 Hello, my name is Gabriel Lore, Surgical Director of the Lung Transplant Program at Baylor St. Luke's Medical Center. I'm also a Co-Chief Section of Adult Cardiac Surgery at Baylor College of Medicine. Really looking forward today to talk to you all about the profusion considerations in lung transplantation. By way of overview over the next 20 minutes, we're going to review the results of a multi-center registry that we established here at Baylor College of Medicine that meant to evaluate the effects of the different profusion strategies on lung transplant outcomes. Then I'm going to break in a little deeper into the translational science that describes what some of these different modes of support may be doing in terms of cytokines and endothelial cells. So in more of a molecular level that could potentially be affecting the new lung graft. So end stage lung disease is familiar to mostly everybody here. It's caused by any particular pathology that leads to irreversible lung damage. So it could be COVID-19, it could be idiopathic pulmonary fibrosis, pulmonary hypertension, chronic obstructive pulmonary disease, COPD. All of these may also have pulmonary hypertension with them or it could be pulmonary hypertension alone. So there's a lot of different ailments that can end up in this end stage irreversible process and people are unable to breathe because of this. So thankfully lung transplantation is an excellent option for this. And this is, you all know, no strangers to this. We're doing lung transplants here day in and day out, but it essentially involves removing a donor lung from the donor, removing the damaged lung from the recipient and basically putting in a brand new healthy lung into the recipient. We do divide the airway, we divide the pulmonary artery and we divide the veins in direct contact with the heart. So we have to be able to support the patient's oxygenation, ventilation and perfusion throughout this operation. And this is a lot of what we're gonna be discussing today. And so there's several challenges to lung transplant that are important for us to discuss right up front. So one is that there's a critical organ shortage. So 15 to 30% of patients who are waiting for a lung transplant die on the waiting list. So they're at home on four or six liters of nasal cannula attached to them at all times when they're sleeping or moving or working or they have high flow. Some are in the hospital on ECMO, some are ventilated, some have a tracheostomy. So there's a wide variety of degrees of illness that these patients present with. And it's not hard to imagine that anything can tip them over to dying before they can even get a lifesaving organ. And some, a lot of them pass away before they even get onto the wait list. Now on top of that, 80% of all of the donor offers that we get are wasted right now. We're only utilizing 20% of them. And that 20%, what that looks like is the donor lung that's relatively young, close by, excellent blood gas. And in this day and age, that's a minority of the type of donor lung offers that we're seeing. So we can't let people just die on the waiting list without trying to identify ways to get more into this 80% pool. So what does that look like? That means we have to be going out farther. That means we have to be looking at older donors. That means that we have to be looking at donors who have lower blood gas ratios before the transplant. Then we have to do these things safely. So what's the concern? Why not just do that? Well, there's this thought that, well, the lung may not work. And there's some truth to that. So what does that mean that the lung may not work? So that is very specifically defined as primary graft dysfunction. When the lung doesn't work after lung transplant, it's called primary graft dysfunction. And primary graft dysfunction looks like this. It's got whiteed out lungs. These lungs are not ventilating. They're filled with fluid in through the alveoli. Inflammatory cells have gone across through the blood air barrier and just cause a lot of edema inside of the lungs. The lungs are very heavy inside of the patient. They can't breathe. And if the ventilator is not enough to support them, we usually need ECMO as this patient here. And if we look at the ISHLT grading, a BF ratio less than 200 in the recipient after a six hour period of reperfusion is definition for primary graft dysfunction grade three, which is the most severe. Now, if it's still lasting up to time 48 hours or 72 hours after transplant, we consider that to be high grade primary graft dysfunction. So we're caught here between a rock and a hard place. We're trying to extend donor organs. We're trying to get people off of the waiting list. We're trying to allow them to have a second chance at life. But at the same time, we don't want the lungs not to work when we implant them. So what do we do? So we started looking at ways that we can reduce primary graft dysfunction in all comers. So we figured if we can figure out how to reduce primary graft dysfunction or if we can figure out what is potentially leading to it in our practice or in any practice around the world. And if we can change that, then we would probably be able to look at more extended donors safer. We can look at more extended recipients safer. We can offer lung transplant to more and more patients without having them be at risk of dying on the wait list and without having them be at risk of the lungs not working afterwards. So that was the impetus behind these studies. So this was a large landmark registry that was developed at Baylor College of Medicine here. And it looked specifically at the effects of the mode of support on primary graft dysfunction. And it includes participants from around the world, including University of Minnesota, Duke, Mayo Clinic, Massachusetts