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: Primum non nocere, first do no harm, is an old dictum, a first-order principle in medicine.
Speaker: It probably originated millennia ago in the Hippocratic era and remains relevant to the practice of medicine.
Speaker: In today's episode of the podcast, we will discuss mechanical power and ventr-induced lung injury.
Speaker: Mechanical ventilation is a common therapy in the ICU and a perfect place for us to apply Primum non nocere.
Speaker: Our guest is Dr. Jason Bartok.
Speaker: Dr. Bartok is an intensivist at Cooper Medical System, and he's a critical care fellowship director at Cooper Medical School of Rowan University, both in Camden, New Jersey.
Speaker: Dr. Bartok is an outstanding clinician, an educator, a ventilator nerd, and a dear friend.
Speaker: Jason, welcome to Critical Matters.
Speaker: Thanks for having me.
Speaker: I really appreciate it.
Speaker: Well, today we're going to tackle a really nerdy topic that, as we were discussing before we started recording, we believe is super important for all our practicing intensivists and APPs at the bedside to hear about.
Speaker: And we're going to talk of physics, formulas, but ultimately what we're really trying to do is
Speaker: apply this physiology to our clinical practice and to what we're doing to patients day in and day out who are on mechanical ventilation.
Speaker: So first, thanks for being here, but also thanks for tackling this problem with me and being brave to talk about an area where only the brave dare to venture.
Speaker: Well, I appreciate the opportunity, and obviously I wouldn't be here if it wasn't for you.
Speaker: And I love this podcast, and any opportunity to talk a little bit about mechanical ventilation, I'll take it.
Speaker: This would probably not be my first choice in terms of topic, but I think it's a really important one.
Speaker: And we will nerd out, but we'll try not to be too nerdy because I think it's important for us to kind of build a practical understanding about this topic of energy and the transfer of power.
Speaker: Absolutely.
Speaker: And I think that we'll start with ventilator-induced lung injury and just kind of establishing some basic definitions.
Speaker: But I think it's important to remind people that
Speaker: despite all the advances and all the bells and whistles and all the new and progressive modes that we discussed at the bedside, the real insight or the epiphany that critical care had was that we could probably have the greatest impact on improving outcomes in critical care ARDS patients by decreasing the amount of damage that we were doing on them as we were treating them.
Speaker: And this really led to the understanding of ventilator-induced lung injury that has been described hundreds of years ago, but really wasn't something that was first in mind and really studied to some decades ago.
Speaker: So why don't we start by just basic definitions of what is ventilator-induced lung injury and
Speaker: And like the classical evolution from barotrauma to volutrauma to a telectotrauma and biotrauma.
Speaker: Absolutely.
Speaker: There's nothing natural about the application of the positive pressure breath, right?
Speaker: You know, on the human respiratory system.
Speaker: And without ventilators, many patients would die, absolutely.
Speaker: And, you know, I think this talk and many other concepts related to the application of the positive pressure breath are so important because, like you said,
Speaker: You know, the machines are getting smarter, the ventilators become more autonomous, the respiratory therapists handle more of the workload.
Speaker: But, you know, what is almost uniformly, if one of the only concepts for mechanical ventilation is there is no right mode of mechanical ventilation,
Speaker: there's only, you know, what matters is the person applying the breath and that's our responsibility and that's why we have to understand this.
Speaker: So, you know, when it comes to ventilator induced lung injury application, the positive pressure breath on a, on a system that is built to breathe negative pressure results in, you know, the, the potential of injury, you know, to the alveolus.
Speaker: And we think about a very simplified respiratory model, you know, kind of a rigid pipe, which is our, our airway.
Speaker: and an elastic balloon, which is, you know, which is our alveolus.
Speaker: And then the application of the positive pressure breath across that, when you reach a certain threshold, will cause injury to the lung.
Speaker: So barotrauma, you know, you know, described as, you know, tissue rupture, I think,
Speaker: we're all classically trained to think about it as high end alveolar pressure causing tissue rupture.
Speaker: That's not incorrect.
Speaker: I just don't think it's the whole story.
Speaker: And that's what we're going to talk about today.
Speaker: Similarly, volume trauma, we think about high end alveolar volumes causing tissue distortion.
Speaker: And that also is correct, but might not be the whole story.
Speaker: Adelacta trauma, you know, the shear forces that we think about with the under-distended or inappropriately distended, you know, alveolus leading to opening and closing, you know, shear distortion.
Speaker: That's true, you know, and most of us think about it as inappropriate PEEP application.
Speaker: Not untrue, but probably not the whole story.
Speaker: And then biotrauma, which is the biologic response to injury, um,
Speaker: you know, through the application of the positive pressure breath, kind of irrespective of, you know, whatever your primary driver is, be it, you know, viral or bacterial mediated endotoxin or whatnot.
Speaker: The biological response to injury as it relates to all the things that we just talked about, the application of high end alveolar pressure and then shear forces and distortion across the alveolar interface.
Speaker: So I think all of these things are what cause worsening injury and this cycle of progressively worsening, you know, baby lung physiology.
Speaker: If we're talking specifically about acute lung injury and ARDS, you know, you have hypoxia.
Speaker: This is one of the things that John Marini sort of –
Speaker: coin which is like the billy board we'll talk more about that you know you have hypoxia you have high application um high respiratory rate then you have you know all of these things that we talked about high distending pressures high shear forces then causing worsening capillary leak and then worsening hypoxia and then you start to lose more and more um lung tissue um and then
Speaker: you find yourself in a place where you can rescue a patient.
Speaker: So ventilator-induced lung injury has been talked about for a very long time.
