, and that, that's the thing about it is you, you know, you understand it maybe tonight you'll go to bed understanding it and then you wake up tomorrow and it starts to disappear. So it is something you need to just keep practising and it, it just sets.
You'll wake up one day honestly and just go, we, I remember and I understand. It's really exciting. Alright.
So I don't see any other questions. Coming in it's pretty much as you said, you know, people have to Absorb a little bit of the information. I'll get you some questions later via email.
And Any questions you guys? Not your chance. Alright, if not, I would really like to thank you on behalf of Nova Biomedical, really thank you for that presentation.
That was a very valuable presentation, and we look forward to hear it again in the near future. I would like to thank all of the attendees also. You're very welcome.
As I said in the beginning, at the end of this presentation, maybe within a couple of days, to be honest, you will receive an email with a link so you can download your C certificate and you can email, you know, Megan directly if you want a copy of the PowerPoint slides. Thank you very much, everybody, and thanks for participating in this webinar. Good
