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Summary

This medical teaching session is perfect for medical professionals who are interested in cardiopulmonary bypass and its history. It involves an in-depth look into the components and function of a bypass machine, plus strategies for venous cannulation. Learn how John Gibbon pioneered the bypass machine, the history of cardiopulmonary bypass and the four main components of the bypass machine. There is also discussion of direct and indirect CAV bi-cable cannulation, and how taping the SVC/IVC can be used for improved drainage. With plenty of opportunity to ask questions, this teaching session offers great insight for medical professionals.
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Description

This is the first session in a teaching series titled Basics of Cardio-thoracic Surgery. The series would provide medical students and junior doctors with an interest with cardiothoracic surgery with a in depth understanding of the basic principles of cardiothoracic surgery.

This session on cardiopulmonary bypass will provide you with the physiological knowledge associated with placing patients on bypass during cardiac procedures.

Learning objectives

Learning Objectives 1. Explain the history and purpose of cardiopulmonary bypass 2. Name the components of a cardiopulmonary bypass machine 3. Understand the steps involved in the bypass circuit 4. Describe different strategies for venous cannulation, their advantages and disadvantages 5. Recognize and explain taping the SVC/IVC as a technique to seal off the bypass circuit from the atrium
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Computer generated transcript

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The following transcript was generated automatically from the content and has not been checked or corrected manually.

Hey guys, can you hear me if you can someone just send a message and the family, me or anybody just put a little message uh reassuring me that you can hear me? Excellent. Excellent, excellent. Ok, let's get started. Thank you all for attending. I'm just gonna share my slides now and we will, we'll get going. Thank you. We're getting a, we're getting a little bit of feedback there, the family I think because you've joined twice uh chest screen. He's cool. Uh When uh here we go. Yes. Ok guys. Can you see my screen? Um Hello Fay. I don't think we can hear you. Um We can't hear anything. Could you maybe you have an issue with your audio? No, I can't still hear you. We could hear you earlier but not anymore. Um Sorry everyone for the technical issues. Um Claudia has left, we will try to rejoin the meeting and see if um we will be able to hear then just give us a few minutes and we should be, you should be able to start. Ok. Ok. So um had has joined back, we'll see if he is able to, you can hear him now. No. How about now? Yes, we can hear you now. Oh, good, excellent. Ok, sorry everyone uh without further ado I will crack straight back on uh so share window uh presentation. So sorry guys. Um well, I mean, you know, it happens all the time but still um so while he tries to share a screen and um set up again, um, let me just do a brief introduction. I'm the junior clinical fellow at in Cardiothoracic surgery at hospital in the UK. And it will just be giving us a sort of uh 15 minutes to one hour teaching on cardiopulmonary bypass daily, the basics. Um And after the session, we'll have a brief um 5 to 10 minutes um question and answer if you have any questions. Um If you have any questions during the session, just note it down or put it up on the chart. And after the after the lecture session, we'll be able to answer you. We will be able to answer your questions as best as we can. Um And yeah, so you can. Lovely thanks to the femi. Yes. So exactly. I'm currently working as a junior surgical member of the team here in the Cardiothoracic Department and I thought I'll give you a quick talk on bypass to try and give you the basic understanding that I struggled with at the beginning and hopefully make it easier for you. Now, I am assuming that all of the attendees today are somewhat interested in cardiothoracic. Er and therefore there is some assumed background knowledge. If you have any questions. As the family has said, please ask me at the end and I'll be more than happy to, to talk to any of you. So I'm going to talk about the history of cardiopulmonary bypass briefly before describing the function of the the circuit, the circuit itself. I'll don't go into venous cannulation, arterial cannulation, venting, and cardio plegia. So the history of bypass, we know that cardiopulmonary bypass was actually pioneered by a gentleman called John Gibbon in September, Twen, who was born on September 29th, 19 03. He first used the bypass machine in 1952 to successfully repair an atrial septal defect. So this is an example of one of the primitive early cardiopulmonary bypass machines. And you can see it's very different to the ones that we use today. However, the principles are all the same. Uh and so to begin with, I'm going to describe the functions of cardiopulmonary bypass, which are firstly to oxygenate blood to circulate the blood around the body to ventilate blood as well as to regulate the temperature of the blood. These are the four main, the four main functions, oxygenation and ventilation. Essentially in this case come together, ventilation is the delivery of oxygen to the blood itself normally done by the lungs. So we're replicating the lungs with the machine and then oxygenation is the oxygenating of tissues, which is only achieved by maintaining ventilation and adequate circulation, circulation, being pumping the blood at sufficient pressures to perfuse tissues. And then temperature regulation is important in the context of cardiac surgery. And we have a heat exchange device built into the circuit which allows us to increase or decrease the temperature of the blood and therefore the patient. So in terms of components of the bypass machine itself, we have the pump which is what provides the necessary pressure to move blood around the body at sufficient