Speaker: You know, I think we all have a good practical approach to trying to minimize this lung injury by thinking about static pressures and the static pressures that we use for best outcomes in our patient.
Speaker: But I don't know that it's the whole story.
Speaker: And I hope that we can sort of tease out some of the important concepts today.
Speaker: Perfect.
Speaker: And I think that you talked about some static pressures, and I want to go there next, but also worthwhile to just remind our listeners that the landmark study that really demonstrated that if we intervened in a way that would minimize what we understood as ventricular lung-induced injury could actually improve outcomes in patients with ARDS was published in 2000.
Speaker: And that's the famous low tidal volume ARDS net study, which we'll include in the show notes.
Speaker: And if you haven't read it, I would recommend that you read it as one of the key studies in ARDS, but also obviously in critical care.
Speaker: We then adopted this idea of lung protective ventilation, which the way I understand it, Jason, is really being very deliberate, intentional, and conscious of settings in the ventilator to the point that we're trying to prevent further damage from the positive pressure ventilation that we're delivering.
Speaker: And you had mentioned that there's some static targets or static measurements that we have utilized or incorporated into our clinical workflow that really move in that direction.
Speaker: Do you mind...
Speaker: sharing with us kind of like the progression and we can start with low title volume and move from there.
Speaker: Like what have we found?
Speaker: What does that mean?
Speaker: And we can move through them and move forward.
Speaker: Sure.
Speaker: I mean, I think all of us who've lived through the pandemic have talked a lot about it, but going back, you know, like you mentioned, the ARDSnet trial in 2000, you know, looking at low tidal volume ventilation, you know, versus, you know, high tidal volume ventilation for patients based off of their predicted body weight.
Speaker: So I think everyone has sort of ingrained into their practice six cc's per kilo ideal body weight.
Speaker: And I think that's important when you understand acute lung injury, you know, and the baby lung physiology that comes with that, that, you know, applying high tidal volumes, you know, lead to the potential for high injury.
Speaker: So, and the things that we talked about causing tissue rupture or tissue distortions.
Speaker: So low tidal volume ventilation, 60 cc per kilo is pretty much ingrained in all of our practical approach and maintaining a low plateau pressure, you know, less than 30 centimeters of water.
Speaker: Another static measure, you know, and that static measure of less than 30 centimeters of water is the surrogate for 20.
Speaker: you know for transpulmonary pressure what we think that the alveolus is seeing provided that we have sort of a negative or negligible pleural pressure and that's what we believe that the end alveolus is seeing again it's a static pressure and we're making the assumption that every alveolus within the system is seeing that and the same thing with low tidal volume ventilation
Speaker: You know, when you apply six cc per kilo, we're making the assumption that every single alveolus in the respiratory system is seeing six cc per kilo predicted body weight.
Speaker: And that's probably not true.
Speaker: Similarly, you know, the PEEP application, which is, you know,
Speaker: know has been studied not showing you know for the high peep trials the mortality benefit that certainly low tidal volume ventilation and low pressure targeting showed but maintaining adequate peep to prevent collapse and and optimize total long compliance is still one of our practical approaches
Speaker: But really that evolution was most impactful when using P for optimal compliance, which brings in the concept of driving pressure.
Speaker: So driving pressure is obviously a measurement that has evolved more recently.
Speaker: It hasn't been studied to the same degree or associated with clinical trials such as the low tidal volume and the plateau pressures with the AridusNet trial.
Speaker: But I do think that, especially like you said, during the pandemic and a little bit before that, it's really picked up steam in terms of interest.
Speaker: So what is the driving pressure, Jason?
Speaker: That's a great question.
Speaker: What is the driving pressure?
Speaker: I think, and this is a question that I, you know, that I ask our fellows and our residents all the time.
Speaker: Every single one of them can rattle off on rounds, six cc's per kilo, ideal body weight plateau pressure less than 30 and driving pressure less than 15.
Speaker: But what is the driving pressure?
Speaker: And to your point, you know, did show an impact in mortality, but what was a retrospective analysis?
Speaker: But, you know, really what is driving pressure?
Speaker: Well, the calculations, the plateau minus the people, really what does it mean?
Speaker: You know, it's title volume as it relates to compliance.
Speaker: So it's really the title volume over the total compliance in the system.
Speaker: And what we feel it represents is kind of the normalized title volume that that baby lung sees.
Speaker: And I hope I'm not using the term baby lung and everybody's like, what are we talking about?
Speaker: This is what we're talking about, ideal, you know, adult critical care.
Speaker: But no, the baby lung physiology where you have,
Speaker: you know, ARDS, heterogeneous, you know, injury pattern, and then you have this smaller portion of the lung that's adequately aerated, and the rest of the lung is diseased.
Speaker: So what the baby lung is seeing is what really what driving pressure signifies.
Speaker: So it's the normalized tidal volume for the baby lung and, you know, the optimum compliance for the delivered breath.
Speaker: And if there's anything that, you know, that mortality impacts, you know, studies have shown is that everything is about lung compliance.
Speaker: Any way that you can salvage lung compliance or any way that you can prevent worsening lung compliance is what impacts patient outcome.
Speaker: So the driving pressure is,
Speaker: I think makes a lot of sense because it's just another marker of compliance.
Speaker: So if you're doing all the other things that we talked about in terms of sort of static application, you know, 60 cc per kilo, adequate, what we believe is end alveolar pressure, optimum compliance for what the baby lung is seeing, then you're probably doing your best at delivering a safe breath.
Speaker: Perfect.
