Do LMAs increase the risk of aspiration compared to ETTs? Part I

Welcome back to Depth of Anesthesia. This is a podcast that critically explores our clinical practices. I'm David Hao and I graduated. Uh it's been a wonderful year completing my fellowship at Brigham and Women's Hospital, and I'm super excited to be back at MGH as a faculty member. This episode was created as part of the Depth of Anesthesia Podcast elective that we've been running for our interns.

They get two weeks of dedicated time to work with me to research a topic and this will be the second episode we've recorded from work done on that elective. Uh big thank you to Dr. Daniel Saddawi-Konefka for supporting that initiative. Our first guest today is Dr. Chris DeCapua. Dr. DeCapua is a PGY2 and CA1 now in the Department of Anesthesia at MGH. And I was fortunate to have Chris join the elective this past year.

He's done a massive job with this episode, and I know our listeners are going to benefit from his research. Chris, welcome to the show. Hi, good evening, Dr. Howe. Thanks so much for having me on. It's a real pleasure to be here.

It's a real pleasure having you, and I appreciate all the work you put forth to make this episode a reality. Our second guest is Dr. Brian Glezerson. Brian joined us for a recent episode exploring BISP monitors and the risk of accidental awareness during general anesthesia. He is a neuroanesthesiologist in Montreal, Canada, and a graduate of the NeuroSurgical Anesthesiology Fellowship here. And if that wasn't enough, he went on to do a diagnostic EEG fellowship at the Toronto Western Hospital You can find him on Twitter at Brian Glezerson.

Brian, welcome back to the show. Thanks so much for having me again, David. I'm really uh excited to be here for another episode of Depth of Anesthesia. Um one which I'm sure will be relevant to almost everyone who practices anesthesia worldwide. Absolutely.

This is an episode actually that I've had requested from multiple listeners, so I'm really looking forward to getting into what we found. Our case today is that of a 60-year-old woman, uh history of diabetes and an elevated BMI who's undergoing an elective laparoscopic cholosystectomy. The med student on the anesthesia rotation suggests an LMA for the case, and the attending anesthesiologist responds that while LMAs are useful devices, they can be limited because of the risk of pulmonary aspiration. So instead the team elects to secure the airway with an endotracheal tube. Uh Chris, what are some of the claims that you're seeing in this case?

Yeah, so the central claim here is really that an LMA represents an unprotected airway, which thereby increases the patient's risk of developing complications like pulmonary aspiration when compared to other devices such as endotracheal tubes. Secondarily, really branching off of this original claim, there's also the argument that certain patient populations are at a higher risk for aspiration with an LMA, and thus the use of an LMA is contraindicated. These populations include individuals receiving positive pressure ventilation, patients undergoing laparoscopic surgeries requiring insuflation of the abdomen, obese patients, and pregnant patients. Here now are two questions for our listeners to think about. What's the level of your agreement with the primary claim that an alamane is an unprotected airway and thus increases the risk of pulmonary aspiration?

And what is the level of evidence for what you believe? So the actual unedited length of this episode was close to an hour and a half, and instead of subjecting you all to a somewhat massive episode, I'm gonna split this into two parts. In the first part, we'll consider the primary claim, and in the second, we'll actually go into the literature around the risk of aspiration with LMA use in some specific patient populations. uh including positive pressure ventilation, laparoscopic surgeries, obese patients, and pregnant patients. I'm also going to experiment a little with the style of the podcast in terms of moving away from a pure interview or QA style. So Bear with me.

Alright, let's get going. Chris, how'd you get interested in exploring the subject? I've been interested in this topic for quite some time, really starting as early as my first medical school anesthesia rotation. I remember seeing it being used in a case that involved a very young, healthy female patient. who was coming in for some type of minor elective peripheral musculoskeletal surgery. And I remember being really surprised seeing just how easily the LMA was inserted. and I was impressed that the patient emerged from anesthesia without any of the typical coughing, bucking, or hemodynamic changes that I had observed on multiple prior occasions when an endotracheal tube had been used.

And even to the untrained eye of a relatively new medical student, it just looked like a much more comfortable way to maintain the patient's airway So I started to suggest using the LMA every chance I could get for most of the cases that I was involved in, and I wondered why we didn't use these devices more often. I eventually got around to asking my anesthesia mentors this question, and one of them cited a lot of the claims we've been discuss discussing so far in the episode. I think as we often do, I took these claims at face value, but it's a really useful exercise to dive deeper into the literature surrounding them and let's see if these arguments hold water.

