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Summary

This on-demand teaching session is aimed at preparing medical professionals for the UK main clinical exams as well as foundation specialty training. The course features a range of teaching topics delivered by different medical specialists. In this session, a seasoned clinical perfusionist from Nottingham Cardiac Center will share her expertise on the key concepts of cardiopulmonary bypass. Essential topics like the history of bypass, its basic components, the bypass machine functions, myocardial protection, and cardioplegia, among others, will be thoroughly tackled. This teaching session will equip you with practical and hands-on perspective on the complexities of bypass.

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Description

Description

Overview of The Functional Intricacies of Cardiopulmonary Bypass Machine and Their Role in Cardiac Surgeries. Topic Presented By Clinical Perfusionist Aisha Ali From Nottingham Trent Cardiac Centre.

Summary

Join the intriguing session on the intricacies of the cardiopulmonary bypass machine, led by clinical perfusionist Aisha Ali. Gain expert insights into the vital role these machines play in cardiac surgeries. This session is highly beneficial for medical professionals keen to enhance their knowledge and skills in cardiac care

Learning objectives

  1. Understand the basic functionalities of the cardiopulmonary bypass machine and appreciate the role and importance it plays in cardiac surgeries.
  2. Familiarize oneself with the component parts of the cardiopulmonary bypass machine and their specific functions.
  3. Gain deeper understanding on how the cardiopulmonary bypass machine takes over the function of the heart and lungs during surgery.
  4. Understand the role and function of myocardial protection.
  5. Comprehend the role of the perfusionist in the cardiopulmonary bypass procedure, including monitoring and operating the machine.
  6. Develop an understanding of the potential complications and risks associated with the use of the cardiopulmonary bypass machine and strategies to prevent or manage them.

Learning objectives

  1. To understand the history and development of cardiopulmonary bypass and its importance in facilitating open-heart surgery.
  2. To identify the primary components of the bypass machine, including the venous cannula, arterial cannula, and oxygenator.
  3. To understand the function of each component within the bypass machine and the way in which they work together to maintain a steady supply of oxygenated blood to the patient's body during surgery.
  4. To discuss the techniques used in myocardial protection and cardioplegia, including the importance of temperature regulation and blood conservation during bypass.
  5. To analyze the risks associated with cardiopulmonary bypass and safety measures put in place to minimize these risks.
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The following transcript was generated automatically from the content and has not been checked or corrected manually.

Thickens. Ok. We'll make a slow start, allow people to trickle in. Um But good afternoon, everyone. Thank you for joining us today on a Saturday and giving up an hour of your time. My name is I'm founder of Teaching Frontier. Essentially a group of president doctors with various grades and various specialties. Um come together to provide a wide range of teaching topics covering medical and surgical. Um and aim to prep you for UK ML and also foundation specialty training overall. Um We'll also frequently offer specialized lectures delivered by experienced specialists, registrars, and consultants within the field and we have a few lined up. So, uh stay tuned to that. And today is that so without further ado, um it's my pleasure to introduce your esteemed speaker who is a clinical perfusionist at Nottingham and Cardiac Center. She has extensive expertise, skills. Her unique background allows her to bring a practical hands-on perspective on the complex of D machines. Today, she will be the key concept of cardiopulmonary bypass, breaking down its mechanics, clinical applications and crucial role in cardiac surgery. So I we're excited and over to you now. Thank you very much. Good afternoon. Everyone. Thank you very much for joining and um thank you to the teacher in frontier team as well for organizing all of this. Um So I'll share my screen and then we can make a start. So can everyone see my screen? Yeah. OK, perfect. OK. So today, um I'm presenting um a little talk just on the intricacies of cardiopulmonary bypass. Um So as I said, I'm one of the clinical perfusionist and I'm based at Nottingham University Hospitals. Um And the aim of this talk is just to give you a sort of brief introduction to cardiopulmonary bypass. Um So we're gonna start with the history of bypass. Then I'm gonna move on to the basic components of bypass. Then we'll go into a little bit about how the bypass machine functions. We'll hopefully go through the basics of myocardial protection and cardioplegia. Some of the basic monitoring during bypass. I'm gonna touch a little bit on hemodilution and blood conservation. We'll go a little bit over temperature regulation and then I'm gonna finish off with some risks and safety devices associated with bypass out of all of these, for everyone who hasn't got much of a background in terms of bypass. I just want you to focus on these main learning objectives as an outcome for the end of this talk. So we'll start off with the history of bypass. Um So bypass was invented by a surgeon called Sir John Gibbons and he invented the bypass circuit in around 1953. And this is when he did the first case on a young lady who had an ASD. So he performed an ASD closure using the bypass circuit. And um interestingly, his wife Mary Gibbons was actually the first perfusionist to run this pump. And the invention of bypass actually pioneered open heart surgery. Prior to this, it's quite difficult to provide patients with um treatment options for various different um congenital issues. Um but also just general cardiac um pathologies that we see later on in life. So there's two pictures on the side which are quite nice. The first one shows um the first case which is the bypass circuit and you can see it's quite a big piece of kit there. Um And the picture below, it just shows a picture of John Gibbons and his wife with the bypass machine there. And this is the bypass machine that we use today. Um It's still quite uh a hefty machine. There's still a lot of components to it. We still use the same principles that John Gibbon um initially invented, but it's a lot safer. Um and it's definitely evolved over