Good evening everyone and welcome to tonight's vet nurse webinar. It's a pleasure for me to finally have the opportunity to chair a vet nurse webinar as a VM myself. And tonight's focus on the ups and downs of technography is definitely going to help me in an area that I have grown very.

Rusty since leaving practise. A little bit of housekeeping, just before we start. The usual webinar rules apply.

If you have any questions, hover your mouse on the screen, click on the Q&A box, and we will cover as many of those as we can at the end of the session. Without further delay, please allow me to introduce your speaker, Michelle Moran. Michelle qualified in 2006 and spent 11 years in first opinion practise, working in a variety of different hospitals, including one of the busiest charity and emergency hospitals in the UK.

It was here that she gained her emergency and critical care certificates and then moved to the North West Veterinary Specialists, where she is the supervisor nurse of the anaesthesia department. Michelle gained her veterinary technician specialist qualification in anaesthesia and analgesia in 2019. She currently sits on the AVTAA C credential Committee and has also recently become the nurse representative for the AVA.

So a warm welcome to the webinar vet, Michelle and over to you. Thank you very much for that introduction. Yeah, so first confession is, I thought I was actually being really creative when I come up with the title for the ups and downs of capnography.

I was thinking of like the waveforms, but then once the programme had actually gone live and out there to everyone, I then thought, actually, that looks like, there's ups and downsides to capnography, and there isn't. So that, is a personal fault of mine, and I burst my own bubble with that unfortunately. So definitely after this webinar, I'm hoping that no one thinks that there's any downsides to capnography.

So, the learning objectives for this evening, we're gonna learn what Carnore is and what it measures. We're gonna understand some respiratory physiology as well. We're gonna look at the different methods of measuring entitled CO2 and be aware of the advantages and disadvantages of each.

We're gonna recognise what the normal entitled CO2 values are, and then the most important, one is probably to recognise and troubleshoot those various strange waveforms that you might see or the abnormal values that you might come across as well. OK, so what is capnography? It's basically the measurement of CO2 concentrations in the expired and inspired area as well, so both of those get measured.

And it's then displayed as a wave form throughout the respiratory cycle. It also measures respiratory rates, which is quite helpful. And just to differentiate caponometry is actually the measurement of CO2 concentration only.

You don't get a graph with that, but usually, the monitors that we have in practise, you are measuring actually capnography, and that can be further divided into either mainstream or side stream analysis. OK, so what, what information can it give you then? So carbon dioxide, it's a byproduct of cellular metabolism and then it's excreted as a gas through the respiratory system.

So in order for us to get that carbon dioxide out essentially and measure it, three things need to happen. So we need to have cellular metabolism, so we essentially need blood perfusion to the tissues. And then we need venous return, so we need that blood returning back from the tissues back to the heart, so we need good cardiac output.

And then we essentially need it to cross the alveolar membrane and get into the alveoli and then be expired for us to measure it. So we need adequate ventilation and, and healthy lungs as well. And the value it displays, when, when you see that figure and that graph can determine how well all of that is being achieved.

And that, as I say, that graph that it represents in front of you as well can also give you so much information and that's what we're gonna go through this evening. So we've got two types of measuring devices. Mainstream, this is probably one of the ones that you're not, so used to.

This, it basically measures directly, at the site, so the respiratory gases passed through that adapter, and that contains really small sensors and it measures it instantly. So we have a faster response time. And it doesn't require scavenging as well, so that's really good and then and then definitely an advantage.

It can be calibrated easily on site, so that's another advantages, but it does come with the disadvantages as well. It's bulky and heavy, so as you can see on that picture, it's quite chunky, especially for some small patients such as the cat in that picture. So we do get some drag on the endotracheal tube and on the circus.

And it is unfortunately easily broken, and they are quite expensive as well. So, especially, moisture getting in so dentals and things that those are the, the, procedures that they often get broken and damaged and they are, as I say, expensive to replace. And you do have more dead space on the side stream method, so, so that yellow connector there that you can see that is all gonna be dead space for that patient.

So it's quite significant in your smaller animals. And then we've got side stream. This is probably what you are most used to use and in practise, if you do have a multi-rometer monitor.

So it actively pulls the airway gases away from the circuit to the monitor and it measures it at the monitor as opposed to that other sensor where it measures it within the sensor. It's very lightweight and therefore you get a lot less drag than that other sensor. It's safe with MRI and CT if you have those in practise as well.

And we do have a slower response time unfortunately, so this is some of the disadvantages now. So you do get a slightly delayed reading, so only a few seconds, but it is worth considering. Because it is such a narrow line that is prone to obstruction and moisture getting into that line.

It does require scavenging because it is pulling the expiratory gases away and especially if you're using inhalation agents, then that does require scavenging. It does require periodic calibration with a gas cylinder that you can sometimes do in-house, but it is quite difficult and not every machine allows you to do it either. So it often has to be sent away.

And then a really high sampling rate. Most of the, the ones in practise are set to 200 mLs per minute that it pulls away from that patient and as you can appreciate, in a really small patient that's quite a lot of its tidal volume. So it can create quite significant problems with really small patients that have a really small tidal volume.

So you need to incorporate that in your fresh gas flow. So the phases of the Kapnograph and I'm just gonna go through this and I'm hoping my, my, cursor works here. Yeah.

OK, great. So we've got our respiratory baseline here. It should ideally be always 0, and this is actually the start of expiration here, this number one here.