Speaker: So these are all static measures to some extent, and especially anything involving the plateau pressure involves inspiratory holds, and there's always a question of how accurate those could be if not under the right conditions.
Speaker: But what are other limitations of using a static measure for such a dynamic and heterogeneous process?
Speaker: Well,
Speaker: You know, I think when you look at some of the work, you know, published on this idea of mechanical power and the transfer of energy, you know, they make it very clear that in all biological systems or all systems in general from a physics standpoint, pressure does not cause damage without pressure.
Speaker: motion, right?
Speaker: So although we're looking at static pressures, we're looking at the plateau pressure, you're looking at the tidal volume, you're looking at the PEEP,
Speaker: we don't take into account how we got there, right?
Speaker: And that's how the breath is applied and how the alveolus is inflated and how one alveolus talks to the alveolus sitting next to it.
Speaker: So when you think about cyclical airway trauma, right?
Speaker: So you have someone who has acute lung injury and they're breathing, you have alveoli that are extended,
Speaker: you have alveoli within that same injury region that are collapsed, and you have alveoli that have restricted distension or expansion.
Speaker: And to the idea that every single one of these pressures is applied the same in those three types of alveoli is incorrect.
Speaker: So using a static measure, assuming that you're protecting all of the lung, I think is an incorrect assumption.
Speaker: there is certainly like regional gradients and regional distribution of the way you apply the breath, right?
Speaker: When you think about the way the breath is applied, apex, the base, dorsal, the ventral surface, you know, each one of those regions will see a different amount of distending pressure.
Speaker: So although the entire system may be adequate six cc's per kilo and 30 centimeters of water, one alveolus might be seeing much more of that than the other alveolus,
Speaker: and that's where injury occurs.
Speaker: Absolutely.
Speaker: And I think that this is a perfect time to transition to the first law of thermodynamics, which states that energy can't be created or destroyed.
Speaker: It can only be transformed.
Speaker: And I believe that
Speaker: Energy transformation is what produces motion.
Speaker: And this is, I think, where we need to go to understand a little bit more about how injury really occurs in a ventilated lung-induced injury.
Speaker: Could you expand on that, Jason?
Speaker: Sure.
Speaker: You know, this machine that we hook people up to, you set parameters that you want out of, you know, from the mechanical system to translate into the biologic system.
Speaker: And it does that through a transfer of energy, right?
Speaker: It transfers energy to the patient and then you get whatever your targets are.
Speaker: And the machine only knows to do that.
Speaker: And it might be okay, or it might cause injury depending on where that injury threshold exists.
Speaker: So, you know, the idea here is, you know, you have stress, you have strain, you have energy and you have power.
Speaker: And I think
Speaker: that everything that we do, all of these concepts already exist in the approach that we talked about.
Speaker: I just think that it's important to think about them in a kind of a dynamic process with each inflation and not just the static pressures that we measure, right?
Speaker: So stress is just the force on a subject, right?
Speaker: So the force applied.
Speaker: And I think that the stress you can think about, I guess the surrogate for that would be,
Speaker: be the driving pressure would be the best correlate that I can think of.
Speaker: And strain is the response to that applied stress, right?
Speaker: So, you know, you apply, you know, a particular stress at, you know, at the junction of an inflated and an uninflated alveolus,
Speaker: And then depending on how, you know, how that that stress is applied, you'll have deformation or strain across each alveolus, one possibly more than the other.
Speaker: You know, when you think about it, like we talked about the damage in any given lung unit, you think about like a non-compliant alveolus.
Speaker: right, you know, you can give a high amount of stress to that and because it's non-compliant, it won't move very much, there's not a lot of strain.
Speaker: But in a very compliant alveolus, if you give the same amount, right, of stress,
Speaker: you'll get, it's able to, it will over-distend and over-stress, and then there's a lot of strain applied on that.
Speaker: So when you think about the lung, I think we all think about these alveoli like they exist by themselves.
Speaker: But the lung, a better representation is sort of like a honeycomb pattern, like you see in a beehive, and all of them are touching each other.
Speaker: So when there's areas that are damaged and there's areas that are soft and compliant, you'll have regional strain applied both at the level of the alveolus, but also with the lack of movement of the alveolus that's connected to it.
Speaker: I think that that's an important concept, stress and strain, and then how that translates to energy.
Speaker: So, you know, strain is very important when it comes to ventilator-induced lung injury, and that's a dynamic concept, not a static concept.
Speaker: So like we just talked about, you apply a certain amount of stress, and there'll be strain across that alveolus.
Speaker: That will cause injury.
Speaker: And then energy on top of that will also cause energy, will also cause injury, right?
Speaker: So, you know, we have with each breath, you know, a certain amount of potential energy and that potential energy is then transferred into kinetic energy, which will be heat and distortion, right?
Speaker: As it's transferred across that alveolar, that end alveolar wall.
Speaker: So,
Speaker: you know, when you think about the energy transferred from the machine, it's what it takes to distend the lung, what it takes to push the gas, and then what it takes to keep the lung open at the end.
Speaker: And that's the total energy transfer, right?
Speaker: So you...
Speaker: just to try to simplify everything, right?
Speaker: You have, you know, regional gradients that all of that, all of these breaths are being applied to.
Speaker: You have a certain amount of stress that will, that will vary depending on which region it's being applied to.
Speaker: And then a certain amount of strain in response to that stress.
Speaker: And it can be exacerbated by high energy, right?
Speaker: So what it's going to take to open and to extend that alveolus, what it's going to take to push the gas in, and what it's going to take to keep it open.
Speaker: So that's the idea of stress, strain, and energy.