time. So what is bypass, then we'll strip it back to the basics. So bypass is a form of life support and it's used to take over the function of the heart and the lungs. Um and it's also used to provide a still heart to facilitate cardiac surgery and in doing all this, we're providing the patient with a supply of oxygenated blood. And there's a few aims and uses of bypass. So we want bypass to provide us with a still bloodless field because it's very hard to operate on a beaten heart. And it's also very hard to operate. If you can't see anything beyond the blood, it facilitates intracardiac surgery. Um So valve replacements major aortic surgery, we can also use it for um treatment in accidental hypothermia. So, an example of this would be a cold water drowning. We can use it to gradually rearm a patient. We can use it to facilitate heart and lung transplants. We can also use an adapted circuit for liver transplants and we can also use it in some thoracic cases. So I'm gonna go over the basic components of the bypass circuit then, and I'll split this into the main circuit and then we'll focus on the cardioplegia circuit. So this is essentially what the circuit looks like. So we start off with the venous cannula and this will drain blood from the right side of the heart. So this is venous blood being drained from the right side of the heart. It comes down the venous line and into the reservoir, which is an essentially a hard shell chamber that houses the blood. This then is pumped by the arterial pump and this acts as the heart. So this will pump the blood into the oxygenator which is a replacement for the lungs. This will oxygenate the blood and then the blood is pumped into the arterial cannula directly into the ascending aorta that goes around the patient and peruses them. And then we repeat the cycle again. So we'll start off then with the venous cannula. So we need a way to drain all of this venous blood to start off with the food that we insert a venous cannula into the right side of the heart. And this will drain the blood from the right heart into the reservoir. And it's purely by a gravity siphon effect. So the heart is higher than where the position of the reservoir is. So from that, we've got a negative pressure through which we get that gravity siphon effect. So venous cannulation can be split into two different types. We've got central cannulation, which just refers to the cannula as being um situated directly in the heart. And then we've got peripheral cannulation options. Uh Some of the sound is weak. Can you hear me clearly? Yeah. Ok. Um So yeah, we've got central cannulation where we're, we're draining directly from the heart. And then we've got peripheral cannulation where we are draining blood from a peripheral site. So in terms of the central cannulation, we can put a cannula into the right atrium and extend it all the way into the IVC and this will have a few perforations. So this cannula specifically is referred to as a two stage cannula and that just refers to how many holes there are. So there's one lot of holes here which will drain blood. And a second, lot of second, lot of holes over here in the right atrium. Um A three stage cannula would just mean that there's three, lots of holes um that we can drain the blood from. So cannul in the right atrium is generally your go to site. Um because you get the best drainage. The second way we can cannulate is by cable. So we can put two single stage, Cannulas, single stage, just meaning there's one set of holes at the tip of each cannula. So one can be inserted directly into the IVC. The second one can be directly inserted into the S VC. These are then joined together and connected to our venous line. Um and we can drain venous blood from the upper and lower extremities. And you can see that there's a little band going around both of these cannulas. Basically what that is doing is it is um snaring off the IVC and the S VC. So that we don't entrain any air into the venous cannula because that what that would do is it would impede the um gravity siphon effect. So B cable cannulation allows us to open up regions of the heart, for example, the right atrium, so that we can uh do tricuspid valve work or even um mitral valve work. Then we move on to the peripheral venous cannulation site. So the first one being the femoral vein. So in this one, the surgeon would locate the femoral vein and then they insert a very long cannula that goes through the femoral vein, um and all the way up into the SPC. And this will have multiple um holes all the way along the cannula and that will help drain venous blood. And then we've got a combination of a femoral venous cannula that extends up to the right atrium and a cannula that the anesthetist would put into the right internal jugular vein. And that would extend into the SVC. We connect both of these together and connect them to our venous line. And again, we can drain the patient from the upper and lower extremities. Now, peripheral cannulation is generally used in more complex cases such as reoperations. Um, when you've got a patient who's coming back in for a reoperation, they've got a lot of adhesions behind the sternum. And that just means that the, the um, a lot of the anatomy can be stuck to at the back of the sternum. So it's quite hard to, for the surgeon to perform a safe stoy, especially if the heart is stuck to the back of it. So, what we can do is we can cannulate peripherally, we can go on bypass, drain the heart and this gives the, the surgeon a bit of leeway to safely perform a median stoy. We also use this when we're doing major aortic work as well. Um Because it, it, it provides the surgeon with um a free surgical field. So we've got a way to drain the blood. We need a way to give the arterial blood back to the patient. Um And remember the whole point of cardiopulmonary bypass is to make sure that blood is bypassing both the heart and the lungs. So we're draining from the right side of the heart and we wanna give it back directly into the aorta. And this is where the arterial cannula comes in. So the arterial cannula will deliver oxygenated blood from the oxygenator directly into the aorta. And again, this can be split into central and peripheral cannulation. So central cannulation, which is our go to. And it's used for most routine cases is into the ascending aorta. So the surgeon will create an uh a little incision in the ascending aorta and they'll insert um our arterial cannula and this will be tightened by something called a purse string. So purse string is just a type of suture that rings around the aortotomy and that will hold the arterial cannula in place. Now, if you imagine when we're on bypass, we're pumping