General, Hanover Medical School in Germany, Belgium, University of Louisville, Pittsburgh, Temple, Florida programs, many different programs are involved in this registry. So what we were interested in most was primary graft dysfunction and determining whether the mode of support affected primary graft dysfunction. And the programs that are included in this particular study are listed here. The inclusion was all double lung transplants that were entered into the registry with complete data between January, 2016 and March of 2020. And the exclusions for multi organ transplants, single lung transplants, the modes of support that we looked at was off pump, ECMO, and cardiopulmonary bypass. So the primary outcome was primary graft dysfunction grade three graded according to the IHLT guidelines. And we were most interested in PGD-3 at time 48 and or 72 hours after reperfusion. We also looked at secondary outcomes like a length of stay, mortality, and we performed statistical analysis to make sure that if there were differences between these groups, which we of course expected that there were gonna be differences between a patient that requires bypass and a patient who is done without any support at all. To account for these differences, we did a multivariate logistic regression with step-wide selection to help us adjust for confounders. So this is the breakdown of all the patients that were entered. There were 852 double lung transplants. 50% of these were off pump, almost 20% were cardiopulmonary bypass and 32% were ECMO. And so this is the first time that this has been seen like this, reflecting a worldwide clinical practice, clearly showing that ECMO is playing an increasing role. When we look at the differences in recipient demographics, what we notice is that the obstructive lung patients, patients with COPD were more common in the off pump group. And that kinda makes sense because those patients are a little bit easier to ventilate. They're a little bit easier to oxygenate than the patients in the restrictive lung disease. The restrictive lung disease group patients tended to be more commonly treated with ECMO and with bypass. That doesn't mean that they needed ECMO or bypass. That just means that there was a bias towards using ECMO or bypass for those patients. And when we look at gender, there was really no difference. Age, there were no differences between the recipients with BMI, we can see that they were a little heavier in the cardiopulmonary bypass than the ECMO groups than in the off pump group. The recipient preoperative lung function was worse in the off pump group than they were in the ECMO and the bypass group. And we were interested in this because it kinda tells us that even though in off pump, you're really relying on that opposite lung to ventilate, that opposite lung can actually be pretty poor and still be able to ventilate and be able to get you through. So we can potentially expand the use of off pump. When we look at the recipients, there were more recipients that were hospitalized at the time of transplant in the ECMO group. The ECMO group had the highest LAS score. The ECMO and bypass group had a greater incidence of pulmonary hypertension than the off pump group. And the cardiopulmonary bypass and the ECMO patients had higher mean pulmonary artery pressures than the off pump group. And much of this is expected because whenever we see elevated PA pressures, there's a bias to go ahead and plan for using support. That doesn't mean that it's required. It just means that that's what we oftentimes we're doing. Now, preoperative ECMO was more common in the patients who had their transplants done on ECMO. That kind of makes sense because a lot of folks that came in on ECMO stayed on ECMO. Although I can tell you that earlier in my personal practice, when people would come in on ECMO, we would switch to bypass to do the case. So it's not necessarily the case that just because you come in on ECMO, you're gonna stay on ECMO for the case. Off pump had no patients with preoperative ECMO and the bypass group had 4% of the patients were on preoperative ECMO. Another thing that was interesting is when you look at other complexities like prior heart surgery, prior lung transplants, prior pleuridesis, prior chest thoracic interventions, a lot of scar tissue difficulty getting into the chest, they were pretty similar across all groups. You would think that maybe people would use support more often in those cases, but that wasn't really the case. Off pump and mechanical support was used equally across all those different indications. When we look at our donors, the older donors were in the off pump group and the lower PF ratios in the donor were also seen in the off pump group. There was a propensity to use more EVLP in the ECMO cases in this study for whatever reason. So what we see is slightly higher risk donors in the off pump group, but slightly higher risk recipients in the ECMO group. VVA or VVA was the most common ECMO support strategy used. The ECMO group had substantially longest and total ischemic time. So 450 minutes out of bodies, longer time in travel, longer time out of the body, those tended to be more common in the ECMO group intraoperatively. So what did the results look like? So PGD3 at 48 or 72 hours occurred 42% of the time in the cardiopulmonary bypass group. It occurred 28% of the time in the ECMO group and it only occurred 12% of the time in the off pump group. Now, even when we adjusted for all those differences that I showed you in the recipients and in the donors, we still saw that same effect. So cardiopulmonary bypass compared to ECMO, two-fold increase in odds of developing primary graft dysfunction. Cardiopulmonary bypass versus off pump, four times greater risk of developing primary graft