AutoPEEP and I:E Ratio Explained - Mastering Mechanical Ventilation

追加: 2026-06-01

[00:00:00]All right, welcome back to another episode here at Whiteboard Medicine. We appreciate you checking it out. Hope everybody is having a good day. Today's episode is going to be a focus on two really important concepts in emergency critical care medicine. That is auto peep and the IT ratio. Auto PEP is one of the most important and often unfortunately commonly missed problems in mechanically ventilated patients. If you've ever seen rising peak pressures, unexplained hypotension, breath stacking, or just a patient that is not improving despite what seems like appropriate ventilator settings, there's a chance auto peep is a hidden issue.

[00:00:38]And this may relate to the key factor here, which is the I to E ratio. This is a lever that can either cause it or fix it. So, in this episode, we're going to break this down into two clear parts.

[00:00:50]We'll start with auto peep. what is it, why it happens, how to recognize it at the bedside, and how to treat it. And then we'll do an even deeper dive into the I toe ratio, what it is, how to set it, how to change it, what it affects in terms of ventilation, gas exchange, and how to adjust it specifically in the setting of auto peep. By the end of this episode, we hope you'll have a practical framework to recognize auto peep and confidently adjust ventilator settings in real time. If you want study guides, practice questions, mini courses, clinical reviews, medical education posts, we've been super super excited about growing our Patreon community.

[00:01:28]We've been super super excited about the growth we've seen in this community at this point. It's probably one of the biggest collections of emergency critical care medical education content out there. Full ICU curriculums, the whole nine yards. And we're just going to keep growing it because it's been something we've been really excited about. So, if you have an interest, if you want to um check it out, if you want to see what we have to offer, we'd love for you to uh go to the link in the episode description or the pinned comment on YouTube and check out our emergency critical care Patreon community. No further ado, let's dive into the episode. Hey everybody and welcome back to another video here at Whiteboard Doctor. We appreciate you checking it out. Today, interesting topic. Um, it's going to be under our ventilator desynchrony kind of set of videos, but there's a little more to it in this one. And that's the topic of auto peep, also known as intrinsic PEEP, also known as breath stacking, also known as air trapping. Uh, would all be different verbiage for the same concept here. So, that's what we're going to dive into today for those. So to get started, auto peep or intrinsic peep or breath stacking or air trapping. I should say peep with the little I after it stands for intrinsic peep. I for intrinsic and then peep. What is it? So these are the scalers here and we're going to come back to this cuz it's nice to demonstrate a lot of these things uh on these scalers. Um but to get into some of the introductory knowledge, what is auto peep or breath stacking or intrinsic PEEP? Well, it in general occurs when a patient does not have enough time to fully expire before another breath is delivered. And this is primarily a concept that occurs when a patient is intubated or on a ventilator, right? because we set a lot of what that patient is going to experience. How fast they have to breathe, how much volume or their title volume that they have to take with each breath, um how much time they have to inspire and expire. All these things are things we can set on the ventilator. So, this is often a self-inflicted wound that usually is secondary to some kind of underlying disease state or illness that the patient has. It's often probably the reason they ended up on the ventilator in the first place. And what happens when the patient does not have enough time to fully expire their full breath, aka the ventilator gives them a breath in and then they're blowing out that breath, they're expiring that breath, but before they're done expiring that full breath, the ventilator delivers them another breath. So what happens if you can picture it is that this leads to an amount of retained volume in the lungs that builds up over time. And that volume building up over time is what causes the auto peep or the intrinsic PEEP or the breath stacking or the air trapping.

[00:04:22]Again, four terms all for the same concept. So to try to understand this a little bit better, um I drew out a a you know really crummy diagram of the trachea, airways and lungs and labeled them conveniently. So this is the trachea here, the wind pipe. It goes into smaller and smaller you know bronchi bronchioles and eventually into the terminal branch alvoli. So this is a very small airway and then this is kind of the air sack alvoli at the end where gas exchange occurs. And what we see with a breath being delivered by a ventilator, I didn't actually mean to delete these other little airways here.

[00:05:02]Uh so we'll just draw those back in. But what we see with a breath being delivered by a ventilator is essentially, and there's some variability to this, right? There's volume control ventilation where we set the amount of volume the patient gets.

[00:05:14]There's pressure control ventilation where we set the amount of pressure a patient gets. For the sake of ease, all uh these concepts we're talking about, we're going to assume the patient is on a volume control mode of ventilation where we set the amount of volume they're getting. And what that means is, let's just say we set the title volume, all right, TV for title volume at 400 cc's or 400 milliliters of air. What that means uh in a simplified form is that every breath the ventilator is going to deliver 400 cc's of air and that air is going to distribute into the large airways, the smaller airways all the way down to the you know incredibly large number of alvoli in the lungs and it's going to distribute throughout all those spaces that are exchanging air. And what happens then is the lungs inflate, right? So these lungs are going to inflate outwards as the ventilator pushes in those 400 cc's of air.

[00:06:25]When it's done pushing that in, the patient then breathes out. They expire.

[00:06:31]And what happens in a a you know normal you know physiology of the lungs or or a ventilator that's that's well set up is when the patient expires right these lungs move inward and they push all the air back out and that air travels up the alvoli into the small airways into the large areas into the trachear windpipe and then out of the patient.

[00:06:58]And in a perfect world, the amount of air expired is equal to the amount of air inspired.

[00:07:05]So there's a little different uh kind of verbiage on the ventilator itself. But for the sake of ease of concepts, we'll say title volume inspired with a little i and then title volume expired with a little e. And again, in a perfect world, these things equal each other. The amount of air inspired is the amount of air expired. But what happens when the lungs are diseased, right? Let's say that there's a bunch of disease in the lungs and those lungs can't expire at a pace fast enough to empty all that volume before the ventilator says, "Oh, it's time to give you another breath."