Now you may think, well, you know, there's no CO2 there, and it's definitely if it should always be zero. Why is there no CO2. But in our trachea and our bronchi, there is no CO2.

There, that's what's called dead space gas. The CO2 is within our alveoli, so that is why that should always be zero. And that first phase of the expiration will always contain no CO2.

Then we move to phase two and that's what we call expiratory upstroke. So rapid emptying of the alveoli, and that's when we see a rapid increase in our CO2 levels. What we call alveolar plateau.

So phase 3, so this is where it starts to level off, tailor off. It does ever so slightly increase on a bit of an angle, as you can probably see, it's not perfectly straight. And that's usually, down to a couple of reasons.

1, CO2 is always being delivered to the lungs. It never stops, unless our blood flow. Which we, we don't want that.

So it's continually being delivered to the lungs and then all the alveoli and at different rates as well. They don't all empty all at once together. So that is where, you get sometimes what's called a bit of a, a slope up, upwards and expiratory stroke, if you like.

And then the highest point there, that highest point is what is your Nidal CO2 number and your, what you're measuring. So the highest number that you see on your screen is your Nidal CO2. And then we've got the phase, what we call 0, the inspiratory down stroke, and that's the start of inspiration.

That's when obviously, the animal is then taken in fresh gas and that should contain absolutely no CO2. And then this again is just to show you a bit, a bit more through a respiratory cycle, if you like. So we've got inspiration here, so this part is all inspiration, and we've got what we call entidal CO2, so the Nidal value, that's what we're measuring, and then the startup expiration again.

So that's just more of a visual demonstration through the respiratory cycle. OK, so normal values, what are we looking at? I've tried to, to differentiate from the awake patients to the anaesthetized and I'll go through that, as to why I've done that in a second.

So in the awake patients, we talk about 35 to 45 being, the normal values, and, and that is definitely the case. 30 to 40 in a cat, but some books even go as low as 28 to 40 in a cat. Again, but this is in our awake, patients, in our healthy awake patients.

But when we anaesthetize an animal, we, the anaesthetic drugs that we give depress the respiratory system quite centrally in the brain. They also cause profound muscle relaxation, so relaxing all the intercostal muscles and the muscles that you need essentially, to breathe adequately and then we put them in lateral recumbency, dorsal recumbency. So we expect some degree of what we call hypoventilation, OK?

So this is where we expect the, the figure, essentially to, to, to, to increase. And with a healthy patient, this is what we, we look at as being what we class as normal, as in nothing too much to get concerned about if the patient is healthy. Some people, and clinically, I certainly do go up to 60.

I'm happy with a dog that is up to 60 in the healthy patients. In a cat, I wouldn't, want that to go that far, 50, 55 absolute maximum. For a cat before we want to start intervening.

If the catnogram is a normal shape and the tidal volume of the patient is good enough, and we've got healthy, essentially, really healthy lungs, then that ntidal CO2 number that you see will represent what's called the PACO2, and that is your arterial carbon dioxide concentration. So essentially what we're measuring on that machine can tell you what's going on in the blood of that patient, as long as, everything is normal looking and the patient is healthy. If we have disease, massively diseased lungs, then that's when we can start to run into problems, and that doesn't necessarily marry up.

So the NLCO2 slightly underestimates, the PACO2 but only marginally by 3 to 5 millimetres of mercury. So a very small amount. So you can use that as an estimation of what's going on in the blood.

So we're going to go through all of the traces that we get now. So this is a normal capnogra trace. Now what I tend to use is a bit of a, systematic approach, when I'm looking at whether a capnography trace is normal.

So I'll just find my cursor again. So we've got what we call a normal looking trace, what the diagram that I showed you before. We've got the, expiratory up stroke, the plateau, and then inspiratory, and it all looks fairly normal.

We've got the number here and titled CO2, which is 45, so that is within the normal limits. And then this FI number, if you've noticed on your machine before, that stands for fractional inspired. So that is the amount of inspired CO2 that the patient is breathing back in.

That should always be zero. There's certain circumstances where that could be 1 millimetre of mercury or 2, but we, and we don't tend to worry too much but that essentially, if we're looking at a normal canograph trace, this should always be 0. And now we're gonna look at troubleshooting.

So all of the waveforms that we're not maybe so familiar with looking at and how we're gonna deal with those. So the more obvious, one I thought I'd start with was that we don't have any CO2 trace. So as you can see, it actually says apnea.

So usually the machine will help you. It either will demonstrate it here or sometimes it's at the top of the, the machine and it will help you. So sometimes just looking at that for a little bit of guidance as to what's going on can help.

So we've got no CO2, we don't have any waveform, we don't have any entitled CO2 number and therefore no racial inspired number either. We've got no ent CO2 trace at all. So the first couple of things that we should be ruling out is if the patient is in respiratory or a cardiac arrest.

So hopefully that won't be the case in a lot of cases, but it's definitely worth ruling out a few seconds checking your patient. If your patient's got a normal ECG, normal SPO2, normal blood pressure, you can see your patient's breathing. We're all nice and pink, all of those things look normal, then it's very unlikely that that is the case, but we need to be just take taking a few seconds just to look at our patients and rule this out really quickly.

Before we then move on to more of a technical problem. So maybe there's been accidental esophageal intubation, or maybe it's just been dislodged, so if the tube tie isn't tight enough and it's slipped a little bit. Obstruction of the ET tube as well or the gas sampling line, so obstruction of the ET tube could be a mucus plug or something.

