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SCCM Pod-438 Patient-Ventilator Dyssynchronies and Their Mechanisms

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The prevalence and consequences of dyssynchronies are largely underestimated due to frequent lack of monitoring. Dedicated software solutions are needed to continuously and automatically detect dyssynchronies, which will allow for both clinical research and application aimed at determining the effects of dyssynchronies and their incidence among critically ill patients. Host Pamela M. Peeke, MD, MPH, FACP, FACSM, is joined by Laurent Brochard, MD, to explore the different mechanisms of the various patient-ventilator dyssynchronies and how to detect these dyssynchronies and evaluate their possible impact on patient-centered outcomes. Dr. Brochard is inter-department division director of critical care at the University of Toronto in Toronto, Ontario, Canada. This podcast is supported by an unrestricted education grant from Medtronic.

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Dr. Pam Peeke (Host): Hello and welcome to the Society of Critical Care Medicine's iCritical Care podcast. I'm your host, Dr. Pamela Peeke. Today, we're going to be talking about patient ventilator dyssynchronies and their mechanisms. I'm joined by Dr. Laurent Brochard. He is Interdepartmental Division Director of Critical Care at the University of Toronto in Toronto, Ontario, Canada. Welcome Dr. Brochard.

Laurent Brochard, MD (Guest): Thank you very much. I'm really pleased to be with you today.

Host: Wonderful. And before we start, do you have any disclosures to report?

Dr. Brochard: I do. I've received grants from different companies, for instance, Medtronic, Covidien and Drager. And I also, get some equipment from other companies like Zentech and Fisher Paykel. Okay.

Host: Excellent. Thank you so much. And before we begin, I just want to make certain we're clear on learning objectives. The first one is to explore the different mechanisms of the various patient ventilator dyssynchronie. The second, review how to detect these dyssynchronies. And third evaluate the possible impact of these dyssynchronies on patient centered outcomes.

This podcast is very much needed because we need to understand the different mechanisms of the various patient ventilator dyssynchronies and also identify the possible impact of these dyssynchronies on patient centered outcomes. By history the prevalence and consequences of ayssynchronies may be largely underestimated. And why is that? It's because of frequent lack of monitoring. We need dedicated software solutions that can continuously and automatically detect ayssynchronies. And this allows for both clinical research and clinical applications aimed at determining the effects of ayssynchronies and minimizing their incideces among critically ill patients. Why should we care about this issue of dyssynchrony, Dr. Brochard?

Dr. Brochard: Well, thank you for this question. This is a fascinating field because this is something we progressively discovered by looking at the wave formed on the ventilator screens and this is where is the products the dyssynchrony are visible on the screen if you pay attention. And if you think about how it should be normally. But they are not analyzed by the ventilators. So, nursing on the ventilator are usually tells you that these kinds of dyssynchrony or these kind of dyssynchrony, of course you can have alarms because the pressure goes up too much or because some volumes are abnormal, but very often the dyssynchrony are just there and not displayed, explicitly.

So, we need to learn about it and I think it's important for two reasons. One is it because some of these dyssynchrony may be harmful for the patient. Find some, some thing of use is the patients are having a lot of double triggering, which means instead of receiving breaths of, let's say six ml per kilogram of predicted body weight, the patient is receiving 12 ml or even sometime 18 mls.

So, it makes sense that this will be harmful for the patients because you don't deliver any more lung protective ventilation. But the other reason why it's important to detect and prevent this assynchrony is because very often it indicates that the dose of ventilation given to the patient is not adapted to the patient's needs.

What I mean is that, there are specific assynchronies which indicate that your patient is over ventilated. And this is at this point that the patient developed this type of ayssynchrony. Other, assynchrony indicates the opposite that the patient is not assisted well enough. And it may be because you don't give enough support or it may be simply because the patient's respiratory drive is so high that these patients will need sedation.

So, this is important because it tells you you're not giving the good amount of ventilation and the management should be adapted to the mechanism. It will be completely different if the dyssynchrony is related to excessive ventilation or to insufficient ventilation.

Host: Interesting. I'm just wondering as you speak, is there a patient profile that has a greater risk of having ayssynchrony. I'm thinking right off the bat of say, for instance, someone who is obese, where you have a large abdomen and you have greater pressure for the diaphragm to work. Is that one example?

Dr. Brochard: Well, that's interesting. In fact, the way I try to describe it is more about when does it take place? And in fact, you have three moments, three times in the ICU. The first one is when the patient is still sedated, you have a very specific assynchrony called reverse triggering. This is something we did not notice for many years, and it's related to entrainment of the respiratory muscle by the ventilator.

So, it's really interesting because it happens in patients who are quite deeply sedated, maybe not the very, very, very deep sedation, but still are well-sedated. They do not seem to trigger the ventilator, but they do have entrainment by the ventilator and they have a contraction of their diaphragm after each mechanical cycle or every other cycle or one of the three, something like that. It's not always completely irregular. And therefore the contraction of the diaphragm occurs at the end of the insufflation or even during the expiration. And this is one of the cause of double cycling, because at that time, the patient can trigger a second breath.