[00:07:41]Right? Cuz the other thing we said on the ventilator is the respiratory rate.

[00:07:45]So if I say that a patient has to breathe 20, what's going to be an easy divisible number? 30 times per minute, right? So that's one breath every 2 seconds. So if this patient takes longer than 2 seconds to fully expire, that 400 cc's, the ventilator is going to stop them from breathing out and it's going to push in another 400 cc's. So what we happen what we have then so let's just say title volume inspired is 400 but the patient for whatever reason and we're going to go over a lot of those reasons below can only expire 350 cc's of that title volume before another breath's prompted. Well that means every single breath you're going to have a net positive 50 cc's of air left in the lungs. And if you're set at 30 breaths per minute, that means every single minute, 30 breaths times 50 cc's of trapped air, that's going to equal, oh boy, I'm going to show that I should go back and do more math in the classroom.

[00:08:46]I think that's about 1,500 cc's of trapped air in the lungs every minute. And you can picture if you're trapping that much air in the lungs every minute, you're going to increase the pressure in the lungs, right? And that pressure is essentially our intrinsic PEEP or our auto peep. Cuz what PEEP is, for those of you that don't know, it stands for positive and expatory pressure. So, it's the amount of pressure that the lungs are seeing when they're done expiring air. And we actually set this value on the ventilator typically, right? You'll say peep of five because that peep is what kind of keeps those airways open, right?

[00:09:34]And you want a little peep, but auto peep or intrinsic peep is PEEP that we did not set, that we don't want. It is PEEP that's added on to the PEEP you set on the ventilator. So let's say the intrinsic PEEP you know is 15. The total pressure in the lungs then when the patient is done expiring is that intrinsic PEEP plus the PEEP you sent set. So it' be 20. And that's a lot of pressure in the lungs. That's a lot of pressure they're seeing. So what causes this then? Why does this happen?

[00:10:08]Well the thing that causes it uh is related to the physiology of the lungs.

[00:10:13]And it's kind of easy to think about if you break it down into a couple different things. So there's three things that affect a patient's ability to fully expire their title volume. One is essentially what we're doing with their uh ventilator. It's their minute ventilation. I I wrote size. That's probably a confusing term. You can just think minute ventilation because what minute ventilation is is the amount of volume they ventilate in a minute which is going to be their tital volume times their respiratory rate. Right? And that's going to equal their minute ventilation.

[00:10:47]And we'll just write minute ventilation again just for the sake of ease. And this is something that we set on the ventilator, the title volume. And this is something we also set on the ventilator, the respiratory rate. So if we're setting these things really high, we sometimes can self-inflict auto peep again because sometimes we're setting the respiratory really high cuz we're trying to get them to blow off all this ventilation to clear some CO2 and we can shoot ourselves in the foot a little bit if they start auto peeping. The other thing which is related the other two things are related mostly to the patient's lungs and one is compliance of the respiratory system. So compliance is kind of like the elasticity of the lungs.

[00:11:32]Elasticity that seems right of the lungs. And it's going to, you know, the mathematical equation if you're interested is change in volume over change in pressure. Uh not super important for the sake of this lecture. We're not going to dive into this concept in any amount of detail.

[00:11:47]But you can picture that if the lungs are more or less elastic, they're going to be able to push out that air either faster or slower, right? Because it's the change in volume over the change in pressure. So, um, if your lungs are more elastic and kind of think of a balloon, they're going to push out that air at a certain pace compared to less elastic. and the time it takes for them to breathe that air out is going to affect their expatory time. And if their expiratory time is too long, that's when you start to get breaths that are stacking on top of each other. The other thing and the most common thing we probably think about with auto peep is the resistance of the respiratory system. Cuz as we drew up here, we have kind of these small airways, these alvoli, right? in there a small airway and then it ends on this kind of air sack, this balloon and this is an alvoli and the air we breathe in flows down these small airways into the alvoli.

[00:12:46]It's oxygen oxygen diffuses into the bloodstream. CO2 from the bloodstream diffuses into the alvololis and then that breathes out into those larger and larger airways and eventually out the mouth. But what we will see happen with um patients with certain diseases is that they get some kind of collapse or obstruction or resistance of these smaller airways. And you can picture if these smaller airways kind of uh are collapsing down or spasming or there's mucus or disease.

[00:13:22]When the ventilator pushes in a breath, it causes positive pressure, right?

[00:13:28]because it's pushing air in to the system and that'll stent open these smaller airways. Well, when the ventilator is done pushing a breath in, this pressure, and again, there's some minutia to this, but uh from an introductory topic kind of standpoint, this pressure is no longer there stenting those airways open or it's much less. There is still, for those of you interested in more of the nitty-gritty, there's still PEEP and the PEEP is what you set, right? that expatory pressure, but otherwise there's not air flowing in, right? It's trying to flow out. And sometimes what happens is these smaller airways can collapse down or sometimes they're just spasming or sometimes there's mucus. And when that happens, there's more airway resistance. So that causes an increase in airway resistance. And that increase in airway resistance sometimes means it takes longer for that air to flow out of the lungs. And again, if the expatory phase is longer is prolonged, they're more at risk to stack those breaths again. So that's what causes it.

[00:14:38]And I'm realizing uh this is maybe confusing verbiage and I think I was trying to be clever, but um let me explain what I meant. So that's what causes it. What does it cause? aka what does the auto peep cause? Why do we care? Right? That's always a question.

[00:14:52]Well, why do we care? Does it do anything? Does it do anything negative?

