And I tried to make this talk as practical as possible, so hopefully give you guys a little bit more of an understanding of what you're doing when you're either using the yellow or the blue pedal for your EMR procedures. These are my disclosures. Learning objectives of the talk today are to understand the concepts of current density, voltage, power, and how they apply to endoscopic surgery, to distinguish between pure cutting, pure coagulation, and blended current, and to familiarize yourself with common starting settings, and recognize nuanced scenarios and how to modify basic settings accordingly. So just one slide on the physics, ESU for dummies. I promise I won't belabor this, but a few of these concepts are important just to get a sense of what we're dealing with before we move on. So a circuit is a flow of electrons from the electrosurgical unit to the active electrode, to the patient, to the pad, and back to the electrosurgical unit. Current is the flow of electrons through the circuit. Resistance or impedance is the opposition to the flow of electrons. And as you apply your current and desiccate tissue, the resistance or impedance increases. Voltage is the electrical force pushing the current around the circuit through varying degrees of resistance. And the one equation to keep in your mind is that power is equal to voltage squared over resistance, or current times voltage. I'll have this on some of the next slides when it's important. So the first thing is really to know your generator. It can be one of three types. Constant voltage, which is the Irby generators, which most of you probably have. Hybrid generators, or constant power generators. And I'll talk a little bit about how each of these work. In general, a lot of the older generators, like the Valley Lab we were talking about today, are constant power. And then the older Irby ones and the Olympus ones are hybrid generators. And the constant voltage ones are the newer Irby, both the VIO3 and the 300D, which is the older model. So constant voltage generators. These work by calculating circuit impedance, or resistance, the same thing, and adjusting the power to match what is needed. The new VIO3 calculates circuit impedance 25 million times and adjusts the power instantaneously. And what this means is that when you're setting a power level, for example, 80 watts, you're setting a maximum wattage level. And that's not necessarily what's going to be delivered to the tissue. On the other hand, a constant power generator, like the old Valley Lab ConMed generator, these ones probably may see your endo unit sitting in the closet somewhere, but hopefully you're not still using. Either way, as tissue impedance rises, because of the equation we talked about earlier, the voltage also has to rise to produce the constant power. So what this means is you can have excessive tissue injury. However, both are fine as long as you understand how to use them. The hybrid generators are constant voltage in cut mode and constant power in coag mode. This is a video that was given to me by the folks at Irby, which demonstrates constant voltage versus constant power. So here I'm playing a constant voltage clip. So basically, obviously, this is a chicken breast here. And you're using forced coag effect to 25 watts, which is generally what most of your generators will be set to for the blue pedal for polypectomy. And even though you're really sitting on the pedal for a long time, you get this nice thermal effect that's really just the outline of the snare here. That's constant voltage, because as the tissue is desiccated, the current has to go down to zero or very low to maintain the voltage at a constant level. On the other hand, this is what happens when you have a constant power generator. So you're stepping on the pedal very similarly to as you are with the constant voltage generator. But when you step off, you can see a much more dispersed thermal effect. And so that's what you want to avoid. So really, with a constant power generator, you have to be able to step off the pedal as soon as you've felt that cut go through. So let's talk a little bit about cut versus coag, yellow versus blue pedal. And these are the standard polypectomy settings here that most of your generators will already be set to. So to produce a clinical cut, we talk about something called microelectric arcing. And the cutting waveform is a sinusoidal waveform that needs a peak voltage of more than 200 volts. The voltage quickly raises the water temperature in the cell to a boiling point. The cell explodes, and you get a cleave plane or a clinical cut. Examples of cutting currents are autocut or pure cut. On the other hand, a coagulation waveform is more of a traditional waveform. You get spikes of high voltage, followed by rest periods. And this high voltage is what can cause a thermal injury. So you have a very much reduced duty cycle, meaning the generator's not working the whole time, around 10% to 20%. And the traditional coagulation modes are forced coag or spray coag. And we'll talk about what each of these are in a few slides. Next, I'm going to focus a little bit more on blended cut, which is what most of us use for EMR. And this is a mix of cutting and coagulation current. And really, a nice understanding of this will help you perform more nuanced EMR. The blended cut current settings are generally endocut I or endocut Q. We use endocut Q with a snare for EMR. And so once the cutting or the arcing of the tissue is present, the yellow waveform is activated, as you can see on the right side of the screen, for 2 to 48 milliseconds. And that's the cut duration. And then you get a blue cycle called the coagulation period, which is a cut interval. And this really produces a precise cut and doses the power appropriately based on the circuit impedance or resistance, which is the desiccated tissue. So you set the effect, the interval, and the duration with endocut Q. So a little bit about each of these. So first, the effect. You can have an effect of 1 to 4. If you have an