If you see the screen, you would see that the first breath is a mandatory breath, but the second one is triggered by the patient. So, these kinds of, assynchronies occur at the early phase, during a sedation. And very often when we start to switch from deep sedation to trying to resume spontaneous breathing.

The second time where you can see ayssynchronu is when patients are assisted by the ventilator. So, it means they are triggering the ventilator, but they have a very high respiratory drive. Okay. So, that would be patients who have ARDS. They have been sedated, but not paralyzed.

They have really bad lungs and maybe gas exchange is corrected, but still they are trying to get a lot of volume and flow so then they may have these type of flow hunger. We describe as flow dyssynchrony if you wish, but they have, and they have also short cycling because we tend to give now small volumes with relatively short inspiratory times. So, they may want more. And this is also the occasion where these patients may have double triggering. So, they trigger the first breath and they trigger the second breath. So, that's the difference here concerns. That's not a patient deeply sedated. That's a patient who is breathing with assisting the ventilator, but with a very high respiratory drive.

Host: Excellent. What's the third one.

Dr. Brochard: This third one is one which has been described initially where patients are a little bit in a later phase. They're on pressure support ventilation. It may be some other mode, but it has been mostly described with pressure support ventilation, and pressure support is a very nice way to assist patients, but it's very easy with pressure support to give too much pressure and too much pressure will mean too much volume and long inspiratory time.

And these patients will be completely different from the preceding ones, which I described the patient with high drive. These patients with very low respiratory drive. So, like very often tend to be sleepy, not struggling against the ventilator, but they will have a lot of missing efforts. So, it will be small efforts during the expiratory time, which do not trigger the ventilator.

Which means that the respiratory rate on the ventilator will be usually low, like 15 to 20 breaths a minute. While their own respiratory rate, maybe 30, 35. And they are comfortable with that. But, maybe half of their efforts are not triggering the ventilator. And the reason in that case, that too much support is given to these patients.

Host: Interesting. This is incredibly clear. And I have a very interesting question related to COVID. Do you see anything specific or unique to the COVID patient who is placed on a respirator?

Dr. Brochard: I would say we see a huge number of episodes of reverse triggering, really huge. And I think we tend to give a lot of sedation to these patients for good and bad reasons. The good reason being to make the patients comfortable, the bad reason is that we want absolutely to be sure that the patient is not moving. So, we give a lot of sedation and when we start resuming spontaneous breathing by decreasing sedation, we see a lot of these triggers triggering and a lot of colleagues calling me saying, what can we do at that time? And that's a difficult call because what it means when you see this reverse triggering is that the patient is in a kind of transition between the sedation phase and resuming spontaneous breathing. So, I think the best solution when it's possible, is to continue to stop sedation and wait until the patient will be able to completely trigger the ventilator, or for instance, you can decrease the minatury rate, decrease sedation. And then the patient will be able to take the control of the vent. Of course, the issue at that time is whether the patient will have a reasonable respiratory drive or whether the patient will go into huge efforts and excessive effort. So, that's where it is complicated.

Host: And also I would think with COVID, you have significant lung damage and a tremendous inflammatory response. And so there one would imagine your thoughts on this, to pay particular attention to the amount of pressure that is being utilized so it was not to increase the amount of damage.

Dr. Brochard: That's a very good point. And that's where the job of the clinician is really complicated because on the one side, you don't want to keep these patients too long on the vent for many reasons. And you want to resume spontaneous breathing, which has good effect, but you're also worried that patients waking up with a very high respiratory drive may add their own breathing effort to the pressure delivered by the ventilator and the total maybe a huge stress on the lung, especially because when you have sick lungs.

So, that's the kind of patients where you continue to keep the sedation. You discuss maybe continuing the steroids, for instance, for the COVID patients and where the good moment to start spontaneous breathing is really a difficult call for the clinician.

Host: This is what I've heard from so many of our colleagues in critical care. These patients with COVID who are on ventilators are an incredible challenge for so many reasons, some of which you've elucidated beautifully here. So, what's the solution here? What would you, as an expert in the field recommend, to be able to help us understand how to detect these dyssynchronies and then what? What do we do?

Dr. Brochard: So, as we mentioned at the very beginning, I think the future, we will have different solution, which will be automated detection of these dyssynchronies because it's a 24 hour/seven. It occurs often in cluster. So, if you're not at the right time, if you're not looking well at the screen, you will miss them.

So, I would say the first thing, when you see something a bit weird on the ventilator is to try to think at these three moments, where are we? Are we in this phase where the patient is deeply sedated, where it could be reverse triggering? Is it a situation where the patient is triggering the ventilator and if yes, is this patient in a situation of high respiratory drive or low respiratory drive. High respiratory drive well, clinically you see the patient is using accessory muscles and trying to breathe with high work of breathing. You can use some indexes on the ventilator, like the oxygen pressure, the PDO1 which is now offered on I would say almost all modern ICU ventilators, some ventilators display breath by breath.