[00:14:55]Does it make a difference? Well, unfortunately, it does. It can cause a lot of really negative downstream effects ranging from hypotension. So, that's low blood pressure, right? And that's because if you're auto peeping, right, you have we'll draw draw it again. So here's your windpipe. Here's your bronchi. Here's your lungs.

[00:15:15]But this is all stuck in this thoracic cavity, right? It's stuck in your chest.

[00:15:20]And this kind of a closed system. So if you're auto peeping, we know that's increasing the pressure right in this system. Well, there's other things in this system, too. You uh have a heart that sits right around here. And that heart has veins that dump blood into them, the superior vennea and the inferior vennea. And if the pressure in the system is really high, one could imagine that it's going to push on these veins and it's going to collapse them down, right? It's seeing all this pressure on both sides. And that can decrease Venus return to the heart, decrease the amount of blood that can flow through these veins into the heart because that pressure is pushing on those veins and that can cause hypotension, decrease cardiac output.

[00:16:09]The other thing that can happen is ventilator induced lung injury. Again, if these lungs are seeing this huge amount of increased pressure, it can actually damage the lungs, damage those small alvoli, right? These are really thin membraneed little air sacks. And if they're seeing all this increased pressure pushing out on them, that can cause inflammation, damage, fibrosis, and they can stop working. It also is really uncomfortable for the patient.

[00:16:34]So, it can cause patient ventilator asynchrony or desynchrony. And you could picture, right, if that patient every single time the vents pushing a breath in, then they don't have time to push it the air all the way out until the vent gives them another breath.

[00:16:47]And you can picture that over time that becomes very uncomfortable for the patient. It can also cause a concept called trigger asynchrony or desynchrony.

[00:16:58]And uh I'll go over that when we go to those scalers up top at the end of the lecture, but it can cause the patient to have trouble triggering a breath. And then the other thing you'll always hear about is increased dead space. And this is a really important topic, but it's one I wanted to explain a little bit more. What does that mean? And to do that, I think again I'm going to have to draw a nice uh nice set of lungs here.

[00:17:22]So you have your windpipe, your trachea into your main stem bronchi. And again, those branch off into smaller and smaller little areas, right?

[00:17:32]And at the end of these little areas is going to be the alvoli, which is much smaller than this cuz that looks to be the same size as the trachea, but it's much much smaller than that. uh and that feeds into these lungs.

[00:17:48]So dead space is the amount of space in this whole system that is not exchanging gas cuz the gas only occurs in the alvoli. So, I'm going to erase this and we'll say, you know, if you were to magnify in a bunch just kind of right here, what you would see is you'd have all these small tiny alvoli, right? And the circles at the end are the alvololis where air is exchanged.

[00:18:23]And this is the only area gas is exchanged, right? Oxygen that's flowing in goes into the bloodstream. carbon dioxide from the bloodstream goes into the alvololis and then flows out.

[00:18:35]There's no gas exchange in the bigger airways. It's all in the alvolus.

[00:18:39]So what you can imagine then is there's a amount of air in this system that's not exchanging gas. Right? Let's just I'm going to make up numbers here. Let's say that the alvoli represent this is truly just a completely madeup number.

[00:18:54]40% of this system. So let's say the alvoli equal 40% of the system. That means 60% of the system are all these airways that are not exchanging gas. And that is dead space, right? It's just the amount of air that's going to be sitting in these airways cuz you take a breath in and that whole breath doesn't go to the alvolus, right? You're done breathing.

[00:19:21]It might get that far. And some of that air is in these small alvololis all throughout the lung. But some of the air is just sitting in the airways. And then you breathe carbon dioxide and you breathe it back out, right? And that carbon dioxide then travels and some of it just sits in those airways and isn't bre uh uh breathe out the mouth. And that's called dead space. That's the amount of area in the lungs that's not exchanging gas.

[00:19:47]And increased dead space can lead to increased carbon dioxide levels because you're not able to ventilate off. You're not able to breathe off that carbon dioxide because there's so much dead space. And when you auto peep, when you breath stack, that increased pressure can cause increased dead space because you're not breathing out all that volume, right? And each breath you might start to breathe out less and less volume. So if ventilation is your tital volume times your respiratory rate, that is your minute ventilation, right? We went over that equation up here.

[00:20:25]And if your minute ventilation is partially related to your title volume, and as we said, your title volume, let's say it's 400, but you start breath stacking, so you only breathe out 350 cc's. That means there's 50 cc's here that are never part of the gas exchange equation. And as you breath stack, as you auto peep, as you get more and more intrinsic peep, this number might get less and less. You might start breathing in and out less and less air because that pressure is increasing. So now the pressure is so high that when the ventilator tries to breathe in 400 cc's, it can only get 300 in. But even with 300 in, there's so much air stuck in there. Now you're only pushing out 200, right? And your minute ventilation can go down and down and down. In addition to that, by hyperinflating all these areas, it can also increase that space.

[00:21:14]So you have less ventilation and that can cause increased CO2 retention or hypercapnea.

[00:21:22]All right? So that's what it causes, right? All bad stuff. Hypotension from the increased intrathoracic pressure, ventilator induced lung injury from those increased intrinsic PEEP pressures the lungs are seeing. patient ventilator asynchrony because it's so uncomfortable for that patient to be building up all that air in their lungs. Then increased dead space from decreased ability to fully ventilate. So how do we diagnose it and how do we manage it? Well, the way to diagnose it is actually over here. It's called and we're going to go into the scalers after this, but it's called an expatory hold maneuver.