pressures. We then have the oxygenator, which oxygenates the blood that enters the uh enters the bypass machine. We have the heat exchanger which regulates temperature. The arterial filter, the venous reservoir and the cannula. So the arterial filter essentially clears the blood of any debris, any clots and any miscellaneous tissue that may be found in the machine. It clears it cleans it and essentially makes it ready for re infusion into the body via the arterial cannula. The venous reservoir, by contrast is the portion of the machine that receives the deoxygenated blood, which drains into it via the venous pipe. And I'll describe all these different components in more detail. There is also other tubing which is used for venting and suction. So let's get into the circuit. Firstly, we have a venous cannula placed into the right side of the heart and this acts to drain blood from the body to the bypass machine. So it's drained from the body via the venous cannula to the venous reservoir, which is where blood first makes contact with the bypass machine. The blood is then oxygenated, filtered and kept at appropriate temperature before being transferred via the pump to the arterial can cannula. So step three, to be honest, if you're, if you want to be a surgeon, you don't need to know everything that goes on in terms of the physics of it and everything within the machine, you just need to know the principles of what the machine is doing. It's oxygenating, filtering and managing the temperature and then pumping uh sufficient pressure through to the arterial cannula, which is placed in the aortic root. So that then allows blood to be perfused to the rest of the body. And you, you have essentially, you can see then how you bypassed the lungs and the heart. Because if we rewind and conceptualize normal circulation, all the oxygenated blood is dumped into the right atrium and it arrives there via two vessels, the superior vena cava, which drains the upper half of the body and the inferior vena cava which drains the lower half of the body. Now, usually then the right ventricle would pump this blood up to the lungs to oxygenate it. But we intercept the circuit here. We place a venous cannula into the right atrium and the IVC, there are different strategies which I'll explain. But we place a venous cannula into the right side of the heart before the blood gets to the lungs. And essentially we drain it out here to then ventilate and oxygenate in the machine. So you can see how we've bypassed the lungs. And then we bypassed the pump function of the heart because we have returned the blood to the aorta just distal of the left ventricle. So it's a, it's a perfect, uh it's a perfect circuit. Uh and then the circuit starts again because the, once you pump the blood via the a a arterial cannula to the rest of the body oxygenate the tissues, the blood is then deoxygenated, returns back to the right side of the heart drained back via the venous cannula and it starts again. So when it comes to venous cannulation, when we say a cannula, of course, you know, just to be clear, all cannulation means in, in this sense is in the insertion of a tube into a lumen. So for those of you, that may be very junior doctors, uh it's the same principle as inserting a cannula into a vein. The difference here is the cannula is much bigger. And the lumen of the vessels that we're putting the tube into is also much bigger. But that's why it's called cannulation. And so when we talk about venous cannulation, we're describing cannulated the right side of the heart. And there are three approaches to doing this. I've already made a mistake. It's not the right side of the heart. It's uh, it because the third option is peripheral. Uh, but we don't do that so, so often. So it's, it's how we drain the, the venous blood from the body, usually from around the heart. The most commonly, um, implemented method is the use of a two-stage venous cannula. And this is essentially a pipe with two openings. You make one hole in what we call the right atrial appendage, which for those of you that don't know is a, a small portion of the right atrium that sticks out, it's easy to access and open. So essentially you open it and then you place the cannula down to the IVC. And once you've placed it into the inferior Vena cava, there, there'll be one hole in the IVC which will drain the IVC and then you'll have another hole that sits in the middle of the atrium itself, draining the remaining venous return coming from the superior vena cava. Note in this particular format, there is no direct drainage of the superior vena cava. So this is the most commonly implemented technique for most operations. Then you have bi caval cannulation, which is where we cannulate the superior vena cava and the inferior vena cava rather than just cannulate the atrium itself and the inferior vena cava. And in theory, if you cannulate like this, you get better drainage and less blood actually collecting in the atrium itself as we're intercepting the venous return earlier on in the cycle. So the way you would do this would be to make the same, essentially you make, instead of making 11 incision, you'll make two incisions, one in the middle of the atrium and one just proximal to the IVC. And then you'll pass the cannula up one to the S BC, one to the IVC. This is called indirect CAV bi cable cannulation. And that's because you're still making incisions in the middle of the atrium. OK? You wanted in the appendage and one next to the inferior vena cava. When you do direct by cable cannulation, you can see the image represents here quite clearly that we make the incisions essentially in the SVC and IVC themselves or as close to them in the atrium as we can. Uh And the, this is a technique that's often employed by mitral valve surgeons as when you have the two cannula placed like this. Firstly, you get ex ex excellent drainage. And if you pay close attention, you may notice on the screen that just above the, just above the SVC cannula entry point, there's, and you can see a piece of tape snared around the SVC and the same on the IVC. So this is intentional, it's called taping the