dysfunction. ECMO versus off pump, two times greater risk of developing primary graft dysfunction. And the secondary outcomes followed this very closely. So the best secondary outcomes were seen in the off pump group followed by ECMO, followed by cardiopulmonary bypass. And that means everything from PGD3 within 72 hours to re-intubations to post-op ECMO use to death in 90 days or death before discharge. So in conclusions, lung transplants performed off pump in the ECLS lung transplant registry were associated with the least risk of primary graft dysfunction and morbidity. An off pump strategy should be the first choice for intraoperative support when it's safe and feasible to do so. ECMO is playing an increasing role in the intraoperative support of complex patients undergoing lung transplant with outcomes as safe if not superior to cardiopulmonary bypass. And in situations where ECLS is required or preferred, ECMO should probably be the strategy to use to reduce the risk of primary graft dysfunction. Now, many of you in the audience now who work with us know that we're using ECMO a heck of a lot more now than we are using cardiopulmonary bypass. In 2016, here, all of the cases, 100% were done on cardiopulmonary bypass. And that was also my practice too before coming here in Minnesota. So there was a thought process that ECMO was not very safe to operate on the beating heart and during lung transplants, removing lungs. I think this study clearly showed that ECMO is not only safe but it's probably safer than bypass in many instances. That doesn't mean that we aren't gonna use bypass depending on the scenario because there are definitely situations where bypass gives us better drainage, better exposure and it's critical to be able to use them. But ECMO I think is really coming out as the middle ground between the two strategies. And as many of you know, whenever we can perform them off pump now we are definitely trying to do that using more nitric oxide or pulmonary vasodilators to help us to stay off pump whenever we can. Now, why is it that mechanical support would cause this increased risk of primary graft dysfunction? So Lorda Chacon did a study here in collaboration with the regenerative medicine, research department at Texas Heart Institute and several of our colleagues and myself looking at biomarkers. So we were able to look at markers that are circulating in the blood during the transplant and after the transplant to try to see if there's any differences in inflammatory markers between patients that have their surgeries done with cardiopulmonary support or ECMO or off pump. So again, our primary endpoint of interest was primary graft dysfunction. And we know that primary graft dysfunction in the literature is associated with an inflammatory process. So this is an endothelial cell lining. So this is the tubes that run inside of all the lungs and run within all the capillary networks of the lungs. There's these tiny capillary tubes and lining every single square centimeter of the lung is an endothelial cell, which is the protective barrier between the blood and the alveoli here, which is where the oxygen gets exchanged. So what you see is that the endothelial cells can get damaged and neutrophils, a different inflammatory cells can be recruited to the lung through this network, through this highway. And when that happens, then any injury that occurred from the transplant, whether it be from the donor procurement, from the lack of oxygen to sudden reintroduction of oxygen, any injury, these cells are coming in to clean that up, to clean up the mess. So the injury starts when you take an organ and from point A to point B without oxygen and you suddenly reintroduce blood. There's a little bit of injury that always occurs in every single lung transplant. Then there's molecules that get signaled out. Then these are called cytokines and they signal and they recruit all these inflammatory cells to come to this region. And then they go into the lung and try to clean up the damage that was done. But the problem is that more often than not, it leads to actual injury of the lung and it can't oxygenate, it gets white and it causes primary graft dysfunction. This is not to be confused with rejection where rejection is where the body suddenly recognizes foreign antigens. That's not exactly what this is, but it has some similarities in that there's inflammatory cells, but it's kind of a non-specific inflammatory reaction rather than a specific rejection pathway. So it's important to know that rejection is very rare compared to primary graft dysfunction. Primary graft dysfunction, again, occurs about 30% of the time. So if this is what we know about PGD, then we figured, well, and we know that cardiopulmonary bypass causes an increased risk of PGD, then we figured it might be interesting to check the blood circulating in the circuits or circulating in patients after the transplant to see if the circuits are causing more of an inflammatory state that could be exacerbating primary graft dysfunction. So we all know cardiopulmonary bypass circuits, there's pump suckers, venous reservoirs, there's a pump oxygenator, and then the blood goes back in to circulate in the body. There's a lot of room for contact between the blood and the air, and that causes an inflammatory response. And the blood through all of this tubing and the pumps and the oxygenators can also cause a prothrombotic and pro-inflammatory responses to occur. And so the thought is that perhaps if you add this to what is already happening in every lung transplant in terms of inflammation, there may be this threshold of inflammation that you exceed leading to primary graft dysfunction. That was our hypothesis. So we looked at ECMO cases as well and we compared them to the cardiopulmonary bypass cases