[00:21:59]And what that means, if you can picture this, is let's uh actually maybe we'll go up to the scaler right now. We're just going to use the scalers one time and then we're going to do more scalar work at the very end. So what an expatory hold is, this is how you diagnose auto peep. So an expiratory hold. You guys might be familiar with an inspiratory hold. That's how you determine a plateau pressure. topic for a different video. But the expiratory hold essentially is you have the patient um you make the vent hold at the end of expiration. So what you'll see is a patient gets a breath in right expires that breath out and you say to hold it and you'll see this line kind of flatten out here. That's the expiratory hold. And what it should be, it should be at the same place when you do the hold, it should stay right here. It shouldn't go up cuz this is just the normal peEEP.

[00:22:59]But if you have auto peep, right? So this is the normal PEEP here. You did an expiratory hold. This is the auto peep or the intrinsic PEEP. It's the difference between the normal PEEP that you set and then the amount of um pressure in the lungs at the end of expiration. Because PEEP is positive and expatory pressure. So when you do an expatory hold, it should just be the PEEP you set. It should just be the positive and expiratory pressure. But if you have auto peep, that will that number on the expiratory hold will be higher than the PEEP you set because that is the intrinsic peep. the auto peep, the breath stacking, the amount of new pressure in the lungs because of that retained volume of air that's building up over time and that vent will kick out a number when you do this expatory hold maneuver and that's called the auto peep. So if we scroll back down the one thing to note is this is very difficult if a patient is spontaneously breathing right because as we me erase that spontaneously breathing cuz as we said let's say hypothetically you know you uh have a breath delivered this is the pressure scaler then you do an expiratory hold after the next breath and it's starting to go up but the patient doesn't like that right so they're going to breathe breathe in breathe out and the scaler is going to get all weird and you're not going to really get any real number. So if a patient's paralyzed, you certainly can do it. If they're deeply sedated and not working against the ventilator, you certainly can do it. But it's really difficult to do if a patient is spontaneously breathing.

[00:24:36]So then that begs the question, well then how do you diagnose it? And that is where we're going to dive into our scalers a little bit more. So if you guys aren't familiar with scalers, I really encourage you to check out some of our other lectures. We have introduction to scalers uh and then a handful of other videos involving different desynchrony and we'll link those in the video description and the video comments because we don't want to belabor the points too much on what these scalers are. But just for a quick intro, this is the pressure scaler, right? Pressure as related to time. And this is all going to be again like we said in volume control.

[00:25:12]This is the flow scaler as compared to time. And this is the volume scaler as compared to time. So what we see with auto peep, if we can't do an expiratory hold, we can look to our scalers to gauge and get a little hints. So if we start with the volume curve, this is zero, right? That's zero volume. And what you see in a normal breath is their volume goes up as they inspire. It goes down as they expire to zero. And then when the ne next breath comes, it goes up again. Right? Makes sense. Let me get rid of those. In auto peep though, what you will see is they'll get their breath in.

[00:25:56]Then they'll start to breathe out.

[00:25:59]But before they fully expire, that vent delivers them another breath in.

[00:26:08]Right? And same thing happens. So you don't go down to zero the way you should, which makes sense, right?

[00:26:15]Because again, let me let's pretend the title volume is 400 cc's. You get 400 cc's that come in, but then only 350 cc's out before the next breath. If we're being thorough, the way these scalers tend to look though is that there's a really prolonged expatory phase, right? So goes up and then the patient takes a long time to breathe out, right? And then you get another breath in. Then they take a long time to breathe out. And that's related to different pathologies, which we'll we'll get into more in a little bit. The flow scaler with auto peep can also be a hint, right? Cuz the flow is you get flow in, then you get flow out, and then it's returns to zero, right? It returns to zero flow before the next breath because there should be a slight kind of pause.

[00:27:06]There should be no flow, right? Right?

[00:27:08]You get a breath in, breathe that out, pause, then another breath in. There should be a period where there's no flow in the circuit. Well, if you're auto peeping or breath stacking, again, it means you don't have enough time to expire. So, you get flow in and then again there's this prolonged expatory phase and it usually doesn't come back down to zero before there's a second breath. Right?

[00:27:33]So, same thing. Look again. prolonged expatory phase doesn't hit zero. Another breath in and that can be a hint on the scalers that there's auto peep as well.

[00:27:43]Your flow is not returning to zero with new breaths. And the pressure scaler is sometimes a little trickier. I I think theoretically, you know, so pressure goes up when you're delivering a breath, comes back down. And as you auto peep, some would suggest that you should start to see this kind of marching up of the pressure scaler, right? where this is kind of your auto peep that's building up over time. Although it doesn't seem to usually demonstrate that on the pressure scaler. It's a little more complex than that. But those are some hints for how you can diagnose it on scalers. Really, the flow scaler and the volume scaler are going to be your two biggest hints. I had a patient the other day who quite literally their expatory face was so long it took up almost the entire screen. you know, the volume would go in and then it'd be this super prolonged expiratory phase and then they would breath stack. It was a really difficult vent to manage, but you you will see that with certain disease states as we'll talk about. So, if we scroll back down, what are those disease states and that's something important, right? Um because treating reversible causes is a major way you can manage this. So, things we see this in COPD and asthma are the two big ones, right? Because these have bronos spasm, bronco restriction, increased airway resistance is the name of the game in these. These patients have a really prolonged expatory phase.

[00:29:08]In fact, just the diagnosis of COPD, prolonged expatory phase is part of that diagnosis when they're not on a ventilator. You'll sit bedside and you'll have this in inspiration and then this really long expiration and you can see them with that prolonged expatory face. So that prolongation of the expatory phase can really affect that. Also, patients with a lot of mucus can sometimes air trap as well. Um, treating the reversible causes, you're going to treat the underlying condition, right? COPD, asthma, steroids, nebulizer therapies to help with bronco constriction or bronco spasm. Sometimes magnesium is indicated. You know, all this is treatment for COPD asthma.