I certainly think that's the approach we advocate for here on the podcast, which is to not take things at face value and to really start questioning why we do what we do. So I'm glad that you're here with us today doing that. It appears that there were a couple of early articles that were some of the key drivers behind the claim that the LMA is an unprotected airway. And these are historical papers with quite a few limitations, but perhaps they can give us some insight into the origins of these claims. Yeah, absolutely, David.

So the LMA has been widely used since its initial inception in 1987. So based on that, I think a really pragmatic approach would be to review the literature on this topic, starting at the beginning chronologically In researching for this podcast, I came across three Sentinel articles that came out in the early 1990s, which appear to have been the initial basis on which this claim was built, and set the tone for some of the future investigations we'll go into. The first article was published by Barker et al. in the British Journal of Anesthesia in 1992. This study involved 56 patients, ASA 1 to 2, who were scheduled to undergo minor elective surgeries. and patients were randomized to receive general anesthesia via the LMA or a face mask with the oral airway.

All the subjects in the study were given a gelatin capsule. with methylene blue and lactose ten minutes prior to induction of anesthesia. They were all then induced with propofol and fentanyl, and they were maintained with halothane, such that they were maintaining spontaneous ventilation After the surgery was done, the investigators then looked at the larynx and pharynx and inspected it with a flexible orangoscope to assess for the presence of methylene blue dye in either of those anatomic locations. If dye was detected in one of those anatomic locations, they would then perform a fiber optic tracheoscopy to see if dye was present within the upper airways. In their results, they found that dye was present in the larynx or pharynx of around 25% of the LMA patients.

No dye was identified in any of the face mask patients. So the authors concluded based upon this finding that the L may places patients at a higher risk of regurgitation of gastric contents and potentially at a higher risk of pulmonary aspiration. But there's a couple things I would like to comment on here. First off, no dye was observed in any of the tracheas of the patients from the LMA group, even in instances where it was previously seen in the larynx or pharynx So we should ask ourselves, does this really represent true aspiration? Similarly, an identical study was performed years later by El Makati et al. and they were unable to reproduce the results of this initial study So I love this study because as the first or one of the first uh studies in this area, it sets the tone for an effect size that's marked, and we would expect, therefore, that it should be something Very clinically apparent and also that it should be reproducible in multiple studies afterwards, which we don't as we'll see, uh note So I think it's in interesting to contextualize this paper by just stating that it doesn't, at least in my opinion, have much clinical surface validity. in that we don't see, for example, bile stained secretions coming off LMAs in numerous patients, certainly not twenty-five percent of our patients.

Yeah, it's certainly a valid point, and um I think most people would agree there are a number of aspects of this study that warrant some skepticism. I think it's kind of entertaining. The authors themselves observed that uh it could be argued that these findings were the result of disintegration of capsules in the lower esophagus. But with all that being said, as you mentioned, this was one of the earliest studies in the space and certainly started raising the question of whether or not LMAs were increasing the risk of aspiration. The second study we have dovetails nicely with this first paper because they use the conclusions of Barker and colleagues to explore some potential mechanistic explanations.

Here's Chris. Exactly, David. So the next study I want to bring up was published by Raby et al. shortly after the initial Barker study. This was also published in the British Journal of Anesthesia in 1992. And it built pretty much directly off of the work performed by Barker et al. In their introduction, the authors state, I'm actually going to take a quick quote from that introduction session. uh section, and I quote, Previous work using dye studies has shown that the incidence of regurgitation of gastric contents may be increased during general anesthesia with spontaneous ventilation using the LMA compared with the group anesthetized via a face mask.

These researchers then go on to say that the real major barrier to regurgitation of gastric contents is the lower esophageal sphincter itself So as such, building off of that, their objective was to measure lower esophageal pressures in patients receiving anesthesia by a face mask with an oral airway versus an LMA to see if any differences became apparent in sphincterone and whether that could explain varying rates of regurgitation which were documented in prior studies like the Barker one. To do this, they included 40 patients, ASA 1 to 2, who were aged 24 to 69 years. Who were scheduled to undergo minor body surface surgeries. More specifically, they measured the lower esophageal sphincter pressure using 3mm diameter or gastric probes that had built-in pressure transducers.

The pressure was calculated in the study as the difference between the intragastric pressure and the peak lower esophageal sphincter pressure at end expiration in the respiratory cycle. They obtained pressures at the induction of anesthesia, and then again mint procedurally. This was a little confusing to me, so I'll take a quick second to summarize. So they basically put in a probe and advanced it from the mouth to the stomach and then slowly withdrew into the lower esophagus while recording pressures. They then calculated barrier pressure, which is the difference between intragastric pressure, pressure in the stomach, and the peak lower esophageal pressure.