KV. So you can tape the SVC or the IVC and that just completely seals off the circuit from the atrium. So you collect all that blood from the vena KV and transport it to the venous cannula and then to the venous reservoir. Uh Also this is useful for mechanical manipulation of the heart in theater as you can use the pipes that are snared this way to expose the mitral valve in a particular fashion that makes it easier to operate on. Uh That's not something you necessarily need to worry about at this level, but just to be aware of this as a cannulation strategy. And then we have peripheral cannulation, which is much more rarely implemented. Uh It's a rarely i it it's, it's a, it's essentially you go on to bypass. Instead of draining the venous blood from the heart, usually you'll go via the right femoral vein. Uh and this is the same principle applies. It's a big vessel, it's a venous vessel, you put a big pipe into it and then you drain the blood out of that into the venous reservoir. The reasons you would use a venous cannula are firstly, it's often used in minimally invasive surgery where we're making very small holes in the chest. We then have to, in many cases use femoral cannulation. Just a word of caution. It's not always the case that you have to use peripheral cannulation when doing minimally invasive cardiac surgery. It depends both on the surgeon and the operation. However, you will often find that in minimally invasive mitral surgery, they do implement a peripheral cannulation strategy. Whereas in minimally invasive aortic valve surgery, they're more likely to use central cannulation strategy. OK. So the second situation where you may use a peripheral cannulation strategy is in a patient who is coming for a second operation. And when this happens, you have to remember the patient's already had an operation. So the the gap between the sternum and the tissues underneath the pericardium, the heart et cetera, that space will can get full of adhesions and can it can be very difficult to open that safely. And sometimes when opening the, you can have a situation where the right ventricle is essentially stuck to the bottom of the sternum. And sometimes the surgeons may be concerned that when opening, they may, they may damage the heart or damage an important structure. So they will in advance of that, implement a peripheral cannulation strategy so that if anything happens, they can go on bypass or sometimes they'll just go on bypass anyway before opening the chest. Ok. So that's a brief overview of venous cannulation just to recap three main types, two stage, which is most commonly used by C of which there are two subtypes, direct and indirect and then peripheral aortic cannulation is more simple. And when I say aortic cannulation, I'm simply describing the act of placing a pipe in the aortic root in the proximal aorta allowing us to return blood to the systemic circulation. No, before the operation, patients will often have a preoperative CT scan specifically with a view to image the aorta in the context of aortic cannulation. Could anybody suggest why they think we use this? You can just type your, your idea, type your answer and, and if you know, or if anyone wants to speak up, I'll, I'll be grateful I'll start picking on people. I'm very mean. So either you have a volunteer or I'll select someone to, to give me an idea. What's the aortic coarctation? Good idea. It's not a bad idea. The thing with aortic coarctation is it's more a congenital issue. So in the stable adult cardiac population, you are less likely to encounter it. But uh good idea, haven't had a dissection or aneurysm or dissection. So Mohammad Abbas, correct in the in those contexts, you would always do AC T. Uh However, I may not have been clear of my question. What I was trying to say was why would we routinely do AC T for patients undergoing cardiac surgery? Uh Some consultants would uh ne no Femme has got the answer. It's essentially to do with aortic calcification. OK. So the general workup for cardiac surgery does not always include AC T, but all patients should get an x-ray including a lateral x-ray view. And if that's if, if there is evidence of calcification on such an x-ray, then the consultant would usually ask for AC T scan in order to image the aorta carefully for signs of calcification. Now, the reason that's important, the reason this is important is because when you have a calcified aorta, you need to know which spots of the aorta are calcified and which spots are not. Because when you place a knife into the aorta and then stick a pipe into it, if you're doing that in an area that's heavily calcified, then you're gonna throw lumps of calcium off and that can have catastrophic results including stroke, that's the main complication. OK. In America, they tend to use epi aortic ultrasound in theater to help identify areas of calcification. This isn't something they really use in the UK. When I've been in theater, usually, we just have a feel with the finger from the outside and you, you, you normally can appreciate just using tactile feel whether or not it's calcified or not. Uh And then once, so now I'm going to move into describing the surgical, the surgical steps of aortic cannulation. So if you're in theater, open the chest, you've dissected all the way down, you have the heart and the aorta open in front of you, what you will do is do something called placing partial thickness P strings. What does that mean? Purse strings are a, it is a strategy of placing sutures. And essentially if you imagine a point on the aorta where you want to put the pipe, the idea is not that you just make a hole and put the pipe in. But before you do that, you're going to place a, a suture around that point in a diamond shape. So that once you put the pipe in, you can then tie that suture, which will bring the aortic tissue that's around the hole and squeeze the hole tightly so that no blood leaks from around the hole. That's the purpose of pla placing purse strings. Uh And this is important for those of you that are surgically minded. So if you're interested in what that looks like, if you haven't seen it, I would advise you