Tanner Smida: iGel vs King in OHCA (5/24/23)

We've done some other words. I'm going to have Dr. Miramonti's baby. Not compliment, but comment on that later on. So just as you hear this, the first thing will be they use the ESO data, which most of us know because it covers about a third of the US EMS systems. So use those to look at cardiac arrest. He'll give you the years in which they looked at it and made their comparison. They only give you survival discharge. I say only, but it's still the sort of standard. And then, but then he also did it looking at the compare with cares, which is the second study. And there you will, you know, CPC ones and twos as well. That'll be looking at. So with that we're going to be looking at tens of thousands of cases and they have their limitations, but they also have their advantages. And Tanner is going to run us through it over the next 10 minutes or so. So with that I want to introduce Tanner. Do you have any questions for me before we get started?

If not, take it away, Tanner. Thanks a lot.

Thank you so and I know all of you are very familiar with the King and the Igel, so I'll just get right to it. So our first paper was published in Prehospital Emergency Care in January investigating this question. And as Dr. Pepe said, we used the ESO annual data sets to answer this question. It was about. We looked at the data sets from 2018 through 2021. So it was about 33 million patient care records overall. And after application of some standard exclusion criter ended up with a sample size of about 93,000 patients. About 55,000 of those were managed with the IGEL. About 40,000 managed with the King laryngeal tube. The baseline characteristics, even before adjusting for baseline imbalances were pretty similar. Two differences I did want to point out. So the King laryngeal tube in these data sets was used much more frequently as a rescue supraglottic airway following failed endotracheal intubation. And also the IGEL was much more likely to be swapped out for an endotracheal tube in the pre hospital setting, which may reflect something like paramedics have less confidence in the IGEL as a method of definitive airway management. Maybe because it doesn't have a cuff.

So we used two statistical methods for this first study. So the primary one was multi level multi variable logistic regression. We also used propensity score matching. They were adjusted for some baseline Utzstein covariables in Addition to whether the airway for each case was placed as a rescue device. So again, following failed endotracheal innovation, we also were able to include the agency identifier for each treated patient because as we know, there are some agencies that are really good at resuscitation, others that aren't so good or have a patient population they treat that's a little harder to resuscitate. So we adjusted for clustering of outcome by agency. We looked at a number of outcomes. Our primary outcome for this first study was survival to discharge to home. About 20% of all transported patients included in the ESO data set have associated hospital disposition data. And we thought looking at patients that were discharged back to their primary resident would be a good way to kind of get a correlate of good neurologic outcome. We also looked at first pass success as documented by paramedics, and then a secondary method of verifying ventilation success in the form of end tidal CO2 thresholds that were achieved during each case, as well as of course, ROSC and RE arrest. Basically, to say this in one sentence, basically, when we looked at our primary analysis looking at all the patients using the statistical model I just described, the Igel was associated with better outcomes than the King laryngeal tube across the board with every outcome that I just mentioned. This was also consistent in subgroups divided by rhythm, witness status, sex of patient, in addition to a couple other classification schemes. And it was consistent also across the statistical methods we used. So both the multi level multi variable logistic regression and the propensity score matching. And so once we had that finding and we realized that there's a couple limitations to the important limitations to the ESO data set. And so first, there's a lot of missing data. So some patients might not even have their initial cardiac rhythm documented. And like I said, only about 20% of transported patients have associated hospital outcome data. And so once we excluded all the patients with missing data, our final sample for analysis was less than 10% of all the out of hospital cardiac arrests included. This provides an opportunity for some systemic bias to creep in and might limit the generalizability of our results. In addition to the fact that there wasn't any concrete neurologic outcome scoring, we didn't have cerebral performance category or modified rank and scale scores for any patients. We just had that survival to discharge to home metric that we used as a correlate for good neurologic outcomes. And so the logical next step was for us to go to the CARES data set, which as Dr. Pepe said covers a large portion of the United States and has fairly complete outcome data. And so we basically replicated our analyses from the first ESO paper in this data set. This time we had about almost 170,000 cardiac arrest patients with complete outcome data. Again, baseline covariables are relatively well balanced. I want to point out that for the King laryngeal tube, the primary outcome of survival with a favorable neurologic outcome or survival with a CPC score of 1 or 2 was achieved by 4.1% of patients that were managed with a King LT and 5.4% of patients that were managed with an IGEL. Once we did our adjusted multivariable logistic regression analyses, these differences were maintained. So the IGEL was associated with better survival with the CPC of 1 or 2 in addition to survival to hospital discharge and survival to hospital admission. Once again, pretty much in every patient subset that we examined, doing some stratified secondary analyses. Once again, the point estimate favored the igel. In every subgroup that we evaluated, there were a couple that didn't achieve statistical significance. Kids less than 18 years of age, patients in nursing homes likely do a small sample size and the rarity of good neurologic outcome in those subgroups. One thing I wanted to point out. So we also included year of out of hospital cardiac arrest in our multivariable model just to account for changes in resuscitation strategies, protocols, guidelines across time. But it also enabled us to see that superglytic airway use is really increasing in the United States across time. Between 2016 and 21, the rate of increase was much faster for the IGEL than the King lt, suggesting that there are a lot of agencies that are really liking this airway device.

