Transcript
Speaker: Welcome to Critical Matters, a sound podcast covering a broad range of topics related to the practice of intensive care medicine.
Speaker: Sound provides comprehensive critical care programs to hospitals across the country.
Speaker: To learn more about our programs and career opportunities, visit www.soundphysicians.com.
Speaker: And now your host, Dr. Sergio Zanotti.
Speaker: Acute asthma exacerbations are associated with increased morbidity and mortality.
Speaker: There's a subset of patients with acute asthma exacerbations that will require ICU care, and among these, a smaller group will require support with invasive mechanical ventilation.
Speaker: In the previous episode of Critical Matters, we discussed the medical management of acute asthma exacerbations.
Speaker: In today's podcast episode, we will dive deeper into mechanical ventilation for severe asthma.
Speaker: Our guest is Dr. Emily Daymuth, an emergency medicine and critical care physician.
Speaker: She's an assistant professor of medicine and emergency medicine at Cooper Medical School of Rowan University.
Speaker: Dr. Daymuth splits her clinical time between the emergency department and the intensive care unit at Cooper University Hospital in Camden, New Jersey.
Speaker: Dr. Daymuth serves as an assistant program director for the Critical Care Medicine Fellowship at Cooper and helps oversee the ECMO program.
Speaker: She teaches mechanical ventilation through didactic lectures and simulation.
Speaker: She's passionate about medical education, serves as an advisory college director at Cooper Medical School of Rowan University, and has received multiple teaching awards.
Speaker: A true honor and pleasure to have her on as our guest.
Speaker: Emily, welcome to Critical Matters.
Speaker: Well, thanks, Sergio.
Speaker: Thanks for having me.
Speaker: So a very interesting topic, I think something that maybe with the spring and it's important to review.
Speaker: But why do you think, Emily, that intensivists should care about this topic?
Speaker: Yeah, no, I think that's a great starting point.
Speaker: And I think, you know, if I think about my role as an emergency physician too, you know, asthma is one of the most common respiratory diseases that we'll encounter.
Speaker: I think it's something like 2 million ED visits a year.
Speaker: And 10% of those patients will require admission to an intensive care unit.
Speaker: And about, you know, 2% to 4% of those patients will require intubation and invasive mechanical ventilation.
Speaker: But we know that when patients with asthma decompensate, it's often rapid and it can be lethal and really doesn't offer us time to sort of devise a mechanical ventilation strategy in real time.
Speaker: So how common it is, how difficult it is to predict those patients that will decompensate to the degree that they require intubation.
Speaker: And also just the added pressure, I guess, is a way to think about it, that these are often very young and healthy patients with a reversible disease process.
Speaker: I think it's a very important topic.
Speaker: And then the final thing I would say is because of how severe asthma is and how important it becomes to
Speaker: make objective measurements of the safety of our ventilator settings, I think that we can take that approach and really apply it to anyone we intubate, right?
Speaker: So it's crucial to measure static airway pressures and asthma, to look at our ventilator graphics and asthma.
Speaker: But when we learn to do that for really severe disease processes like asthma, we realize that we should be doing that in everyone that we mechanically ventilate.
Speaker: So I think that a lot of the concepts that we will talk about
Speaker: are relevant to all of our patients when we're trying to ensure the safety of mechanical ventilation.
Speaker: Excellent.
Speaker: Before we dive into the proper management of mechanical ventilation and severe asthma, could you give us an overview of the role of non-invasive ventilation and severe asthma, just at a high level?
Speaker: Yeah, so I think that just intuitively, as intensivists, we would probably assert that
Speaker: Non-invasive ventilation in obstruction, certainly the literature is very well supported in COPD, but similarly in asthma, we would expect that it would reduce perhaps the need for invasive mechanical ventilation, maybe even improve mortality.
Speaker: And I think the literature in COPD for those two endpoints is very supportive.
Speaker: It's been a little less clear for asthma.
Speaker: Specifically, there was a Cochrane review that evaluated just a handful of RCTs, actually, where there wasn't a clear benefit in mortality or reduction in intubation rate.
Speaker: But certainly there was improvement in peak expiratory flow, FEV1, hospital admissions, some sort of a little less patient-centered
Speaker: outcomes.
Speaker: More recently, there's been a multicenter retrospective study looking at the use of early non-invasive, and I think that that's really the crucial thing to consider, that within 24, often just several hours of asthma,
Speaker: And in those patients, there was an association with a reduced requirement for intubation and a small but significantly lower odds of hospital mortality.
Speaker: So I think we just intuitively think that it probably does in many patients avert and avoid the need for intubation, but it's also just as crucial to not rely on it too much such that we're delaying intubation.
Speaker: And so I think that that...
Speaker: is also a really important point to make.
Speaker: So we try in some patients, like you said, people might try non-invasive.
Speaker: And I think, as you mentioned at the beginning, a lesson that can be translated to other diseases is don't sit on your non-invasive ventilation too long, right?
Speaker: If it's not working in a short period of time, you probably need to move on.
Speaker: And I think that is also true for asthma.
Speaker: So if you decide to move on, Emily, any pearls or pitfalls to avoid in intubating asthmatic patients?
Speaker: Yeah, so great question.
Speaker: I think the when to intubate is hard, but I also think that we shouldn't overthink it, right?
Speaker: So of all the skills that we learn in intensive care medicine, you know, recognizing when a patient requires intubation for respiratory failure, I think is one of our greatest skills, whether it's
Speaker: failure to oxygenate, failure to ventilate, failed airway protection with progressive encephalopathy that often happens in asthma, or just fatigue and increased work of breathing.
Speaker: And so I think that not overthinking it and not changing your approach, so still looking for accessory muscle use, paradoxical abdominal motion, tripodting, especially in asthma, being wary of like exaggerated pulses, paradoxes,
Speaker: suggesting that perhaps they're trapping gas, trapping air inside their lungs, and sort of making, which is further increasing their work of breathing.
Speaker: So I think the major thing is something we already reflected on a little bit is that recognize failure and calling it failure, and don't be afraid to intubate a patient with status asmaticus, just like we might say in DKA.
Speaker: You know, we don't want to do it, but when it's necessary, we absolutely want to do it, and we need to proceed.
Speaker: And so...
Speaker: I think the two major things are noting a fatiguing patient who's really just sort of at a mechanical disadvantage with respect to their respiratory mechanics, and then also neurologic failure where if their mental status is getting worse and they're starting to have failed airway protection, we definitely need to intervene.
Speaker: And so I think the biggest pitfall would be not reassessing our patients frequently enough,
Speaker: because it is just you're at the edge of a cliff often with asthma and things can suddenly take a turn.
Speaker: And so really frequently reassessing the need for intubation.
Speaker: And during the intubation itself, are there any special words of wisdom you can share?
Speaker: No, I don't think so other than...
Speaker: Especially if you're worried that the patient already has a great degree of respiratory acidosis, you would want to be very expeditious.
Speaker: So, you know, perhaps the most experienced person in the room, you know, we use RSI to just get the best view and get the tube in.
Speaker: I don't think in general they're, you know, if they're already on non-invasive, certainly continuing it.
Speaker: as you're prepping to intubate.
Speaker: But overall, I think just moving forward and not having a long apneic time would be the most important.
Speaker: And also not bagging vigorously such that your respiratory rate is fast, which is only gonna further shorten your expiratory time and worsen air trapping, which as we will discuss is really your biggest opponent when it comes to mechanically ventilating a patient with status as maticus.
Speaker: Let's move on to the topic specifically of mechanical ventilation and severe asthma.
Speaker: And I would like to start this portion with maybe some physiology.
Speaker: If you can just discuss some important physiologic aspects of severe airway obstruction and asthma that have an implication for what we do with the ventilator.
Speaker: Yeah, absolutely.
Speaker: So, you know, the physiology we know boils down to just severe airway obstruction and the airway resistance in asthma can increase to up to 15 times normal.
Speaker: And that's from, you know, smooth muscle thickening from bronchospasm.
Speaker: You can get inflammation of the bronchial wall, inspissated secretions, you know, sloughed endothelial cells that can all create mucus plugging, eosinophils, et cetera.