to go and just Google, uh what you can watch. There are loads of videos on aortic cannulation and specifically on the placement of purse strings. Uh So once you've done that, you then make an incision into the center of those purse strings and then you place the cannula, which is usually a 24 French gauge cannula. Uh And, and now you have access to the arterial system. So this is an open question to all of you. Uh What should you do first? Aortic or venous cannulation? I completely don't mind if you don't know. Of course, that the purpose of this is for us all to learn and explore ideas. But it will be interesting if everybody could just put in their concept or their idea which one they think aortic versus venous, which one should we do first? We'll just get a, a rough idea of what everyone thinks. And then I'll, I'll tell you what the right answer is and explain why. Come on, come on, go first. Yes, I know. Getting everyone going. We like to see that. So eer votes aortic, my votes venous. Ok. Ok. Ok. Very good. So we got a nice spread. I think we've got more venous, more votes for venous than aortic. So I'll explain firstly why I, I understand why people have probably put venous. And it's because logically you think that's the first part of the circuit, you wanna drain the blood first before giving it back, which I completely understand in reality, the the the practical correct thing to do surgically is to go with what some of your other colleagues have said, which is to place the aortic pipe first and I'll explain why it's all about safety. Ok. Remember the function of the, the heart and lungs is to oxygenate tissues. Yeah. So essentially, if you have a aortic pipin, you already have a big cannula directly aiming at the systemic circulation that we can give tons of blood to the patient. If anything goes wrong, here's how it goes. If you do venous cannulation first and you have a catastrophe, then you're going to struggle to save the patient because you'll have catastrophic bleeding and you have no access to the arterial system. Whereas if you put the arterial cannula in first, if you have issues with the arterial cannula, then you have issues with the arterial cannula and you're in trouble anyway, how was assuming a safe arterial cannulation, then you, you can get out of trouble if you have difficulties with the venous cannulation. And that often can be the case the aorta, the the the the atrial tissue is quite fragile. So when you're putting sutures, cause you also put a pru suture in the right atrial appendage before you make any hole, before you make any hole in the aorta or the heart. Really, you put a purse string. Uh If you put in a hole to put a pipe in, you put a purse string so you can secure the pipe. Yeah. So when you are cannulated the right side of the heart, you can essentially cause arrhythmias, you can lose a lot of blood. And when that happens, you wanna make sure you have a pipe in the aorta so that you can return all that blood to the patient. So that's why when you get asked this question, which you invariably will if you're on the wards for the first time, aortic cannulation first. And the answer is cause it's safer cause if something, if you have complications of the venous side, then you can just re uh you can just transfuse the blood directly back to the patient via the aortic pipe. So one thing I haven't included in the slides, which is of utmost importance is putting the pipes in the patient is not the same as going on bypass. Ok. So does anyone know what medication we must administer to patients before we can safely institute cardiopulmonary bypass. The answer is Heparin. We must give Heparin before putting a patient on bypass. The reason we must give Heparin is because when we drain the blood from the patient into the machine, remember that machine is full of prosthetic material. Uh You know, you got a heat exchanger, you've got a filter, all these things. And so if you drain that blood without giving Heparin, it's gonna clot and then you're gonna return a bunch of clotted blood back to the patient and they'll just stroke off and die. So that's why you have to give Heparin. The key thing here is to understand how we measure the effect of Heparin in theater. Yes. Agatha well done. Muhammad. We give Heparin not Warfarin, Heparin, Heparin not card cardioplegia. We have to give for a different purpose, but we don't have to give cardioplegia to safely get the patient on to bypass. We have to give cardioplegia to safely perform and complete the operation and I will touch on that have you. But the answer is Heparin. Uh and the reason we give Heparin ham is because Heparin is rapid acting and rapidly reversible. Whereas Warfarin takes a lot of time to work and is difficult to reverse. Ok. So Heparin, you give intravenous an intravenous big shot of Heparin and you measure the impact of Heparin in real time in theater by taking blood samples from the patient at time intervals after giving the heparin and measure what we call the AC T. OK. The AC T is the a measurement of the action of heparin and it stands for the activated clotting time. Most, almost all surgeons, the threshold at which the activated clotting time is high enough to institute bypass safely is 400. OK. This is a good thing to be aware of activated clotting time. Greater than 400. Means that the blood is thin enough, thin enough to put the patient on bypass. Remember, we are thinning the blood in order to safely prevent the blood clotting in the bypass machine before it's being returned to the heart. Ok. Right. So we've put the heparin into the patient. The AC T is normal. We have the aortic pipe in the venous pipe in, it's all connected, it's all ready to go. Then we could ask the perfusionist to put the patient on bypass. And that means we essentially switch the machine on and remove any clamp between the machine and the venous reservoir. Once you remove that clamp the pipe that's in the right side of the patient's venous system. We'll be able to drain blood to the machine and we get started. Ok. So now you have that overview of an arterial cannula in the aorta, a venous pipe. They're both connected