around 5 L of volume through this um cannula every minute. So the last thing we want is for this cannula to be loose and brisk it coming out. Then we've got the peripheral sites for cannulation and the main one is the femoral artery. So again, the surgeon will locate the femoral artery and then they will insert the arterial cannula through this artery and the floor you will see will go through the abdominal aorta up to the thoracic aorta around the arch into the heart and up to the head and neck vessels, we refer to this as retrograde flow. So in perfusion, as two types of flow, antegrade or retrograde antigrade refers to normal forward flow that's na native to physiology. And retrograde flow refers to backwards flow that's not native to physiology. So you can see rather than the floor going from the heart around the arch and down to the lower extremities, it's going in the opposite direction. So it's going from the lower extremities to the upper extremities. And then finally, we've got axillary and all subclavian artery cannulation. So this diagram here specifically is showing axillary artery cannulation, but subclavian is pretty much similar, similar to this. So the surgeon would place the cannula directly into the axillary artery. This is the right axillary artery specifically. So you can see the floor would go through the axillary artery up into the innominate artery down into the heart around the rest of the body and also into the left common carotid and the left subclavian artery. There are a couple of other arterial cannulation strategies we can use, but I just wanted to highlight the main ones that you would probably see, so once we've cannulated, then um we can go on bypass. Um So this is where then the venous reservoir would come into play. So remember, the venous reservoir is housing the venous blood. So you can see the venous inlet here is where the venous blood will drain from the right side of the heart. So that will drain into the venous inlet and it will go through a series of venous filters. And the role of the filters is to remove any debris, deform the blood and also DEA any of the blood before it's returned back to the patient. On the other side, you can see a series of ports which offer suckers and vents. I'm gonna touch on this in just a little while. Um But essentially suckers and events will also return blood from the surgical field. Um And they go through their one set of cardiotomy suction filters again to remove any surgical debris to get the blood deform the blood. And then you can see there's some sampling manifolds with the red, white and blue taps. Um These are used so that we can take blood samples, but also so that we can give drugs while we're on bypass. So from there, then the blood will enter the pump and this is referred to as the arterial pump. The arterial pump replaces the function of the heart because remember in a while, we're gonna stop the heart from beating. So there's two main types of pump. There's the roller pump and the centrifugal pump. Um in our center, specifically, we 100% use a roller pump. Um but I know the majority of centers now do use the centrifugal pump. So I will cover that in just a minute. So a roller pump is also referred to as a positive displacement pump. And the way that works is you've got um tubing which is in a raceway and then you've got two rollers which will rotate in this case, it's going in the anticlockwise direction. So the blood will enter through the tubing. And the way it will enter is because there is a ruler that is compressing the tubing. And as it's making its way around anticlockwise, it's creating a negative pressure and drawing that blood in from the reservoir. And then as the roller makes its way around, it's now compress the tubing to make a positive pressure and that will push the blood out into the oxygenator. And I've just got a little video here to show you what that looks like on our circuit. So you can see the ruler pulling the tubing in and the second ruler on the opposite side is pushing that fluid out. So then we've got the centrifugal pump and um we refer to this pump as an afterload dependent pump and um I'll explain why. So the way that this pump works is the pump head is placed on a motor and that motor will cause the drive shaft just at the bottom there to rotate. And when that rotates, it causes the magnets within the base of the centrifugal head to start rotating. And they are basically two magnets that are chasing each other. If you think about two north magnets chasing each other, um they would, they would rotate and that's essentially what is happening in the base of the centrifugal head. So when those magnets are chasing each other, they rotate the pump and they will rotate what we call um impella. So these are stacked cones. So this is the side on view you on the left hand side and you can see the ego view of the impella um on the right hand side. So those Impalas will then rotate um and they rotate at a certain number of revolutions per minute. And when they rotate, they create a vortex, so that vortex will essentially pull blood at the inlet. Um because there's a negative pressure there. So as they pull blood in the impellers also exert a centrifugal force. And what that will do is it will push the blood to the circumference of the centrifugal head and eventually push it out of the outlet. Now, I mentioned that these are after Lord dependent pumps. Um And the reason for that is because we, we, we run these pumps based on a certain number of revolutions per minute. So for example, 1500 revolutions per minute might give us 500 mils of flow per minute. Now, if you've got an increase in afterload, for an ex for example, an increase in systemic vascular resistance, then the b the blood leaving the pump is faced with a bit of resistance. So what you would find is that although you've got 1500 revolutions per minute, your flow will now drop from say 500 to 400 mils per minute. And the same is true if you have a reduction in afterload, um you would find that the same number of revolutions per minute, you would have an increase in floor. So these are floor dependent afterload, dependent pumps. Whereas the roller pumps, you set it at your desired floor and it will keep pumping at that floor no matter what happens to the afterward. So from the arterial pump, then it is pumped into the oxygenator and the oxygenator replaces the lung function and it also aids in cooling and rewarming of the patient. So the lungs itself have a surface area of around 100 m squared. Um Whereas our oxygenators have a surface area of around 2 m squared, so they're very, very, very efficient. Other perfusionist have run um uh bypasses for much, much longer