Speaker: And so you have this resistance to airflow that ultimately mostly impacts expiratory flow.
Speaker: And the problem that patients, as they continue to decompensate, is that
Speaker: when they start their dyspneic and they start to breathe more rapidly and more shallowly and they have expiratory flow that's persisting at end inspiration, but then they take another breath, it's that gas trapping.
Speaker: So intrinsic peep, auto peep, this can happen in spontaneously breathing patients as well.
Speaker: That dynamic hyperinflation that ultimately can sort of lengthen the respiratory muscles.
Speaker: It flattens the diaphragm.
Speaker: even the intercostals.
Speaker: And so it puts your respiratory muscles at a mechanical disadvantage such that they now in inspiration are sort of combating now an elastic load.
Speaker: So you already had the resistive load because of high airways resistance.
Speaker: And now as air and gas is trapped in these
Speaker: typically very compliant lungs, now there's an elastic load that needs to be overcome, and that makes inspiration hard.
Speaker: Now the work of breathing increases, and ultimately it can just result in flat-out respiratory arrest, which is why one of the most common causes of death in patients with status asthmaticus
Speaker: is often hypoxic ischemic brain injury from either pre-hospital cardiac arrest, often before the ICU environment.
Speaker: So that physiology is just this vicious cycle where the more dyspneic they become and the more increased work of breathing they have, the shorter their expiratory time, more gas is trapped, and then ultimately the combined elastic and resistive load is difficult to overcome, even with a mechanical ventilator.
Speaker: The other thing I would say, Sergio, that sorry, is that one of the things that I've learned more recently is how heterogeneous this process is.
Speaker: You know, it's very similar to ARDS in this regard.
Speaker: And we all know that when we look at a chest X-ray and it shows diffuse bilateral opacities, we know that if we have 3D imaging and a CT in a supine patient, they have dependent lung water and we essentially, there's consolidated alveoli posteriorly and we're ventilating this baby lung.
Speaker: But the same concept can happen in asthma where the mucus plugging and occlusion of distal airways is not uniform.
Speaker: And then you have regional areas of hyperinflation where the alveoli are hyperinflated.
Speaker: And all it takes to create more dead space is if you have a hyperinflated alveoli or region of hyperinflated alveoli that then exceeds the capillary pressure,
Speaker: And that can even further occlude more distal airways.
Speaker: So it's just a very heterogeneous process.
Speaker: It's not that all of the airways are equally swollen or all of them are equally occluded.
Speaker: You have areas of hyperinflated alveoli that are causing an extrinsic compression on distal airways and sort of clamping them off that way.
Speaker: And then you have other airways that are plugged up with secretions and then other air patches of the lung that maybe have completely peat in distal airways
Speaker: and hyperinflated alveoli.
Speaker: So I think that that's important when we think about the process of auto PEEP or dynamic hyperinflation and how we try to mitigate it with our mechanical ventilation strategy, how some of the pressures as we measure them on the ventilator sometimes aren't always completely accurate because it is such a
Speaker: heterogeneous disease process, despite the fact that when we look at an x-ray, we just see flattened diaphragms and hyper aeration.
Speaker: It's really much more heterogeneous than I truly appreciated before reading more about it.
Speaker: I think that's a great point, Emily.
Speaker: And I think it's a reminder that the way we see diseases don't ultimately represent what's really going on.
Speaker: And especially, I think, with mechanical ventilation and asthma and ARDS, we look at an x-ray, we do a physical exam, and we think of this diffuse
Speaker: kind of, like you said, very homogeneous process in the lung.
Speaker: And we apply changes that are one change that applies to the whole lung, but how it impacts different areas of the lung.
Speaker: And with that heterogeneity, I think, is also an important consideration as we try to figure out what works and what doesn't work.
Speaker: Yeah, exactly.
Speaker: So when people talk about...
Speaker: Mechanical ventilation, I like the framework of goal-directed mechanical ventilation, understanding that in the initial phase of a disease like severe asthma, you might have a kind of like a resuscitation and stabilization initial goal, and then people might be just supportive, and then you try to get them off the ventilator, right?
Speaker: So in terms of the initial mechanical ventilation strategy, what are the general goals for an asthmatic patient?
Speaker: Yeah, I think that's a great way to frame it because it's hard to know how long that period lasts, but the sort of peri-intubation period in particular, sort of early hours of mechanical ventilation of severe asthma are extremely delicate, where we're trying to figure out, and it's, you know, by nature of calling it dynamic hyperinflation, it's a very dynamic process.
Speaker: And so what that means is that we need to make very small adjustments on the ventilator.
Speaker: And then as we'll talk about, you know, measure and inspiratory and expiratory pressures, look at our ventilator graphics, get a blood gas, make other small adjustments and sort of keep doing that.
Speaker: I mean, you may get,
Speaker: an ABG hourly in the first six or eight hours of a patient with status as maticus on a ventilator, depending on how severe their obstruction and their respiratory acidosis is.
Speaker: So I think the, and also the early periods where, and we'll talk about mode and strategies of ventilating, but almost always in the most severe patients where our pH is under seven or right around seven or seven one,
Speaker: These are patients where we're going to pursue a strategy probably of controlled mechanical ventilation, meaning we are deeply sedating and or potentially using neuromuscular blockers to completely take over in a strategy of controlled hypoventilation.
Speaker: But the primary goal, I think, especially in that immediate period, is trying to limit dynamic hyperinflation.
Speaker: And so often,
Speaker: And that's why I think we're scared to do it.
Speaker: When we put the tube in, we can now, like patients often can't breathe above total lung capacity as they start to, their FRC increases sometimes two to three times as they develop more and more auto-PEEP.
Speaker: But then when we institute mechanical ventilation, iatrogenically, we can impose, you know, trying to breathe at lung volumes, particularly in high degrees of auto-PEEP above total lung capacity.
Speaker: And that's where we start to
Speaker: encounter, you know, barotrauma and hypotension and some of the complications.
Speaker: And so it's really important early on that we approach it with controlled hypoventilation, but also are making serial measurements to assess the safety of the settings that we chose.
Speaker: With that in mind, what would be the initial settings that you would consider and how you would approach a patient that you had just intubated for severe asthma?
Speaker: Yeah, and this is the question, right?
Speaker: And I think it's best to keep it highly clinical.
Speaker: You know, the real answer is, unlike an ARDS, we don't have a litany of RCTs to tell us what is the best mechanical ventilation strategy and status as maticus.
Speaker: But we know based on the physiology of asthma, and there are some studies showing that controlled hypoventilation, which I'll talk about how low do we go, is associated or has shown a decreased mortality over the years.
Speaker: But it's really our job to find that delicate line between providing just enough minute ventilation, but the primary goal being controlling dynamic hyperinflation.
Speaker: And so it becomes this
Speaker: this tightrope walk where you're trying to give just enough rate and tidal volume, i.e.
Speaker: minute ventilation, but also breaking that cycle of progressive air trapping.
Speaker: And so when we think about the mode of mechanical ventilation, and I'll just put out there that my preference would be to use volume control.
Speaker: Now, if you really look at the mechanical ventilation literature, it's unfortunately
Speaker: Unfortunately, it's fraught with sort of proprietary vent modes and there's over like 500 different modes if you take into account different brands of ventilators.
Speaker: But what we really wanna focus on is how is the breath delivered?
Speaker: And I think that fundamentally we can differentiate pressure control from volume control.
Speaker: And I would advocate for volume control and I'll sort of say why.
Speaker: So one of the most basic principles of mechanical ventilation is that we simply cannot control pressure
Speaker: and volume at the same time.
Speaker: So if we choose to limit pressure in a pressure control mode, that means we will deliver a breath where the pressure is held constant throughout inspiration.
Speaker: But then as a result,
Speaker: depending on the airway resistance and asthma or the lung compliance, the tidal volume and subsequent minute ventilation is dependent upon those variables.
Speaker: So the airways resistance, the lung and chest wall compliance, and if the patient is interacting, also the patient effort.