And it's generally thought that adequate barrier pressure is thought to be necessary to prevent regurgitation, and so the authors were looking to see whether or not any of these pressures were affected by LMA insertion. Alright, back to Chris with the results. In their results, they didn't see any differences in the baseline pressures that were obtained at the start of each case, but they did see that at the mid-procedure point, the barrier pressure was lower in the LMA group. It actually decreased by 7.4%. This drop in barrier pressure was not observed in the face mask group.

The authors subsequently concluded that this may represent a reflex mechanism. whereby distension of the pharynx after placement of the LMA subsequently results in relaxation of the lower esophageal sphincter and a reduction in the barrier pressure And what I really like about this work is that they try to draw a clear a clear link between this study and the original Barker study. They identified a possible mechanistic explanation for the results of that earlier research. So we have a study that suggests a possible mechanism for the results of the Barker Dye study. The authors demonstrate a reduction in lower esophageal barrier pressure through a presumed sphincter reflex. But the clinical significance is unclear as it relates to the risk of aspiration.

And that leads us nicely into our next study, which was published by Owens et al. three years later in 1995 in Anesthesia and Analgesia. This study involved fifty five ASA 1 3 patients who were scheduled for elective surgeries, and they randomized these patients to general anesthesia with spontaneous ventilation under use of an LMA versus a face mask with an oral airway. Individuals were excluded from the study if they had a history of morbid obesity, a history of reflux or hiatal hernia, previous upper GI surgeries, or were currently or recently using H2 antagonists or other antacids. And the goal here was really to reproduce the Barker study, but instead with a more sensitive tool, the methylene blue dye.

They accomplished this by using a pH monitoring apparatus that consisted of two different pH electrodes that were each 10 centimeters apart. The first electrode was designed to sit securely in the proximal esophagus, and the other one was designed to sit in the pharynx. They started recording these pH measurements. at the induction of anesthesia and actually continued these recordings until 30 minutes after the end of the surgery period. And it they defined reflex in this study as a decrease in the measured pH on either of those probes to four or less. In their results, they noticed that at the distal electrode, which in this case corresponds to the upper esophagus, 30 centimeters from the anterior nerves, there was a significant difference seen in the incidence of reflux.

In the LMA group, the incidence of reflux was 53.6 %, while in the face mask group with the oral airway, the incidence of reflux was only 22.2%, and this was a significant difference. However, that difference disappeared at the level of the proximal electrode, which corresponded to the pharynx, 20 centimeters from the anterior nerves. There was no difference in the reflux at that level. So here we have a study that approaches the question in a similar manner to the Barker study, but using an alternative measurement modality. The authors observed more reflux, specifically defined as a pH of four or less, at the level of the distal electrode, but not the proximal.

So three early experimental studies, two observing differences in regurgitation or reflux with LMA use as measured by dye or pH monitoring. And one observing a difference in barrier pressure with LMA use that's then put forth as a possible mechanism. Now it's worth emphasizing the data publication of these studies. The original LMA was invented and developed sometime between the years of nineteen eighty one and nineteen eighty eight, and none of the three studies mention anything more about the device used in these experiments except that it's a laryngeal mask airway. But as our listeners know, the number and types of superglottic airway devices have drastically expanded in the years since.

So we'll take this opportunity to cover one more experimental study that factors this into consideration. and looks at the seal across seven different superglodic airway devices. This study was published by Berker et al. in Anesthesia and Analgesia decades later in 2008. Here's Chris with more about how the study was designed and conducted. This study design utilized cadavers to investigate the seal of seven different superglatic airway devices. They looked at the classic LMA, the LMA ProSeal, the intubating LMA fast track, the laryngeal tube, the laryngeal tube LTS2, the Combi tube, and the EasyTube.

So a variety of different devices here were studied And they looked at these devices in five unfixed human cadavers, four female, one male, within twenty-four hours post-mortem. The design here is really elegant, so I'd like to go into it in some detail. The cadaver were first prepped, with the trachea and the esophagus exposed. The esophagus was then sutured to a tube that was suspended vertically and filled with a column of water. This enabled the investigators to apply a very precise esophageal pressure, up to 130 cm of water, to the esophagus.