to the same machine. And we understand how the heart and lungs are being bypassed. The final thing to understand in terms of the circuit itself is the additional pipes, you have additional pipes that are connected to the bypass circuit as in also connected to the bypass machine that are not the arterial or venous cannula. And these are three small pipes that are, it's, they're more like little tubes that you can use in the operation to suck blood out of areas. That's essentially what they're there for. And the reason that we use these, once the patients on bypass is as follows. Normally in the operation in any operation, you have a sucker. Right now. This sucker is called a rough sucker, the usual standard sucker that you use and that will just suck stuff out that then gets thrown away, thrown into the bin. When you're doing heart surgery by the, just by necessity, by virtue of the fact, you're operating on the heart, you're going to have a lot of blood accumulating in the operative field. That makes sense. We don't wanna lose all this blood and throw it all away and then have to reran blood from the blood bank. That doesn't make sense. So, because we've given Heparin and the AC T is above 400. In general, we can use small suckers that are also connected to the bypass circuit to suck any blood in the operative field out, return it to the bypass machine and put it back into the patient's systemic circulation. And we have three pipes that we can use to do this, that each one has a color, uh the, the yellow, red and green pipes. And these can be used either as suckers or vents. And there's a difference between a sucker and event, not in terms of the physical act. It's the same thing. It's a pipe in a place sucking blood. But the difference is in, in how the surgeon is choosing to use that pipe at that time. Ok. So when we call something a sucker or when we say we're using this as a sucker, what we mean is we are just haphazardly placing it in different parts of the operative field to suck blood as and when it accumulates in the pericardium, uh I I say in the pericardium because for those of you that haven't actually watched cardiac surgery, the way we operate on the heart is by opening the pericardium. OK? From the, an the anterior pericardium is opened and we then lift the right side of the pericardium and the left side of the pericardium and we clip them, stitch them to the sides. So essentially, we, it's like, it's like we lift the bag that the heart sits in up and we lift it torch so that we operate on the heart. Whilst the bag that it normally sits in is lifted up so that any bleeding that happens, bleeds into the pericardium and not just into the thorax generally. So then we could just place the suckers into that what we call pericardial well, and suck any blood up. So if there's any little bits of bleeding here and there, we can use the sucker to address that a vent when we use one of these pipes as a vent, that is something separate and venting is the act of sucking blood out of a particular location in order to maintain a bloodless or to reduce the blood in the operative field. And specifically, it's the left side of the heart that we need to vent. There are a couple of reasons why we do this. Firstly, so you can see what you're operating on. But secondly, because we want to minimize distension of the heart during cardiac surgery. Now let me explain because this is something that took me a while to get my head around. What you may think. Why is blood entering the heart? Why, what, what's, you know, we've got the patient on bypass, we have a massive pipe in the right side of the heart that's sucking all of the deoxygenated blood out of the heart into the bypass machine, right? So why do we need additional vents to keep the heart from filling up? The reason we need additional pipes to do that. It's because there is some deoxygenated blood that normally physiologically returns to the heart, not via the right atrium, but via the left atrium. And you might be surprised to hear this if you don't already know this. It's something I only learned about when I, you know, started reading about cardiac surgery and cardiopulmonary bypass. Now, there is the main source of deoxygenated blood that returns to the left atrium rather than the right atrium is the bronchial circulation. That is the blood supply to the bronchioles and the alveoli themselves, bronchial deoxygenated blood returns to the left atrium, not the right atrium and where we don't have any venous pipe or any drainage pipe in the left side of the heart, it's all on the right side because that's where the, the bulk of the deoxygenated blood is, is, is dripping down into. Now, you might think, oh, well, if it's just a bit of bronchial circulation, it's probably not that much. Well, you'd be wrong. It's actually 150 to 200 mL of blood per minute that returns to the left atrium as venous return from the bronchial circulation. Ok. It's not just the bronchial circulation. There's also something called the, the bees veins which are essentially veins that drain deoxygenated blood from the heart itself. And they also drain partly into the left atrium, but it's mainly the bronchial circulation. So if you think about it, 100 and 50 to 200 mils of blood per minute is entering the left ventricle via the left atrium. If we allow that to accumulate over time, you're talking about liters, the majority of the cardiac output over a few hours will end up distending the left ventricle massively and that essentially results in ischemia and death. So if you don't get this right, the patient dies, this is very important. So that's why we need to vent the left ventricle vent. Think of it. It means like it just means it's just another way of saying like suck or re remove or ventilate, you can think of ventilate. But I i it's, it's just a, a term used in surgery uh in cardiac surgery. So now that you know the purpose of venting, which is to drain blood from the left side of the heart, and then you would be able to understand the different ways of doing that. And I'll explain surgically the different ways that you can vent the left ventricle because that's