Speaker: So in status asthmaticus, where we know airway resistance is extremely high and also can be dynamic,
Speaker: that tidal volume can suddenly drop from breath to breath over time and can quickly go below a critical level and produce severe acidemia.
Speaker: We don't have a way in pressure control to sort of guarantee minute ventilation.
Speaker: Now volume, and the reason for that is when you deliver a breath in pressure control, the pressure is held constant and the breath terminates after a set amount of inspiratory time.
Speaker: with, as I said, the tidal volume being dependent on the airways resistance and lung and chest wall compliance.
Speaker: Now in volume control, on the other hand, when you deliver a breath, it holds the inspiratory flow rate constant or the rate of change of inspiratory flow constant.
Speaker: And so you can deliver a set tidal volume because the ventilator will cycle from inspiration to expiration after the delivery of a set tidal volume.
Speaker: So you can essentially guarantee minute ventilation, which is really crucial in a disease process where we're dealing with severe respiratory acidosis.
Speaker: The other benefit is in the way that we deliver a breath and volume control, because you can control the inspiratory flow rate, you can do what's called a square waveform pattern where you can deliver the entire inspiratory volume at the peak inspiratory flow rate, like holding that inspiratory flow rate at a constant value.
Speaker: And so that allows you to relatively to descending flow where you start out at a peak rate and you kind of trail off.
Speaker: At a constant flow rate, you can make inspiration the fastest.
Speaker: And why is that so important in asthma?
Speaker: Because in asthma, we really need to lengthen expiration as much as possible.
Speaker: So I think the two features of volume control that are preferable for the way the breath is delivered is that one,
Speaker: You can guarantee minute ventilation, sort of regardless of your airways resistance.
Speaker: And then the other part being, because we can deliver a constant high rate of flow, we can actually relatively shorten inspiratory time, which allows us to lengthen the time and exhalation.
Speaker: So I would sort of argue, and many experts, and there are a lot of review papers on this, that volume control might be preferred in asthma for those reasons.
Speaker: And as you mentioned, this is based on physiology, expert opinion and experience and our understanding of the disease and not necessarily on large randomized trials, which for obvious reasons, I think would be very hard to pull off with decent numbers.
Speaker: But I think it's a great explanation of how we think about the mode.
Speaker: So the next thing that you probably would have to set is the rate.
Speaker: How do you think about rate?
Speaker: Yeah, so I think, you know, in volume control, we think about rate and tidal volume in tandem.
Speaker: And I think that this is the hardest step in the management of patients with severe asthma.
Speaker: Because, you know, sort of as we alluded to, when airflow obstruction is severe as it is in status asthmaticus, minute ventilation becomes the most critical determinant of dynamic hyperinflation.
Speaker: And so what we choose here is
Speaker: is really important.
Speaker: And unlike, we know the paradox, right?
Speaker: And severe asthma, we know that unlike in any other disease process that I can think of other than COPD, which is also airways resistance problem, that when we increase minute ventilation, when we either increase tidal volume or increase rate or increase both,
Speaker: it relatively shortens the expiratory time and that can result in more alveolar hyperinflation, more dead space, and we can actually worsen our pH rather than improve it.
Speaker: And so it runs counter to any other disease process we manage.
Speaker: And we know that, but I think it's hard to sort of reel that in.
Speaker: And so really our strategy is what we call controlled mechanical hypoventilation, where permissive, not unlike an ARDS, permissive hypercapniacinitis,
Speaker: Hypercapnia is our strategy, but we do that by intentionally limiting both rate and tidal volume so that we are allowing the most time for the patient to exhale and avoid dynamic hyperinflation.
Speaker: So the obvious question is, okay, so how low should we go?
Speaker: as a starting minute ventilation and go to be evasive but then not be evasive.
Speaker: So I think it depends.
Speaker: It depends on the severity of airflow obstruction.
Speaker: It certainly depends on the patient's height, their ideal body weight, which is the way we sort of scale our tidal volume.
Speaker: And it also depends on the degree of auto-PEEP that is already present.
Speaker: But a safe place to start
Speaker: I would argue is around six cc's per kilo.
Speaker: Again, not unlike in our ARDS patients.
Speaker: Now, if you go back to the literature in the eighties, they, they describe, they describe this strategy of controlled hypoventilation.
Speaker: And then they talk about using tidal volumes of, of, you know, 10 to 12 cc's per kilo or eight to 10 cc's per kilo.
Speaker: Well, that's,
Speaker: That's not hypoventilation and modern mechanical ventilation.
Speaker: So I think when you start at a lung protective tidal volume of six milliliters per kilogram of ideal body weight, then you rarely have to go below a rate of around 10 to 14 or 10 to 16 breaths per minute.
Speaker: in order to control auto PEEP, which is your primary goal.
Speaker: So just as an example, let's say we had a patient who was, I don't know, 5'8", and had a, so the ideal body weight is going to be right around 70 kilos.
Speaker: So if we select a tidal volume of 400 milliliters and a very conservative rate of 12, that's around 4.8, you know, five liters per minute of minute ventilation.
Speaker: Some of the earlier papers, again, dating back to the 80s,
Speaker: in what they termed controlled hypoventilation, but I think that is less so, you know, they say under 10 liters per minute.
Speaker: Well, depending on the patient's height and body weight, it's still a pretty substantial minute ventilation.
Speaker: And so what we'll talk about is, so we're starting there, right?
Speaker: But then we need to measure our static airway pressures.
Speaker: And that's really the next step, because if you don't have significant auto PEEP,
Speaker: well, then you may be able to go up on your minute ventilation.
Speaker: However, the flip side is if you have significant auto-peep, then maybe that's too much.
Speaker: And so this is why the early period of ventilating a patient with severe asthma is so crucial because you just need to make small changes and check your static airway pressures and read your ventilator waveforms as sort of a guess and check to see the safety of your settings.
Speaker: But I think a good starting place is
Speaker: tidal volume between six and eight cc per kilo.
Speaker: I would advocate starting with six and then a rate between, I don't know, 10 to 16 breaths per minute, and then sort of going from there.
Speaker: And the last thing that you are setting in different ways and you alluded to, as you were explaining the mode and the rate and title volume is the inspiration to expiration ratio, right?
Speaker: So the time of inspiration compared to the time of expiration.
Speaker: Can you talk a little bit more of the I to E ratio and reemphasize why it's so important?
Speaker: Yeah, absolutely.
Speaker: We talked about the fact that asthma at its physiologic basis is a problem of airway resistance and where we encounter the most problem is in exhalation.
Speaker: And so the starting point is picking a low minute ventilation.
Speaker: And by picking, let's just to make the math easy, if you pick a rate of 10, that allows six seconds of
Speaker: for the entire respiratory cycle for every breath.
Speaker: So if you're at a rate of 10, you get six seconds to both breathe in and out for every breath.
Speaker: Now, when we're thinking about how we're going to distribute inspiration and expiration, we clearly want to spend a lot more time in expiration.
Speaker: So one of the default settings, and I just want to point this out when you're in volume control, is the ventilator will often build in an inspiratory pause.
Speaker: And I think we should talk about differentiating peak and plateau pressure.
Speaker: But the point of that is so that you can see in your pressure waveform, your peak pressure relative to your plateau pressure and every breath visually.
Speaker: Now, an inspiratory pause, first of all, it's not very comfortable, right?
Speaker: Nobody breathes in, pauses.
Speaker: and then breathe out.
Speaker: So from a comfort standpoint, it's not ideal.
Speaker: In an asthmatic patient, we definitely do not want to have an inspiratory pause.
Speaker: And you can just, if it's set at 0.2 or whatever it's set at, you can just make that zero, remove any inspiratory pause.
Speaker: You don't want anything to lengthen inspiration that's not going to help you ventilate your patient.
Speaker: So once you've done that,
Speaker: The way that you would shorten your inspiratory time relative to your expiratory time is by increasing your inspiratory flow rate.
Speaker: And, you know, I'll often increase this up to 80 liters per minute, even 100 liters per minute.
Speaker: So we're talking about inspiratory times, maybe as low as 0.6 seconds.