[00:29:51]Another thing to always make sure is that the ET tube is not kinkedked. the endotracheial tube is not kinkedked cuz kinking the endotrachial tube can sometimes cause auto peep. If you picture the kink, right? We'll draw a tube here and let's say there's like a little bit of a kink there. Well, when the breath gets pushed in, it can flatten out this kink, right? Cuz that's more positive pressure. And then when a patient is expiring, sometimes this kink will get even worse and they won't be able to expire outward. So, make sure that endotracchial tube is not kinkedked. That's an important one.

[00:30:22]In addition to that, um, sometimes we cause this ourselves, as we said, patients that were trying to really increase their minute ventilation. Um, sorry, I realize I wrote minute ventilation up here for an easier shorthand. Um, but yes, their minute ventilation, right? Because if we set their respiratory rate way high, we set the respiratory rate at 30, their title volume at 500, cuz we're really trying to get them to breathe a ton of air.

[00:30:46]They might have an acidosis. We're trying to help them breathe off. Well, as we said, respiratory rate of 30 means that they get one breath every 2 seconds, no matter what. We're telling the ventilator, we want you to give that breath no matter what. And their tital volume of 500. So, even if they don't have that prolonged of an expatory phase, you know, that can certainly mean patient breathes in volume scaler is breathing out and a another breath comes in, right? Out, another breath comes in, out. and that can cause them to auto peep because they just simply don't have enough time to breathe out that amount of tital volume in 2 seconds. Um uh so sometimes this is a self-inflicted wound. So treating reversible causes is absolutely important. All right, increasing expiratory time. This makes sense, right? This is what you'd think.

[00:31:32]Well, if they need more time to expire, let's increase their expiratory time.

[00:31:37]How do we do that, though? Well, a couple ways. It's important to remember that uh a cycle here is 60 seconds, right? So when we're talking about respiratory rate 30, it's 30 breaths in 60 seconds. So you kind of have some limitations here. One way to increase the amount of time they can expire is to simply decrease the respiratory rate.

[00:31:57]Right? If you have the this is going to be a volume scale. If you have the respiratory rate set at 30, I'm just drawing a bunch. That doesn't give them that much time to expire. Whereas, if you have the respiratory rate set at 10, they can take all the time they need to expire, right? Cuz there's not a ventilator that's going to be giving them another breath right away.

[00:32:17]The other thing you can do is adjust the inspatory time. It's actually something you set, right? On a ventilator, there's an I to E time, inspatory to expy time.

[00:32:26]Often times, this is set like 1 to two maybe. And that means that the amount of time they get to inspire is half the amount of time they get to expire. So let's just say this is one breath, right?

[00:32:39]This if you look at kind of the amount of time this is going to be once uh compared to two it's going to be half.

[00:32:45]So for the sake of ease if you were to set the breath at uh maybe n let's say 9 seconds they had to take each breath which is unrealistic. That would mean that this is 3 seconds of time to inspire and 6 seconds time to expire.

[00:33:00]Well if you you could change this you totally could. This is again for the sake of the example. You would never make the IDE 1 to9. But let's say you made it 1 to 9. You know that means in this example instead of 3 seconds they get 1 second to expire. And I guess uh my math is still not quite on but 9 seconds to expire. So one and then they have much more time to expire. So you can decrease the inspatory time and essentially prolong their IT to E ratio, aka give them more time to expire with each breath. The other thing you could do is decrease their title value, which makes sense if they only have one to two seconds to expire and you're giving them uh I'm just going to make up some ridiculous. you're making them breathe 800 cc's of air with each breath. Well, you know, that means they're going to get these huge breaths that they're trying to expire out. And they might just simply not have enough time to expire out that huge breath. Whereas, if you decrease the breath down to 400 cc's for them, that might be enough time to inspire and expire fully. Uh, and you can decrease their title volume.

[00:34:11]Obviously, there's limitations to this depending on their physiology, but those would be the big things, right? Decrease respiratory rate.

[00:34:19]Decrease t uh sorry, decrease title volume. These are supposed to be arrows down for those keeping track of my scribbles. Uh decrease title volume. And you can prolong the I to E ratio, aka decrease the amount of time they're taking to inspire each breath and increase the amount of time they're expiring each breath.

[00:34:41]Okay. Excellent. Other things to note, we're almost done. I promise.

[00:34:46]So there's this thing called trigger asynchrony or difficulty with a patient prompting the trigger. The trigger is what the vent needs to see to have the vent understand the patient is trying to take a breath in and thus prompt the ventilator to give a breath. Cuz the ventilator is smart, right? If a patient breathes in, the vent is supposed to say, "Oh, okay. The patient's starting to breathe in. I'm going to deliver a breath with the settings you gave me.

[00:35:14]title volume, right? PEEP, uh, I to E time. But the patient prompted this breath. They triggered this breath.

[00:35:26]Well, the way the ventilator often detects that is by detecting a change in pressure. And that change in pressure has to be this net change. And this is a I'm going to put out a separate video on this topic in general. Um, so if this is confusing, I promise we'll make it more clear in another video because it it requires more time. Um, but what this means is, uh, if you set the peep higher, so let's say you have an auto peep, you're auto peeping, you're breath stacking, and that auto peep is 20. It's a high auto peep. um that patient will have a lot of trouble triggering a breath because they're trying to breathe in against all that stacked intrinsic peep, all that stacked air, and they have trouble mobilizing enough negative pressure to overcome that. But if you were to increase the PEEP they were set at, right, cuz this is their intrinsic PEEP. So, if you were to say, "All right, well, I'm going to set the PEEP at 14, just the normal PEEP," that is going to allow that patient to mobilize a uh breath a lot easier because there's already all this PEEP set to help them overcome the auto peep. Again, I probably shouldn't even included it in here, but for sake of thoroughess, I did. But, uh, stay tuned for another video on that. And if worse comes to worse, let's say a patient's now hypotensive, they're not able to get in enough air, their breath stacking, so terrible. Um they're kind of on the cusp of coating, disconnect them from the ventilator.