than six hours. And you don't really see a drop in the efficiency of the oxygen air. So there's a few different components to the oxygenator and um I'll talk you through all of them. So what you'll get first is you'll get the entry of venous blood. So that'll come into the inlet and as it enters, it will go through an RT W filter. So the RT wheel filter is an integrated filter that will again DEA any um any air that might still be in the blood. So it's sort of the final filter before it enters the patient, then it will flow over the heat exchanger. So you can see the heat exchanger is the middle compartment. Now, this is a separate compartment, it's completely enclosed and through it, we flow either hot or cold water. And on the outside of that compartment is stainless steel which will conduct this heat or the cold. So when the venous blood will flow over that stainless steel, it will either warm or it'll cool depending on what, what what water they're flowing through and then we will um oxygenate the blood and this happens through gas exchange. So you can see air and flow and inflow via this green port here and it'll go through hollow fiber membranes which look something like this. So gas will flow through the middle of the lumen of the hollow fiber er of the hollow fibers. And these hollow fibers have perforations all the way along the length. So what that facilitates is gas exchange by diffusion. So the gas entering the lumen is rich in oxygen, whereas the blood is rich in C two. So what would happen is the oxygen from the gas would diffuse over into the red blood cells by going down the concentration gradient. And the CO2 from the red blood cells will move down the concentration gradient into the inner lumen of the hollow fiber. And that CO2 is collected and it is blown off uh the CO2 exhaust. So what we end up with is either warm or cold blood that is oxygenated and that will leave the arterial blood outlet and be pumped into the aorta. So we've got a circuit now. Um but we need to anticoagulate the patient in order to go on bypass. So, anticoagulation is absolutely essential for bypass um to anticoagulate our patients, we use Heparin. Um So heparin is an indirect thrombin inhibitor and it will interfere in the coagulation cascade to um stop the blood from clotting. And the reason we need to anticoagulate the patient is because if you imagine this entire circuit that we've gone through, start to finish is a foreign surface. It's made up of PVC silicon polycarbonate surfaces, all of which if the blood came into contact with it without um any heparin, it would clot off and you can imagine the result would not be very nice. So we anticoagulate the patient just before we go on bypass. And um there's, there's two lots of doses that the patient will eventually receive. The first is a bolus dose. This is usually given by the um anesthetist and the dose is generally 3 to 400 units per kilogram. And we'll put a bolus dose into our bypass prime as well. So in our center, we put 10,000 units in for patients under 100 kg and patients who are over 100 kg, we will put 20,000 units of heparin into the prime and we monitor the effect of heparin by measuring the s generally every 15 to 30 minutes, we might increase this. Um Depending on what point of the operation we're in, whether we're warm, whether we're cold. Um But the aim is to get the around 400 seconds and above. Um and just for reference, um a normal range of A CT is about 100 to 100 and 20 seconds. So we're increasing the activated clotting time by almost four fold. And then we can reverse Heparin once we're off bypass with the antidote, protamine. And this is why Heparin's quite a nice anticoagulant to use because it's got a nice halflife. And also we can reverse it as soon as we're off bypass to help with um clotting. Ok. So we're on bypass. Now, um we've established a nice floor. We've got a cannula, we've got two Cannulas in place. We've got the reservoir, we've got a replacement for the heart and a replacement for the lungs. Now, we need to move on to the actual operation itself. So at this point, the surgeon will place something called the aortic cross clamp onto the aorta. So this diagram here shows you just where that aortic cross clamp is placed. So you can see our arterial cannula is here. The venous cannula is situated in the right atrium and this is just a cardioplegia cannula here that we would use to stop the heart from beating. So between that cardioplegia cannula and the arterial cannula is where the surgeon will place that cross clamp. Now, what the cross clamp does is it completely occludes the aorta. And once that cross clamp is placed, the heart is isolated from the rest of the systemic perfusion and it's basically ischemic. So this is the point at which we need to rapidly arrest the heart. So we move on to myocardial protection then and cardioplegia. So, cardio refers to the heart pegia refers to paralysis. Cardioplegia is paralysis of the heart. Cardioplegia is a solution that we use to electrochemically arrest the heart temporarily. And this provides myocardial protection as well as this, it stops the heart from beating. So it gives the surgeon a nice still heart to operate on and cardioplegia works by changing the electrochemical gradient across the myocytes um in order to induce this arrest. So there's a few aims that we expect from cardioplegia. The first is that we want the cardioplegia to arrest the isolated heart immediately and we want it to arrest the heart in diastole. The reason we want it to arrest in diastole is because this is the least energy consuming state. It's not using much oxygen at this point. And it's also nice and flaccid for the surgeon to um operate on and manipulate the heart. We also want the heart, uh the cardioplegia to protect the heart and its function. We want the cardioplegia to provide AAA nice still heart for the surgeon to operate on. And we wanna make sure that after we take the cross camp off the heart beats and preserves its function. And this is what our cardioplegia circuit looks like. So this is a circuit of a high potassium blood cardioplegia, which is probably one of the most common types of cardioplegia circuits you'll see. Um So it's based on a dual pump and it's delivering blood cardioplegia. So blood cardioplegia is generally given in a 4 to 1 ratio where it's four parts of oxygenated blood and one part of high potassium cardioplegia. This is then mixed together and it is delivered via the cardioplegia system and delivered directly into the aortic root to the coronary arteries. So you can see that we're shunting some oxygenated blood directly from the reservoir. And this will come into pump A and then from pump