Speaker: And I think that it's, you know, that's a dynamic process.
Speaker: And it's not just about static end alveolar pressures.
Speaker: You know, in order to cause damage, you have to have motion.
Speaker: And with each one of these breaths, we cause motion.
Speaker: And it matters where it's being applied.
Speaker: It matters how it's being applied and with how much energy it's requiring.
Speaker: And I find it interesting that there's obviously an analogy to when we talk about hemodynamic monitoring and static measurements and dynamic measures.
Speaker: And I think it just speaks to the reality that...
Speaker: biological systems, and everything that we're interested in is a dynamic and complex process, right?
Speaker: So as we move from a chalkboard static analysis and a reductionist kind of view to something that's more integrated and dynamic, we probably are closer to what's happening and hope to be closer in predicting what we need to do, which I think is very interesting.
Speaker: And we just have
Speaker: What's intensity, Jason?
Speaker: So intensity is an interesting concept, right?
Speaker: So, you know, you have energy, right?
Speaker: And I guess we can just kind of jump into the concept of power, which is just energy transfer per unit time, right?
Speaker: So here with each one of these breaths, right, we're trying to open, apply a volume, and then maintain an end alveolar pressure.
Speaker: And with that, we transfer energy across that alveolus and
Speaker: potentially, you know, in a high energy state will cause worsening damage.
Speaker: Energy, right, you know, when we said, you know, what it takes to descend the lung, to push the gas into the alveolus, and then to keep it open at the end of exhalation, that's volume, total pressure applied, flow and peep, and then power is energy transferred per unit time.
Speaker: There are various mechanisms of power amplification.
Speaker: So, you know, when you think about the total amount of power applied to the alveolus, there are certain things that will amplify that power and then amplify the potential for energy, for injury, I should say.
Speaker: So intensity is one of those things, right?
Speaker: So it's really the amount of energy applied, you know, or power per amount of surface area.
Speaker: So when you think about, you know, baby lung physiology,
Speaker: if we're applying a high energy breath, right?
Speaker: Because you have a lot of heterogeneity and a lot of disease as the surface area that you apply that, that breath or that energy over starts to decrease the intensity goes up and the potential for injury goes up.
Speaker: So yeah,
Speaker: So what does that mean in terms of static pressures, right?
Speaker: So you can have,
Speaker: two ARDS lungs, right?
Speaker: Both of them could have, you know, the same plateau pressure of 30.
Speaker: Both of them could have the appropriate PEEP for compliance, meaning the right, the same driving pressure of 15, but one could have significantly less surface area than the other.
Speaker: and you're applying a six cc per kilo breath to that one with the one with the less amount of surface area will have a much higher amount of power delivered per breath if that makes sense your static pressures are all still the same right plateau pressure is the same driving pressure is the same total surface area and one is less so there's more power there's more energy transfer per breath so there's more injury per breath
Speaker: So I think that that's why it's also important that the static measurements don't speak to everything because we're not thinking about it in terms of dynamic transfer of energy.
Speaker: And I think that's a great point.
Speaker: And it's just the evolution.
Speaker: And obviously, we'll talk about this a little bit later.
Speaker: And full disclosure, we still don't have all the studies to really tell us how to use mechanical power at the bedside.
Speaker: But...
Speaker: Understanding these concepts and limitations is important because what the static measurements, such as low tidal volume and plateau pressures of 30, have demonstrated is that on average, in larger populations, they make a difference.
Speaker: But as we evolve in our understanding of critical illness, our goal eventually is to, for each individual patient, optimize our treatment and minimize the lung injury that we might be producing in
Speaker: And that's where we hope some of these concepts eventually will be very, very helpful.
Speaker: So let's talk a bit more about mechanical power.
Speaker: So mechanical power, like you said, is a measurement of energy over time.
Speaker: And it's expressed in joules over minute by convention.
Speaker: There are different ways that mechanical power can be measured.
Speaker: Some of them obviously require sophisticated interventions that are more efficient.
Speaker: likely to occur in a research setting than in a bedside clinical setting.
Speaker: But a lot of investigators are also trying to develop formulas and validate formulas that perhaps are a little bit simpler and eventually could be integrated to what we're already measuring at the bedside with mechanical ventilation.
Speaker: But why don't you tell us a little bit about the components that influence mechanical power and
Speaker: And specifically, what does it bring to the table that's new from the static pressures that we were talking about earlier?
Speaker: Right.
Speaker: When you think about the equation of motion and we think about the total pressure within a system, we think about the elastic compartment and we think about the resistive compartment and, you know, the things that impact that, right?
Speaker: The total of the things, the variables that impact compliance and the variables that impact resistance, particularly, you know, tidal volume and alveolar pressure, PEEP,
Speaker: You know, and flow and total diameter.
Speaker: I don't think a lot of us were ever taught that the resistive compartment makes a lot of has a lot of impact on.
Speaker: on alveolar injury, right?
Speaker: I mean, it's supposed to be the large airways.
Speaker: But there, even at the level of the small airways, there is flow application, and across the alveolus, there's flow application.
Speaker: And with that, you know, brings things like resistance and transfer of heat.
Speaker: So, you know, the...
Speaker: When we think about the equation of motion, like I said, start with the idea of energy and that's taking into account volume, total pressure, the flow applied, like I said, not something that we think a lot about, and then certainly end alveolar pressure.
Speaker: And, you know, sort of PEEP is a double-edged sword, you know, with good PEEP application, you can optimize lung recruitment and compliance and the system will benefit from it.
Speaker: with high PEEP application or PEEP above optimal compliance, it will certainly add to additional strain across the alveolus.