And the gas sampling line can have water in, and also, as can the water trap, but again, usually looking on top of your machine, sometimes it does tell you the problem if it is more of a machine fault. It can't differentiate what's going on with your patients, but if it is something, such as the gas sampling line's got a bit of moisture in it usually does tell you. There can be disconnection of the sample line connector completely, so maybe at the machine that someone's been pulling the patient and it's accidentally disconnected.

Maybe you've not even connected it yet. I know I've been guilty of this. I've been wondering why there's no CO2 trace, and I've not even connected it to my patients, just one of those human error things that you've forgotten to do.

And then something that I've had really recently happened a few times and whether we've just got a dodgy batch of, sampling lines, I'm not sure, but, we've had a few where they've completely split and almost, snapped off if you like, the CO2 analyzer, the water trap. On the machine, so we've had quite a few of those, and again, it can look like everything's connected, but when you look really closely, there's a massive hole, where it's snapped off, so that's something else to, to bear into consideration. OK, so looking at this one, where's my cursor, there we go.

So we've got a normal looking shape trace, albeit, you know, a very long, more rectangle shape, but it's, it's, it's normal in, in that we've got an inspiratory, down stroke here and that looks normal. So the, the shape looks normal, but our entitled CO2 number is 87, so it's massively high. We have a fractional inspired of 2, so, it's rebreathing some CO2 back in ever so slightly, but in the grand scheme of things, considering the entitled CO2 number of these patients, it's not huge.

And then another example of this, so we've got, a normal, I appreciate that, this picture looks a little bit cut off. It is obviously a live graph that it demonstrates, and I'm trying to take a picture. So I've not timed my picture very well.

So just ignore that part for now. This is looking fairly normally, you might want to comment on that little, bit looks potentially a bit abnormal, and then you've got a fairly normal looking graph there. We've got a CO2 number and total CO2 number of 50, so we're actually, high, we're above the normal limits and a fractional inspired of zero, so that's good that we're not rebreathing any of our CO2 back in.

And both of these examples, oh, and this one as well. Sorry, I've forgotten. I've put this one in.

So we've got, a bit of an unusual shape in, in the sense it's not the typical shape. It's fairly consistent. We're not quite hitting baseline here either.

CO2 and total CO2 of 50 and a fractional inspired of 3. So we're a little bit high here as well, and we're rebreathing that some of that CO2 back in as well, and a slightly increased respiratory rate. If you were looking at that as well.

So hypercapnia, so all of those traces that I've just shown you are, examples of hypercapnia. So it's common during anaesthesia as drugs depress the respiratory system, as we talked about earlier, and they cause profound muscle relaxation and then the patient position, all of which affect the, the respiratory system. So essentially what this causes is hypoventilation.

Now, we often think of hypoventilation as a low respiratory rate, and that's not the case. When we give these anaesthetic drugs and we depress all of the respiratory system and the muscle relaxation happens, what happens first is there's a decrease in tidal volume first, so the air moving in and out of the lungs is actually a decrease in that. Then obviously as the depth increases, then you'll start to get a lower respiratory rate.

So hypoventilation can happen even with a normal respiratory rate or sometimes even an increased respiratory rate as well. Hypercapnia is still defined as an entitled CO2 of more than 45, even though what I said earlier is that we often allow, and we call it permissive hypercapnia, so we allow the entitled CO2 in our healthy patients to go up to 55 to 60, as I say, depending on, the, the anaesthetist or the better you're working with what they, kind of prefer, and also the species as well. When we get an entitled CO2 of over 55 to 60, we start to get what's called a respiratory acidosis.

So that's when we start to see that pH starting to decrease. And as we know, the body needs a normal pH in in order to function adequately. Carbon dioxide excretion is directly proportional to what's called minute volume, so your tidal volume times the respiratory rate.

So therefore, if you are running into any problems, if you change one or both of those, you will decrease the PACO2 and therefore your entidal CO2. So whether you increase the tidal volume for the patients or you increase the respiratory rate, you will essentially solve the problem unless, as I say, you've got a disease, a diseased lung patients, for instance. So we want to decrease the depth of anaesthesia where possible before initiating any manual or mechanical ventilation.

Often just decreasing the depth is enough usually to, to bring that down to a more sensible level. And I've put malignant hypothermia, that's actually really rare, but anything that causes hypothermia, whether it's stress, yorexia, maybe it's a hot day, big dogs, long coats, that kind of thing, anything where the animals got a higher than normal temperature will increase CO2 production and also as will shivering, which hopefully most of our animals don't shiver under general anaesthetic, but I thought I'd pop that in. Shiring is not the same as when the animal is cold, so when the animal is actually cold, actually we get a low CO2, so there's actually less CO2 production.

It's the shivering, it's actually the muscle activity that causes the increase in CO2. And then for anyone that does laparoscopy in practise, you will also see an increase in CO2 levels there as well, and that can be a reason. Oh OK good.

For some reason, Mike, just bear with me a second. It's gone a bit slow. Give it a minute, try not to be too impatient.

Ah, there we go. So, We're gonna look at this now, so, very unusual trace as you can see. Hopefully, hopefully as well you've spotted that it's got an abnormal SPO2 as well.

But we're just looking at the capnography chase for now. So, got an abnormal shape. It's very fast.