The trachea was then exposed and sutured to a reservoir bag designed to collect any aspirated tracheal fluids that might have occurred during the study period. These LMAs were then inserted and inflated per the manufacturer recommendations, and they were filled, the esophagus was filled with varying columns of water to see at what point any evidence of regurgitation or tracheal aspiration occurred. This is a super fascinating study and there's actually a figure at the experimental setup in the paper, so I'll do my best to describe what I see because it can be a little bit confusing. So basically there's a cadaver with the head and neck dissected out. The upper half of the cadaver's face is covered with a sheet.

And then the esophageal tube is upright and connected or sutured rather to the esophagus. and then right next to it there's a tracheal reservoir bag and that's connected uh to the trachea. They then filled the esophageal tube either slowly at ten second increments or immediately to one hundred thirty centimeters of water. and loss of seal was defined as any fluid leaking from the esophageal tube into the pharynx or trachea and subsequently collect connected in the tracheal reservoir bag. Now the column height at the loss of seal was then recorded. So, in their results, they noticed that these different area devices really fell under three categories. First, the combi tube, easy tube, and intubating LMA fast tracks each withstood water pressures in the esophagus up to 115 cm of water in the case of the intubating LMA, 120 cm of water in the case of the Easy tube, and 125 cm of water in the case of the The KamiTube Conversely, the laryngealomask airway pro seal, the laryngeal tube, and the laryngeal tube LTS2 were each able to block the esophagus up to mean pressures of 71 centimeters of water in the case of the pro seal 70 cm of water in the case of the laryngeal tube, and 74 centimeters of water in the case of the LTS2.

The classic LMA fell in its own category. It was slightly less effective at blocking esophageal pressures It lost its seal at around 48 centimeters of water, but really only minor leakage was observed in the trachea in patients that were intubated with the classic LMA. And the authors felt that this was because the LMA actually created a protective seal over the trachea, preventing any regurgitated esophageal contents from translating into any kind of aspiration. So in essence they simulated an increase in esophageal pressure and evaluated the ability of various superglottic airways to seal the esophagus. I do want to point out that a couple of devices, specifically the Combatube, EasyTube, Pro Seal LMA, and LTS, all had esophageal lumens which were also tested.

Now, when opened, these looms were able to effectively drain fluid, which is another feature to these LMAs. As Chris will talk a bit more in his takeaways, even the authors are not ultimately clear about how to put these results into clinical perspective. Here's Chris. One main takeaway is that leakage from esophageal reflux is not synonymous with tracheal aspiration. They're actually separate entities entirely.

And it's the latter one, pulmonary aspiration, which we care about clinically and has more clinical significance in terms of leading to clinical complications for the patient Moreover, multiple types of superglottic airway devices exist, and I think there's a tendency in discussing this topic to conflate them all into a single category. But they have different designs. So I would I would be hesitant to claim that they all carry an equal risk of regurgitation or aspiration. So one of the things I really love about this study is that although it has significant limitations, I mean critics would argue that dissecting a cadaver neck uh installing all sorts of tubes and manometers and then placing superglodic airway devices in could not be farther from clinical application of LMAs.

However, if you accept those limitations, they were equally applied to all the devices. And so you see that there's nonetheless a breakdown of devices and their capacity to create a seal around the glotic inlet. And this is particularly interesting when you consider the anatomy of the seal of an LMA or a superglotic airway device in the oropharynx. If you ever get the chance to read a book called The Laryngeal Mask Airway, a review and practical guide, which was published by Brimicom and Brain, Brain, of course, being the inventor of the LMA. There are some rather breathtaking and quite descriptive photographs and x-rays of the positioning of an LMA in the superglatic space.

And so you can see actually to what degree it is. really surrounding the tracheal inlet or the the glodic inlet. And you can appreciate that this study has a lot of validity, so at least surface validity in that There's quite a bit of contact you would need to overcome with whatever pressure you generate behind the LMA to get stuff into the trachea. So I felt that this study was a relatively dramatic demonstration. of uh just what it would take to actually get fluid past an LMA and into the airway. I think that's a very sensible take on this paper and how to think about r its results. Now, after these initial experimental studies, some evidence has subsequently emerged to inform us from a more clinical perspective regarding the claim that LMA use increases a patient's risk of pulmonary aspiration compared to an endotracheal tube.

And I believe the paper we'll start with is the first large meta-analysis on this topic that was published back in nineteen ninety-five. Is that right, Chris? Yeah, exactly it is. I think one of the challenges of these earlier studies is that they were published either in smaller patient populations or they were not performed in a real clinical setting as in the case of these cadaver studies. So this first large meta-analysis that was actually performed was done by Brimicombe and Berry in nineteen ninety-five and it was published in Journal of Clinical Anesthesia.

