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Hello. My name is Jonathan down and I'm an advanced critical care practitioner in intensive care in the UK I've worked in critical care for over 25 years and recently with the pandemic have had much experience of the prone patient. I'm going to discuss what is a R d s, how we treat it. Why do we prone? When do we prone? Does it work on what is new? So what is a R d s? This was first defined in 1994 by the America European Consensus Conference, but do two issues with the reliability validity of this tool. It was then redefined in a collaboration with the European Society of Intensive can medicine endorsed by the American Thoracic Society on the Society of critical commits. And he's noticed the Berlin definition. So ARDS is non cardiogenic pulmonary edema with fluid in the viola space. It has three different incretin area acute onset of bilateral a pass it ease on the chest. X ray, low oxygen levels and pulmonary edema is not due to heart failure. The Berlin definition further defined mild, moderate and severe ARDS using the PF ratio which have increasingly levels of mortality I will go on to discuss the PF ratio later. ARDS condemn Vellapan after direct long injury such as in pneumonia or aspiration of gastric contents. When the lvot lie are subjected to damage directly or because of indirect lung injury. Such a zen sepsis, pancreatitis or severe trauma, in which case inflammatory mediators in the circulation will make their way to the lung. Vasculature mortality remains above 40%. So let us look at the normal alvie. Oh, I on the left side of this illustration, you can see the normal alvie. Oh, lie. I have a thin epithelial layer and the inside is coated with surfactant. The gas exchange, therefore, could take place very easily across this area by diffusion, the epithelial a A is normally tight and prevent any fluid from crossing over into the alveoli, the type two cells or where the surfactant is produced. On the right side of the illustration, we can see the damaged L V o L. I where the inside has filled with this protein rich pulmonary edema fluid. This is filled with inflammatory cells. These inflammatory cells are releasing chemicals which can make the process worse. The LDL lower macrophage is recruit neutrophils and circulating macrophage is to the site of the injury. This thing goes on to encourage protease is and cytokine is a month's others, which perpetuate the inflammatory response. The border between the epithelial and the end of thelial oh XYZ swollen. Creating a bigger gap for the gas is to diffuse across, making that process harder. The basement layer is a thin, pliable, sheet like type of extracellular matrix that provides cell in tissue. Support on protects the alveolar life from stress. This's now denuded or stripped of it's covering on necrotic. The capillary end of the lien is also involved as the end of feeling, um is acted upon by a range of stimuli, itself becomes dysregulated, leading to the endothelial surface, becoming abnormal on having larger gaps for fluid on other substances. To move through, neutrophils can cross over into the interstitial. On there is greater platelet activation. These neutrophils were released. Protease is which combretum down the elastic tissue around the alveolitis, affecting the compliance. The overwhelming activation of neutrophils contributes to surrounding tissue damage on even long dysfunction. In co, the 19 ARDS patient's hae accounts of neutrophils are observed and represent a predictor of poor outcome. The worst thing inflammation and injury will damage the type to endothelial cells, reducing the production of surfactant, causing a decreased compliance. Type two cells also have a role in managing lung fluid. Activated fiber blasts secretes several extracellular matrix proteins within the interstitial, but also my great into the alveolus space where they fall attachments to damage basement membranes on contribute to the intra-alveolar fibrosis which can predominate. In some cases, this can lead to establish fibrosis on the obliteration of alveolus spaces with a dense, irregular matrix. Overtime scarring will occur which will go on to reduce diffusion across the membranes. How do we treat it? There are several tools in our armory for the treatment of a R. D s on here. I refer to both the faculty of intensive care medicine guidelines on the society Critical care medicine guidelines both release before the current pandemic. There is general agreement from them both on some of the treatments we can use. But if I think I can use the thick um graphic, I think you can see that prone ng is considered highly effective treatment backed up by the research. Think, um quote this matter analysis is the main source discovered a trials with the other 2000 patients being either prone or not. Mortality rates with the prone and supine patients were 41% and 47% respectively, with a P value is 0.2 on a risk ratio of 0.9. It was not associate it with an increase of cardiac events, or VAPs was linked to an increasing pressure. Sores thicker. Do have some reservations about the quality of some of the studies, particularly there where this relates to the impossibility of blinding but do go on to say they recommend is use in moderate to severe ARDS low title volume therapy. Sit alongside it has another well backed away of ventilating the patient. And again they both in a fire in agreement on this fly doing probe, the physiology of rivalry Prone is key to it's understanding on D, I think gives a greater appreciation of its efficacy. There are three terms that play a key part in the understanding of why we pro ventilation perfusion and gravity. The's papers are the ones I learned most from Andi last a little science heavy in places, I think well worth the read. The first part to understand is the shape matching of the lung on the effect that it has on the patient's ability to Bentyl. Eight. Well, let us start with a simple diagram of the lung, which we will gradually add 2 to 8. Understanding. Imagine that the patient is now lying on their back on that we have taken a slice through their lungs. We are now looking at that slice from the position of the feet up. We represent each lung in an enclosed box, which represents the pleura on the chest wall, giving the long some limitations as to how it can expand. You can see the individual Alvie Oh, I represented by the circles within the box. In this diagram, they are all an equal shape and size. However, our lungs are subject to the force of gravity, just like everything else on when we add that you can see that the picture changes. Now the alveolitis, the top of the image or the ventral part of the lung are pressing down on the alveoli in the lower part of the lung. All the dorsal part. So do two this compression. In fact, we have larger alveolitis higher up on more compressed Alvie. Oh, like lower down. We now consider the true shape of the lung on. I represent this by the tear shaped long I have a list rated here. This is an exaggeration of the true shape but helps illustrate the principles we need to understand. This shape means that when the patient is on their back or supine, there is slightly less room a top on the bottom. Consequently, with the added gravity, much of the lung tends to drop into the lower part, where it is compressed by the lung above it. The key point