Okay, good morning, everyone. Raj, Adam, thank you so much for the invitation. It's my pleasure to talk about a topic that is not transcecal appendectomy. It's something that I think everyone can learn and everyone really should learn at this point. I think we're far along in the kind of maturity of this procedure that I think we're all getting a little bit more comfortable using it and then also teaching it. And I think I've been on the fence about teaching this for many years, but now I think we're ready. I think we're ready to kind of teach this to fellows and get it out there. And so, Raj, great title, Deep Dive. And in keeping with that, we're all going to take the plunge here. I actually had this as the background for the entire presentation, but I was getting dizzy, so I've changed the slides to the regular background. This is, these are my disclosures, and none of them are actually really relevant for this talk. I need to give credit where credit is due. Dr. Ben Moeller described this technique back in 2012. The tall gentleman sitting next, or standing next to him is Dr. Christopher Hamersky, actually one of my co-fellows and was Dr. Ben Moeller's partner for many, many years and has probably done more underwater EMR than anyone in the world. And Chris has sort of been like a bit of a mentor to me with the underwater story. I went up to CPMC back in 2015 and learned the technique from them and, you know, haven't really looked back since. When I brought this technique back to UC Irvine, my mentors at the time were like, no, don't do that. It's dangerous. It doesn't make any sense. Why would it work? You're not lifting. And so I'm here today to tell you it does work and it is safe, and if you do it correctly. I guess that goes for anything. So conventionally EMR, you know, we're injecting a solution in the submucosal space under the lesion to create a safety cushion. Theoretically, this decreases the risk of hydrogenic perforation and thermal injury to the deeper tissue layers. That's the understanding. But submucosal injection may paradoxically make snare capture of a flat polyp even more difficult. Also when we inject a lesion, sometimes we take a one and a half centimeter situation and make it a two and a half centimeter situation. And the opposite is actually true with underwater EMR, where we're basically filling the lumen with water and it really eliminates the need for any submucosal injection before resection. But without a lift, shouldn't the risk of perforation be higher? And that's sort of the fear I think we all have when we start this technique, and it kind of makes sense. But the theory behind underwater EMR can be sort of appreciated based on this EOS image. The folds of a non-distended colon consist of these involutions of the mucosa and submucosa analogous to the rugae of the stomach. And the MP layer remains circular and does not follow the involutions of the fold. So the snare is preferentially capturing mucosa and submucosa and leaving behind a muscle layer. Also in the original description, the water was felt to maybe float the mucosa and submucosa away from the deeper muscular. I'm not sure if that's entirely true, but I will say that this is probably close to what's happening. And the thing I'll highlight is really the involution of the mucosa and the submucosa. So what's the data on this technique? Well, the original description was in 2012. This was a prospective observational study of 62 large sessile polyps. They used a standardized technique where they did some APC marking. They used a 50-millimeter duckbill snare, used PureCut. They didn't APC the edges. They did not close anything with clips. The median size of lesions was 30 millimeters, so large lesions. Median time of resection was 18 minutes. And there was a 2% recurrence rate at follow-up endoscopy in three to six months. And that's actually very low compared to conventional EMR rates. There were three cases of delayed bleeding. But it sort of set the stage for, you know, this seems feasible. And now there's been more randomized control trials on this study comparing conventional and underwater. And I was fortunate to be part of the largest international multicenter randomized control trial that I'm going to talk about right now. This is yet to be published and is soon going for submission. This is a presentation that we gave at DDW. The aim was to compare the outcomes of underwater EMR and conventional EMR in a prospective international multicenter randomized trial. These were the four participating centers. And we looked at lesions that were laterally spreading tumors 15 millimeters or larger. All the endoscopists were very experienced in both techniques, underwater and conventional. These were the exclusion criteria. So with conventional, we used CO2 insufflation. Standard injection technique with saline, methylene blue, or indigo carmine. Sneer size and cautery settings were really at the discretion of the endoscopist. And clips were used if they felt needed for bleeding perforation. With underwater EMR, the loom was filled with sterile water. All gas was suctioned. And we'll get more into the technique a little bit later. But the primary outcome was curative resection, that meaning the rate of residual neoplasia