Some other it's a maneuver. And we know when it's the normal value is around one centimeter of a fourth or a one or two. So, when it's above 3.5, four, 4.5, it means the drive is very high. And this may be a situation where you have these short cycles and these double triggering. So, you need to decide, should I give more ventilation to my patient because he wants more? Or should I give more sedation? And that's depends, of course, on what's the priority with the severity of lung injury. And if the patient has a low PDO1, low respiratory drive, for instance, below one, 0.5, something like that, or you can be sure that your patient is receiving too much ventilation compared to he's on her needs. So, you have to say, okay, I should decrease ventilation or decrease sedation. Of course, if sedation is still on board. And that's important because this situation of a patient triggering with a very low drive means the patient is not using the diaphragm enough. This will be a situation creating diffuse atrophy of diaphragm. So, in this situation, it's simple. You need to decrease the amount of support, even if this results in an increase in respiratory rate, because this will be the true respiratory rate of the patient.

Host: Other options?

Dr. Brochard: So, a lot has to do with titrating sedation. And, it's important to realize the type of sedation you can use and their effect on the drive. Because as we say, the mechanism, whether it's a high drive or low drive is very important, it's very different. And obviously, for instance, you can use a drug which does not reduce the drive or very little like dexmedetomidine. So, this will give sedation to the patient. If the patient needs sedation, for instance, he's agitated, but this will not reduce the drive. By contrast, if you think the drive is too high, you need to use a drug which will decrease the drive like propofol, for instance. So, it's important to know how each drug is working. Opioids have complex effects because of course opioids can decrease the drive, but sometimes they can have a huge impact on the breathing pattern, more than on the drive. So, you can have a low respiratory rate, but with huge efforts. So, you need to pay attention to which drugs are on board and which one can be used to optimize this interaction.

Host: Excellent. What about tools that can actually provide the continuous and real-time monitoring of the assynchronies? I would imagine, you know, clearly the problem is that not enough physicians have been paying attention to this interaction between patient and ventilator and so something that would obviously help are tools. So, what do you see as the promise here?

Dr. Brochard: No, you're absolutely right. This is what we need. And this is where is the products? Because these, assynchronies are displayed on the wave forms and they are there. You can see it, but until now, the ventilators did not work at detecting these assynchronies. And I think this will come. I know that several ventilators companies are interested to either detect and the diagnose assynchrony. Or simply help to better detect when the patient is starting the effort, which would be the right time to trigger the breaths or detecting when it's good timing for ending the breaths or the good cycling. And I know it will come and it will help enormously. So, I think, the next generation of ventilators will offer a much better way to deliver physiological assisted ventilation.

Host: And in the interim, what should the physicians do? Exactly what you just said, which is there's a lot more hands-on. A lot more having to manage more manually as it were, and to really, I think more than anything else, be aware of the fact that this assynchrony has great consequence that they need to know that it's there, be aware and train their team to be able to stay aware and manage it I guess in a more granular way. Would you recommend that?

Dr. Brochard: Absolutely. And you know, I did not mention that, but the last one I described which are these ineffective efforts during expiration, because the patient is receiving pressure support. It's also associated with a specific pattern, is that the patient tried to go to sleep. And when you go to sleep, you can become apneic. Because you don't have apnea when you're awake, but when you start to sleep, if you are hyperventilated, you become apneic. And this is something which occurs very often with special support ventilation and the slight degree of hyperventilation. So, it does not mean you have a PCO of 20. It just mean that you're a bit akalotic and your ventilation is a little bit too much.

And so these patients go to sleep, become apneic and the apnea induce an arousal or an awakening. And these patients 24/7 continuously try to go to sleep and can never go into a deep sleep. So, this may have a lot of clinical consequences. So, one very simple thing to detect is when your patients has a low, minute ventilation alarm on pressor support. And for instance, at night, it's not because the patient is not tolerating pressure support. It's because you give too much ventilation and these should be detected and known by the clinician.

Host: I love it. This is fantastic. Everyone out there who is listening, I would highly recommend, Dr. Brochard's excellent article, Monitoring, Patient Ventilator Ayssynchrony, which was in Critical Care Current opinion, which really describes everything we've been talking about. This was published June of 2016, volume 22, number three. And summarizes the issues at hand. In your crystal ball as a last thought, Dr. Brochard, when do you think we're going to have these new technical tools, and new ventilators to be able to help us?

Dr. Brochard: Oh, I'm hopeful. That this will come after the end of this pandemic. So, it should not be years away. I hope in the months to come, there will be several options on different ventilators.

Host: Excellent. And thank you so much, everyone. We have been speaking with Dr. Laurent Brochard, who is Interdepartmental Division Director of Critical Care at the University of Toronto in Toronto, Ontario, Canada. And we have been speaking specifically about assynchronies between patient and ventilator. This concludes another edition of the iCritical Care podcast. For the iCritical Care podcast, I'm Dr. Pamela Peeke.