B, at the same time, we've got the high potassium cardioplegia solution being pumped around and this will mix and that is what is being delivered to stop the heart from beating. And I'll just show you that again. Now that you've got a bit of an explanation as to what is going on. So there's two types of um cardioplegia, two main types. One is extra cardio, uh extracellular cardioplegia, also known as high potassium cardioplegia. And um the way this works is it uses, it utilizes its high potassium to induce an electrochemical arrest. So, if we take a normal action potential in the heart, you'd start off at phase four, which is the hyper repolarise state where the membrane potential is about minus 90 mi. And then because of your sodium potassium channels and um your leaky channels, your membrane potential will eventually rise to the threshold which is minus 70. And at this point, sodium gated channels are opened and you get a rapid influx of sodium from outside to inside the cell. And at this point, this is um phase zero or depolarization. The cell then depolarizes all the way to phase one at which point potassium gated channels open and potassium from inside the cell will move outside the cell down its concentration gradient to try and lower the membrane potential to about zero at which point we get to phase two. So at phase two calcium channels also open. Um and this is the point at which the heart will beat in phase two. So you'll get systole and then the calcium will be sequestered into the sarcoplasmic reticulum. Then what would normally happen is the cell would repolarise and the way it would repolarise is the potassium inside the cell will move down its concentration gradient um to the outside of the cell. And that will help reduce the membrane potential in phase three. So that we're back down to phase four. But what happens when we give high potassium cardioplegia is the high potassium floods the extracellular space just outside of the myocyte. Um So what that means is when we get a after phase two, when phase three is ready to initiate the potassium can't actually move down its concentration gradient anymore because the potassium concentration outside the cell is much higher than inside the cell. So what we get is a depolarized arrest in diastole. And the next type of cardioplegia is intracellular cardioplegia. Some might know this as custodial or HTK solution. This is a low sodium and low um virtually no calcium concentrated solution. Um So the way this arrests the heart is it arrests the heart in a hyper repolarise state. So we flood the extracellular space with this low sodium no calcium solution and that will reduce the sodium in the extracellular space. So when the cell eventually does reach threshold, the sodium gated um channels won't open because they um sorry, the sodium will not influx into the cell because it can't move down a concentration gradient because the sodium outside the cell is much, much lower than it is inside the cell. And then that means that we can't enter phase one, we can't enter phase two and the heart won't contract. And of course, that means we can't enter phase three. So what we've got is a heart that is arrested in hyperpolarized state. But remember because it's in phase four, it's already um it, it, it, it's, it's basically prevented from um contracting. So it's, it's still in a diastolic phase. So there's a few ways we can deliver this cardioplegia. The first way is through the aortic root and this is antegrade, remember, antegrade means forward flow. So to deliver this, um you can see the cardioplegia, cannula is just inserted into the aortic root. And this blue strip here is the um the aortic crossclamp. So the cardioplegia will be delivered directly into the root at a very high floor under high pressure. What that will do is it will snap the aortic valve shut and the cardioplegia will flow directly into the coronary ostia down the coronary arteries and induce a rest. Now, when we give antegrade, cardioplegia through the root where depending on a competent aortic valve, if you've got a regurgitant aortic valve, it won't um it won't create a tight seal. And what that will mean is if we pump in that high potassium cardioplegia at a really high pressure, it will just leak directly into the left ventricle and it won't go into the coronary arteries. Um So you won't get a proper arrest, which is what we don't want. So we can use alternative methods to this. And one of them is um direct osteoc cardioplegia. So sometimes what the surgeon might do is they'll cross the aorta and then straight away, they'll open the aorta and stick two cannulas one into the left coronary ostia, one into the right coronary ostia. And we can deliver this floor antegrade directly through to the coronary arteries. And this method is also used during aortic valve replacements as well because the aorta is open and in uh major aortic work, then we've got retrograde cardioplegia, which is an alternative. If you've got a patient who's got severe aortic valve regurgitation, you can arrest the heart using retrograde cardioplegia. So remember, retrograde means backwards flow. So the way retrograde cardioplegia works is the surgeon will place a uh cannula into the coronary sinus. Now, most of the coronary veins drain into the coronary sinus and then the coronary sinus drains into the right atrium. So what the surgeon can do is put a cannula into that coronary sinus. And the perfusionist can pump cardioplegia backwards into the coronary sinus. It will get delivered through the coronary veins, it will flow over the capillaries and then into the coronary arteries and it'll come out of the top of the coronary ostia. So, like I said, this is really good when you've got a patient who's got um aortic valve regurgitation. But the downside of this is that not all coronary veins drain into the coronary sinus, some of them will directly drain into the right atrium, which means that you're not actually getting a homogenous distribution of this cardioplegia. If you'll only need to give it into the coronary sinus, because the, the arteries that are linked to those vessels draining in the right atrium aren't actually receiving any cardioplegia. So, normally, what we'll do is we'll give retrograde cardioplegia, but we'll also top it up with some osteoc cardioplegia going down the right coronary artery to make sure that we're also protecting the right side of the heart, which is where most of the vessels drain into the right atrium. So we'll move on to stuck as in bent. Now. Um, so the, the aim of suckers and events is basically to return any blood in the operative field. So, an aortic root bent is placed in the aortic root. Um, this is used