Speaker: And so if you think about it and that patient on a rate of 10, which might be a little lower than I'd pick at a 60 C tidal volume, but just for the math, then now you're spending, you know, 5.4 seconds in expiration.
Speaker: So really important.
Speaker: And it's, the other point I would make is that if you had set a patient at a normal inspiratory time, so let's say their, their inspiratory flow rate was, I don't know, 60 liters a minute, and that put them out of an inspiratory time of around 0.8 seconds.
Speaker: If you even lower that by 0.2 seconds, just that one breath, right?
Speaker: So now each breath expiration is going to be 0.2 seconds longer.
Speaker: Well, if we have 10 breaths a minute,
Speaker: Now we're talking about two seconds every minute of more inspiration.
Speaker: You can see that over minutes to hours, just shortening the inspiratory time by fractions of a second really matters.
Speaker: Now, what is the cost to that?
Speaker: Well, if you're going, if you shorten or if you increase your inspiratory flow rate and you shorten your inspiratory time, the peak airway pressures are going to go up.
Speaker: But interestingly, and I think it's a good segue to talking about the difference between the peak and the plateau pressure, that has really not been shown to correlate tightly with barotrauma and hypotension and these complications that we're worried about.
Speaker: So I don't know if this is a good time to, because I know it's a very, very basic physiologic principle, differentiating peak and plateau pressure and what it tells you.
Speaker: But this is a concept I remember struggling with in fellowship and that I think is so crucial to ventilator management in patients with asthma.
Speaker: And we will discuss it, but just hold that thought for one second.
Speaker: I want to flush out the I to E because like you said, at the end of the day, what we're trying to do is allow the trapped air to come out by prolonging expiration.
Speaker: So how do we do that since we don't control expiration is we make the inspiration shorter and shorter.
Speaker: So in general, right, you can impact that inspiratory to expiratory ratio by decreasing the rate, right, or by increasing the rate.
Speaker: The rate will have an impact, like you mentioned.
Speaker: The flow rate, the inspiratory flow rate, and sometimes the flow pattern, depending on what you're on, would also play a role.
Speaker: The tidal volume plays a role, right?
Speaker: A larger VT will have a higher I to E ratio.
Speaker: A smaller VT gives you a longer expiratory time.
Speaker: There are some ventilator modes that we didn't discuss that actually do control the I to E ratio specifically, right?
Speaker: But that's not something that really would be first in mind when you're dealing with asthma.
Speaker: Is that correct?
Speaker: Yeah, I think you hit it on it.
Speaker: So like all the ways that you can maximize that expiratory time, all the pharmacology, bronchodilator, steroids, magnesium, all that, epi, and then lower rates, lower tidal volumes,
Speaker: shorter inspiratory times, higher inspiratory flow rates.
Speaker: And you can actually see when you go to the settings on the ventilator, and I encourage everyone to sort of spend time at the bedside with the ventilator, with your respiratory therapist.
Speaker: As you're making changes, you can see what your inspiratory time is, see what your IDE is.
Speaker: And you can sort of know that as you turn it down and you're checking serial blood gases, you know, which direction you're going.
Speaker: So absolutely.
Speaker: And by deeply sedating,
Speaker: And oftentimes in the early stages, paralyzing patients, then we know there's not going to be any spontaneous effort that's going to affect that respiratory rate and affect that IDE ratio.
Speaker: Now we can talk about PIP versus PLAT, but let's focus on how do we monitor patients who are in mechanical ventilation with severe asthma?
Speaker: And we can start with the alarms.
Speaker: And the two alarms that you mentioned are the peak inspiratory pressure versus peak plateau pressures.
Speaker: And maybe you can talk more about that.
Speaker: Yeah.
Speaker: So one of the things, you know, and going back to, we, we set the vent, right?
Speaker: We, so we picked volume control and we set our rate and we set our tidal volume.
Speaker: Oftentimes in severe asthma, you may next walk in the room and, and the pressure alarm is going off and on your ventilator screen, there's, you know, depends what brand you have, but there's often a red, a red flashing light and a really loud sound and telling you your airway pressure is high.
Speaker: Now,
Speaker: In the vast majority of cases, that's because of your airway resistance, but the implication of what that's doing to your patient and your ability to ventilate them is very important to understand.
Speaker: So when a ventilator goes off and says that, has that red alarm on the screen saying airway pressure is high, once it exceeds that preset safety limit that's tucked in the settings of your ventilator, and I'll show you how to look at it,
Speaker: it will dump the rest of the breath.
Speaker: So let's say our patient, we talked about selecting a tidal volume of 400.
Speaker: Well, you might've, you can, yes, in volume control, you can guarantee minute ventilation and set your rate and set your tidal volume.
Speaker: But if that peak pressure safety alarm is reached,
Speaker: let's say it's typically set around 40 centimeters of water, the ventilator will dump the rest of the breath.
Speaker: And so when you walk in the room, you may look at your ventilator screen and think, hey, I've set a tita volume of 400, but my patient's only receiving 180.
Speaker: And so that can be catastrophic in these patients where
Speaker: It's so essential to guarantee the minute ventilation that you're delivering.
Speaker: And so what we have to do in the patient with severe asthma and volume control and pressure control is go into settings and RR ventilators.
Speaker: It's a panel on the left.
Speaker: It's called alarm limits.
Speaker: And you actually go in under the peak pressure limit.
Speaker: Again, by default on many ventilators, it's 40 centimeters of water, which for your ARDS patient, that's a great number.
Speaker: Well, for asthma, the peak airway pressures can often be 60, 80 centimeters of water.
Speaker: So I typically go in and turn it up, well, with our respiratory therapist, turn it up to 80 so that that entire breath
Speaker: can be delivered.
Speaker: And that's sort of step number one, that makes sure the settings that you set are the settings that your patient's actually receiving.
Speaker: And so that safety alarm is one key concept in a critical first step to reset the upper pressure limit above your patient's peak inspiratory pressure.
Speaker: Now, if you're worried about just jumping from 40 to 80 because you're not sure what your plateau is, you can walk up by 10 centimeters of water at a time and recheck your plateau pressure.
Speaker: But it's very important to reset that.
Speaker: The ventilator won't actually let you check a plateau pressure at end inspiration if the peak pressure is higher than your pressure alarm limit because it won't deliver the whole breath.
Speaker: So what do we monitor?
Speaker: So we need to monitor the peak inspiratory pressure as well as the plateau pressure.
Speaker: And then we'll also talk about the end expiratory pressure.
Speaker: So I want to spend just a second differentiating the peak from the plateau pressure and the relationship between the two, because all three of those concepts are really important in status asthmaticus.
Speaker: and not just status asthmaticus, any patient that we ventilate, we should be looking at our peak airway pressures and measuring manually our plateau pressure immediately after intubation.
Speaker: And really no matter the disease process.
Speaker: So the peak inspiratory pressure is measured during every breath.
Speaker: In fact, it's typically just right on the ventilator screen, every breath it will tell you what the peak inspiratory pressure is.
Speaker: And the way the ventilator measures that
Speaker: is during inspiration.
Speaker: And during inspiration, there's gas flow present.
Speaker: And so when there is flow present, there is resistance present, airways resistance.
Speaker: So the peak inspiratory pressure is the pressure required to overcome the resistance of the airways, both native and artificial, as well as the compliance of the lungs and the chest wall.
Speaker: Now the plateau pressure on the other hand, we know we measure using an end inspiratory hold.
Speaker: There's often a button that we hold down with our finger for one to two seconds.
Speaker: And what that does is it pauses at end inspiration with that breath trap, that tidal volume trapped inside the chest.
Speaker: It pauses, it closes the inspiratory valve and it takes away flow.
Speaker: And when there's no flow, there's no airways resistance.
Speaker: So now that plateau pressure is our best
Speaker: estimate of the alveolar distending pressure or our lung compliance.
Speaker: And so the value in asthma is that we can compare, or in any disease process really, our peak inspiratory pressure to our plateau pressure.
Speaker: And what we expect
Speaker: In patients with asthma that typically have very compliant lungs, we suspect that they have an airways resistance problem.