ultimately what we're doing. We're, we're sucking blood out of the left ventricle to prevent it over filling. So firstly, you can literally stick, uh you can make a hole in the left ventricle and stick a sucker through it. It's not really conventional because you know, the less holes we make in the heart, the better. But it is an option. The second option is to make another small hole in the aortic root and then to put a pipe through the aortic root and then through the aortic valve into the left ventricle that way, or we can just sit it in front of the aortic valve. And if we turn the sucker on, then it will cause the aortic valve to open and then suck blood up through the, from the left ventricle through the aortic valve. And then thirdly, there is a, a AAA strategy which is very commonly used, which is a right superior pulmonary vein vent. Now, if you think about what feeds into the left atrium, it's the pulmonary veins as opposed to the vena cau for the right atrium for the left atrium, it's the pulmonary veins which bring oxygenated blood for the most part to the left atrium. One of these, the right superior pulmonary vein is anatomically very well located for surgical entry of a small pipe. So again, surgically, they'll make a small purse string around the uh around uh a point on the right superior pulmonary vein. Then they'll make an incision and then they'll, they'll then feed a pipe through that incision into the left atrium down through the mitral valve into the left ventricle. And then you have a nice, a nice pipe in place ready to suck all the blood out of the left ventricle, keep it empty and stop it from over distending. Ok. And then finally, so that's venting. Basically venting is the strategic deployment of pipes in order to remove excessive blood from the left ventricle. And then finally, we have cardio pleases. Now, cardioplegia is the administration of a high potassium solution to me. We are trying to essentially stun the heart. We are trying to chemically induce cardiac arrest. The purpose of chemically inducing cardiac arrest is to of course, stop the heart contracting and therefore to minimize the oxygen requirements of the heart. Because remember the heart is uh is not really receiving any blood, we're stopping it to operate on it. So if, if the heart isn't receiving oxygen rich blood and we let it pump and pump and pump and pump, then as it's pumping away, it's gonna burn up its oxygen reserves and become ischemic and then infarct. So that's why we, we stop the heart using high potassium solution to essentially arrest its metabolic demands and allow us to operate on it. The second reason is for surgical purposes, if we're wanting to do grafts or if we're wanting to do some uh some work on the on on the valves, then we obviously want the heart to sit still so that we can work on it. So they're the two reasons that we give cardio patients. Now, in terms of how we actually give cardio pleases in theater. Broadly speaking, there are two approaches. Approach. Number one is only available and applicable to those patients that have a competent aortic valve. This is not an option in patients that have aortic valve regurgitation or in patients whom we've opened the aorta and are doing aortic valve surgery on. So the, the, the, the the this method is injecting high potassium cardio plegia solution into the aortic root in patients with a competent aortic valve. That's an option because essentially, if you think about your anatomy, the coronary osteo, which is the openings of the right and left coronary arteries, they exist just above the aortic valve. So if we inject high potassium solution into the aortic root, then essentially it will fall down. You can think of it as falling down to the aortic valve and then it will spread through the left and right coronary osteo and perfuse the heart with high potassium solution. And the heart will arrest. The second option if we're opening the aorta creating an aortotomy to do a valve operation is we take a small cannula and we inject the high potassium solution directly into the left and right coronary osteo. The purpose of these is both to r uh arrest the heart, as I said for myocardial protection. Now guys, this is all under the umbrella term of antegrade and to grade cardioplegia. Antegrade cardio plasia means we're giving cardio SIA via the same path that blood normally enters the coronary circulation. Antegrade. Now, if there's antegrade cardia plegia, that means there must be retrograde cardio plegia. Now retrograde cardio plasia is where instead of delivering cardio pleases via the arterial system, we deliver cardio pleases via the venous system. So we ca instead of instead of delivering it to the left and right coronary osteo, we would create a small opening around the coronary sinus which sits around the back of the heart and place a cannula there. And we would give the cardioplegia solution. This way, the reason you would do that is if the patient has bad coronary artery disease, and that's the reason we're operating on them, then we can't guarantee that just giving cardioplegia solution down, those bad coronary arteries will sufficiently expose the heart to high potassium and, and uh and, and cause it to arrest. So we, we do a dual pronged approach. We may try antegrade but also retrograde by filling the veins with enough of the solution. It should also perfuse the heart and cause the heart to arrest. Finally, when we're actually doing the operation to fix narrowed coronaries, we are literally grafting veins to those coronary arteries, right. So we make a small opening in the coronary artery just beyond the point of tightness and disease. And then we sew the conduit, the venous conduit onto the healthy part of the artery just past the blockage. Once we've done that, we have direct access to the arterial system of the heart. And then we can inject cardioplegia solution down the graft that we've just sewed onto the heart again, in order to perfuse the heart with high potassium to arrest it. This is one of the so cardioplegia. So these are the main forms of cardioplegia and to grade retrograde retrograde is by the coronary. It