in, uh, basically every single, um, open heart surgery. What that will do is it will remove any additional cardioplegia that we've given. If we've given it through the root, it will also remove any accumulation, um, to avoid aortic distention and we can use it to deer the heart just before we take the cross clamp off. And then the next type of vent that we use is an LV vent. And this is used in every single valve, um, case or if we're doing any major aortic work, there's two ways. Um, we can place this valve, generally, it's through the right superior pulmonary vein. So it'll be inserted through the right, superior pulmonary vein, be extended into the mitral valve. And then down to the left ventricle, you can also directly cannulate the left ventricular apex and put the valve in that uh the LV bent in that way, the LV then prevents ventricular distention. Um The reason why the ventricle would even distend in the first place is because you actually get an accumulation of blood into the left side of the heart. And you might be wondering why. And the reason for that is because there are actually some veins that drain into the left side of the heart. So that the B and the bronchial veins will drain into the left side of the heart. And over time, you'll get an accumulation of blood. Now, if you combine that with cooling a patient, um who eventually becomes bradycardic, the left ventricle can't assuming the cross comp isn't on the left ventricle can't remove that um blood. So we need to make sure we're sucking it out because if the ventricle does distend with an accumulation of that blood over time, it will damage the um myocytes. And that's the last thing we wanna do when we're trying to fix someone's heart. The LV vent is also used to help um remove any air as well. So we use it to de air just before we take the cross clamp off in conjunction with the aortic root vent. And um of course, it provides a bloodless field for the surgeon. Both of these meds also will help maintain um the temperature. So when we deliver cardioplegia, most, um most of these um doses will be delivered cold if not all of them in our center. Um And the reason we deliver it cold is because when, when we deliver it cold, we're also cooling the myocardium itself and that will reduce the oxygen demand of the myocardial tissues. So, if you imagine a left ventricular bent and an aortic root bent will help keep to keep removing any accumulation of blood that would otherwise slowly warm up the heart. And then finally, we've got a sucker. So a sucker is just placed in the cardiotomy field um around the heart and that will just suck any blood back to the um venous reservoir. And then I'm just gonna really quickly touch on the pulmonary artery vent, pulmonary artery vents aren't very common. Um But again, they use two D and um create a blood, a blood in this field. So temperature management, then this is very important in bypass. Um So on the right hand side, you can see uh what looks to be a big silver box that's actually a heater cooler. And in there you've got ice and water and that is what will flow through either the oxygenator or the cardioplegia delivery system to help warm or cool that blood. So that will flow through blood will flow over the top of the heat exchangers and that's how the, the blood will warm or cool. Now, temperature management is very important in bypass. Um, generally we cool for routine cases, we'll cool patients between 32 and 34 degrees. So for every one degree of cooling, there's a 7% reduction in the oxygen demand, which is um quite significant. If you cooling to 32 degrees, that's a 35% reduction in oxygen demand. Then we've got some monitoring. So we monitor the patient's blood gas every around 15 to 30 minutes while we're on bypass. And this will ensure safe perfusion. So we can alter the patients via chemistry. Um just to optimize them during the time that they are on bypass. And on the right hand side, you can just see a blood gas from a, a case that we did a week ago. So from the blood gasses, then we monitor and adjust the ph we try to keep that within normal ranges. We will also monitor and adjust the gasses. So you can see the P CO2 generally is kept within normal ranges. We might actually um run it a little bit higher if the patient has previously had a tia a stroke or they've got carotid stenosis. And the reason for that is because CO2, it actually promotes cerebral vaso dilation. So that can increase the flow that we're delivering to the brain to make sure we're protecting it. Um And then the po two, you can see we're running it a lot, lot higher than normal ranges in our center. We run it between 20 to 40 Klopas. There's a couple of reasons for that. One is when you go on bypass, it's a massive insult to the patient and they will suffer from an inflammatory response. And because of that, their oxygen consumption will increase. And the other reason is because any component of bypass can fail at any point. And if any component fails, we're essentially off bypass until the perfusionist can quickly attend to it, change whatever that component circuit is or resolve the problem and get back on bypass. Now, in that time, that might be about two or three minutes. If we've got a high content of oxygen on board, it means that the patient's got a little bit of a reserve of oxygen. In case of those types of scenarios, we also monitor and adjust the acid base balance. Uh the electrolytes, specifically potassium and sodium, we'll, we'll monitor the glucose. Um We don't actually do anything for the glucose. Um We'll kind of just let the anesthetist know and then they'll start running some insulin if it gets too high and we'll monitor the lactate as well. Um which is a very good indicator of perfusion. And the other thing we're looking at is um venous and arterial oxygen saturations as well as the hemoglobin. And I've highlighted the hemoglobin here because you can see it's quite low and on the ward that might um trigger a little bit of concern. But on bypass, this isn't actually something that's very uncommon. Um And the reason for that is hemodilution. So to go and bypass, we have to prime the cardiopulmonary bypass circuit and we prime it with clear prime. So now our center that's a combination of colloid fluids such as gel plasma and crystalloid fluids such as plasma light. And we prime the circuit so that we make an airfree connection with the patient. In our sense, our prime is about 1.75 L. So if you imagine when you go on bypass, that is a massive amount of volume to be pushing into the patient within a couple of seconds. So what that can do is it can severely drop the HB. Um So what we do is we predict what the HB will be on bypass. And if