Speaker: So PEEP will increase the energy in the system if it's above optimal PEEP and above threshold is what I wanna say with that.
Speaker: So I don't want you to think that PEEP's a bad thing just because it's on the energy side of the equation.
Speaker: But certainly the volume, the total pressure applied, the flow and the PEEP make the energy.
Speaker: And then, you know, that energy transferred per unit of time, which is the rate, gives you the mechanical power.
Speaker: So all the things that matter in terms of tidal volume and total pressure, you know, delivered at a particular rate is mechanical power.
Speaker: Okay.
Speaker: What else was your question?
Speaker: Boy, I just got lost in my own head there for a second.
Speaker: No, no, no, that's perfect.
Speaker: So I think one of the things that also you were talking about, the different components of mechanical power, the resistive component and the elastic component, and how we have really not paid a lot of attention to the resistive components, right?
Speaker: But I think that studies have shown, more recent studies, and these are animal studies, that you can have, like you said, the same tidal volume, right?
Speaker: the same pressure and PEEP applied, yet a difference in respiratory rate will have a different impact on the amount of lung injury.
Speaker: A difference in flow or how that breath is delivered and inhalation and exhalation can also have a different impact.
Speaker: So could you reemphasize that or the relationship or the impact that respiratory rate and flow have in this mechanical power component?
Speaker: Absolutely.
Speaker: So, you know, with flow application, when you think about, you know, increasing, you know, the insertory flow rate, you know, some of us may do that because we may want to deliver the breath faster.
Speaker: Or if you change, you know, flow patterns, you know,
Speaker: whether you're sort of using a more traditional or widely used mode of mechanical ventilation like volume control that has continuous flow or if you're using something that's pressure control or PRVC where you have a decelerating flow ramp or if you have a smart ventilator, you may have a ventilator that can give you a volume control ventilation with a computer-generated decelerating flow ramp.
Speaker: Okay.
Speaker: I didn't hope I didn't lose anybody on that, but just the way that you deliver the flow, the rate at which you deliver, you know, flow,
Speaker: you know, for a fixed say diameter will increase resistance.
Speaker: And with that, there's transfer of energy, right?
Speaker: You know, usually thermal energy or heat, which will cause distortion and potentially injure the alveolus.
Speaker: You can see this in some animal models, you know, where they look at variable flow patterns, right?
Speaker: And variable modes of mechanical ventilation.
Speaker: John Marini published a paper
Speaker: looking at different flow applications, promoter mechanical ventilation and seeing different injury patterns.
Speaker: There's another paper looking at histopathology of pig lung with different flow patterns.
Speaker: So something that, you know, that may have, you know, a higher peak flow or generate your tidal volume quicker.
Speaker: Certainly, you know, you have to, you can imagine if you're going to generate that volume quicker,
Speaker: you know, like, like something you would see in a decelerating flow ramp.
Speaker: All right.
Speaker: Where the, where the, where the application of flow is highest at the beginning of the breath lowest at the end.
Speaker: So, and to get the pressure or to get the volume faster, there's more energy delivered across that,
Speaker: you know, that unit, whatever unit you're applying that to in the diseased lung.
Speaker: So there is the potential flow causing ventilator-induced lung injury, which is a component, you know, of the equation of motion that we never really used to think was deleterious to our patient, you know, when we would augment flow rates or breath timing.
Speaker: I guess would be one thing to take into consideration.
Speaker: And certainly, respiratory rate is very powerful.
Speaker: You know, we can appreciate how powerful the respiratory rate is when it comes to impacting something like auto PEEP, right?
Speaker: I think that we're all sort of classically trained, you know, to think about the power of the respiratory rate versus all other components of breath delivery when it comes to reducing auto PEEP or intrinsic PEEP in our patients.
Speaker: The same thing
Speaker: and probably be said for ventilator induced lung injury.
Speaker: And, you know, it's, it's probably the most obvious, you know, if you're, if you're walking on a broken, broken ankle, you shouldn't hop on it all day.
Speaker: You know what I mean?
Speaker: Anything you can do to reduce the number of,
Speaker: you know, of cyclical airway traumas that you cause, right, to a particular, you know, a particular situation
Speaker: area of injury in the lung would be beneficial.
Speaker: So the respiratory is very powerful.
Speaker: You know, we looked at some simplified models, you know, one just looking at driving pressure times respiratory rate, not taking into account, you know, other parts of the energy equation.
Speaker: I think that that's probably a good start, you know, because you're thinking about, you know, the stress that the lung is seeing and you're taking into account finally, you know, the rate at which it's applied.
Speaker: But I do think that there's more to it.
Speaker: you know, when it comes to flow and certainly PEEP application, that if you really want to be a good steward of providing a low energy transfer that we need to take into consideration.
Speaker: So, you know, there's, well, we can talk about ways, you know, soon that this can be applied, you know, clinically or at least could be considered clinically, but certainly something as simple as respiratory rate probably has a huge impact, you know, on the amount of ventilator-induced lung injury because it's the total quantity of, you know, cyclical airway trauma that you see in the course of a day.
Speaker: Absolutely.
Speaker: And I think that what I like about this concept of mechanical power, and that's why I wanted to bring it to a discussion at the podcast, is that I believe that the plateau pressure and the low tidal volume are extremely valuable because they're linked to randomized studies that have shown improved outcomes.
Speaker: And they probably represent one way that we're producing lung injury that we can minimize.
Speaker: But if we only focus on that, I think we have a very narrow view of what we're doing with the ventilator.