documented on a three to six month surveillance colonoscopy. Because we felt based on the original data that there would be a statistically significant difference in recurrence rates. Secondary outcomes was resection time, procedure time, monoblock resection rates. And the need for additional techniques to achieve a complete resection. And also adverse events, of course. So resection time was defined as the start time at insertion of the first instrument. And the stop time when all the visible adenoma was deemed resected by the endoscopist and hemostasis was achieved. The procedure time was scope in to scope out. So the results, we have over 300 patients now in the study. This was 218 patients at an interim analysis. And essentially, this was what the patients looked like. In terms of the lesions themselves, most of these were essentially right-sided lesions. You can see the Paris classifications were similar in both groups. And one thing to note was the tattoo involving the base of the lesion was statistically higher in the underwater EMR group. You've got to love those tattoos. Hopefully somebody's going to talk about tattoos and maybe banning them from the GI lab. So in terms of pathology, very similar distributions in both groups. And in the conventional EMR group, seven LSDs required crossover to the underwater group. And in the underwater group, one LSD required crossover to the conventional group. In terms of on-block resection, there was a statistically significant higher on-block resection rate with the underwater EMR group. And in terms of additional techniques required, there was a statistically significant difference in the underwater EMR group using less additional techniques required to get the job done. In terms of resection time, the resection time was about 10 minutes with underwater versus 16 with conventional. And also, total procedure time was shorter. In terms of adverse events, really no difference between conventional and underwater. There was one perforation in the conventional group. There was a post-polypectomy syndrome in the underwater group. One patient did have bacteremia after presenting with a fever. In terms of our primary endpoint, there was a 6.8% residual adenoma rate versus a 10.9% residual adenoma rate in the conventional group. So not quite statistically significant, but lower. So our conclusions at that point were, compared to conventional EMR, underwater EMR resulted in a shorter resection time and shorter overall procedure time, higher on-block resection rates, and less need for additional adjunctive therapies for resection, no difference in adverse events. But there may be a trend towards lower rates of residual adenoma. At that point, the conclusion was maybe underwater EMR should be considered a first-line option in the treatment of colonic laterally spreading tumors. So there's since been some other studies and meta-analyses. This is one that our group did. And this is a more recent one that I can touch on. This was lesions just greater than 20 millimeters over 1,800 patients. And again, similar types of themes as the RCT that we did. The RCT that we did was included in this meta. So superior on-block resection rates compared to conventional EMR. Similar R0 resection rate, piecemeal resection, diagnostic accuracy. But in the meta, there was actually a lower rate of polyp recurrence, and that was a statistically significant result. So how do you do this? So I kind of break it down into kind of the following steps. So lesion assessment, and you heard just sort of a perfect lecture from Dr. Oppmann about lesion assessment. There's diathermic marking. And there's sort of a capture skill, a cut skill that comes with underwater EMR. You can talk about vessel management. And then site assessment. And the site assessment using underwater technique really is different than using just air or So we'll take these one at a time. So what we typically do is do an air inspection or a CO2 inspection as well as a water inspection. And again, we heard a great lecture just now about classifying lesion morphology. But one of the things I guess could be a disadvantage is when we lift a lesion, we do get that non-lifting sign. That's a pretty good sign that this is probably submucosal invading cancer. And so with underwater, you don't do that. So you don't actually have a non-lifting sign. So paying even more attention to the polyp pattern and the morphology is probably key. We often do, actually, in every kind of EMR, we do a catheter probe BUS to look for submucosal invasion. Not always helpful, but sometimes it is. But that's one of the downsides, I guess you could say, with underwater is you don't get that non-lifting sign. The other thing I think is important is examining for tattoo underneath the polyp. I think the principles of underwater kind of rely on sort of the submucosa, mucosa together working independently of the muscle layer. And if there's something else that's tacking down the submucosa to the muscle, like the carbon particles of tattoo and fibrosis, that could be a problem. And so I think just be mindful and look for tattoo. And maybe underwater might not be the best approach, although in the randomized trial, there were more tattooed lesions in the underwater group