Here they included 101 different publications for a total of 12,901 patient cases. These pubs were primarily observational in nature, and they looked at the LMA as the primary area management technique. And the majority of the patients in these studies had their airways maintained via spontaneous ventilation, and that came out to be 52.6%. Versus 19.4% of patients who were maintained using intermittent positive pressure ventilation, and 28% who were maintained with some form of mixed or unspecified ventilatory modes. In their results, the authors identified only three cases of aspiration in the entire study population out of all 12,901 patients This translates to an incidence rate of 2.3 per 10,000 patient cases, and they define aspiration pretty rigorously, as either the presence of bilious secretions in the tracheobronchial tree by bronchoscopy or, if bronchoscopy was not performed, by post-operative chest radiography with the identification of infiltrates.

On top of that, of the three cases of aspiration that were seen in the study, the authors saw predisposing factors in two of those three cases. In one of them, it was an emergency case. And in the second case, the patient was placed in Trendellenberg with intraabdominal insufflation. So with this meta-analysis, the authors were able to calculate a final incidence of pulmonary aspiration with LMAs at about two in ten thousand, and this was across all published literature up until September 1993. I do want to qualify that of the uh about 101 publications included, 26 were abstracts and 11 were mini-papers.

On top of that, the authors of 64 of the publications did not include much granular data in terms of how the studies were con were actually conducted. So we do have some data on incidence of aspiration with LMA use, but I would say that the quality of the data included is not the most robust. Yeah, yeah, I agree with that, Doctor Howe. I think it's one of the challenges that comes with all the literature in this space. Um One of the really important things I would like to highlight is just the relatively low incidence of aspiration in general.

And that creates a lot of challenges when one is attempting to study these events And this will keep coming up throughout the episode. It's a common theme throughout the literature. And the way I've eventually come to think about it in researching for this episode is that rare events are inherently hard to capture, and therefore they're just hard to study. So I think one of the really important points in this study is that their definition of aspiration was, although rigorous, in my opinion, clinically relevant. They're looking at obvious secretions that uh come from the stomach or from the lower gastrointestinal tract And they're looking for patients who obviously raised a red flag to a clinician and prompted a post-operative chest x-ray, which is clearly not a routine intervention.

And so although there might be a great deal more aspiration that we are not aware of, and the stuff that they identify in this study, the incidence here of 2.3 per 10,000, perhaps that's the tip of the iceberg. But I think it's important to look at this through a clinical lens and appreciate that this is the kind of aspiration we probably care about. And so I think this value is one that we can take forward with some value placed on it as being of clinical relevance. Brian, that's a great point and something that's generally advisable to consider when interpreting literature. I think how a study is conducted and how outcomes are measured are pivotal in guiding how we ultimately interpret and apply results.

We have one more systematic review in meta-analysis, which was published about five to six years ago. Chris, tell us a little bit more about the study. Yeah, this study aimed to look at the overall incidence of airway complications during and after general anesthesia in patients who are using the flexible LMA versus endotracheal tubes for airway management. The study was comprised primarily of randomized controlled trials. The procedures that were included were primarily involving the head and neck.

In the end Out of all the studies they reviewed, they ended up including ten randomized control trials for a total of 996 different participants. Unfortunately, the incidence of aspiration was investigated in only two of those ten studies And in terms of the pooled incidence of aspiration with an LMA versus an endotracheal tube, the rates were very similar. The relative risk was calculated as 0.76, with a 95% confidence interval of 0.06 to 8.88. Regarding some of the other outcomes of this study, the flexible LMA was found to have a lower incidence of hoarseness, coughing, and oxygen desaturations when compared to the endotracheal tube, and each of those results was statistically significant. So my overall takeaway when I looked at this study was that although the incidence of aspiration was similar between both groups, the conclusion is a little bit limited, because only two subjects in either of the studies were analyzed.

And the criteria and the methods that were used to diagnose aspiration also differ between the two studies looked at. As an interesting excursus, there is a reasonable amount of evidence that comes partly from the Knap 4, the fourth national audit project of the Association of Anistotists of Great Britain and Ireland. as well as some literature that preceded it, that suggests that aspiration, when it occurs, may have absolutely nothing to do with the device that was in or it was about to be put in the airway. In fact, in some studies, upwards of sixty percent of aspiration episodes occurred during laryngoscopy, that is to say, before any device was placed. and after extubation. And so it's at the very least interesting, if not informative, to s to consider that the reason LMA and ETT may be comparable in their incidences of aspiration may simply be because most episodes of aspiration occur when neither device has been placed Brian's commentary here actually prompted me to revisit the NAP4 report.