effect of 1, you really have no coagulation at all between cutting cycles. So this is the equivalent of a pure cutting current. As you increase the effect from 2 to 4, you get the maximum amount of coagulation between cycles. But it's important to note that this coagulation you're getting using the endocut mode is not the same as a forced coagulation or a soft coagulation. It's not going to give you that same coagulation effect. It's going to be much reduced. That being said, it certainly helps with hemostasis. The interval is the time of a cutting and coagulation cycle combined. And it can be settings 1 to 10. A short cutting interval means more rapid cut or less coagulation time between the cuts. And the larger cutting interval, longer cutting interval, means a slower, more controlled cut, so more coagulation time. So on the top here, this image is a cutting interval of 1. So you have less time between cuts. And on the bottom, you have a much longer blue cycle, which is a much higher cutting interval of 10. Lastly, duration. This is the time spent cutting. And this affects the length of a cut. Important for a sphincterotomy, for example, not as much with a snare. But this is settings 1 to 4 again. Setting 1 is a brief duration, limits the length of a cut. And this is what we use for polypectomy in general. Setting 2 is a little bit of a longer cut. Same with setting 3. And setting 4 is the longest, most rapid cut. Setting 3 is generally what we use for a sphincterotomy. So these are the standard polypectomy settings on the VIO3. We use an effective 2, a duration of 1, and interval of 4. So I'll return to this later. But what would you do, for example, if you had the standard polypectomy setting and you were having a lot of bleeding in your EMR defect? There's three things you can do based on the previous slides. You could increase the effect, because that's going to produce more coagulation. You could decrease the duration. But the duration's already at 1, so you can't really do that. Or you could increase the cutting interval time. So probably the easiest thing to do is just simply to increase the effect. And 2 to 3 are both generally what we use for EMR. The global overview of waveforms, this is really to give you a sense of the different currents that can be used on the ERBI generators. And so as you move from left to right, we're increasing, in general, the voltage, and hence the thermal injury. You can see the endo-cut and soft-coag really work at a very low peak voltage. And as you move to the right, you get dry-cut, precise-cut, force-coag, and spray-coag, which is a very unwieldy current that operates at a very high voltage and can produce a lot of thermal injury. And they all kind of have their role in the procedures that we do. Precise-sec is a new current that's available on the VIO3. Hopefully some of you have had a chance to experiment with that. But it's really called a smart current. It helps to modulate between cutting, if you're, for example, encountering, when we do third-space procedures, submucose that's vessel-free. And when vessels are encountered, it's more to a coagulation mode. This is from Dr. Raju and MD Anderson. And another nice way to think about the difference between the currents, soft-coagulations on the left. And you can see that you really don't produce a lot of thermal injury, because you're working at less than 200 volts, in terms of your peak voltage. As you move to the right, a pure cutting current certainly has the potential to produce a deeper cut without any coagulation. And we get the standard blended current. And the real coagulation current, like a forced coag that we would use for EMR, really can produce that cut. But it comes with a lot of thermal injury and coagulation. So it's almost like you're just using the mechanical force of the snare to kind of burn through the transsection of the polyp. So you may be saying, why are you telling me all this when Heiko Pohl published this paper that showed absolutely no difference between the blue petal and the yellow petal in a large randomized trial? There were 928 patients randomized to either the blue petal forced coagulation or the yellow petal endocut. Using the standard settings, we've been talking about 214 endocut or 2 in 25 for forced coag. And there was no difference in severe adverse events or recurrence, maybe a little bit more of a trend towards bleeding in the yellow petal group. But really, there was no difference. And I think the takeaway here is that for simple scenarios, like a straightforward EMR in 2022 with a constant voltage generator, yeah, it probably doesn't matter that much. And you'll probably be OK either way. But there are certain nuanced scenarios, which I'll talk about over the next few slides, that I think having a little bit more of an understanding will help you and make your life easier. So one of these is the concept of current density. So this is a video I like, again, from the folks at Irby. Using a soft coag at effect 5 and 80 watts, which is a setting we use a lot with these coag graspers. And here, the piece of chicken is really being tented away nicely with the coag grasper. And it's really producing this very limited effect. And although you set at 80 watts, only about 10 watts was delivered to the chicken. It sounds weird to say that. But with an average of only 1 watt. Now here, the coag graspers are not used in an ideal technique. It's really a broad way it's grabbing on the tissue. And you can see the subsequent thermal insult here. So this is something to certainly keep in mind. So let's go through a couple of scenarios. The first is standard lift and cut EMR. As I mentioned, we like to use Endocut Q241. We want to use a stiff snare to maximize current density. And this produces a nice, clean cut with minimal injury. This is a video from Michael Burke. And again, if you were to encounter bleeding in this, a simple way to make your resection bed a little neater on the next pass might be to just simply increase the effect here on your Endocut Q