And so for my last couple slides here, I just wanted to briefly mention a couple of mechanisms that could be underlying these differences in outcomes that we're observing. So, first of all, our analyses with the ESO data set found that there were many fewer patients that were managed with a King laryngeal tube that achieved end tidal CO2 values, maximum end tidal CO2 values of 5 and 10 millimeters of MERK. This suggests that there may be more unrecognized failed airways among the King group than among the Igel group, which of course, may lead to worsened outcomes. Also, something that always gets brought up when we're discussing the King airway is the potential that whenever you have that big inflatable cuff in the oropharynx, there's potential to compress the carotids and decrease Cerebral blood flow. I've attached some photographs, radiographs from a proof of concept study that was published in 2012. You can see the King tube in the bottom left with the big balloon there impinging on the internal carotid arteries. Now, I would like to if in the paper pointed to this study and said, well, this is probably the cause, the mechanism of restriction in cerebral blood flow. But a subsequent study actually came out also evaluating the Igel, and they found that the Igel was also associated with a very significant decrease in cerebral blood flow. It's tough to compare these studies. They have very different experimental protocols and the way that they measured cerebral blood flow. So I'll just say that the verdict still out with regard to this kind of pathophysiological mechanism.

And then finally, one thing that I was thinking about and our group was considering when we were kind of thinking about differences between these devices and potential mechanisms. What paramedics complain about the most, it seems, with the Igel, is that they have very low leak pressures. And so, you know, and it's true that the Igel does have a much lower leak pressure than the King laryngeal tube. But it's also possible that this might counteract the negative effects of overzealous hyperventilation, keep pressure in the chest low, and enhance venous return during cpr. Although this has never been studied in a physiologic model, any animal models, clinical studies. And so it's pure speculation at this point.

And so with that, that's a summary of our two studies. I'm happy to answer any questions that anyone has about our methodology or results. Thank you very much.

Thanks a lot. This is really ambitious. And you thought about a lot of things, especially your analyses, such as, you know, doing propensity scoring and all those, which are really so. Yeah. But then again, there's a lot of issues that are also limitations here in terms of saying this is a definitive work possibly. So what my question for you would be is, you know, what do you think about that? Do you think, would you change your practice? What do we always say after journal clubs? Right. Would we change our practice based on this? Right, sure.

So, you know, I'd really hesitate to many make any recommendations about clinical care or, you know, throwing all of our kings away and buying Igels based on these retrospective data. You know, of course it's open to all sorts of bias just because of the retrospective observational nature. One thing I would say, though, is, you know, because our ESO analysis suggested that one of the potential Causes of the disparity in outcomes between these two devices is unrecognized airway failure. I think something that we can do is attempt to mitigate this as much as possible. Make sure that we're incurring our medics to use waveform capnography and confirming the placement of these devices and just using, you know, all around, you know, good airway management practices, pulling devices, having a low threshold of suspicion for pulling devices that may not be functioning correctly.

Yeah. And there's so, so many different things that are also involved here, I guess, by the way, great presentation and great work, you know, by the way. And really appreciate you doing it in a timely manner that's unusual for us here on this call. So please us to have some time for other people make comments and so on. And then I didn't see that Joe Holly or any of those folks were on this particular call. But you're real familiar with the work in the laboratory they did with these different devices as well, right? Just from that point of view. Right. David Miramani's, if those of you have met, David Miramani's is working with Project Florida. And so he's here with us. And David, you've done a lot of work. And if you don't know, David is the medical director, by the way, for San Antonio. If you don't know, get to know him. Right. David, what's your opinion and what can you tell us about the laboratory studies that were done on looking at Igels and looking at King Airways and so on.

So looking at a couple things that. That make me. That led me to get rid of the Kings. I did. I got rid of them. I did. It took a couple of years to do it through attrition. But Joe Hawley's work showing the occlusion of the venous side of the external jugular by the King Ltd with its inflated balloon, the unrecognized airway misadventures that veer Valani from Fort Worth showed us that 40% of these errors, the medics didn't even realize they're ventilating the air because the King was not seated correctly. The. The King is a weirdo airway that you have to pull up in order to get a seal, as opposed to. Which is not.

It's not intuitive, as opposed to the eye gel where you're pushing down to get a seal. And that's more intrinsic as far as when you're ventilating, you're pushing airway into place. So a couple of those things and I think you said something that's really key is that the negative pressure in the CH is key in cardiac arrest. It is all about the suck. It's not about the blow, it's about the suck. That negative thoracic pressure, those lower airway pressures are key in getting the blood flowing from the arterial to venous side with that process. So, great work. Please put the references or your DOI number in the chat so we can all just click and get that article out real quickly. But that's great work.

And then the next thing I wanted to point out is, well, first I want to go and see what everybody else has opinions. But it's not a perfect device either. You know, there was a great studies that they did up in St. Paul with respect to this. First of all, they found that the Igel worked much better up in the Minneapolis area. And I don't think that work came out in a published form that I'm aware of. But they also found out that you could get air leaks also with mechanical ventilation, you know, with the eye gel. So it's not a perfect device either. But, you know, if you use things that lowered intrathoracic pressure, like a active compression decompression pump, then that. That could actually be. This could be very favorable under those circumstances as well. Okay. Anybody else have any comments or questions? I didn't see any hands raised, so I haven't been stalling a little bit. Anybody want to pipe in and ask a question for Danner? Sure. What year did they add the strap to the head? Can you tell them who you are and what you do? By the way, Angus.