In chapter 19, there's a summary focusing specifically on aspiration, and in table two they provide some information as it relates to timing of primary aspiration. Of the 23 events reported, only thirteen occurred during maintenance, and the remainder actually occurred either before or during airway management or during emergence itself. Which I think lends further credence to Dr. Gletzerson 's observations. Before we wrap up this episode, I want to touch on a concept that was brought up to me by Dr. Keith Baker, and that is the statistical concept of the rule of three. This is especially relevant when it comes to literature like this where the incidence of our target outcome is particularly low.

Brian shares some of his thoughts on this. In statistical analysis, the rule of three states that if a certain event did not occur in a sample with n subjects Then the interval from 0 to 3 over n represents a 95% confidence interval for the rate of occurrences in the general population. To illustrate, suppose a pain relief drug is tested on 1,500 human subjects and no adverse event is recorded From this rule of three, we can conclude with ninety-five percent confidence that fewer than one person in five hundred, or three in fifteen hundred will experience an adverse event. Importantly, the premise here is that the incidence is not zero. Zero is the number we recorded, but there is some statistical uncertainty that surrounds that value If you think of this intuitively, if n goes to infinity and you still see a zero incidence, well then you can say with confidence that there is zero incidence.

But similarly, if you test one subject and they don't get the outcome that you're looking for, you can't say much about the population incidence. In fact, your confidence interval will become very large. You know, I actually thought this concept was so important to this episode that I actually also reached out to Dr. Baker to get some of his additional perspectives on the topic. So here's Dr. Baker talking a little bit more about the rule of three. I think most of us can think of situations in medicine when nothing goes wrong after doing a number of procedures or after using a drug a number of times.

For example, let's imagine that you've recently used a drug on 60 consecutive patients. and no untoward events occur. Does this mean the drug is safe? Of course not, because the number of patients, 60, is too low to have much confidence that nothing will go wrong in the future. The rule of 3 is a very handy formula for determining just how much confidence we should have that nothing will go wrong after no events occur in some number of consecutive patients. Using this rule, we can say that if no events occur in n consecutive patients, we can have 95% confidence that the actual rate of an unfavorable outcome is less than 3 in n.

So, going back to our example, if we had had zero negative events in 60 patients, then we can say with 95% confidence, that the rate of adverse events is less than three in sixty. This rate can also be calculated as one in the number of patients divided by three, which is less than one in twenty patients or less than five percent of patients in this example. So, far from having no negative complications, we now know with 95% confidence that the rate of an event is less than 5%, which means that there is still a real possibility that the drug may not be safe. The rule of three should really only be used when events are independent of each other and when the sample size is greater than 30.

And here are his thoughts when I asked him about how the rule of three applies when we think about the evidence base for the risk of aspiration with LMAs. This question is really made for the rule of threes. We have a number of LMA studies showing no aspiration events using sample sizes well above 30, so we can ask if LMAs really have no aspiration risk associated with their use. Using the rule of threes, we can easily calculate that if there were no aspiration events in, say, 300 consecutive LMA uses then we can know with 95% confidence that the real aspiration risk is less than 3 in 300, which is the same as less than 1 in 100 patients, or less than 1% of patients.

So what I'll ask of our listeners is that when you're thinking about this data, keep the rule of three in mind, especially as you consider how you might broadly apply some of the findings from this literature. So we'll leave part one here, having covered the literature around our primary claim that an LMA represents an unprotected airway and thus increases a patient's risk of pulmonary aspiration compared to an endotracheal tube. Coming up in part two, we'll dive into the arguments that certain patient populations are at higher risk of aspiration with LMAs, including patients undergoing positive pressure ventilation, laparoscopic surgeries, obese patients, and pregnant patients. I'm gonna do my best to try to get part two out in the next month or two.

It's recorded and Ready for editing, but unfortunately I'm in the middle of studying for oral boards, which by the way has probably given me about ten years worth of depth of anesthesia episodes in terms of the sheer amount of dogma I'm seeing So there's a chance that the episode gets a little bit delayed, but bear with me. Stay hungry and keep asking questions and I'll talk to you guys next time. First valuation is a waste of face wood, is a waste free spolution, it's a weird is a waste of their