is used in patients that have bad coronary artery disease. Antegrade is either into the aortic root. And those patients that don't have aortic regurgitation or if they do directly into the left and right coronary, osteo and cardio plasia itself is one of two ways we protect the heart from high uh from high oxygen demand. The second way we do that is by keeping a lower temperature of the heart when we're in the main stages of the operation, which we do by cooling the blood in the bypass machine. But also just basic, simple, good old fashioned physics which is getting a jug of cold sterile water and pouring it all over the heart during the operation. We do do that. So by giving cardioplegia and cooling the heart down, we reduce the heart's metabolic demands and therefore reduce the risk of the heart. Uh getting ischemic and dying and that my friend is essentially that the only other thing I would add is at the end of the operation. When we're happy with everything, we give a drug called protamine which reverses the impact of heparin and uh restores a normal AC T which is between 100 and 100 and 20. Um But yeah, that, that's, that's everything that I had prepared. I hope it was helpful and not too abstract. I know it's a lot of content. So I'll be more than happy to answer any of your questions if you have any. Hi. Thank you very much for the, if anyone have any questions, please put it on the chart or um you can just um pick up, put it on the I don't think you you allowed to mute yourself. So just put it on the chat, please. Yeah, you can put it in the chart and I, you know, I'm more than happy to reply to. Mhm. Yeah. OK. I'm going to be sending the feedback form to the chart. So please fill the feedback form so that you can get your um uh um attendance also will help the also to know where to improve on and how the, how the teach went. So I put it up on the message, I'll just reply to that question if I mean it's a good question. Uh They ask, when do you reverse the cardiac arrest? So essentially the these kind of things vary from surgeon to surgeon and they, you know, each consultant has different preferences. There's not a, there's not a um how can I put it? There's not a reversal agent per se for cardio pleases the way it works is we give a specific concentration of the, of the high potassium solution. And then essentially, if you think about it like this, that dose buys us a certain amount of time of cardiac arrest. So if you give like, you know, 500 mils down the left coronary osteo and 500 down the right coronary osteo that might give you 45 minutes of a rest. So the surgeon is timing it in their head. So they'll give, they'll give a dose, the final dose of cardio plegia 45 minutes before they anticipate they will finish the key steps of the operation and then hope that it wears off just as they're finishing the final. And then if the operation ends up taking longer than needed and the heart starts beating again a little bit early, then they'll just give some more cardio plasia. But yeah, the key point is there's no, there's no reversal agent. It's just about, uh, looking forward and uh, and, and timing when you give the cardio plegia knowing that it will wear off in a certain amount of time. Um And if OK, asked a good question, are there contraindications to bypass? Yes, certainly. So firstly, the first obvious one is if a patient has what we have, what we would call a, a porcelain aorta or in other words, a heavily calcified aorta whereby the calcification is so extensive that it's present all the way along the aorta and there's no entry point to cannulate then that may contraindicate bypass in certain cases. Uh There are the that sometimes you have elderly patients with calcified aortas, but they may also have, for example, severe osteoarthritis of the hip and knee. So you can't even cannulate peripherally. You can't do femoral or cannulation or central cannulation. Um Then, I mean, this is the main one that I can think of that there certainly will be more, uh, if you give me one second, I will just check my notes cause I do have something on this. I think, to be honest, that's the main one. and fun other, other than that, I, I think it's more just about, uh MDT discussions and whether or not patients are generally considered fit for surgery. But I mean, because bypass is such a big replacement of the main function of the heart and lungs. In a, in a sense, I would say the main, the, the the main contraindication would be those patients that are very frail, maybe those patients that have a very uh poor cognitive state because bypass is often associated with some delirium, et cetera, post-op. So for patients already very uh has very poor cognitive cognition, preop, then, you know, they may often not receive, they may not, may be considered inoperable, but these are all relative and they're surgeon decisions. It's not like, you know, it's not like some, it's not like for example, how you wouldn't give penicillin to someone with a pen allergy, they're complex decisions. Um Mohammed Abbas, what is the pathway to becoming a cardiac cardiothoracic surgeon after graduating again, a great question. Uh Very much depends where you are in the world. Uh I can only speak for the UK as that's what I have experience with uh the pathway once you graduate in the UK is you need to apply for what we call specialty training. And uh the cardiothoracic training has its own specialty program. Uh I would employ you to essentially, if you go on Google and just search cardiothoracic ST one program UK, you'll find most of the information that you need. Um The process is you apply with, you apply, you have a certain amount of points based on a preset criteria which you can see in the matrix. And then if you score enough points on that matrix, you'll have an interview. If you do well enough at the interview, you get a job. Basically, there is another ro called this Caesar route. That's ce sr and that's, if you don't get a training job, then you basically find your own little jobs. You work those jobs for enough years manually, sign off all the same competencies and then you can get signed off as a