Speaker: We would expect that maybe that peak airway pressure would be, let's say 65 centimeters of water.
Speaker: But the plateau pressure, because it's not accounting for airways resistance, it's simply the pressure required to overcome the compliance of the lungs and chest wall should really be normal.
Speaker: in an asthmatic patient.
Speaker: And so let's say it's 18 centimeters of water in the 20s, the low 20s.
Speaker: And so you have a big gradient between your peak to plateau pressure telling you that you have a airway resistance problem that's causing that high airway pressure.
Speaker: Now, another common scenario, right, ARDS, where the peak is always greater than the plateau.
Speaker: So in ARDS, let's say we have a peak airway pressure of
Speaker: 36 centimeters of water.
Speaker: And when we measure our plateau pressure, it's also high.
Speaker: Let's say it's 30 centimeters of water.
Speaker: So yes, we have a relatively high peak, but we have almost just as high plateau and we have a small peak to plateau gradient.
Speaker: And so why that's so important is when you have a pressure alarm going off on the ventilator, as we often do with patients with asthma,
Speaker: the next move should always be to measure your plateau pressure to figure out what's causing that elevation in airway pressure.
Speaker: And if when you look at your peak airway pressure and it's really high, what your plateau pressure is normal,
Speaker: Well, now you're thinking about airways resistance problems.
Speaker: So like bronchospasm in the patient we're describing, or maybe their ET tube is occluded, or they're biting it, or there's a kink in the inspiratory limb of the ventilator circuit.
Speaker: We're dealing with an airways resistance problem.
Speaker: On the other hand, if you measure, you have a high, you have a airway pressure alarm going off and you measure that peak pressure and it's high, but the plateau pressure is also high.
Speaker: Well, now we're thinking about lung and chest wall compliance problems like
Speaker: pulmonary edema or a large pneumonia, a large pleural effusion, a pneumothorax will affect the pleural pressure and creates a poor lung compliance, pulmonary fibrosis, atelectasis.
Speaker: So if you mainstem the airway, yeah, it's kind of an airway problem.
Speaker: When you cause whole lung atelectasis, that's going to manifest as a high peak, high plateau, similar with abdominal compartment syndrome.
Speaker: So the key
Speaker: The reason I bring up that differential diagnosis is we already said that when we measure our peaks in asthma, yeah, we're kind of expecting they're going to be high, maybe as high as 80 centimeters of water.
Speaker: But if when we measure our plateau pressure and it's also high in a patient with status asthmaticus, there's two...
Speaker: life-threatening complications we need to be worried about, and they are pneumothorax and auto-peep.
Speaker: So, you know, certainly get out your ultrasound, look for lung sliding, get a chest x-ray.
Speaker: We need to exclude a pneumothorax in an asthmatic patient with a high peak and high plateau,
Speaker: But assuming you've excluded pneumothorax, that plateau pressure is telling you that you have an elastic load on this patient, there's something affecting lung compliance, and it's probably dynamic hyperinflation.
Speaker: So that's one of the best surrogates.
Speaker: When we're trying to figure out, I just set my minute ventilation, my rate and tidal volume, is it too high, too low?
Speaker: Is it just right?
Speaker: Looking at that plateau pressure, if you have a very high plateau pressure and no pneumothorax, you probably have a lot of auto-peep.
Speaker: And so that's when we turn to our ventilator waveforms.
Speaker: And it's a little hard to describe ventilator waveforms without having the visual, but in general, you have sort of three discrete waveforms that are all looking at the same breaths.
Speaker: You have the variable of pressure, so centimeters of water, it's often at the top.
Speaker: Then you have flow in liters per minute.
Speaker: And then finally you have tidal volume in milliliters.
Speaker: And one of the most important parts of the ventilator waveforms to look at is the flow waveform, especially in expiration in a patient with high airways resistance, where we want that patient to fully exhale before the ventilator delivers that next controlled breath.
Speaker: Because if there is still persistent flow at end expiration,
Speaker: then that means that that air that's still in the lungs is going to be trapped and trapped.
Speaker: And from breath to breath, if that continues, that can result in severe hypotension or even barotrauma.
Speaker: And so just a quick and dirty on the way we interpret the ventilator waveforms, the flow waveform just by convention on the positive y-axis is inspiration.
Speaker: It's flow into the patient.
Speaker: And then when that breath cycles to expiration, it goes down to the negative y-axis.
Speaker: So your peak expiratory flow is actually at your most negative value.
Speaker: And then as you look at it, it will start to curve.
Speaker: It's this curvilinear wave form that curves to that zero baseline, which is sort of your x-axis.
Speaker: And the reason it's curved and not like a square waveform is we're not controlling it, right?
Speaker: It's the elastance of the lung and the chest wall.
Speaker: Exhalation is a passive process.
Speaker: And so what we want to see is that it's coming all the way back to zero before that next breath is delivered.
Speaker: Otherwise, there is the presence of auto-peep.
Speaker: And you can go one step further.
Speaker: You can see it on the expiratory limb of the flow waveform, and then you can actually measure it.
Speaker: So just like we can do an end-inspiratory hole maneuver and measure our plateau pressure,
Speaker: we can do an end expiratory hold and get an estimate of our auto PEEP or our dynamic hyperinflation.
Speaker: And the key there being that unlike the plateau that you often just hold for one to two seconds, you need to hold that end expiratory hold button in a severely obstructed patient, sometimes for several seconds.
Speaker: And what you will see is that
Speaker: the pressure will keep going up and up and up, and eventually it will sort of plateau.
Speaker: And the PEEP level readout at the time that it plateaus is the total PEEP in the system.
Speaker: So then to figure out your auto PEEP, you simply subtract what your set PEEP is.
Speaker: So if you have a set PEEP of five and you're measuring a total PEEP of 20, that means you have an intrinsic PEEP or a level of auto PEEP of 15 centimeters of water, which is an astronomical amount of auto PEEP.
Speaker: And there are some limitations in that measurement of auto PEEP.
Speaker: And so it's important to incorporate all those measurements.
Speaker: So your plateau pressure, your ventilator graphics, and also that end expiratory hold, which gives you kind of an estimate of your auto PEEP that's present.
Speaker: Well, that's a lot to unpack.
Speaker: I think a very important point.
Speaker: So I wanna follow up with some additional questions.
Speaker: First, the thing that came immediately to my mind is that this is a very dynamic process.
Speaker: And you don't check for pressures and you don't look at ventilator waveforms once and you're done, right?
Speaker: This is something that you continue to do because the patient might be changing and what was working six hours ago might need to be adjusted again.
Speaker: I think that's a very important point.
Speaker: As your patients are being stabilized, this is something that you're probably to do on a regular basis that I think in general, I can safely say we don't do enough.
Speaker: Yeah, definitely.
Speaker: Yeah.
Speaker: And the other thing I would say is that there's kind of a great schematic drawing where it gets to that heterogeneity problem and the limitations of actually the measurement of autopede that the ventilator can only measure the pressure of
Speaker: of airways that are patent sort of through the distal airway.
Speaker: And remember, we have sort of in patches, we have secretions and plugs and maybe extrinsic compression from dynamic hyperinflation regionally.
Speaker: And so let's say in one alveolus,
Speaker: that's secluded, the alveolus is actually hyperinflated and has a pressure of 20 centimeters of water.
Speaker: And then next door, you've got another alveolus that's widely opened and expiratory pressure is five because that's what the PEEP is.
Speaker: And then you have a partially occluded alveolus that is a little hyperinflated and it has a pressure of 10.
Speaker: And so when you hit that button, it's sort of averaging
Speaker: the pressures that it can measure with the communicating airways.
Speaker: But it can, as you can see, it can underestimate if you have a bunch of occluded airways prior to hyperinflated alveoli with higher pressure in them, the ventilator is not adequately measuring that.
Speaker: And that's why I think it's also important to incorporate that the plateau is like, hey, if I have a high plateau pressure in asthma,
Speaker: I need to be really worried that I have a lot of auto PEEP.
Speaker: And so that's what makes you circle back and maybe further reduce your rate or further reduce your tidal volume.