We've got our CO2 number here again, I appreciate it's blades, but 17, so very low and inspired CO2 is 0, so that's great, and a really high respiratory rate to go with that. So that's hypocapnia. So we often see that with high respiratory rates in cats and small dogs.

We often see it with what's called nooception, and so basically pain, that's just a pain response or a light plane of anaesthesia. You can see reduced cardiac output, so as I said before, we need a really good cardiac output in order to bring that CO2 back from the tissues and back to the lungs. So if we don't have great blood pressure, we're not gonna have a good amount of CO2 being brought back.

Early pulmonary disease or pulmonary embolism? It can be a compensatory response to a metabolic acidosis if you've got a metabolic acidotic patients. Although once we kind of anaesthetize these patients, that compensatory response is dampened.

So you often see this more in the, awake patients, but you can see it in a sort of a lighter play in anaesthesia. Profound hypothermia, as I said before, if there's less heat, there's actually less CO2 production. The sampling site can be too close to the fresh gas inlet and it's being diluted often with our non rebreathing circuits that can happen.

And occasionally we can actually by accident intubate one bronchy . Initially, obviously you, you, if you integrate one bronchi, you're only going to get, CO2 being essentially measured from one lung, but the arterial CO2 will be so, so much higher. So if you were to leave that and go unnoticed, it would eventually creep up the entireal CO2 number, but as with the PACO2 to quite dangerous levels.

So we should be cutting our ET tubes down and measuring it from the nose to the point of the shoulder and hopefully avoiding this, but it might be worth if you've kind of ruled out all of the above and you can't quite grasp what the other reason could be. It might be worth untying the ET tube and just pulling it a little bit forward and seeing if that makes a difference. And basically treatment should be tailored to the underlying cause, as with all of these.

So again, just gonna look at this trace. So we've got a fairly normal trace. We have got a nice upstroke, a little bit of a plateau and the inspiratory down stroke.

We're not hitting this what we call baseline. If we look at our CO2 number and titled CO2 of 44, so that's good, that's in normal limits, but our fraction inspired is 5, so that's quite high, it should ideally be 0. So this is an example of rebreathing.

It's something that we see quite often with small patients that have got a high respiratory rate. Basically, the expiratory pause pause isn't long enough before they inspire again, so they often still expire in their CO2 before they then take a breath in and then then pulling some of that CO2 back in. You can get it with an increased dead space apparatus.

So, kind of medium to large dogs don't tend to have a problem if you say have a HME and then maybe you've got them on a circle system with a white piece. But when you have got some really small animals, that can be quite a big deal to these patients. So that is another reason for cutting RET tubes down to the appropriate size, and using paediatric, whether you can use, you can use the circle system on paediatric and smaller patients, but use the paediatric breathing hoses and the white pieces, or you obviously choose another circuit that is suitable for that, for that case.

Light anaesthesia or nociception, a pain response or any respiratory problem that that patient may have can also cause rebreathing, as you'll see an increase in respiratory rate. The carbon dioxide could be exhausted in your, in your rebreathing circuit, so your circle systems as well. So the soda lime is there to absorb the CO2 and if it is being exhausted, then some of that CO2 will then enter the inspiratory limb of the circle system.

The fresh gas flow, might not be high enough for that patient's minute volume or circuit, but that is only in non-rebreathing circuits, so your T pieces and your lacks. So the higher the respiratory rate, the higher the fresh gas flow will need to be in order to get rid of that CO2 for that patient. Once you've corrected the problem, whether it be a pain response and you then go and give some analgesia, you can then lower your fresh gas flow right back down again, .

So yeah, I just thought I'd mentioned that is only a non rebreathing circuits only. You might have a defect defective inhalation or exhalational valve in the rebreathing circuit. So ideally, when you're doing your leak checks, you need to be, every morning, you need to be checking that the valves move just one way and the way, the direction that they're supposed to, because that can cause a massive and really dangerous problem if it's left undetected.

And if you use vein circuits, you should be not only checking the leak, you know, placing a cap on the patient's ends, but we should be leak checking the inner tube and the integrity of the vein so that inner tube also needs checking separately. And basically treating the underlying cause once you've looked into the reason and that will usually correct the issue. So a couple of the more unusual and sort of non-textbook if you like, not every graph that you see will be absolutely textbook, and I've tried to demonstrate that with a few of these traces.

So we've got a quite an odd looking and definitely not a normal shape trace, and it doesn't just happen the once, it happens each time. We've got a CO2 of 37 and total CO2 37, so that's good, that's normal, and we've got an inspiration inspired CO2 0, so that's great. We've then got a very odd look and trace again, it's really, really strange.

We've got an entitled CO2 32, so a little bit low. I appreciate I've missed out the FI number here, but I'm fairly certain it will be 0 as it's hitting baseline here. And then another example again, as I say, these are all the same problem, but they're all really different looking catnographs.

So we've got, you might argue a couple of these look fairly, fairly normal, but maybe a little bit of a pointy tip here, especially with what we class as more of a normal. Respiratory rate. This one especially looks a little bit what I call pointy, and this one as well.

You might see this described, as a shark fin in some books, but this isn't actually a shark fin problem, as it were, and we'll, I'll go through that in a short while. This is actually a leak. OK, so they actually look really similar, but they're all examples of a leak.

So the Nidal CO2 is often really underestimated because some of that expired gas is basically going around the ET tube or being lost elsewhere. It's common if the endotracheal tube is too small or your cough isn't inflated or maybe you didn't check that in the first place. And then it can also be seen if there's a leak in the CO2 sample line, as I said earlier, .