it's more than 80 g per liter, that's fine, we'll continue. Um And we'll basically try and concentrate the patient on bypass and opti optimize their HB. And if it's lower than lower than 80 g per liter, that's not very good. And um we'll have to start looking into some preoperative blood conservation um strategies and also maybe priming with donor blood. So on the right, there's a table of some blood conservation strategies that we use. Um So preoperatively, we can try and improve a patient's HB if we already know that they're either anemic or maybe they're a Jehovah witness patient and can't accept a blood transfusion. Um So we can optimize that by giving them um iron supplements or erythropoietin, which is an I um A red blood cell stimulating drug. So we can try and increase their red cell production. We can also try and cut out any excess tube in and use a smaller circuit to reduce our primary volume intraoperatively. Again, we use a, a smaller circuit, reduce the prime. We can do something called retrograde autologous priming, which I've not actually gone into in this talk, but essentially what it is is we use the patient's blood to um prime the arterial and venous lines and simultaneously remove that clear prime. That was in those lines, we can hemoconcentrate. So if you think of this as something similar to almost dialysis, so you've got a filter that we can connect to our, we can um hook up to our circuit. Um and we can pump blood through the hemoconcentrator. What that will do is it will remove excess um fluid and it will concentrate that blood up. Um and return it back to the patient. We can also promote an increase in urine output. Um So we might adjust our pressures and floors on bypass, but we can also give diuretics like Mannitol and Fura. Um And if we can't do any of that, we can blood prime using a um a, a unit of um donor blood or we can on bypass, we can give um a unit of blood. So in our center, the trigger for giving a unit of blood is 70 g per hour bypass. And postoperatively, we can use cell salvaging, which is essentially where we save the patient's own red blood cells, we wash it and we return it back to the patient. So there's also other essential monitoring that the perfusionist is always keeping an eye on. The first one is ECG and this is essential especially for myocardial protection. Now, there's two rhythms that patient uh that perfusionist absolutely love to see. One is sinus rhythm and the other one we always want to see is asystole. And of course, we only want to see asystole once we've given cardioplegia. Um So if there's any change in um the ECG, whilst that cross clamp is on, then that might trigger us to think about delivering more cardioplegia or think about um other delivery routes um to make sure that we're fully protecting the heart. The other thing we monitor is the mean arterial BP. And the reason I'm I'm I'm highlighting that it's the mean arterial BP is because the when we're on bypass, the flow that the patient is um receiving is not a pulsatile flow, it's a nonpulsatile flow. Um So generally, we'll keep the mean arterial pressure between 6085 millimeters of mercury. And of course, when the heart is beating again and we're ready to come off bypass, then we will be looking at this um systolic BP as well. But throughout the course of bypass, it's generally the, I mean arterial pressure. And we also monitor the venous, uh the central venous pressure. And this is really good for perfusionist to understand how empty or filled the patient is. So, um when the patient comes in, we'll make a note of what their baseline CVP is, which might be five, for example. And then when we go on bypass, we want this to be as close to zero as possible. And that basically means that we're adequately draining the venous blood. And then when we're ready to come off bypass, we wanna fill the heart again and make sure we're getting it back up to around five to make sure that we're adequately filling the patient. Um We've also got cerebral monitoring. So this isn't used in every single case. It's mainly used for patients who've previously had a tia a stroke. Um have carotid stenosis or when we're doing major aortic work, then we'll use cerebral monitoring and that will just tell us what the oxygen saturation is in the left and the right sides of the brain. Um And it'll help us optimize um protecting the brain. I've not included arterial and oxygen saturations. Um But of course, we're also always monitoring this as well, then we move on to drugs and fluids or throughout the entire course of bypass. Um, all the drugs and fluids are given via the circuit. So the drugs that will routinely or no will, will, will, will most commonly use, um, are the following. So Heparin we've already discussed. Um, and we can top that up if we see a drop in the T and then we can use vasopressors such as metram to raise the BP, basal dilators, such as phentolamine to drop the BP if it gets too high, um we can give positive inotrope such as mone. Generally, we'll give this to patients who've got a compromised um left ventricular function. Um And we can also use antifibrinolytic such as aprotinine which will help in post operative bleeding, um and then fluid management as well. So we're always measuring the patient's urine output. We're always looking at the HB and using these two meas uh parameters, we can balance the patient's fluid management. So we use a mix of colloids and crystalloids to maintain fluid balance, but also to maintain oncotic pressures because the last thing we want is to um come off bypass with an edemic patient. So finally, we're gonna move on to some risks and safety devices that are associated with the bypass circuit. Um So the first one is if you've got inadequate anticoagulation. So, if you had inadequate anticoagulation, what could happen is your reservoir and or your oxygenator could cut off completely. In which case, you can't provide any floor to the patient and you need to do an emergency change out of the reservoir or the oxygenator or both. Then we've got circuit component failures and there's a few different components that can fail or the first one is the reservoir. So this can either explode or implode. Um So it can explode if you've got a constant build up of positive pressure and no way for that pressure to be relieved. Normally in the reservoir, there's a vent which will relieve that excess positive pressure. But if that was to be CLD, for example, this nice little video will show you what will happen. So in that red circle, you can just see the the reservoir at the bottom and all the time, if you build up positive pressure, it can explore. In which case you are off bypass, you've lost the entire