Speaker: Because if you're measuring high amounts of auto PEEP, you need to be concerned about complications that can arise from that.
Speaker: And predominantly the most lethal are hypotension, cardiac arrest from decreased preload from that high intrathoracic pressure, and then also barotrauma.
Speaker: And even though these alarms and these waveforms seem to be very popular for board type questions, they also have tremendous value at the bedside.
Speaker: And I would encourage our listeners to go back to their ICU and where you have an asthma patient or not to really interact a little bit more with your ventilator and try to understand.
Speaker: So just to kind of recap, you talked about three very important waveforms, right?
Speaker: The pressure time waveform.
Speaker: So the x-axis for all these waveforms is going to be time.
Speaker: The Y axis for the pressure time waveform is your airway pressure, like you said, in centimeters of water.
Speaker: And it usually can show you your peak inspiratory pressure.
Speaker: It will show you your plateau pressure if you apply a hold.
Speaker: And it can help you identify out of peak, right?
Speaker: So I think in non-asthmatic patients can also help you with patient effort.
Speaker: When there's negative deflections before inspiration and assisted mode, you might be thinking, okay, there's patient ventilator, the synchrony, there's things that I might need to change.
Speaker: The second waveform, which I think is very pertinent to our discussion today, is the flow time waveform.
Speaker: So the x-axis is time, the y-axis is flow in liters per minute, and it usually will show you the inspiratory and expiratory flow patterns.
Speaker: And you might have, like you said, a square, this accelerating depending on what mode you're using.
Speaker: But really what you're trying to figure out here is whether full exhalation has occurred, right?
Speaker: Are you seeing air trapping?
Speaker: And there's full exhalation, so the expiratory flow returns to zero.
Speaker: You can assume that there's no air trapping or very little minimal air trapping.
Speaker: And finally, the volume time waveform, which is, again, the x-axis will be time.
Speaker: The y-axis is volume.
Speaker: This shows you the delivered tidal volume, which in this case, because you're using a volume control mechanical ventilation mode, should be fixed, correct?
Speaker: Yeah, and the other thing I would just add,
Speaker: For those interested in sort of reading more about this and understanding this, the best journal out there, I think, for this physiology and particularly ventilator waveform interpretation is the journal Respiratory Care.
Speaker: So Dean Hess is the editor in chief of that journal.
Speaker: He's a respiratory therapist who I think still runs the respiratory therapy department at Mass General Hospital.
Speaker: And just it's incredible the way that they explain it.
Speaker: You can really learn it through that journal Respiratory Care.
Speaker: And finally, the other thing that I would add is that I often ask the question, and when I give lectures on ventilator waveform analysis, like, would you ever walk in the room of a critically ill patient and not look at the cardiac monitor?
Speaker: you know, not look at the blood pressure, the heart rate, the cardiac rhythm.
Speaker: And I think, you know, no, like no one would raise their hand to that.
Speaker: And so then I would ask the next question then is, would you ever walk in the room of a critically ill intubated patient and not look at the ventilator waveforms?
Speaker: And with full disclosure, I would have unabashedly raised my hand, you know,
Speaker: about eight years ago before I, so learning part of it in fellowship, but then taking an advanced mechanical ventilation course through CHEST, it really opened my eyes to the number of, you know, a leak on the ventilator, so many ventilator emergencies that you can diagnose by looking at the ventilated waveforms.
Speaker: And I think that the way to sort of have an analogy, and you very well described the scalars and sort of what you're seeing graphically, is really interpreting an EKG.
Speaker: So when you look at an EKG,
Speaker: you can look at, let's say, a QRS complex, a ventricular contraction in multiple different leads.
Speaker: The inferior lead, the anterior leads, or from different vantage points, you can pick out and line up that same ventricular contraction.
Speaker: Well, the same thing happens on the ventilator screen.
Speaker: When you're looking vertically,
Speaker: and let's say you've got your pressure waveform at the top, flow in the middle, volume at the bottom, and you have breath number one vertically, you're looking at the pressure of breath number one.
Speaker: At the same time, that flow waveform is showing you the flow of breath number one, and then the volume of breath number one.
Speaker: And as you alluded to, now you can figure out how your patient's interacting with the ventilator.
Speaker: when they're trying to trigger the ventilator by inspiring during mechanical expiration, you can see that as a pressure deflection at the same time there's flow reversal in the expiratory waveform.
Speaker: So a lot of this stuff is hard to talk about, but I guess my point is that it's very much like an EKG.
Speaker: You're looking at the same breath just like
Speaker: Like you can look at the same ventricular contraction, but you're looking at different variables of that breath, the pressure of that breath, the flow of that breath, the volume of that breath.
Speaker: And once you start looking at it and you learn to recognize some of these things, it's like you walk in the room and you're like, why did I never look at that before?
Speaker: Of course I would look at that.
Speaker: So just as inspiration, but also the disclosure that I spent probably –
Speaker: Most of fellowship and five or six years as an attending not taking full advantage of ventilator waveforms.
Speaker: So it's a good practice to sort of work in no matter where you are in your career.
Speaker: And like you mentioned, we're discussing it within the context of asthma, but it's applicable to many other diseases and any patient on mechanical ventilation in the ICU.
Speaker: We talked about alarms, we talked about waveforms.
Speaker: The third monitoring tool that I would like to hear from you is ABGs.
Speaker: How do you use ABGs in asthma?
Speaker: Any particular point that you want to emphasize to our audience?
Speaker: Yeah, so great question.
Speaker: I don't know that I have a perfect rubric for the utilization of ABG.
Speaker: Certainly, again, in that quote-unquote delicate period where you've just intubated your patient, you're setting your ventilator, you're assessing your degree of auto-peep or dynamic hyperinflation.
Speaker: Perhaps you're making a small adjustment in rate, you know, up by one, a small adjustment in your inspiratory time, down by 0.2 seconds, right?
Speaker: you know, check another ABG 30 to 45 minutes later, because you need to see the trajectory of where you're going.
Speaker: We had a recent 18 year old gentleman who had status as Maticus and his first gas
Speaker: was 696 with an unmeasurable PCO2 of over 95.
Speaker: And so where do you go from there?
Speaker: And when do you think about, have I failed invasive mechanical ventilation?
Speaker: Am I failing to adequately ventilate?
Speaker: Do I need to think about mechanical circulatory support like ECMO?
Speaker: And so I think...
Speaker: To figure out where you are and whether you're improving, you need to get serial gases every time you're making an adjustment.
Speaker: And so I think the adjustments that you might make up front are those that shorten inspiration, lengthen expiration, that limit controlled hypoventilation as we described.
Speaker: As you move forward and you're maybe making some progress and you're measuring your auto peep and it's a little lower this time and your plateau pressure has come down and it's, let's say it was 30 and now it's 25 centimeters of water.
Speaker: Then you can maybe tick up the rate by one or two.
Speaker: These are minor adjustments and you might get another gas 30 minutes later and
Speaker: and see what that is.
Speaker: At the same time, when you're changing your rate, you're re-measuring your total PEEP, your end expiratory hold, you're re-measuring your plateau pressure.
Speaker: So managing the ventilator and asthma is less sort of physiologically complex and more just about diligence, I think, and paying attention to the details.
Speaker: And when you make adjustments, you know, make baby steps, make small changes, recheck your airway pressures, relook at your graphics,
Speaker: send another ABG.
Speaker: And on the first day of, I think in that patient, I presented his case recently.
Speaker: I mean, I think we had close to 10 ABGs over the first 12 hours of his care.
Speaker: And then we started to make progress and then the intervals obviously lengthened and his auto-PEEP improved.
Speaker: And then we were able to actually increase minute ventilation.
Speaker: without seeing a concomitant increase in auto-PEEP and we're making progress.
Speaker: And then you can move forward with reducing sedation and coming off neuromuscular blockade and thinking about weaning.
Speaker: But until you see that break in the cycle of air trapping, frequent gases, frequent airway pressure assessments, I think is the key to managing asthma.
Speaker: You mentioned ECMO.