consultant. Uh You don't need to do core training before cardiothoracic specialty training to low pain. No, it's, it's direct, you can do a year of core training first, but it's direct. You don't need to do core training. Um And uh are there any complications of the bypass? Yes, certainly. So the most serious one of, I guess is death. Um uh, you know, uh uh and that's, for example, if you're not venting the heart properly, if you're not using myocardial protection properly, uh, then you know, those things in and of themselves can cause what we call myocardial stunning So if the heart remains over distended for a long period of time, that itself causes ischemia and then uh then cell death. So, you know, it, it can happen that patients just never come off bypass because when you're trying to wean them off bypass, the heart's so stunned by having been so distended that it can't recover and contract. Uh The second is stroke, stroke is one that we worry about. And again, that's because any manipulation of the aorta carries a certain stroke risk. And even if done perfectly, you know, about 1 to 2% of cardiac surgical patients will have some small uh some small embolic event. Uh Thirdly patients after cardiac uh after cardio uh uh sorry, after bypass specifically, uh may often become cardio we sorry, what we call what we call vasoplegia, which is essentially all their blood vessels distend. Uh And they're hypotensive and they often need a lot of filling. So these patients often need a lot of fluids in the itu department. So we said vaso pleases, we said stroke, we said death, uh other complications. Um So uh patients can go into a, even though we haven't manipulated the bowel directly because of all the changes to perfusion oxygenation, et cetera. Sometimes patients uh remain, uh patients don't open their bowels and they can go into an ileus in the most severe cases, which of course is a form of bowel obstruction. And then you treat that as you treat any bowel obstruction, drip and suck and just wait for it to resolve. Ok. Yeah, I mean, there's a range of complications and another one is heparin in heparin induced thrombocytopenia. So some patients as a result of having had heparin will basically lose all their platelets. Uh And yeah. A F isn't really a complication of bypass. A F is a complication of the operation. Like A F is a complication of the handling of the heart, et cetera. But strictly speaking, it's, you wouldn't say it's a complication of putting the patient on bypass. That's why I didn't mention it. But A F is a very common complication of cardiac surgery seen in one third of patients, by the way, sorry to lope just to be very clear when I'm saying bypass, I mean cardiopulmonary bypass. I see what you mean. You may, you're saying coronary artery bypass grafting. So to be very specific, I'm I'm talking about specific complications of cardiopulmonary bypass. But yes, you're absolutely right to say that af is a common complication of coronary artery bypass grafting. And actually A F is the most common postoperative complication really in cardiac surgery. You see in about a third of cases. Um And for those of you that are going to work on the wards, et cetera, just know that there are two approaches to dealing with, sorry, that, that, that there are a range of things to consider when dealing with POSTOP A F and these are number one potassium, you want the patient's potassium to be above 4.5. If it's below 4.5 and they're in A F, it may be because of the magnesium levels. Number two fluid status, if the patient is unfilled, if they're hypotensive, then that can also precipitate A F if both of those things are corrected and sorted. Then in that case, often, if the patient did not have a f preoperatively, you will find a lot of consultants opting to use antiarrhythmics such as amiodarone, which is what we often use in my, in my center here and PAP. OK. Thank you very much for de I think that was a really good um teaching session. I think you're able to answer the questions. Um Don't forget. No, no, no worries at all. Thank you for having me and we can wrap it up now. Um Thanks NAMI for organizing this session and for organizing all these sessions. And um yeah, very grateful to be asked to give this session. Thanks a lot guys. Thank you. Um Yeah, so guys don't forget to fill your feedback form so that I can get a certificate. All right. And that brings us to the end of today's session. Um Just uh an announcement, the next session, the second session on this teaching series is going to be holding on next week, Thursday as opposed to two weeks time. That is because the um presenter wouldn't be available in two weeks and can only be available next week, Thursday. So we'll be having the second session on Thursday 7 p.m. I will put the poster up um and um the event is already on the C AV um page, so you can sign up for that also. And um I should have the poster before the end of the week, hopefully and um hope to see you guys in the next teaching session. Bye your question. And how long does it take to become a cardiothoracic surgeon? Um So we will be doing a later on. There will be sessions and uh mentorship sessions on how to become a cardiothoracic surgeon in the UK in the US and Canada. And um all these questions will be answered, but usually cardiothoracic surgery generally takes about 7 to 8 years. Um Normally, and if you are going to be doing an additional phd with the program, sometimes it takes as long as 10 years and um if it's in the US, it's a bit shorter. I think it takes about 5 to 6 years. So it depends on where you're doing your training basically, but in the range of 6 to 10 years in total, just to answer your question, we'll be doing uh sessions on how to become a card surgeon in different parts of the co in different parts of the world. Um later on following this teaching series. So just watch out for that. There is already a session on how to become a card surgeon in the UK on this uh card card unit sometime last year. Um If you go to the CG page, you should be able to see the vi the video recording of that session and you can just watch that. I hope that answered your question.