SCCMPod-563 PCCM: Ventilation Strategies in Infants With Bronchiolitis

Dr. Madden: Hello and welcome to the Society of Critical Care Medicine podcast. I'm your host Maureen Matten. Today I'm speaking with Dr. Javier Barela about the article, Acute Bronchiolitis in Infants on Invasive Mechanical Ventilation, Physiology Study of Airway Closure, which was published in the September 2025 issue of Pediatric Critical Care Medicine. To access the full article visit pccmjournal.org. Dr. Barela is an intensivist in the Department of Pediatrics in the Pediatric Intensive Care Unit at Hospital Padre Hurtado and Clinica Alma Mena de Santiago in Santiago, Chile. So welcome Javier.

Before we start, do you have any disclosures to report?

Dr. Varela: No, I don't have any. Thank you very much for the invitation.

Dr. Madden: No, it's my pleasure to talk with you. So I know that this is a very important study for Pediatric Critical Care and I've enjoyed reading it and having the opportunity to discuss it with you. So first I wanted to ask what's your interest in this study?

Dr. Varela: Yes, of course. Well, I work in a Pediatric Critical Care Unit in Hospital Padre Hurtado, Clinica Alma Mena de Santiago. Our main reason to admitting patients in winter season are maybe acute bronchiolitis, one of the main reasons, and we have a lot of patients with mechanical ventilation with this illness.

And we have observed that different groups manage this illness with different ventilatory mechanical strategies. So we think or we thought that these differences or these various mechanical ventilatory strategies are based because acute bronchiolitis is an illness that have different phenotypes. We could observe that some patients manifest with obstructive patterns and other patients manifest with restrictive patterns.

And we thought in that moment that acute bronchiolitis doesn't have all described about its pathophysiology. And we read about the work of Dr. Chen and Dr. Brochard describing airway closure in patients with Acupunctural Distress Syndrome. And we thought that patients with acute bronchiolitis have characteristics that pose them in a great risk of airway closure.

So we try to identify patients with this phenomenon of airway closure. And in order, the final goal is to understand how we are managing the ventilatory strategies in these patients. This study has a physiological character in order to understand how the subset of patients with these phenomena is the behavior of these patients.

Dr. Madden: Very good. So I just want to read some of the research in context items as we move forward to discuss your study. So there were three different items and it talked about airway closure, as you said, is a phenomenon mainly characterized by the cyclic collapse of the distal airways leading to alveolar air trapping, atelectasis, and bronchial inflammation.

And your population were infants with acute bronchiolitis that were supported on invasive mechanical ventilation and felt that they had characteristics that placed them at risk of airway closure. And since that airway closure may affect the respiratory mechanics as well as the mechanical ventilatory strategies, you carried out this prospective physiologic study. So you had enrolled 12 patients in that study.

And what you found was seven of the 12 had evidence that airway closure was present. And what you found was airway opening pressure was very high and largely exceeded the positive end-expiratory pressure levels that the infants were receiving on mechanical ventilation settings. So from this, and clearly a large population for most pediatric intensive care units are these children with bronchiolitis, particularly as you said in the winter season.

But some questions I have when you looked at it, you had included patients that had evidence of wheezing and did not include other patients that didn't exhibit this obstructive type of pattern. So we know bronchiolitis because we're now bundling more than respiratory syncytial virus into that category. We used to talk about bronchiolitis as only RSV, but now a whole host of viruses.

Can you explain the rationale to include or rather exclude those who didn't wheeze as part of enrollment in the study?

Dr. Varela: Yes. Well, really the definition of acute bronchiolitis was taken from a guide of 2014. And in this definition, we can have in the patients wheezing, but to RAILs and other manifestations or clinical manifestations.

And finally, we didn't take just patients with wheezing. In fact, the most of our patients had RAILs, not only wheezing. So we think that we took all the aspect of patients with acute bronchiolitis and not just patients with wheezing.

Dr. Madden: So I had a question in regards to looking at the population that was included. When you found that almost 50% of them had a bacterial co-infection, you also had identified a fair number of limitations, which I think that limitations also can be seen as opportunities for future research. But tell me how you felt that the bacterial co-infection and some of the other limitations may have impacted the results.