Speaker: When does Dr. Dehme think of ECMO in an asthma patient?
Speaker: Well, it depends whether I'm the primary intensivist managing the patient and then I want to just use the ventilator or if I'm on the ECMO team that day.
Speaker: Our group where I work is we are ECMO enthusiasts.
Speaker: But I think everyone in intensive care knows the risks of ACMO.
Speaker: It turns out that outcomes in status as maticus, at least retrospectively, when you look at the ELSA registry, the survival is very high.
Speaker: It's over, it's like 83%, I think, in pooled registry analyses.
Speaker: The cases where it would be indicated are severe hypercapnic rastery acidosis.
Speaker: And so clearly, you know, our patient met that criteria at his first blood gas.
Speaker: But that's where we then measured his auto PEEP and measured his plateau pressure and realized that we could adjust things and improve that and then see where we went.
Speaker: And his gas has improved.
Speaker: So, you know, persistently having pHs under 7.2 or 7.15 and the inability to alleviate auto P
Speaker: to the degree that you can sort of improve dead space and improve your pH, that would be one indication.
Speaker: Less often, but I think if you had severe hemodynamic instability that you thought was secondary to the high intrathoracic pressure or just the high RV afterload,
Speaker: You can think about VV ECMO or even what we call VP ECMO, where you're kind of bypassing, almost like an RVAD, your return cannulas in the PA.
Speaker: And then high-flow bronchopleural fistula.
Speaker: So I think when a patient already has...
Speaker: complications from barotrauma, you know, a large volume fistula, you just want lung rest in order to close, you know, that defect in the lung.
Speaker: So those are certainly cases where you might turn to ECMO even sooner because it's a way that you can really then limit minute ventilation and limit sort of inflation pressures of the lungs in order to heal that BP fistula or a large pneumothorax.
Speaker: It's usually failure to ventilate.
Speaker: It's not usually hypoxemia would be the criteria.
Speaker: Yeah.
Speaker: Excellent.
Speaker: Could you put everything together maybe in summarizing your approach as we close, Emily?
Speaker: Yeah, absolutely.
Speaker: Setting the ventilator, our primary goal is controlled mechanical hypoventilation, limiting rate and tidal volume, with our primary goal being to limit auto PEEP or dynamic hyperinflation.
Speaker: So selecting
Speaker: You know, I think a mode where you can deliver inspiration the fastest, but also guarantee your minute ventilation, which volume control is certainly a mode that we can do that in.
Speaker: Picking then a low tidal volume.
Speaker: I think a good starting point is 60 cc per kilo of ideal body weight.
Speaker: A low respiratory rate between, you know, 10 and 16 breaths per minute.
Speaker: And then that first step, remember that you're plugging in those settings, kind of see what your peak airway pressures are.
Speaker: If your airway pressure limit alarm is going off, you need to reset that pressure limit above the peak inspiratory pressure level so that your patient's actually getting the settings that you just input.
Speaker: So that's the first critical first step.
Speaker: Once you've done that, you can accurately look at your peak inspiratory pressure because it will just read 40 if your pressure limit is set at 40 and it'll dump the rest of the breath.
Speaker: So once you've reset that pressure limit, now you can actually see what your peak pressures are and you can also measure your plateau pressure.
Speaker: If you're expecting a high peak inspiratory pressure and maybe a low to low 20s, mid 20s, high teens, low to normal plateau pressure,
Speaker: From there, measure your auto PEEP.
Speaker: If instead you're seeing high plateau, high levels of intrinsic PEEP or your total PEEP, then you may need to go back to step one and further limit, reduce that tidal volume by 20 CCs or reduce that rate by two.
Speaker: So once you get to where your plateau pressure and your auto peep levels are somewhat acceptable, you also need to think about your IDE ratio.
Speaker: So shortening your inspiratory time, you can go directly into your settings and increase that inspiratory flow rate such that you're spending very minimal time in inspiration, maybe 0.6 to 0.7 seconds.
Speaker: And then the rest of the time is in expiration.
Speaker: So classically, one to four, sometimes even one to five, depending on what your rate is, your I to E ratio.
Speaker: And again, take a look at your ventilator waveforms.
Speaker: Look at your expiratory flow waveform.
Speaker: Is there evidence of auto PEEP?
Speaker: by plateau, by end expiratory hold maneuver, and by your ventilator waveforms, then you might need to go back and further limit your minute ventilation.
Speaker: And each time you're doing these adjustments, you want to wait a little bit, get a blood gas, make a small change.
Speaker: But that's sort of the algorithm to turn down radentita volume, accurately measure your plateau and your end expiratory pressure,
Speaker: shorten your eye time to the greatest degree that you can, even if it means your peak pressure goes up.
Speaker: And then look at those ventilator waveforms as you go, as you make adjustments.
Speaker: And once you start to see that plateau pressure normalize or that auto-peep come down, well, now you can maybe go up a little bit on rate or go up on tidal volume and recheck a gas.
Speaker: So it's just a lot of serial measurements of airway pressures and ABGs.
Speaker: And you talked about baby steps and serial interventions at small steps, right, over time.
Speaker: And it makes me think of a topic that I've discussed previously on the podcast about marginal gains, right?
Speaker: How small improvements in multiple areas end up making a huge difference for our patients.
Speaker: And I think a lot of what you discussed, Emily, is very applicable here.
Speaker: So thank you for such a wonderful discussion on
Speaker: mechanical ventilation for severe asthma.
Speaker: We like to close.
Speaker: I was just going to say, thank you for having me.
Speaker: We're still not done.
Speaker: So we like to close the podcast with a couple of questions that are unrelated to the clinical topic we discussed, usually trying to learn something from your, from the wisdom of our guest.
Speaker: Would that be okay?
Speaker: Yeah, that's okay.
Speaker: So the first question relates to books.
Speaker: Is there a book or books that have influenced you significantly or a book that you often have gifted to other people?
Speaker: So that's a good question.
Speaker: So the books, I would say the genre books that have influenced me the most also might not be the ones I'd give to other people.
Speaker: But I'd have to say that, you know, sports nonfiction is my favorite thing to read about.
Speaker: You know, classically stories of the underdog, you know, biographies of famous coaches and athletes, you
Speaker: um, you know, like Seabiscuit comes to mind, Lance Armstrong, although perhaps he's not as much of an underdog as we thought he was, um, you know, Pistol Pete, Coach K, Jimmy Valvano.
Speaker: Those are, you know, my dad used to get me every year when I was a kid for my birthday and for Christmas, a nonfiction sort of inspirational underdog story.
Speaker: And I was just, I, there, it's incredibly moving to me, um, to read those types of books, but I, it's a little bit of a niche, um,
Speaker: genre.
Speaker: So I think the gift, the book that I have already gifted to people, I've actually not even finished with them.
Speaker: I'm in the process of reading, but it's really good.
Speaker: And I think it's so worth bringing up is it's called Good Inside.
Speaker: And it's a national bestseller that's written by Dr. Becky Kennedy, who's a clinical psychologist and actually a mother of three.
Speaker: And the basic underpinning of the book, it's kind of like a parenting guide, to be honest.
Speaker: But it's
Speaker: is that children are good inside and that our approach to parenting really has to be grounded in validating their emotions and sort of in empathy, which like just sounds incredibly self-evident, right?
Speaker: And I think that nothing in the book is, is on, you know, drastically different than how you might view it.
Speaker: But what's so special about
Speaker: her approach is she really talks about how you can help kids, and I have three kids, they're first grade, fourth grade, sixth grade, how when they have a behavior that's challenging,
Speaker: that I would argue is often more challenging than high stress encounters in the ICU.
Speaker: And when they're fighting or they have sibling rivalry or whatever it is, that they're often sort of expressing a need that they're having difficulty regulating their emotion.
Speaker: And that rather than reacting to the behavior,
Speaker: Instead, she sort of directs you to be curious about, you know, what are they feeling and why would they act out that way?
Speaker: And instead, also checking in with yourself about how you're feeling and how you might demonstrate to them or validate their emotions and kind of show them how to regulate them.
Speaker: And the thing that I think that's great about this book is like clearly it's centered around parenting and interactions with your children.