[00:36:55]Literally just take the endotrachial tube off the ventilator and that patient you'll you can push on their chest even they'll just breathe out all this air that's been breath stacked over time and you'll immediately see their blood pressure get better. you'll see their plateau pressure is getting better because it's another thing I probably should mention as diagnostic maneuvers.

[00:37:15]Auto peep increases plateau pressure.

[00:37:18]All right, so plateau pressure for those of you that don't know is the inspatory pressure. Um, so if you push a breath in, make the patient hold it, the ventilator then just detects the amount of pressure there. And you can guess that that auto peep would increase the inspatory pressure, right? Because you have all this pressure built up in the lungs that if you push another breath in and then pause, you don't let any volume leave the lungs. It's an inspatory hold.

[00:37:46]The auto peep will be all that air that was already in the lung in addition to the air you pushed in the lung during the inspatory hold. So that's going to increase the plateau pressure. So when you disconnect a patient from the ventilator, push out all push on their chest, let them breathe all that auto peep, all that stacked breath out, hook them back onto the ventilator, you'll see that plateau pressure go back to normal, their blood pressure get better and all that good stuff. Hey everybody, welcome back to another episode here at Whiteboard Medicine. We appreciate you checking it out. Today's topic is a really important one and it's one we sometimes overlook and that is the I to ratio or the inspatory toxy ratio on the mechanical ventilator. um it's something that we set, it's something we choose, um it's something that varies and it's some things that can be really significant and especially for certain pathologies like obstructive lung disease. So today we're going to dive into all things IE ratio by the end of this we hope that you'll have a great foundational grasp of what this is, what it means, why it matters, how to adjust it. Um and as a friendly reminder, if you want this study guide, this PDF that we're using to go through this episode, um it's available on our Patreon page.

[00:38:49]You can download it, save it, annotate it, print it out, whatever you want. Um, lots of great information there. It can be a great reference. And in addition to that, on that Patreon page, we kind of got a full ICU curriculum. It's probably one of the biggest collections of emergency critical care educational content um, out there. Uh, many courses, practice question banks, study guides, PDFs, medical education, postclinical reviews, the whole gambit. We've been really excited. Lots of people have joined. We've been putting a ton of effort into building up resources on there. So, definitely check that out.

[00:39:17]It's linked in the episode description as well as the pin comment on YouTube.

[00:39:20]We hope to see you all there. With no further ado, I to ratio. So why does the I toe E ratio matter? Well, the IE ratio is how long the ventilator spends delivering a breath, right? That'd be the inspiration, which makes sense versus how long the ventilator allows passive exhalation or expiration. So if you just think about that, right, that makes perfect sense. The IDE ratio is the ratio for which the patient is spending time in inspiration getting a breath in versus how long they're spending time in expiration or passively exhaling. And one of the keys here is exhalation on the ventilator is passive.

[00:39:58]Right? The ventilator isn't sucking breath out of the lungs. The ventilator is just not giving a breath and is allowing the lungs to passively exhale.

[00:40:07]Whereas inspiration is active. We are setting things that is are pushing air into the lungs. And there's a lot of different ways we can do that. So inspiration is active. Expiration is passive. Um, which plays a little bit of a role when we're talking about the ID ratio. The ID ratio in general, it's one of the most underrated but physiologically powerful levers you can pull in mechanical ventilation. It can be really, really significant. We probably don't give it enough time at least on the dayto day. At least not everybody. Those of you who are excellent out there are probably spending more time thinking about this.

[00:40:37]So at the bedside, the IDE ratio, what does it impact? Why are we saying this is so relevant clinically? Well, one, it impacts gas exchange. The amount of time you spend in inspiration is going to affect your mean airway pressures, and your mean airway pressures contribute to oxygenation. All right? It also affects air trapping and auto peep. This is critically critically important. This is one of the most important things about the IDE ratio. And we've put out a whole episode on auto peep, breath stacking, air trapping, whatever you want to call it. Um, so just search whiteboard medicine auto peep and it'll pop up. Um we're not going to dive into auto peep deeply in this episode but we are certainly going to talk about auto peep um and the ID ratios contributions to it. So auto peep is when air builds up in the thoracic cavity. It can lead to not just difficulty with the ventilation but even hypotension hemodynamic collapse pneumthorax all sorts of stuff.

[00:41:26]So we'll talk a little bit more about that. Hemmonamics which you just hinted at are certainly affected by the ID ratio. Um because the amount of time you spend in inspiration that's going to be an increase in positive pressure in the thoracic cavity which can certainly lead to hemodynamic changes. Uh not to be broken record but we've put a whole episode out on the hemodynamic changes that happen in mechanical ventilation.

[00:41:47]So you can search that as well. Um and then the hemodynamics are also affected by things like auto peep. And then bar trauma risk is important too when it comes to IDE ratios. You can see here there's lots of really important physiologic things that are affected by the IDE ratio. And again, we probably don't talk about it enough when we're managing patients on mechanical ventilation. So, getting to the core core concept, starting to understand what this is. All right. So, what is the IDE ratio? Simply speaking, as we mentioned, it's the time in inspiration compared to the time in expiration.