because ECMO has less tubing, does not have an air blood interface. And so we hypothesized that probably ECMO would have a little less inflammation and that that would explain why we have less graft dysfunction. And there are groups, this group from Vienna swears by ECMO and uses ECMO for every single one of the transplants indiscriminately. And the thought process is that it helps standardize the procedure and they see less primary graft dysfunction. So this was popularized there. So we thought it was very reasonable to assume that ECMO we would see less inflammation. So we included 26 patients in the off pump group, 18 in the bypass group and 15 in the ECMO group. We collected blood at many times after the lung was implanted. So the circuit is no longer in play here. This is, they've been exposed to the circuits, but this is six hours after the circuit, 24 hours, 48 hours. And we looked at cytokines and inflammatory cells. So we looked at the off pump group, cardiopulmonary bypass group and the ECMO group. And what we saw in terms of demographics, recipient and donor demographics were similar splits to what we had seen in the multi-center registry. So there were slightly older patients in the bypass group. Mean pulmonary pressures were slightly higher in ECMO in the bypass patients. The donor ages were a little older in the ECMO and the CPB cases. The gender mismatch was also more common in the circulatory support cases. The bilateral lung transplants were 100% of the ECMO cases and 100% of the CPB cases, whereas the off pump cases had some single lung transplants included and bilateral lung transplants included. So we saw very similar pattern in primary graft dysfunction that we'd seen before with bypass having the worst and ECMO in between. Post-op ECMO support followed a similar picture as well as well as post-op mechanical ventilation. We looked at a variety of different cytokines and inflammatory cell populations to try to understand if there were differences in the circulating milieu between these three modes of support. So macrophage inflammatory protein one is a cytokine that's released and it starts to signal to other inflammatory markers in the periphery that there's a problem and it starts to activate them to start to release additional pro-inflammatory agents. What we saw is that in the off pump group, the spike for MIP1 beta was not that high, but in the ECMO and the CPB group, six hours after transplant, the spike is pretty profound. So there's more inflammatory activation after the transplant in patients that were exposed to bypass or ECMO. When we look at interleukin-6, we see a similar scenario and when we look at interleukin-1RA, we see the same thing. And by the way, overlap waiting means that we control for confounders and for different donor and recipient characteristics. We also control for singles versus double and we got the same results. TNF alpha is a potent pro-inflammatory enzyme and this was significantly higher in the ECMO and CPB group than in the no support group. Chemokines are an interesting group of signaling agents. They're like glue or it's like blood in the water. So just like blood in the water attracts sharks, chemokines in the blood attracts inflammatory cells. So inflammatory cells migrate to the highest concentration of chemokines. So RANTES is a chemokine and we saw significantly higher levels in the ECMO and the bypass patients. We saw higher levels of eotaxin, IP10, MCP1, all of these are chemokines and also MIP1 beta. We also looked at endothelial cell toxicity. So if we took serum from patients exposed to bypass and poured it over a petri dish of endothelial cells, we saw a greater amount of cell death in the patients exposed to cardiopulmonary bypass. And we also saw a worse endothelial cell survival in the patients exposed to cardiopulmonary bypass. ECMO was a little bit less than we saw in cardiopulmonary bypass. And in terms of endothelial cell survival, you see the cells very disrupted and dying in the CVB patients compared to the ECMO group, which was a little bit better. And then the off pump looked very healthy when you, and this is again is serum from these patients poured over a petri dish of endothelial cells. And this shows those findings a little bit more dramatic with cells clumped in the bypass group, a little bit better cell junction in the ECMO group and the best in the off pump. So in conclusion, the use of MCS during lung transplant with either ECMO or bypass was associated with greater inflammatory response than when MCS was not used. So ECMO was probably a little bit less, but it wasn't necessarily completely privileged. In comparison to CPB cases, ECMO showed no attenuation in inflammatory response, but it did show less PGD and it did show less endothelial cell injury. So it is reasonable to consider the use of ECMO or bypass when MCS support is necessary. And we really believe that further research into attenuating these inflammatory markers are gonna lead to novel therapeutic strategies because as I mentioned before, ECMO still is responsible for 50% of all lung transplants that we use and that's never gonna go away because there's just simply patients that require this kind of support in order to ventilate and to oxygenate. So we have to be able to understand that relationship between the circuit and the lung in how we're able to reduce inflammation to have less primary graft dysfunction. So we're really excited about this research and really thank everybody for listening to this at this incredible 50th profusion conference and thank you so much for allowing us to present and thank you to all of our colleagues who've been responsible for doing the hard work on this research and our generous funders. I wish I could be there in person and thank you very much for inviting me.