Dr. Varela: Yeah, you're absolutely right. We have to recognize that our study have limitations, but we think that these limitations doesn't affect the results of our study. With respect to the bacterial co-infection, yes, we found that at least 50% of the patients have bacterial co-infection.

And this is an issue that is present in other studies where in acute bronchiolitis, we know that the bacterial co-infection is frequent. We identified that not all patients with a co-infection had airway closure. For this reason, we think that it's important to know that bacterial co-infection, we think that it doesn't affect or didn't affect the results of our study.

We have another limitation on a single center study, and maybe it could affect to the generalization of our results. But as it has a physiological character, this study continues to have great validation or great importance. Another limitation is that maybe important is that we couldn't eliminate completely in the resistive component, but to eliminate doing an adjustment after obtaining the BB cure, that maybe we're going to talk about this later.

And we think that we continue to have very, very exactitude in the results.

Dr. Madden: EIT was used on seven patients out of the 12 that were enrolled. So when you look at that, did it have any influence on your results in terms of documenting who had airway closure?

Dr. Varela: Really, no. The answer is no, because the methods of the study, we identified the phenomena of airway closure with the pressure-volume curve, a low-flow pressure-volume curve obtained from the pneumotachometer. It was the main method in order to identify the phenomena of airway closure.

And we used electrical impulse tomography in order to corroborate the presence of airway closure. We could see that when we identified airway closure on the pressure-volume curve in seven patients, we could corroborate that there was really airway closure. But the main method in order to identify was the PV curve obtained from the pneumotachometer.

In this, I would like to define how we define airway closure, that it was defined from the pressure-volume curve. When in this low-flow pressure-volume curve, we observed a flat initial part of the slope. And when the airway opened, we can observe an important increase in the slope of the curve.

When the slope is in this part flat, on this flat part, we can suppose that the airway is collapsed in that moment. And this slope corresponds with the compliance of the theoretical airway compliance. And once the airway opens, the slope of the curve is in the compliance of the alveolar component.

And through the impedance geometry of the electrical impulse tomography, we obtain an impedance pressure curve, in which we can see exactly the same result of the PV curve. We can see a flat portion of the curve at the beginning of the inspiratory cycle. And when the airway opens, we can see a change in the slope of the curve corresponding to the airway opening pressure.

And we can see that both in the impedance pressure curve and the PV curve, we can see that the airway opening pressure is exactly the same in patients with this phenomenon. So electrical impulse tomography we use in order to corroborate the presence of airway closure, but that is the diagnostic method.

Dr. Madden: Thank you for explaining that. So you had described that you did three cycles of the low volume ventilation, but you chose to use the second cycle as part of the analysis. Could you elaborate on that?

Dr. Varela: Yeah, of course. Really, we don't have physiological reason in order to obtain the second cycle. We choose to use at the beginning of the study, or when we were designing the study, we chose to do it in the second cycle in order to do it homogeneous, and thinking that maybe the first cycle could be affected by the initial setting of the mechanical ventilator.

But finally, we see that the three cycles, respiratory cycles were similar, were the same, and there was no difference between one and another cycle of the three. And really, at the final, it doesn't have any repercussion, choosing the second respiratory cycle. I think that it was more in order to do homogeneous, the methodology of the study.

Dr. Madden: So appreciating that this was a physiological study, but so many people always want to know how it translates to the clinical side. So what do you think this information, this data that you've identified in this population, who we normally use mechanical ventilation in either a pressure or a volume mode, is there some consideration because of the airway opening pressure that you've identified or that it actually, the collapse actually occurs in seven out of the 12 patients, is there some consideration for a different mode of ventilation for them?

Would you consider something more like APRV or knowing that their compliance changes pretty quickly at times due to the secretions and the potential bronchospasm? What are your thoughts on that?

Dr. Varela: Very interesting, your question, because this is a physiological study. And this physiological study, we think that is the start of the initial work that we are doing in order to do more research and to obtain personalized ventilatory strategies. But we don't think that with this study, we can do suggestions about how to ventilate our patients.

It's very premature to do that considerations. With the results of our study, we can see that airway closure and consider the airway opening pressure is very important in order to don't mislead or don't get misinterpretation of the respiratory mechanics. Because you can read in the study that we don't consider airway opening pressure in order to calculate respiratory mechanics, mainly driving pressure and respiratory system compliance, we could obtain, we misinterpretate the driving pressure.