[00:42:17]Typical or normal is going to be 1:2.

[00:42:21]Inspiration is half as long as expiration. Does that make sense? So, 1 to two. uh if you want to put a time on it, which it doesn't work out perfect, but it' be 1 second of inspiration for every two seconds of expiration. So when you give a breath, it's going to be 1 second that that breath is given. And then you're going to allow for 2 seconds to that breath for that breath to be exhaled, right? So this would be one compared to a ratio of two. Okay? And that's normal. That's kind of what's happening physiologically when you you and I are breathing right now, not on the ventilator. Um, our inspatory cycle is about half as long as our expatory cycle. Um, and you can just do that if you take a breath, right? Just take a normal breath in, breathe in, right? Expiration is longer than inspiration.

[00:43:07]Now, when someone is on mechanical ventilation, we set this eye to E ratio.

[00:43:11]And again, we often start at 1:2 cuz that is what is physiologic. But when patients are sick on mechanical ventilation, they're sometimes not in a physiologic norm. They're not often at hemostasis. So the IDE ratio is something that we set directly and we often need to adjust it depending on what is going on. And the things that determine, you know, the IDE ratio or the things that we can adjust to help change the IDE ratio are three different variables.

[00:43:40]And we're going to kind of spell this out. All right. So the first is the respiratory rate, the second is the inspiratory time or flow rate. And the third is the mode of mechanical ventilation. And what we want you to think about to understand this is one 60-second breath cycle, right? So 60 seconds. Um, and the ventilator, you have given it different settings to achieve a certain amount of respiratory rate within 60 seconds, right? Let's just make the math easy. Let's say you were set the respiratory rate at 20. So you told the ventilator, you have to give 20 breaths in 60 seconds. Well, that tells the ventilator, okay, that means I have about 3 seconds for every breath. Does that make sense? Right. 60 seconds. You said 20 breaths in 60 seconds. So, that's 20 breaths over 60 seconds, which means one breath about every 3 seconds. So, the ventilator says, okay, that is the amount of time I have to give each breath. If I decrease the respiratory rate, let's say I decrease the respiratory rate down to 10, it's still 10 breaths over 60 seconds. Now the ventilator is saying, okay, I have about 6 seconds to give every breath, right?

[00:44:50]60 seconds divided by 10 breaths is going to be 6 seconds to give every breath. And that's a lot different, right? That means that the ventilator has a cycle of 6 seconds. So if we say again for the sake of ease if we say the IE ratio is 3:1 all right so three inspiration actually let's say the IDE ratio is 2:1 which is 2 for inspiration one for expiration actually we bear with us here let's just make this a physiologically normal patient the ID ratio is 1:2 1 second for inspiration 2 seconds for expiration and let's just say that we're using a respiratory rate of 20. And we already said that if it's over 60 seconds and 20 breaths, it's going to be about 3 seconds per breath.

[00:45:36]And our ID ratio is 1:2. So that means that for 1 second, you're an inspiration for 2 seconds you're in expiration cuz that's going to equal the 3 seconds that you told the ventilator it has to give each breath. So you'd have 1 second of inspiration, 2 seconds of expiration.

[00:45:52]If you used a respiratory rate of 10 and you had an IDE ratio of 1:2, well, that math changes then, right? That means you're actually going to have so you have an ID ratio of 1:2. You told the ventilator that you wanted a respiratory rate of 10, which if a breath cycle is 60 seconds, that's resp rate of 10 breaths per minute. That's going to be 6 seconds per breath. And then the IDE ratio is 1 second uh one inspiration to expiration. And if you have 6 seconds to do that, that means it's going to be 2 seconds for inspiration and 4 seconds for expiration, right? Cuz that's going to equal a ratio of 1:2. See how that changes? So the ID ratio of 1:2 stayed the same. But just by adjusting the respiratory rate from 20 to 10, you change the amount of seconds a patient is in inspiration versus expiration. All right. So for respiratory rate, the higher the respiratory rate, the less total cycle time and the shorter the expiratory time.

[00:46:48]All right. What else affects this? Well, the inspatory time or the flow rate is going to affect this as well. So a longer inspatory time means a shorter expiratory time which makes sense. If you are saying that the patient has more time to inspire, they're going to have less time to expire because again you are stuck in this respiratory rate per minute that you have set that has told the ventilator how many seconds they have for each breath. So if you increase the inspatory time, that means there's going to be less time left to be an expiration.

[00:47:27]That one is probably easier. That one probably makes more sense. So you can literally change the I time, which is going to change this I to E ratio.

[00:47:36]The thing that's maybe a little more confusing, but bear with us cuz we're going to spell it out, is if you lower the inspatory flow, there's going to be a longer inspatory time, which as we just said above is going to shorten the expatory time cuz you have a set amount of time for each breath. That's the thing to keep in mind. You've told the ventilator, you only have 3 seconds to give this breath. So, every time you adjust the inspatory time, it's going to affect how much time is left for expiration.