and there were no perforations. So diathermic marking, I think, is optional. I think for the really, really flat, subtle lesions, it might be helpful. But honestly, I think when you're examining underwater, you just get some really amazing crisp images. You get this sort of natural kind of optical zoom with having water. And so I don't know if it's always necessary. You can use APC underwater to mark, but otherwise, a snare tip cautery with soft coagulation can work well. Some kind of words on the water installation itself. I think one of the things that I see our trainees sort of doing after hearing about underwater is kind of over-extending with water. But really what you're trying to do is actually decompress the lumen as much as possible. You really kind of want it, and I say we want things like loosey-goosey. You kind of consider, you know, you can turn off the gas, but really decompress the lumen down first so you really can't see anything, and then instill really enough water to remove the airspace and maintain visibility of the polyp. You can see really how close we are to the polyp. And you often can't see the whole polyp in the same view, but getting close, keeping everything as tight and decompressed as possible really is the goal. In terms of capturing the lesion, you know, the original snare that was used was the 15-millimeter duckbill snare. Most of us are using a stiff snare, and I know, you know, Chris uses a 33-millimeter snare pretty much in every case. Again, do not, you know, over-distend with water. Keep things under-distended, and as you're capturing the lesion, it's often a good idea to actually suction water. It's going to help bring things tighter together and actually involute the foals even more during the capture. You know, one of the things that was really kind of remarkable to me when I went to CPMC was seeing how much sort of normal tissue they were capturing around the polyp. And it was sort of like, you know, the first couple of times I was like watching Chris do these resections, I was just like, kind of like just cringing, you know, because I was just like, that is way too much polyp, that was way too much tissue, and like you're taking all this extra tissue, but it's actually fine. And I think that's one of the advantages, and I think probably one of the reasons why you get higher on-block resections, because you're really capturing these like really incredible margins. But again, the way you're able to do it, even with a 15 millimeter snare, you know, I've taken 30 millimeter polyps out with a 15 millimeter snare, because with peristalsis, you know, and the involution, things are sort of sliding up through the snare, and then you're just sort of almost making a flat lesion, kind of pedunculated, and then you're able to kind of, you know, kind of cuddle around the bottom and take some normal mucosa, and it's pretty remarkable what you can remove on-block with even a 15 millimeter snare. One of the things that I think I learned that probably isn't talked about enough, and it's something that I teach our fellows, and their EMR skills sort of literally overnight get 100% better, is this concept called pushing the catheter to meet the closure. And I think it's, and I've got this amazing illustration that I did to talk about this concept. And so, I don't know why the polyp is blue, but essentially, closing the snare and pushing the catheter together is really, really important, and I think, you know, some of us may have kind of closed the snare, and you close the snare, and you close the snare, and you're not really moving the catheter, and then the snare will kind of fall over the polyp, or it won't capture, like, the back edge, or, and that's a pretty common kind of, I guess, mistake or a technical thing that I see some of my colleagues do, and some of the fellows. And so, the idea here is, if you're looking at the snare around the polyp, and this can, as this is actually probably more important for piecemeal resection than even on-block resection, to be honest, but we have, you know, what we're trying to do here is an on-block resection, but even with piecemeal resection, I think it's extremely important to think about this. So, as the snare is closing, you are pushing the catheter, and I'm sort of imagining an imaginary sort of central point in this polyp, and I'm thinking about closing the snare, and I'm pushing the catheter, and meeting at the center below that, below that point. That's sort of my target. So, you're pushing, you're closing, pushing, closing, pushing, closing together, and then what you'll see happen, and I think with underwater EMR, this is even more important, and this works even more if you kind of think this way. So, pushing the catheter to meet the closure, you end up getting sort of these beautiful kind of collections of polyp in your snare. And that's really, I think, one of the most important things, and sometimes people might like push the snare too much, sometimes they'll oftentimes not push it enough, and that's why you're not capturing polyp well enough, but here's a video that's not underwater, it's not conventional, but it's someone who's a master endoscopist in Japan who truly understands this concept of pushing the catheter to meet the