Speaker: And as we broaden that view, we realize that other settings that we do manipulate, such as the PEEP, such as the respiratory rate, such as the flow, also add to the potential of stress and strain, energy transfer, and ventilator-induced lung injury.
Speaker: And finding the optimal settings, I believe, is ultimately what we're aiming for.
Speaker: And it sounds like, from what I understand, Jason, mechanical power is a more comprehensive representation of some of the factors that cause lung injury through these mechanisms.
Speaker: And what I understand in animal studies is that if you look at the same tidal volume, other factors, right, will determine the degree or can determine the degree of lung injury.
Speaker: However, if you equalize mechanical power, even if the factors that got you there are different, those mechanical powers are equivalent in the amount of injury that
Speaker: that they produce in these animals.
Speaker: So that is, I think, what has got a lot of experts in this field excited as a potential application at the bedside.
Speaker: Yes, I agree with that.
Speaker: And I want to move to the next step, which is, what do we know about mechanical power and patient outcomes?
Speaker: You know, I think much of the data, or I should say all the data that I know of is retrospective.
Speaker: You know, I think when you're able to, you know, and some of it will be interesting, you know, coming out of the COVID-19 pandemic, where I think our practical approach is,
Speaker: to ARDS care really became nice and systematic.
Speaker: I can certainly say the same in our own practice.
Speaker: When you're able to control a lot of these variables and all patients, you know, are the same in terms of static, you know,
Speaker: measures, right, and have similar PF ratios, the ones with lower mechanical power had better survival.
Speaker: And I think that that plays into going all the way back to the very beginning, that there's a lot of heterogeneity going on within this respiratory system, that the static, the static measures give you a global idea of what's being applied, but doesn't give you
Speaker: you know, the appropriate insight into
Speaker: um, you know, sort of the regional application of, of those, you know, of the breath and how their, how injury might still be occurring.
Speaker: Right.
Speaker: So, you know, if you are able to control for, for all of the static variables, but the ones with lower mechanical power, it did better.
Speaker: I think it makes sense because either you're able to get to a lower mechanical power because you're better able, um, to, uh, apply that stress, um,
Speaker: you know, over the entire system, or you're able to reduce the total number of cycles that that system sees.
Speaker: And I think that that is what we should be trying to think about in terms of clinical application of mechanical power concepts.
Speaker: Excellent.
Speaker: So let's move into the clinical application, like you said.
Speaker: And it seems that there are a couple of things that are still missing from mechanical power.
Speaker: One of them is measurements of mechanical power that are readily accessible at the bedside.
Speaker: So a lot of these real measurements require techniques or require setups that are more likely to occur in research settings, like we said, than the bedside.
Speaker: But there are groups, and under Dr. Gattinoni and other groups, that have actually proposed
Speaker: for specific types of mechanical ventilation simplified formulas that could easily be incorporated into measurements on software in the ventilator.
Speaker: And I would imagine that's going to come soon, and we'll see more of that.
Speaker: The other thing that seems that, from what I understand, Jason, that is missing is we still don't have prospective studies that have shown that a strategy targeted at a mechanical power of X versus Y
Speaker: Makes a difference, right?
Speaker: So hopefully those will come in the near future as well.
Speaker: But could you tell us what we can do today?
Speaker: And really it's how would you encourage our listeners to be better stewards of the ventilator and minimizing ventilation?
Speaker: Venture induced lung injury.
Speaker: But before you go there, actually, what I think we didn't really cover is, could you just throw out some numbers out there in terms of mechanical power?
Speaker: I know that there's still a lot of debate, but just to give people an idea of some of the numbers that people have looked at as being a discriminator.
Speaker: Yeah, absolutely.
Speaker: You know, I think there is no consensus as to what, you know, like you would with driving pressure or plateau pressure.
Speaker: I don't know that there's a consensus as to what a safe mechanical power is.
Speaker: I think if you look at studies as a whole, retrospective studies as a whole, you know, we measure mechanics.
Speaker: mechanical power in terms of joules per minute, you know, really joules per minute per kilo predicted body weight.
Speaker: If you really want to, uh, if you really want to drill down, uh, the mechanical power.
Speaker: Um, and you know, I think, you know, from, you know, all of the studies that I've read somewhere between 15 and 17 is your threshold.
Speaker: I don't know how helpful that is per se, but I sort of think about it right along the same lines as, um,
Speaker: you know as uh you know as driving pressure if i can remember 15 that's probably the place um where i want to be um and then i think you know like you mentioned uh when there's easier applications than than us sitting sitting down you know doing calculus at the bedside um i you know or or ones that correlate um you know better um inter irrespective of mode of mechanical ventilation which um which can be a little bit tricky depending on
Speaker: the mode you use.
Speaker: It may impact the formula that you need to use.
Speaker: So I am excited to see if there's that there'll be, you know, software, you know, added to the mechanical ventilators that, you know, might be able to give you, you know, sort of a, you know, a visual readout as to where you stand with your mechanical power.
Speaker: And then you can augment, you know, some of these variables for the breath being delivered.
Speaker: And then you can also think about some of the things that you can do for the patient that may reduce the overall mechanical power while all of the other best practices in ARDS remain constant, right?
Speaker: Tidal volume, driving pressure, plateau pressure.
Speaker: And now you'll have a continuous readout for mechanical power.
Speaker: What are some examples, Jason, of other things that you would be paying attention to at the bedside?
Speaker: So obviously, I do believe it's important to reemphasize that let's start with what we know, right?
Speaker: So lower tidal volumes, keep the plateau pressure below 30, look at your driving pressure, keep it below 15.