here is that there is a lot of room for this compress, long to fall into. On to this, the fluid that will also be affected by gravity. And you can see now that we have a compressed alvie oh, lie surrounded by the fluid making diffusion in the's Alvie. Oh, lie much harder. The perfusion to the dorsal part of the lung is a little better than the perfusion to the ventral part on the key here is that does not change significantly when the patient is prone so you can see in the first illustration where the patient is supine. We have the better profusion where there is the poorest ventilation on the better ventilation with the slightly less good perfusion. In other words, a VQ mismatch. In the second illustration, we have prone outpatient. So because of the shape matching on the effects of gravity on the fluid in the patient's lungs, we now have the better perfusion taking place where there is the better ventilation, improving the wiki balance. Thea Other effect to be considered is the way the abdominal contents can add pressure to the diaphragm when it is moving up and down in this illustration. We're looking at the patient from the side. The arrows indicate the pressure from the abdomen on the diaphragm. Remember that there is already a VQ mismatch in this region when the patient is supine on this, added pressure contributes to make it worse. If we then turn our patient on to their front, the pressure remains the same but is now pressing on the front of the diaphragm and no longer the back again. Remember that the back of the lung one prone is where we have the improved VQ matching. So now we have also relieve some of that pressure, too. We could also help the patient by placing them slightly head up, which will drop the abdomen the other way. A. Z well as the benefit of effectively sitting the patient up helping in the prevention of ventilator acquired pneumonia is much like we do when we try to sit them up to 30 degrees when they're on their back. The final point is about the position of the heart within the chest cavity. The heart is nearer to the front of the chest in the back. This means that when the patient is lying on their back, the weight of the heart gravity in action again is lying on top of much of the lung there. By adding to the compression, you can see here that when we lie the patient on their front there is less lung for the heart to lie on top off. Much of it is supported by the sternum. This again reduces some of the compression on the Alvesco lie on certainly takes some of the weight off that area off the lung. With the best leak you match I think the CT scan image helps demonstrate some of these principles. We can see the shape of the lung, which I industry tid with an exaggerated teardrop shape. In the top two images, the patient is supine with the second one at the end of inspiration, it clearly shows the fluid has collected at the dependent part of the lung. Ross. The nondependent part looks much clearer. The bottom images show the same patient in the prone position. On again. You can see the effects we were discussing earlier. I think this image also demonstrates, well, the position of the heart on the fact that much of it's it's on the lungs in the supine position. But once proned, the sternum takes much of the weight, relieving the pressure on the lungs friendly prone. The definition of the severity of ARDS is what leads us to the action of prone ing. This realize on the PF ratio. So ask yourself two questions. First, what is the patient's f I 02? Is it 20.3 point five or 50.7, for example, then with your latest blood gas divide that into the latest P 02 now, depending on Whether you use kill a Paschal's or millimeters of mercury, you will have a value which will tell you how severe that ARDS is. If the value is less than 300 millimeters of mercury or 40 killer Paschal's, then it is considered mild. If less than 200 millimeters of mercury or 27 killer Paschal's, then moderate. And finally, if less than 100 millimeters of mercury or 13 Keller Paschal's than it is severe. The intensive care society recommends prone in the patient with moderate to severe ARDS. Does it work? One of the latest studies, the Perceive a study, showed a significantly decreased 28 day and 90 day mortality in 28 day mortality. It was 16% prone on 32.8% supine. There are several criticisms of this study where again blinding is an issue on the fact that all the centers involved in the study were considered experienced with greater than five years of regular prone ing, and there were all in France in this matter analysis off 11 randomized controlled trials, which include 2200 patients. They found that prone in significantly reduced overall mortality on the effects were more marked in the subgroup, which was prone for more than 10 hours. A meta analysis in 2015 also found it to be a safe strategy. It reduce the need for oxygen in patients with severely impaired oxygenation. It went on to add that it should be started early for prolonged periods on combined with a lung protective strategy. What is new? Perhaps one of the key changes to come about from the cove it 19 pandemic is that more prone ng is now occurring in the awake nonventilated patient or self prone ing. The studies on this practice are limited now, but early signs are encouraging that this practice is a useful one in reducing the number of patients who then go on to be mechanically ventilated. This Italian study of 44 patients proned awake patients for a minimum of three hours, with the main study outcome being the variation in oxygenation. The PF ratio between baseline on research been a shin. They found that oxygenation substantially improved from supine to prone positioning and there was some improvement when the patient was recently find, although this was not significant. Interestingly, those patients who did respond at higher CRP on platelet levels than those who did not. Some interesting points are raised in this discussion paper. They know the data. No neonatal postulate that there may be two phases of cove it 19 Human itis on early compliant long stage When awake protein will prove beneficial on a later noncompliance stage when it may not. The minimum duration of awake prone ing may also need to be more defined. Expecting an awake patient to stay prone for similar times to the sedation patient is impractical for many reasons. The longest duration in any study so far was eight hours, and I suspect most patients would not achieve anywhere near this. It would seem sensible than to base studies on what patients can achieve rather than on what we think they should. It also noted that the prone position, because of its effects on the ventilation mainly to increased secretion clearance which could further lead to greater aerosolization great care, would need to be taken to ensure that adequate pee pee is provided in those areas for the healthcare stuff. It may be then that there is a place for a wake prone ing on could certainly have a place in the low resource economies which may have limited access to mechanical ventilation. What is clear is that more studies I needed? All the articles are used for this discussion on a summary of much of what I have said could be found on my website as well as a recent podcast I recorded discussing the process of educating staff from bench to bed side. You can access this by using the QR code seen here. Thank you.