closure. And so, he's basically doing piecemeal resection of a large LST in the rectum, but as you can hopefully appreciate now on the video, the closure of the snare and the pushing of the catheter are perfect, and they are meeting the polyp at the center of the target area that they're trying to get. And so, and honestly, I think, especially for those areas that you're just trying to finish up, those last little bits, you know, this is really the concept that makes that possible. You know, if you're ever, you know, struggling and your attending comes in and they're able to kind of remove that little piece of polyp that you were just struggling with, this is probably the reason they are understanding this concept of pushing the catheter to meet the closure. Okay, so next step is cutting. Most are using a blended cut setting, and the original description was a dry cut, effect 5, 60 watts, and the randomized we were using autocut, but even, you know, endocut is, you can use. With the cutting, I think, you know, tenting the lesion is a very good idea. And it doesn't have to be a dramatic tent, you know, I'm usually, you know, pulling the catheter closer, you know, towards the scope tip. You know, one thought or theory is that, you know, the water provides a bit of a heat sink and it might actually prevent post polypectomy syndrome and deep injury. And so I'm not sure if that's entirely true, but it's, you know, we definitely get very, very clean cuts with underwater EMR. So you know, one of the most annoying things with underwater EMR is when things start bleeding. But a lot of the bleeds we can actually, actually a lot of the bleeds actually stop spontaneously. But some of the bleeds we can just treat, you know, underwater. So here's a, you know, a spurting artery. And oftentimes with the snare tip, you can sort of just put a little bit of snare out, kind of make it look like a needle knife, and then use soft or forced coagulation. I usually use forced underwater because I sometimes feel that soft doesn't quite have the oomph that we need to close that and seal that vessel. And so here we kind of, the snare, just a tiny tip of the snare out, making it look like a needle knife, and then treating it. Now for bigger bleeds, we oftentimes need to, and what usually happens is it starts bleeding and then you kind of get this like murky red water. And so then it's sort of like, okay, this is a big bleed. You sometimes can't localize it because it's bleeding so much. And so at that point, we'll just take out the water, turn on the CO2, and just address it like we would a conventional case. So in this case, hot forceps or coagulation graspers with soft coagulation works really well. So soft coagulation 4 and 80 is usually what we use for this. So I think one of the best parts of underwater EMR is the underwater assessment that you get. And I actually hypothesize that this is the reason why recurrence is less because, and this is not the video that I want to show you. The video that I want to show you wasn't working, but I think you can see the imaging that you get underwater at the close of your case is just phenomenal. And especially looking at the edges, and you can see little strands of adenomas tissue literally waving at you. And that was the video I wanted to show you, but there's no adenoma here. You can see even like a single little villus strand of adenoma just sort of waving at you. And I think this is excellent. In fact, when I do conventional EMR, I actually do an underwater assessment after a conventional EMR as well to look for a residual adenoma. And so at least in my patients, I had a 0% recurrence rate, and I really think this is part of the reason. All right. So we're going to do just a couple of more videos. So this is a smaller lesion. One of the annoying things with underwater is the prep has to be pretty good. This patient had a horrible, horrible prep, but I was determined to do this underwater. But you can see the prep isn't great. This is in the ascending colon. And I think, again, the benefit is without lifting, the lesion stays small. You're able to get your snare around the polyp, but also a lot of normal tissue. And I think the initial kind of part of the learning curve of underwater EMR was getting comfortable with taking that much tissue. And this was a kind of a smaller polyp. But taking that normal amount of tissue, and you can see sort of how much normal tissue we've taken there. But there's absolutely no question that we've got an on-block resection of this polyp. And maybe we could have achieved it with a conventional EMR, but that took all of like 30 seconds. And so you can see the really wide margins that you're able to get. I was a little nervous about doing underwater EMR after a prior resection attempt, but lots of people are doing this now. And so this is another one of Chris's cases where, again, he loves that 33 millimeter oval snare and just kind of goes big. But again, I hope you can appreciate the technique of not over distending, keeping things really tight, keeping things really compact. Again, visibility sometimes isn't great, but you eventually get a sense of sort of where the snare is and how much tissue you're capturing. But that's really kind of part of the key. So this