With the dodgy batch potentially that we've had over the past few weeks, I've seen what looks like a leak trace, and I've checked the patients. I've checked the ET tube and nothing's been a problem there and I've then gone to the machine and found that the line is essentially half snapped. So it could be the line or it could, as I say, be something to do with the patient and the ET tube.

So ideally, the first things first, ideally, we should be doing this every time you intubate the patient, so you need two people usually it is you're working with your vet, so it's yourself and your vet. One person closes the APL valve and inflates the patient's lungs, and the other has got a syringe attached to the pile of fluid on your ET tube, injecting in until a leak is no longer his, and that's how you truly check whether a patient needs their cough inflating on their AT tube. Having said that, obviously, anaesthesia does depress, all of those systems that we talk about and especially the muscular system causes muscle relaxation.

But if your patient's a little bit light, maybe they've, you've intubated and they're coughing and they're actually a little bit light. Once you've got that patient to more of, of an adequate depth, it's worth checking if there's a leak again, cause all that musculature around the neck area, or maybe you've turned the patient on the back and that just that movement can kind of almost reveal a leak. So it's almost worth doing this twice, especially if you're, as I say, moving the patient quite a lot or the patient was light to begin with.

The entitled CO2 sampling line and connection to the water trap, so that's what the experience that I've had recently, so it's definitely worth checking. And then just to clarify, so what I'm gonna do is I'm actually gonna go back. So that, that graph.

Once I'd injected it into the cuff, that is its, trace, so that is the exact same patient. So I've injected it into the cuff and obviously as you can see, the numbers are wildly different. It was massively underestimating the CO2 number.

So we've now got a CO2 of 58. So yeah, definitely worth checking the leak around your cuff, and that was just from, from the prep area into theatre, just moving it, the patient into a different position that revealed that leak. OK, so what about this one?

So where's my cursor again? So this looks fairly normal. We've got a little bit, not the nice upstroke that we have, it's a little bit kind of slow almost to expire, a little bit of a hint.

We have still got the, the nice plateau and an inspiratory line, then this looks wildly abnormal. This looks potentially even worse. Then we've got a bit of a normal shape going on again and then this looks abnormal.

I appreciate there's no CO2 number here. I basically took this picture very quickly and then dealt with the problem. So that is why I missed the CO2 number as it was flashing.

And then this is another example of, of, of the same problem, as I say, they look completely different in, in appearance of the graph, and they're not always textbooks. So, we've got almost like a little bit of a hump appearance, a very slow respiratory rate, so we definitely should have a nice square, graph here, but we don't. We've got a CO2 number of 30, and this was actually a Rottweiler.

Just to give you a bit of a hint, this isn't a cat, so should be with that respiratory rate and a Rottweiler a lot higher. So we have a CO2 number of 30 and an inspiratory of 0, which is good. So basically both of those represent an obstruction.

So the first one that I showed you was actually a French bulldog, and it had a massive mucus plug obstructing it and endo kill tube, and it was actually breathing it in and out, which is why sometimes we have a normal trace and sometimes we have quite a severely obstructed trace. You can also have bronchoconstriction as the reason this can happen. So with asthmatic cats, anaphylaxis to any drugs, or if you are doing any bronchoscopy and BAL.

So that Rottweiler was actually, it had a size 14 EC tube in, and we were actually using a bronchoscope, down the middle of it. So we were, we were purposely obviously obstructing the endoschial tube, which is why. They're not always textbook, and it is important to kind of look at different graphs and differentiate what's going on and kind of what the patient's telling you, and also what you're doing at that time with the patient.

This is essentially an expiratory problem, so that's why the graph looks quite abnormal. So the endotracheal tube could be too small or you might have hypoplastic tracheas like in our, in our, brachycephalics. And not only that, they can then be really prone to mucus plugs, so kind of they're at double risk if you like.

And it could be a really obvious obstruction as well, there could be a king CT tube if you've flex the neck in any way, or if you've got a sandbag leaning on it, etc. So suction the endoscale tube will replace it. Alert the veterinary surgeon quickly if you suspect that bron constriction has happened.

Check the AT tube size and replace as necessary. And you want to check all the equipment, especially if you, if your patient's under the drapes and you're not sure what's going on, the the ET tube could have kinked something could have happened there that is causing that obstruction. So another couple of pictures just to represent.

So fairly, fairly normal graph if you like, if you look at all these, I appreciate I don't have a number there, but I'm just hoping that you're focusing on this little tiny almost bump, if you like. So this was something that I spotted really quickly and took a picture of. This is then the same patient, a minute or so later.

So again, normal trace, we're not quite hitting baseline. So I appreciate I don't have the FI number over here, but I suspect we are rebreathing slightly. But again, we've got a normal shape capnograph trace, but we've got this little funny thing here going on.

We've got an endo, sorry, ETT tube, sorry, endo. Oh goodness, Nidal CO2 of 50, so we are a little bit hypercapnic as well and as I say, I suspect they're rebreathing a little bit there. Then we've got this one, again, these are all examples of the same problem.

We've got this kind of shape here, they all look fairly normal, but then it's these little almost triangular shapes that are the abnormal traces. We've got an ent CO2 of 35. This is in a cat as well, and we've got a fractional inspired sub zero.