Speaker: But what are other therapies that perhaps, I mean, we should be at least think, or not therapies, but interventions that should be in the back of our mind and should at least...
Speaker: pose some pause to us and question if I really go ramp up the PEEP, if I really ramp up this respiratory right, could I be having more damage?
Speaker: Absolutely.
Speaker: You know, and these are the, and I'll just, you know, full disclosure, this is sort of my practical approach.
Speaker: But, you know, when you have all of the, you know, all of those best practices applied, you know, and you're, and I think about Dr. Marini's concept of the Vili Vortex, right, which is, you know, similar to the way we think about, you know, the cycle of heart failure or anything else, you know, you have, you know,
Speaker: you know you have hypoxia you have injury you have you know increased minute ventilation then you have more um you know biotrauma then you have worsening um you know baby lung and then you can you know the surface area that you're applying that breath you know even though you can't really um objectively appreciate it continues to dry
Speaker: and then you have more power amplification, you know, with the same, you know, applied best practices.
Speaker: And those are the things that concern me as I have someone sort of sit on the ventilator and I'm waiting for them to get better with all of my static measurements optimized.
Speaker: You know, I worry that there's, you know, ongoing strain, which is then leading to progression,
Speaker: you know, less, you know, reduced ventilator capacity of that baby lung and then more power.
Speaker: So what can I do?
Speaker: you know, to try to limit the power, you know, and to limit the total number of cyclical airway traumas that I deliver with my ventilator, I'm doing it, you know, every single day.
Speaker: So I think the first thing that I think is most powerful is thinking about the respiratory rate.
Speaker: And, you know, where you, you know, and where you are with relation to,
Speaker: to permissive hypercapnia.
Speaker: I think that if your patient is otherwise optimized, stabilized, you can certainly think about dropping that respiratory rate to live in an area of permissive hypercapnia that we thought about
Speaker: all the way back in 2000 with the ARDSNet trial.
Speaker: You know, I think we all like to see a normal pH when we come in the morning, but we don't need to.
Speaker: And I think that if you can make the argument that everything else has been optimized, you can lower the overall mechanical power just by limiting the number of injurious cycles that that patient sees in a 24-hour period.
Speaker: So I do think respiratory rate might be one of the most powerful variables that we have that also is the easiest to augment and probably the safest to augment because you'll have a real-time idea of if it impacts them in a negative way, right?
Speaker: So I think you can safely augment your respiratory rate without making a whole lot of changes elsewhere.
Speaker: um you know i think for the other parts of power amplification you know that we were that we didn't really touch on you know position you know which we did sort of talk about the the regional position of each alveolus um you know and their position to each other you know where one is pulling on the wall of the other and there's focusing of some of that power
Speaker: you know, that alveolus wheel, you know, when we look at it, you know, diagrammed out for us as this perfectly, you know, round sphere, but that's just not what's happening when you have diseased, you know, when you have disease around it, when you have some, some, some alveoli that are collapsed and some that are under distended and some that are over distended, um, the geometry, um, uh,
Speaker: on each one of those units, you know, will cause push and pull and you'll have focusing of that power.
Speaker: Well, how can I change like the vector which I'm applying that power and now my head hurts and I don't want to think about it.
Speaker: These are things that we do every single day.
Speaker: You know, prone positioning, I think, is a very, we know is a very powerful intervention.
Speaker: And probably has the biggest impact on mortality when you think about, you know, the relative risk reduction from the PERCEVA trial, you know, for interventions in, you know, in ARDS.
Speaker: So, and I think that that has a large impact on mechanical power.
Speaker: Yeah.
Speaker: So yes, you place someone in the prone position, you will better redistribute their ventilatory capacity, apex, abase, dorsum, deventrum.
Speaker: Yes, it does all the great things with VQ matching and everything.
Speaker: But I think more uniformly now those alveoli will see that static pressure
Speaker: or surrogate that you're looking at, right?
Speaker: So there's going to be, you know, less power delivered, you know, against individual units and more delivered against the total system.
Speaker: which I think is probably impactful.
Speaker: And also certainly anytime you have the opportunity to improve compliance, you can improve the ventilating capacity of that baby lung and then the total power in the system per unit breath will go down.
Speaker: So I think that something that we already do, the question is, well, what are your targets when you do it?
Speaker: There is a time where I think we prone patients and
Speaker: we don't see much of a change in their vq matching we might not see a big impact um in the total compliance um is it worth continuing prone positioning and i would say in my own practice as long as it's safe and i have
Speaker: a well-trained staff, I would continue proning that patient, you know, because especially in the early stages of their lung injury, I think it would be beneficial to maintain a low power system.
Speaker: So I think respiratory rate, and again, you know, prone positioning, like we talked about, decreasing total intensity across that system is important.
Speaker: for alcohol.
Speaker: So that's, those are two of the clinical applications I can, I can take to the bedside.
Speaker: Cause I, I, I think they all sort of live under one umbrella, but I can also, I can appreciate them being, uh, you know, uh,
Speaker: a reduced power application on top of ARDS best practices.
Speaker: And I can live within that arena and feel confident while I wait to see what comes out of the world and the literature.
Speaker: Perfect.
Speaker: And I think that those are great examples of how we can apply physiology and a better understanding of mechanical power to our daily practice.
Speaker: As you said, Jason, while we wait for clinical trials and more of this fascinating topic to be delucidated, but
Speaker: It is obviously, it's not a revolution, it's an evolution.
Speaker: And as we understand more and more the dynamics of lung injury, I do believe that we will get to a point where we can apply better therapies to individual patients and not only to large populations like we do in clinical trials.