is a piecemeal resection of a large rectal lesion. Mohamed, this one would be a difficult one to classify. So diathermic markings, again, not even sure if it was really necessary. I find the key to this lesion is you really want to make sure you're hitting mucosa and normal tissue on every cut. If you kind of graze the top and you don't actually get into the submucosa, then you've kind of left a very, very flat kind of polyp that's going to be more difficult to remove. So this idea of pushing the catheter to meet the closure I think is really, really important here. And so again here, pushing the catheter to meet the closure and trying to get some normal tissue as well as the adenoma, I think really, really important here. But yeah, it's variable on the patient, but I did one actually this week and pleasantly surprised even with a kind of a regular HQ190 gastroscope, the anal sphincter were tight enough to retain, so it is possible. In fact, this is actually the case. So I did the underwater inspection, I identified three little areas that appear to be adenomas. One of the things that you might appreciate is you see that submucosa? That submucosa, it's almost like edematous. It's soaked up like a lot of water. And so now, instead of just biping off this little nubbin of tissue, I'm going to do this. I'm going to snare it again and just like take it off that way. And because of the submucosal water that it's absorbed, it's actually very, very easy to do this. And again, keeping in mind that concept of pushing the catheter to meet the closure. So that little nubbin of adenoma, I just don't want to leave it to chance and just remove it with a forcep. I really want to get clear margins on this little piece as well. I definitely don't want to leave anything behind. And as good a job as we do going seam to seam with the different piecemeal resections, I want to make sure I'm getting tons of margin on all these little bits of potential adenomatous tissue that's left behind in the resection bed. And so I think there's one more coming up here. But I really feel like even though you haven't instilled water directly into the submucosa, the submucosa is very kind of like water heavy by the end of the underwater case. And you can sort of appreciate here how easy it is to kind of just take and snare that little nubbin off. And there's no question that we're getting clear margins around all of that. OK. So the last couple of minutes. Can we do EMR outside of the colon? So Dr. Ben Muller's group looked at underwater EMR of non-ampullary duodenal adenomas. This was just 12 polyps, medium-sized, 35 millimeters, so big ones. All were completely resected, but three had delayed bleeding, two of whom required transfusions. There was one stricture. And one patient actually had water intoxication syndrome with altered mental status and hyponatremia. So I think, you know, something to keep in mind in the duodenum. But I'm not sure if this is the ideal technique for duodenum, to be honest. And underwater EMR of adenomas of the appendiceal orifice. So this was pretty neat. And you'll kind of appreciate this video. It's not a transceical appendectomy, but I think it's still pretty cool. Prospective observational study, 27 polyps, medium size was 15 millimeters. 89% were completely resected. Only 3% to surgery because they couldn't guarantee that the polyp wasn't extending deeply into the appendix. So this is part of the video that's kind of neat. So you can see maybe they're appreciating a little bit of polyp within the appendiceal orifice. And they're actually, again, suctioning underwater to kind of bring the AO closer and then ensnaring it. And again, you know, if you do underwater EMR, this feels very, very natural, this sort of suctioning in, bringing tissue closer, and then cutting it. And then after that, you know, you'll be able to appreciate that, yeah, there's definitely doesn't look like any mucosa left there. So they had a 10% residual adenoma rate in this study. So for appendiceal orifice adenomas, this might actually be a pretty reasonable option, although there are other things that we can do these days. So in summary, I think underwater EMR, it's ready for prime time. I really do believe that it is. In the colon, there's randomized controlled data that support this now. I think the largest benefits are it's fast. And I think for this audience, I think doing things efficiently with higher on block rates and decreased recurrence rates, it just hits a lot of the boxes. The disadvantage could be that there's no non-lifting sign. I think you have to be careful with tattoo lesions, lesions that have had prior attempts, and lesions in the duodenum. But again, on the technical side of things, really do not over distend with water. It doesn't work. Involute those folds. Take wide margins. It's actually safer than you think. And again, push the catheter to meet the closure, especially on those piecemeal resections. And underwater inspection really, I think, is key to preventing a recurrence. Thank you very much. Thank you.

underwater endoscopic mucosal resection

colonic laterally spreading tumors

Dr. Ben Moeller

Dr. Christopher Hamersky

conventional EMR

prospective observational study

multicenter randomized control trial