And then another example, very strange looking catnograph trace. I don't think I need to tell anyone that this is very abnormal. We've got an entitled CO2 number of 52 and a fractional expired of 0, and all of those traces, despite them looking all, very different, are all spontaneous ventilation where with positive pressure ventilation.

So whether you're mechanically ventilating using mechanical ventilator or whether you're delivering manual IPPV, that patient is basically trying to breathe over the top of that. This can happen with light anaesthesia or nociception, so a pain response. It can be in response to hypoxemia, which it was on that cat.

I don't know if you saw the, I think the SPO2 was 89 on that cat. That's where as well we were, with an arterial trace, this is where you can't use entitled CO2 as an estimation of PACO2. We took an arterial trace on that cat, and it's PA CO2 is 990.

So despite the animal being on a mechanical ventilator, that patient was trying to compensate itself, for the CO2 that was going on in its blood and the low oxygen levels by trying to breathe as much as it can over the ventilator. . Recovery from neuromuscular blocking agents if any of you do eye surgery or anything and use those drugs.

Under ventilation and hypercapnia, if you're using a mechanical ventilator or maybe you're doing it manually but only very periodically, if you're not delivering enough tidal volume to that patient or a normal enough respiratory rate, and the animal CO2 is going up, then it will respond by booking what we call bucking the ventilator or trying to breathe over the top of what you're doing. Again, the CO2 sensors are what drive us to breathe in the first place in the awake patients. And in the anaesthetized patient to some extent, it is dampened with anaesthesia and the deeper plane of anaesthesia you go.

Obviously, the more dampened that is. But if you've got a normal to light plane of anaesthesia and you're not, adequately ventilating that patient, then it will essentially try to override what you're doing. There could be an underlying problem which again there was unfortunately with that cat, it had a massive pulmonary disease.

It could just be manipulation of the chest or the cranial abdomen during surgery again. So, probably not the, the last two traces, but certainly the first trace that I saw that I showed you with just like almost looked like a little notch. That could just be the, the, the surgeon kind of maybe the, the patient's tipped a little in the cradle and they're just pushing it back over.

Maybe someone's knocked the T tube. If it just happens as, as a one-off, then it probably, and it happens in time with that, it's probably that. But something to keep an eye on because it might be the start of that patient trying to breathe over the top of what you're doing.

OK, so then we've got this. I appreciate this is a tiny bit blurry, but we've got It is a moving trace and my, my phone probably wasn't as sharp as what, what it could be for this picture, but we've got a fairly normal looking trace albeit it's very rounded at the top. Our CO2 is 34, which, I can say that this was actually a cat, so it is actually a normal CO2, and it inspired, so we are rebreathing a little bit.

We've got, 2 millimetres of mercury on our inspired CO2. And again, this is another example. So this is essentially very pointy.

It's, I wouldn't even say it's rounded. We've got an entitled CO2 of 43 and a fraction inspired of 2. Both of those are basically just what we call sinusidal, and that it just is the shape.

It's just the shape and it happens, happens with higher respiratory rates. So whether you need to basically look for that cause, whether it be, as I say, a pain response or like anaesthesia, like what we've said before. Hypoxemia, again, it's, it's usually high respiratory rates and it essentially you don't get that square trace because there's not that massive pause in between breaths.

It's too quick if you like. So it's almost pulling that trace down again, expiring, pulling it down, so you get that almost hill looking trace, and that is what we class as normal in the sense that you don't have to worry too much, but you should just be looking for the underlying cause of why is the. The respiratory rate high.

We do have high respiratory rates in our smaller patients naturally and, and rabbits and things like that. So it could just be normal for that patient as well. And hypercapnia can also drive that again, as I've just said before.

As I've said before, it can be normal in cats and very small dogs, and as I say, rabbits and, and your small fairies as their respiratory rate is naturally on the higher side. But again, check for a leak, more so if the respiratory rate is a normal or even low. The traces I've just shown you, they, they're massively high between sort of 25 and 35, so that, that would definitely demonstrate as to why that looks that way.

But if you have that kind of pointy shape, but you have a normal respiratory rate or low, that's probably more indicative of a, of a leak. And they are often rebreathing alongside that because as I say, there's not enough expiratory time to get all the CO2 out before they're then rebreathing a tiny portion of that back in. And then this is a very odd shape again after it's removing graphs so we'll kind of just ignore this line here.

We'll look at this, so we've got a nice expiratory up stroke, there's nothing too wrong with this, and then it starts to look really, really odd here. We've got an entitled CO2 35, so we're within normal limits, but our inspired is 22, so that's massively high. And all this is is what we call cardiogenic oscillations.

So the oscillations actually corresponds with the heartbeat of that patient. It's common in large dogs with a good cardiac output and a slower respiratory rate because there's more time to see it happen. And it's actually the pulmonary artery exiting the heart.

It's closer to the trachea and we've obviously intubated the trachea and that pulsates against that. The respiratory rates and the inspired CO2 are often massively incorrect, but if your CO2, eventually, if you're getting inspired at 0, that animal isn't rebreathing. What it is is it is just a machine and it's essentially measuring each of those steps down and thinking that you are rebreathing some of that in and you're not.

So as long as it eventually decreases to 0 at some point through the respiratory cycle and you can see it hitting the baseline of the graph, then the animal isn't rebreathing. What it can also do though is it can give you lots of different values of entitled CO2 because it's measuring each and every one. So the highest one that you see on that screen is the entitled CO2, and you might not see that in every single, with every single breath.