We think that we need more studies, more research in order to identify the subset of patients with acute bronchitis that have airway closure in order to do suggestions about mechanical ventilatory strategies. I think that the next step is related to identify how this phenomenon of airway closure is influencing the respiratory phase of these patients and what is the repercussion of parameters as positive end-expiratory pressure on this phenomenon in order to do suggestions about ventilatory mechanical strategies.

Dr. Madden: Since we don't really have the ability to establish what the airway opening pressure is on every patient, how does it translate to the patient at the bedside? Because your findings were that the baseline mechanical ventilation that the individual patient was on, oftentimes the PEEP was lower than what their airway opening pressure was. So we have a missed opportunity there, or it may be why we struggle with this patient population when they're on invasive mechanical ventilation.

But would you be willing to talk about right now what types of strategies could be utilized without further research?

Dr. Varela: Yes, excellent question and excellent observation, Maureen, because effectively, we thought that we identified in the study that the airway opening pressure was higher than the PEEP levels that we were managing in these patients. And in adults, it has been proposed that positive end-expiratory pressure should be set in the level of the airway opening pressure. But we think that it is very premature to do a suggestion for setting the PEEP in this level, in the airway opening pressure, because we need to research or to investigate more about what is the behavior of the airway in these patients, mainly in aspiration, because the phenomena of airway pressure that we are identifying in this study is in aspiration.

And maybe it is possible that this phenomena of airway closure could manifest in a heterogeneous way. But as I said, it's very important to investigate more about it before to suggest that the PEEP level should be set in the level of airway opening pressure. At this point, I would like to say that bronchiolitis is a phenomenon, it's an illness that has several phenotypes.

And we can find, as I said before, an obstructive pattern and a restrictive pattern in these patients. Inclusive, recent investigation has identified that up to 20 to 30 percent of these patients present with acute respiratory distress syndrome. So we need to investigate more the phenotypes, which patients present with airway closure, which is the repercussion or the influence of this airway closure in the respiratory phase of the respiratory cycle.

And in order to investigate if this phenomena of airway closure is homogeneous or is heterogeneous of all the distal airways. And with this investigation, we will be able to do recommendations about which is the best level of PEEP to manage these patients. And if there is some ventilatory mode that have better outcomes in order to manage this patient with less morbidity and less time in mechanical ventilation of these patients.

Dr. Madden: Yeah, that's always our goal is to improve our patients' outcomes. So this has been a great opportunity to talk with you. It's fascinating research and I can't wait to see where it goes because we have such different populations.

And as you said, whether it's going to be homogeneous or heterogeneous and their airways, and there's a lot more work that's starting to happen with bronchiolitis, both physiological and clinical. So it has significant implications for those that work in pediatric critical care. Our time has come to an end.

So before we conclude, I just wanted to ask if there was anything else that you wanted to mention that we haven't touched on yet?

Dr. Varela: Really, we have said about the main findings of the study. I want to say that this is a physiological study, very important. And this study, we think that established basis in order to do more investigations and in order to the final goal of us is to establish personalized ventilatory mechanical strategies, identifying the successful patient who has airway closure and who has obstruction secondary to airway closure.
But it's very important to continue with this investigation, with this research in order to do suggestions about the ventilatory management of these patients.

Dr. Madden: Yes, I agree. It is very important work and it's fascinating. So hopefully you'll be coming up with new work soon for us to see and to discuss.

But for now, this concludes another episode of the Society of Critical Care Medicine podcast. If you're listening to your favorite podcast app and you liked what you heard, consider rating and leaving a review. For the Society of Critical Care Medicine podcast, I'm Maureen Madden.

Announcer: Maureen A. Madden, DNP, RN, CPNC, AC, CCRN, FCCM, is a Professor of Pediatrics at Rutgers Robert Wood Johnson Medical School and a Pediatric Critical Care Nurse Practitioner in the Pediatric Intensive Care Unit at Bristol-Myers Squibb Children's Hospital in New Brunswick, New Jersey. Join or renew your membership with SCCM, the only multi-professional society dedicated exclusively to the advancement of critical care.

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