Speaker: But as you can imagine, it also has relevance to the work environment, working with adults, particularly in medicine where things can be strained and be difficult and challenging.
Speaker: And so she just really does a great job of using concrete examples and how you can frame and validate things
Speaker: what your child's feeling.
Speaker: And rather than try to absolve that emotion, say, oh, just calm down.
Speaker: Or, you know, why are you sad about that?
Speaker: Or why are you angry?
Speaker: Really trying to get at the heart of like, what's driving that emotion and validating it.
Speaker: And then sort of being an empathetic model of how you might control that emotion rather than acting out on it.
Speaker: I think it's fantastic.
Speaker: So, so that would be the book that I would say.
Speaker: Awesome.
Speaker: And thanks for sharing those.
Speaker: And we'll definitely link all those in the show notes.
Speaker: And I think as you were discussing why this book is so relevant to you right now, it made me think, Emily, of something I read not too long ago that really stuck with me.
Speaker: That said, you can't be furious and curious at the same time.
Speaker: Choose to be curious.
Speaker: And I think it applies to when your kid is maybe having a behavior that misbehaving, let's call it, or your colleague is misbehaving.
Speaker: You really want to ask questions.
Speaker: Why?
Speaker: What are they feeling?
Speaker: And then the other aspect, which I think is something that I've definitely recognized later in my life, but is really powerful, is
Speaker: is the importance of validating people's experience, right?
Speaker: Whether it's a patient, a colleague, or your child, um,
Speaker: For them, this might be the worst day of their life, even though for you, it's kind of a trivial issue.
Speaker: Right.
Speaker: And I think that validating that experience is also very important.
Speaker: So we'll definitely put those on the show notes.
Speaker: And I have not read good inside.
Speaker: So definitely we'll look it up.
Speaker: The second question has to do with changing your mind.
Speaker: So could you share something you change your mind about over the last couple of years?
Speaker: Yeah, I know what my kids and my husband would say.
Speaker: They would say my opinion on dogs.
Speaker: I always said we never have a dog, we have a puppy.
Speaker: But that's not my answer to the question.
Speaker: That's what they would say.
Speaker: I think for me, and maybe not a few years, I would say last like five to seven years.
Speaker: The idea that, and I don't think this is novel to me or that I have really struck a balance with this, but the idea that you can be passionate about medicine,
Speaker: and motivated in your career as a physician and perform well at the bedside, but also not have it consume your entire identity or even most of your identity.
Speaker: And I think, you know, in training, you know, you're in medical school, you're in residency, you're in fellowship.
Speaker: It's like, I mean, I really sort of felt it was my entire identity and perhaps the time intensiveness of it required that.
Speaker: And certainly if you want it to be your primary identity, it's not a judgment of that.
Speaker: But I would say that within myself now internally, like my primary identity is
Speaker: is a mom.
Speaker: And that's, I'd say that's closely followed by a youth basketball coach, which is something I enjoy, you know, more than I can even articulate.
Speaker: I identify as like a teacher.
Speaker: And, and so I think that, that when I meet and I'm an advisor at our medical school,
Speaker: When I meet with students or even residents and fellows, one of the questions that most often comes up, and I think this happens to a lot of physicians is, you know, well, am I going to be able to have a family or balance family or, or even, you know, have hobbies within medicine and, you know,
Speaker: My office is sort of egregiously covered in photos.
Speaker: And part of that is because I know that when I bring in medical students that I have scheduled meetings with that, like, yeah, to just really exemplify and not just that, except that it's possible, but that it's really possible.
Speaker: you know, preferred or even totally attainable.
Speaker: And I think that because it's such a concern among trainees that perhaps we're all doing this and we all believe this, but I think that for our younger trainees, we don't often publicize it enough, if that makes sense.
Speaker: And I think this is so relevant, Sergio, in speaking to you, because when I think back to
Speaker: To all of my teachers and mentors in medicine, you are the physician, certainly in addition to my own father, who's a physician, that most inspired me to pursue my passions and
Speaker: and hobbies outside of medicine with, with equal vigor to which I approach medicine and that, um, and that you encourage that and you exemplify that.
Speaker: And, and, you know, all of us as fellows who trained under you just knew that you were this like excellent photographer, you're an incredible chef, you'd read every book on the shelf.
Speaker: I think you're sort of an expert in jazz music, if I'm remembering correctly,
Speaker: And I think just modeling that really just can enrich a career in medicine.
Speaker: And rather than detracting from sort of your passion for medicine, I think it can add to it.
Speaker: So I think that's my answer, that we can absolutely have an identity outside of being a physician and that it doesn't take away from our commitment to the practice of medicine.
Speaker: And if anything, maybe it just enhances it.
Speaker: Well, thanks for the kind words.
Speaker: And the way I think about it is that there is no life balance.
Speaker: There's only life.
Speaker: And the real important thing is not to balance things, but to be fully immersed in the activity at hand, right?
Speaker: And to follow, I mean, things that really fill your cup.
Speaker: And you're right.
Speaker: I think you can be passionate about many things.
Speaker: And I think what's important is to try to learn and excel for the sake of learning and excelling and nothing else, right?
Speaker: That is really the goal.
Speaker: But thanks for sharing that.
Speaker: And the last question is, what would you want every listener to know?
Speaker: But I almost don't want to ask that, Emily, because I think stopping here would be perfect because what you just shared, I think, is so powerful and it should be food for thought for everybody.
Speaker: So I don't get to answer it?
Speaker: Well, you do.
Speaker: I'll give you that opportunity.
Speaker: So what would be the last thing you want to share with us?
Speaker: A departing thought, fact or quote?
Speaker: For me, it's a quote.
Speaker: And I, it's my favorite quote.
Speaker: And it's a little hard.
Speaker: It's like picking your favorite movie or favorite, you know, song.
Speaker: But my favorite quote, and I remember the first time I saw it or I read it.
Speaker: I was like 20 years old.
Speaker: I was spending the summer at the University of Georgia as a research assistant in an exercise science lab while we were,
Speaker: testing gastric emptying times of Gatorade versus Powerade, sort of like obviously the hypothesis being if it's faster in the bloodstream, energy consumption, the better.
Speaker: I can tell you the punchline is there was no difference.
Speaker: But I worked with these elite cyclists and we would measure their VO2 max.
Speaker: And there was a postdoc fellow in the lab and he had a sign on his door.
Speaker: with a quote by Harry Truman that like really struck me because at the time I was playing basketball in college and it said, it's amazing what you can accomplish if you do not care who gets the credit.
Speaker: And I think that for me, that quote at that time in my life was so impactful.
Speaker: But as I've moved through my life,
Speaker: To me, it's just the underpinning of medicine, of any sort of valuable team-based experience.
Speaker: If you can get to the point in a resuscitation or, you know, and it doesn't happen like magic in every interaction that we have in the ICU, where I think COVID is a great example, where everyone's sort of working towards the common goal of,
Speaker: of the patient and not caring, not trying to take credit, not caring who gets the credit.
Speaker: I just think that that is a philosophy that's sort of an ideal, but that we often meet in medicine.
Speaker: And I think we need to acknowledge, you know, those times when we can band together as a team, because medicine is certainly a team sport.
Speaker: So that's the quote that I would reflect on.
Speaker: And that is a perfect place to stop.
Speaker: I really appreciate you giving us your time and sharing your expertise.
Speaker: Definitely learned a lot.
Speaker: You did put me on the spot in terms of reminding people that I was your program director and helped train you.
Speaker: But obviously, like every great student or mentee, you're now teaching me.
Speaker: So I really appreciate it.
Speaker: And I look forward to having you back on the podcast, Emily.
Speaker: All right.
Speaker: Thanks for the conversation.
Speaker: I appreciate it.
Speaker: Thank you for listening to Critical Matters, a sound podcast.
Speaker: Make sure to subscribe to Critical Matters on Apple or Google Podcasts and share with your network.
Speaker: Sound's transforming the way critical care is provided in hospitals across the country.
Speaker: To learn more, visit www.soundphysicians.com.