It might be that you need to just watch a few of them, and the highest value that you get is what you're then going to write down as your entitled CO2. You're gonna ensure the inspiratory line, such as the baseline again, just to definitely check that there is no rebreathing going on because it is just a machine and it can't differentiate between those two. There's no correction required as long as everything else looks normal.

It's actually some anaesthetists will even say they like when they say it because it shows that the animal's got really good cardiac output, so not always a bad thing. This is another example of a graph that you might see. We've got a nice expiratory upstroke and then we've got this little pointy bear.

It's still, we've got like that nice slope upwards like what we expect, and then we've got this little odd pointy bit and the inspiratory down stroke again, we've not hit baseline just here, we have on the other two. I appreciate we don't have an entitled CO2 value, but I just, not very often you get this trace, so I kind of just took a bit of a snapshot of it. This is what we call phase 4.

So on that, Capnograph diagram that I showed you where we have phase 123, and then 0, there is actually what we call a phase 4. And unfortunately, it's seen with really pregnant or obese animals, which I think we're seeing a little bit more commonly, nowadays. Basically, this is just uneven emptying of the alveoli and it's causing that extra little hump or a little wave.

No correction required, especially if everything else is normal, although IPPV is often required for those patients. Whether, and I think I maybe I've missed out as well, so they can be pregnant or obese, or they could be full of ascites or there's a massive tumour, maybe the spleen's huge, all these like little things, but often actually they don't need necessarily correction for that phase 4, but often these patients do require help with their ventilation for those reasons, when everything's pressing on the diaphragm. And then one of the last traces I think is a couple of examples of this.

We've got a, a trace that looks fairly normal in appearance, I suppose, most of them, but it's kind of, we can see it's, it's gone from here to here. We've got almost, it's slightly fading and falling. We've got an ently of 220, and I've missed the FI number there.

Hopefully though, you wouldn't be worried because this concerns you quite a lot. And then, oops, then we've got another example again, it's, we've got a normal shape, but it's falling, falling, fallen, and I couldn't tell you obviously what, which one of these, but, it's the measurement of this, but the entire CO2 is 10. So this isn't good.

So we have a fall in entidal CO2. Basically, this is the one that you massively worry about. Usually a fall in entidal CO2 is a cardiac arrest, essentially.

Basically, the perfusion is starting to slow down. There's no cardiac output. There's no blood flow returning back to the lungs.

It's everything's slowing down. So this is where you need to start getting, everyone on board and help them with this and alerting everyone. You're gonna check for a central pulse or an apex beat, whatever you prefer, and you're gonna basically start CPR.

It does indicate a rapid decline in cardiac output and then, as I say, the blood returning to the heart and starts to slow and then eventually stop. It can also be from a major pulmonary embolism, and that can, as I say, you can get air embolisms happen when you're doing laparoscopy procedures or rapid haemorrhage. Again, I've seen a fall in entidal CO2.

It was about, I don't know, 45, 48 in a Doberman, and there was a massive haemorrhage and it rapidly decreased. I think the lowest it went to 28. And we obviously started initiating massive transfusions and fluid bolus and things, and it did start to climb.

So, so yeah, kind of talk to your surgeon as well, see what's going on, if there, if there is any haemorrhage, and basically get the whole team on board and starting to help you. And this is why we always say copnography is actually an essential piece of equipment during CPR, I think that would be capnography and CPR as a general rule is, is some, a topic for another time. But yeah, it is a, a massively important part of CPR using your capnograph.

I think the take home messages are to look at the number. So what entitled CO2 number are you getting? Is it normal?

Look at the shape, is that normal as well, or is it abnormal? How is the patient? OK, so what, what are we doing that could be the cause and how is the patient overall?

And can I identify the problem and fix this? They're the four things that I would probably say, it's gonna massively help you understand and troubleshoot your capnograph on a day to day basis. And thank you very much.

That was brilliant, Michelle, thank you so much for that. I'm just gonna give everybody a few minutes just in case they want to pop any questions into the Q&A box, but certainly for me. I, I feel like I've learned so much, you've taken me right back into the back into that operating room, my, my brain's going it's brilliant.

I mean I've made so many notes you wouldn't even believe. You did mention . You know, when you kind of touched on more on the obstruction side like the the bracephallic, and obviously, you know, we do see a lot more bracephalic species is still quite popular in practise, .

What would you say, because you mentioned like the permissive hypercapnia being a little bit species dependent and different things like that, I was just wondering, you know, where would you kind of pitch the permissive hypercapnia for those really brachycephalic breeds? Oh yeah, that's a really, actually, that's a really good question because . I think a few of the nurses that we obviously do a lot of our our surgery and things as well, and that obviously we see kind of the worst ones if you like.

So a lot of brachycephalic live hypercapnia, like, you know, so they are actually over that normal limit. So they live hypercapnia and they basically have a, a dampened response almost to their CO2. So CO2 is what drives you respiration to breathe.

And yeah, they live basically a little bit hypocapnia. So what tends to happen is when you, have them under anaesthesia, they do definitely have a higher CO2 than, than average. I still intervene, as I say, when it hits kind of 60.

Because I think the, the, you've got the risk of then them becoming acidotic. But essentially, you know, if they've intubated the brachycephalic and the entitled CO2 numbers 50859, I'm not too worried. It's probably not that much higher than when it was awake, unfortunately.