setting. Underwater EMR we heard about today. Generally, the settings, AutoCut Effect 5, 80 watts works well, although most of us do tend to use a blended current. So really, the same setting as will be used for EMR. I prefer that, the Endocut Q setting. Forrester Dry Cut really don't work very well underwater. So avoid those settings. Certainly don't try to do an underwater EMR and use the blue pedal at Forrester Coag 2 and 25. That's not going to work. Hot Evulsion, again, we spoke about this today. I really enjoy this technique. I think it's really great. The setting's really easy to remember. Raj mentioned you could just use a sphincterotomy setting. I also started off using Endocut I111, which is really easy to remember, because it's just Is and 1s the whole way down. But obviously, these got a bad rap, because people were using constant power generators back in the day. They were using hot biopsy forceps. They weren't tenting away, and they were producing a lot of thermal injury. But when we think about what we spoke about earlier in the lecture, using an effective 1, you really have no coagulation at all here. So you're just going to minimize the deep thermal injury. The interval of 1 and the duration of 4 means that you're going to have a lot of time to cut. And so you're really just tenting away and you're really going to produce minimal thermal injury, and it works very, very well. And it's really quite safe if you do it right. Using a high current density, like I said, just really having a nice grab, tenting the mucosal away, and just gentle traction as you apply the current. Snare tip soft coagulation, we spoke a little bit about today as well. Again, soft coag effect, 4, 5, 80 watts. You have to remember to switch to soft coagulation, even though that's in the name. You'd be surprised people don't remember to do this. Or a lot of times, former fellows call and they say, I can't get this to work. And what they do sometimes, they just switch to soft coagulation and they don't increase the watt. They're still using 2 and 25, which is what you use for forced coagulation. So you have to remember to change the setting or this is not going to work. You also want to use a braided snare or something with a little bit more of surface area to really have this work well and just a little bit of exposed snare tip. Lastly, and this is for Raj to talk a little bit about the stock pile up here, the endo loop. So this is something I learned recently. And I haven't had any issues with it, but it was something that was brought to my attention. A lot of us, when we see these, we really like to use these mechanical adjuncts, like the endo loop, or two, or three, or four of them, or clips, or sometimes we'll inject epi to the stock. But there's a theoretical risk if you tighten the endo loop too tight and it's too close to the bowel wall that the highest current density can actually be at the loop and not the snare. And what you can end up is a situation where you don't get any thermal effect at the snare and it only happens at the loop. And if it's too close to the bowel wall, you could have a potential perforation scenario. So again, it's been described. I think it's happened once in a live course. It's very theoretical, but it's a possibility. So one way to get around this and to make this less likely to happen is to use the endo cut or the yellow pedal when you do this if you've already applied a mechanical adjunct. Because theoretically, you've compressed those vessels at that point. You don't need to add a coagulation current at that point, or a full, straight-up force coagulation current. If you don't, it probably is reasonable to use a coagulation current, like a force 225, or even a precise sect. This is a video from Doug Rex, where not a lot of us would have the fortitude to do this, but you can see here he has a huge polyp with nothing around the stock. And he's just using a precise sect, which is that new current on the VIO3. And it cuts right through it and seals those vessels. And again, not everyone would do this, but just to show you that this is possible to do. And you're not always going to have massive bleeding. That being said, obviously, the ASGE recommends to prophylactically do something to these stocks. So just a theoretical to show you guys. Lastly, in the last minute or so, hemostasis. Again, you can use soft coag, effect 4 or 580 watts. Works very well. You can either coagulation graspers or the snare tip. If you are going to use graspers, make sure you use the same techniques we spoke about with avulsion. Maximize current density. Tent the mucosa away to avoid thermal injury. The good thing about soft coagulation current is it has a maximum peak voltage of 190 volts. So what that means is that even as the tissue is desiccated, as you're applying heat to it and you're producing your thermal effect, the current is going to drop down to almost nothing once the tissue is completely burned to keep the voltage the same and limit it to 190 volts. So you can really be very confident you're not going to apply very deep thermal injury. However, if you used a forced coag or a spray coag here, you really could produce some thermal injury. So the key to using a spray coag if you were to use it is to really make sure you're not in contact with the mucosa, kind of like an APC. These are the suggested EMR settings which we spoke about already from the Multi-Society Task Force, just here for your reference. We've already gone over this. And I'll leave you with a few conclusions, which are to know your generator, whether it's constant voltage or constant power. You can use either. You just have to be aware. Know your modes, endo-cut, forced coag, soft coag. Use high current density when using the avulsion, coag graspers, hemostasis. Make sure your snare is tight. And at the end of the day, do whatever you're most comfortable with. Really, this is just as much an art as it is a science. Thank you, guys.

electrosurgical procedures

current density

endoscopic surgery

generators

EMR