Speaker: I think, finally, what I would say as a take-home message is that
Speaker: Thinking of lung injury, thinking of how everything we do in the ventilator or in the ICU for that matter can have an unintended consequence that could harm our patients is probably the most important for us.
Speaker: Just to be thoughtful of how we treat patients and how everything we do can have a consequence.
Speaker: And as we learn more, I think we will improve, but also just I think it reinforces the importance of sticking to what has been proven, but also expanding the way we think of our patients.
Speaker: This has been a fascinating discussion.
Speaker: More to come, like you said, Jason.
Speaker: It is some of these topics are a little bit, let's say, abstract and very nerdy, but I do believe they're important for our critical care clinicians.
Speaker: So again, thank you for discussing this.
Speaker: I would like to end the podcast with a couple of questions that are unrelated to mechanical power.
Speaker: Would that be okay?
Speaker: Sure, please.
Speaker: I'm ready for something else.
Speaker: So the first question relates to books.
Speaker: Are there any books that have influenced you deeply or that you have gifted often to others?
Speaker: Yeah, you know, there was this guy.
Speaker: He was pretty talented.
Speaker: He was my program director.
Speaker: And when a week before graduation gave me a book, Crucial Conversations.
Speaker: And still to this day, I have it on my desk right now.
Speaker: Probably one of the more impactful books I've read, especially for my life as an intensivist.
Speaker: It's become part of our dedicated curriculum here at Cooper for our Going Into Practice series.
Speaker: And
Speaker: You know, we live in a world that is high intensity and a lot is asked of us.
Speaker: And I think, you know, it's not always about necessarily what we can do, but how we deliver care and, you know, and how...
Speaker: how we're able to support those around us to deliver that care.
Speaker: And that starts with your ability to communicate.
Speaker: And certainly the stories you tell yourself, which I think is just one of the more powerful chapters.
Speaker: So that is one of the books that I go back to every year.
Speaker: And like I said, one of the mandatory readings and work groups for our Critical Care Fellows.
Speaker: Awesome.
Speaker: And I think crucial conversations really, for those of who are unaware, really relates to any conversation where the stakes are high and the point of view might be different from different parties.
Speaker: And emotions are high, right?
Speaker: So these are conversations that occur with patients, with colleagues, with family members.
Speaker: And I think, like you mentioned, Jason, it's a super skill to be able to carry these conversations, but it's one that you can learn.
Speaker: So this is a great place to start.
Speaker: And we will definitely include links to everything that we discussed, the studies, more information on mechanical power.
Speaker: There's a wonderful website that Jason and his faculty have created for mechanical ventilation that is open access that he will share with us.
Speaker: And also there's previous podcasts that you mentioned
Speaker: Dr. Marini, he's been on the podcast.
Speaker: We did talk about the Vili Vortex, so I'll definitely link that as well, and I think it would be of interest for our listeners.
Speaker: The second question, Jason, relates to beliefs.
Speaker: What do you believe to be true in life or medicine that most other people don't believe or don't act as if they believe?
Speaker: That's a great question.
Speaker: You know, in medicine, I think we are taught to chase pedigree when I think we should be chasing competency.
Speaker: And what does that mean necessarily?
Speaker: You know, it doesn't really matter where you came from.
Speaker: or who taught you.
Speaker: What matters is when you're called to rescue someone, can you perform?
Speaker: Can you transfer knowledge?
Speaker: Can you execute?
Speaker: And I think that for medical education, it's really
Speaker: really important for us to have clear competencies and milestones.
Speaker: And when we're postgraduate, to continue those and chase competency and make that be, you know, the most important part of what we do, because that's what makes us great clinicians is being able to do
Speaker: something that other people can't.
Speaker: So I think that, you know, I have nothing against, you know, great pedigree.
Speaker: And with that, I'm sure it comes with great competency.
Speaker: But for all the people out there that think they can't do what they want to do or can't be what they want to be, I challenge you to chase competency and you will find yourself in a place that you never thought you would be.
Speaker: I think that's a great observation and believe in it 100%.
Speaker: I think of competency in a different framework.
Speaker: I've talked about skills, super skills and ultra skills.
Speaker: But again, the same idea that it's what we develop and what we tackle that ultimately defines the impact we have on others, which is really what we're looking for in our career.
Speaker: So that's a great thought.
Speaker: And the last question is, what would you want every intensivist listening to us today to know?
Speaker: Could be a quote, a fact or just a comment.
Speaker: Yeah, I have a lot of quotable people in my life.
Speaker: But, you know, I'll go back to, you know, to the quote from Mahatma Gandhi.
Speaker: It is unwise to be too sure of one's own wisdom.
Speaker: I think that that's really important in critical care.
Speaker: It goes with what we talked about today.
Speaker: You know, we need to continue to question what we do and why we do it.
Speaker: Nothing in critical care, I think, should be completely dogmatic.
Speaker: um you know having kind of a baby career um but still being able to be around you know giants like yourself steve treziak and um and phil delinger you can see how cyclical um critical care can be you love one thing one day you hate one thing the next day and you come back around a few years later and you start to love it again um i think we uh
Speaker: We need to continue to question what we do and why we do it as this specialty continues to boom and grow.
Speaker: And I challenge everyone, you know, to with this, you know, continue to grow your competencies and own your space as an intensivist in an ICU, no matter whether it's medical, surgical or surgical subspecialty.
Speaker: And I think this is the perfect place to stop.
Speaker: Jason, thank you so much for sharing your expertise and your time with us.
Speaker: Definitely look forward to having you back and talk about this and maybe other topics.
Speaker: Sure, love to come back anytime.
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.