With the severe, severe, severe BAS patients, like the really severe boas, they can actually, the CO2 response can completely go. Again, more studies are being done on this, and they think what happens is then they revert to an oxygen, essentially low oxygen levels is what drives their respiration as opposed to CO2. So some, yeah, so sometimes when you intubate a really severe boass and you're giving them 100% oxygen, they're like, Oh great, I just wouldn't breathe.

Like, because, you know, I've got 100% oxygen and I'm used to like, I don't know, 15, 16% or whatever, . So they're the ones that again, they just want you to ventilate because they're never going to ventilate themselves if you're delivering 100% oxygen. So they can be more tricky, in the sense that how long do you wait before you know, to completely take over the ventilation, but yeah, don't worry too much, they're often a lot higher.

But again, I usually intervene at the 60 mark just because I know from a pH point of view, that definitely decreases the pH massively, when you start to hit the 60s mark. So biologically, you want to intervene at that point. Yeah, I just don't want the cells to be too old, I don't want the body to be too acidic, essentially.

So yeah, I would still intervene at that point. Brilliant. OK.

And just on other species, I mean, you kind of, you mentioned a little bit, you know, you obviously we can still use carnography for rabbits and even you did mention small theories. I mean, it's been a, it's been a long time since I've done a, a small theory anaesthetic, and I'm sure things have moved on a little bit, but how, I mean how. How, how does it work really with a small furry, you know, because obviously you're not not gonna be able to, well, rabbits, you can intubate, but it's not as easy, you know, so are the, is the catmograph, you know, as effective as, as a monitoring tool for those that are making masks and things.

Yeah, I was, I was hoping you were gonna ask me what the normal ranges were for the aquatics because I don't know what the top of my head. I won't be that mean for you to revise that the exam, but then it quickly went away because I don't, I don't do exotics anymore, but I, . I, I think anything that you can intubate, ferrets are really easy to intubate.

They're sort of like ferrets, rabbits aren't as easy, but you can, as you say, intubate. Obviously, anything smaller that you can't intubate, it's probably not going to be, that useful. You can put it in a mask, you can kind of put the line in the mask and You can get some kind of reading, at least just, you know, if you are busy opening kit for the vet and you can, you can at least see that the, the, patient is breathing.

It's probably not a reliable entitled CO2 number to write down when it's in a mask and such a small patient that's not intubated, but definitely for like ferrets and, rabbits and anyone that works for like with bigger exotics as well, things that I think birds are really easy to intubate, so. All those kind of things definitely. I just couldn't tell you the normal entitled CO2 numbers unfortunately.

Don't worry, I'm not putting you on the spot, I promise. No, that's been great. That's wonderful.

OK. And, and just 11 last question just for me, just because obviously you've, you've really got my brain ticking over. If, you know, with all your experience and kind of.

Although obviously you've got within the the practise environment where you are, you've got a lot of all the machines and gadgets and everything you could possibly want, . We, we, we didn't massively touch on obviously pulse ox and and that side of things and the other things which you would use obviously ideally alongside capnographs, so that, you know, you're looking at the whole picture and pulling in little information from everything. But if you were in a situation where you could, you were only using one, would, would you use a capnograph as your key indicator for anaesthesia?

Oh, you've come up with amazing questions. So yeah, basically, I've always been in two minds as to the catnograph would just edge it. Capnograph and blood pressure, I think are both my, you know, two pieces of equipment that I think the rest I can kind of live without, because even if you have abnormalities on your ECG, you then go, well, how's the blood pressure doing?

And we kind of always revert back to is the blood pressure OK, even when you get an ECG abnormalities. But yeah, I think the Capnograph just edges it because again, I can put a finger on a pulse, a peripheral pulse, and estimate what the blood pressure is doing, whereas I have no idea about a number of what I couldn't guess. I could, I could say the respiratory rate is low or high, and I expect it to potentially be this, but honestly, as I've shown in those traces, you can have a really high respiratory rate with actually a high entitled CO2 value.

A really low and tad CO2 value with a normal respiratory rate. Like it can just be so variable and it does tell you so much and it will tell you if the animal is crashing really, really quickly. So I think capnography definitely just edges it for me, if I had to pick one, it definitely would be capnography.

OK, well, that, that's the way to end it, isn't it? That's the way to go. That's how to monitor our anaesthetics, but I think we'll, we will have to get you back to do some other talks, mate.

We'll do one on pulse ox and we'll do one on blood pressure. Build up a whole picture and you know, we'll have everybody will be completely 100% on what they're doing with the anaesthetics going forward, which is great. I mean that's well it's been fantastic, Michelle I can't thank you enough.

It's been great. And I can only assume that nobody else has got any questions because I'm just babbling on and asking you everything as it is. But I just want to say, you know, to everybody that has joined tonight, thank you so much for giving us your time.

I hope you have enjoyed it as much as I have. Please do spend a couple of minutes to do the survey that pops up at the end, because it's really good for us to know what you want to hear about next. If it is, you know, more from Michelle, let's hear more about Paul socks and everything else.

That'd be great. Also, that's to say thanks to Helen, the control and. Background here, who's been making sure that everything runs smoothly tonight.

And most importantly, of course, thank you again to Michelle, for helping us truly get to grips with the intricacies of capography. And here's to some lovely smooth anaesthetics tomorrow and onwards. Yeah, yeah.

So on that note, I wish you all a very good night, and I hope we will see you again soon on the next Nurse webinar. Thank you. Thanks, Michelle.