circulating blood volume of the patient and possibly in trained air into the patient, more than likely in trained out into the patient, then we've got oxygenator failure. So this could occur. Um Just because you've got a faulty oxygenator, it could be because you've been on bypass for nearly 13 hours and the efficiency of the oxygenator is now reducing. And you think you might, I might have to do an elective change out. You might have a crack in the oxygenator. Um In which case, it might be in training some air which you don't want to pump into the patient. So you might have to change this out. So you have to come off bypass and quickly do a change out um and put a new one in, get back on bypass with it replied and airfree, the other thing we see, especially with baller pumps um is pump failure, uh pump with rupture, sorry and arterial pump failures. So if you've got an arterial pump failure, we will pull out something called a hand crank, stick it into the roller and we will hand crank um in, in an anticlockwise direction in this pumps case to provide the patient with the floor that they need. Um So you can imagine that it, it would be quite a high um and high pressured and stressful environment that your hand cranking and trying to keep up with this patient's flaw that could be anywhere between 100 and 20 to 100 and 60 revolutions per minute to make sure that you're providing a, a patient with that floor. Um And you get some very similar for centrifugal pumps as well if they fail. Um you can place a centrifugal head onto a manual hand cr and manually um provide floor to the patient. Um specifically in roller pumps, you can get a pump boot rupture so that can happen for a few different reasons. One, you might have something sharp sitting in the raceway which might perforate the tubing and completely split it. In which case you're off bypass and you have to do an emergency, um, pump boot change out. It might also be, um, after wear and tear. So you might be on bypass for 13 hours and this Waller has been compressing that tubing for 13 hours, it's become very thin and it could tear that way as well. Then we move on to gas failure. Um, so you might lose gas from your um from your main source. So usually this is like a pendant that the Heartland machine is connected to. In that case, you'd either use the anesthetic machine as backup or you would use an air and oxygen cylinder to provide you with gas flow again. So now I'm gonna move on to some of the safety devices and risks associated with bypass. So the first one is if you've got a low um reservoir volume, so a few reasons for this could be that the um you're not getting very good venous drainage. And this could be because the venous cannula is a bit too small for the patient. It could be because the cannula position hasn't been placed very, very well. So it's obstructing some of that flow. Um It could be because the surgeon is manipulating the position of the heart to perform a certain part of the operation. In which case, some of these holes might be occluded and that might um prevent your drainage or it might be because your reservoir is just really high. Um in comparison to where the heart is. So you're not creating that optimal gravity siphon effect. Um Now, in that case, what would happen is you've got a level detector just here. Um And what this does, it's, it's, it's stop linked to the arterial pump. So when your level reaches the um level detector, which in our center is 300 mils, the level detector will stop the pump. So I'll just show you that again. So we start off with a full reservoir and then over time we've lost venous drainage. Um We've hit the level detector and the pump has stopped pumping, then we move on to a venous airlock. So venous air can be um entrained through the cannula. Maybe the purse string isn't on tight enough. Um Maybe we've got B cable cannulation and the SPC and IVC Cannulas haven't been snared off and then the surgeons opened the right atrium which has entrained lots of air into your venous line. What that would do is it would impede in the venous drainage. And we refer to that as a venous air lock. So what you get is, um, you get a reduction or no drainage at all. And what that will do is it will reduce the volume in your reservoir that will in turn, um cause your level detector to stop the pump from pumping. Um And then you're not providing any floor to the patient anymore. So in that scenario, it's essential to manipulate this venous air and get it out of the system. Then we've got air and bubbles. So what you see on the um bottom, right, just after the oxygenator is something called bubble detector, we have this on the main circuit and the cardioplegia circuit. So what that will do is again, it's stop linked to the arterial pump. If it detects any air or bubbles, it will stop the arterial pump from pumping um and prevent us from pushing that air into the patient. And at that point, what we would do is we would remove that air and I'll show you what that looks like. So you can see the air is detected by the bubble detector, bubble detectors triggered main main arterial pump stops and we've got the same thing in the cardioplegia system. So you could entrain air from the oxygenator, you might accidentally empty out your cardioplegia bag. Um at any point you can entrain some of that air. So it would flow through into the cardioplegia bubble detector that will detect it and stop both of these pumps from running. And then the effusion will get that air out before it reaches the patient. I'll just show you that one more time. So, of course, we've got these safety devices. Um but the perfusionist is the first line of defense in all of this. Um These are just backup devices um in case you know, the the perfusionist misses it or is distracted or there's something else going on in the case that is a lot more chaotic. Um We've got these as sort of backup safety devices. So that is basically everything from me. Thank you very, very much for um listening. I hope that made um a bit of sense to you all. And um I'll have you take any questions if anyone's got any, you can post your questions into the chat. By the way, you're welcome guys. Thank you very much for listening. So if you've not got any questions, then um is it, what's that? Sorry. No, go ahead, go ahead. I was um so if there's no more questions, then um Vikram's asking if the slides will be sent out. Um I'll send them to RHA and then I'm sure he'll pass them on to you guys. Um So there's feedback forms, you can scan this QR code. I would be most. And so the teaching frontier team be really grateful for any feedback to help improve these sessions. 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