[00:48:06]All right. So, let's see if we can make this into math. So, um you have a patient on a ventilator. They're on volume control, assist control, volume control. You set the title volume at 500. Okay, that means that the ventilator has to give 500 cc's of title volume about with each breath. you have a flow rate of, you know, let's just make it up, um, 50 L per minute and you decrease that flow rate to 10 L per minute, the ventilator still has to give 500 cc's of title volume during inspiration, but the rate at which they can give that 500 cc's has gone way down. Instead of being able to give 50 L per minute of flow, you said you can only give 10 L per minute of flow, but they still have to get to the 500. So even though that flow is slower, you still have to get to the total amount, right? Let's say that this is 500. Whereas when the flow rate's faster, you can get up here much more quickly, right? So the time it takes in inspiration to get to your title volume is going to be a lot longer if you decrease the flow rate, which means you have to spend more time in inspiration to give the same title volume. Whereas if you increase the flow rate, right, you're going to be able to give that title volume more quickly. You'll spend less time in inspiration and thus your eye time, inspiratory time will be shorter, which will allow more time for expiration. All right, does that make sense? This is really important. Um, and maybe we'll erase some of this here to make this less clumpy. Um, this is really important. Um, feels confusing at first, but makes a lot of sense. So, we're just going to go over it one more time. So, increasing the I time is going to decrease the expatory time or the E time, right? And that makes sense because you only have a set amount of time per each breath. Okay? Again, that's based on the respiratory rate.

[00:50:02]And if we say the respatory rate is 20, that's 20 breaths in a minute. That means each breath has 3 seconds. So if I increase the time I'm in as uh inspiration, that is going to decrease the time left in expiration cuz we only have this 3second interval. So if it was originally an eye time of 1 to 2, you have 1 second for inspiration and 2 seconds for expiration, right? We'll just say that's 1 second. But if you increase the eye time, right, increase the time you're in inspiration, that's going to shift this cuz you'll be in inspiration for more time. You still only have 3 seconds, which means you have less time for expiration.

[00:50:42]All right? Same thing with flow rate.

[00:50:44]You have a certain title volume, a certain cc's of title volume that you're going to give this patient with every breath. And the rate in which you can give that title volume is dependent on the flow rate. So if you decrease the flow rate, decrease the rate in which you can give that title volume, the inspatory time has to be longer because you need more time to give that title volume, which then reflexively means the expatory time is shorter because you only have a certain number of seconds to give each breath.

[00:51:14]All right, hopefully that is starting to register. We're going to revisit some of those concepts as we go through and then we have some practice questions at the end. So stick around cuz that's where things will really be kind of solidified. All right. Modes of mechanical ventilation affect this too, right? Volume control and pressure control are two main modes. Um, and in volume control, the flow determines the inspatory time. Now, sometimes you set the flow on, sometimes you set the eye time. It's probably more common to set the inspatory time to affect the IE ratio. Um, but some ventilators you can also set the flow rate too and that will affect the IDE ratio on volume control.

[00:51:48]Pressure control you set the inspatory time directly, right? because flow is going to um this is going to get a little more complex. Um in volume control flow is a variable that you can adjust because you set the title volume and to achieve the title volume you have to have a certain flow rate. Whereas in pressure control the flow is um somewhat determined by patient. Now there's some barriers there but by patient effort because you're not setting a title volume you're setting an inspatory pressure right and that inspatory pressure then creates tital volume but the patient can somewhat determine their flow based on how you know much they're um inhaling the rate in which they're inhaling. All right, that's a little more advanced. If that doesn't register, that's okay. That's a smaller part of this um but something to keep in the back of your head to learn about more.

[00:52:37]Uh and maybe we'll put out a dedicated episode if that would be helpful. So physiologically why this matters? Well, it matters because inspiration is the positive pressure phase. When we're delivering a breath of mechanical ventilation, we're creating positive intrathoracic pressure. And that can do a couple of things. One, it can worsen Venus return. Right? You have positive pressure in thoracic cavity. Um that positive pressure creates some degree of force on the right atrium. Um and that can decrease Venus return. This can worsen hypotension. So if you have a really prolonged inspiratory time in a patient who has hemodynamic changes from that inspiratory time you can worsen hypotension. All right. The other thing is expiration is passive. We talked about that inspiration is active.

[00:53:21]Expiration is passive. Expiration happens when the ventilator is not delivering any volumes or pressures um other than your PEEP your positive and expiratory pressure. This allows lung emptying and prevents air trapping. It is absolutely critical in obstructive lung disease. So if you have too short of an expatory phase um especially an obstructive lung disease like COPD or asthma or bronus spasm this can cause auto peeper error trapping which can be really really detrimental and again we'll talk more about that in a second.

[00:53:50]So what happens when you adjust the ID ratio? Well shortening the expatory time we said normal I to E is something like 1:2. So if you shorten the expiratory time so the ID is now 1 one this increases mean airway pressure and in some patients this can improve oxygenation because you're increasing the time in which the patient is getting that positive pressure um but it depends on the patient. The um exchange here though is you increase the risk of auto peep, you increase the risk of air trapping, hyperinflation, hypotension.

[00:54:22]So this is very risky. Um not something that's heavily recommended. And as always, none of this is intended to be acted upon as medical advice. This is all just educational. Please read uh definitive guidelines, different research studies, your institutional guidelines before you make any medical decisions. Um okay. So uh shortening the IE well increasing the inspatory time and decreasing the excavatory time to a ratio of closer to 1 one sometimes can improve oxygenation, but there's lots of risks here that can happen. All right.

[00:54:49]What about prolonging the expatory time?

[00:54:52]So, we just talked about shortening the expatory time. And just to say it out loud, right? Anytime we say shorten the expatory time, right? That inherently means that you are increasing the inspatory time, right? These are two sides of the same coin. So when we say longer expatory time that means you're shortening the inspatory time because you only have so many seconds to give that breath. Um and this IDE can sometimes be 1 to 3, 1 to 4, 1 to 5. Remember normal is 1:2. So you're prolonging the expatory time which means you're shortening the inspatory time. This can improve lung emptying, reduce auto peep, reduce dynamic hyperinflam, hyperinflation and could be safer for hemodynamics. Okay.

[00:55:35]So again, normals 1 to2 that does well for most patients, but especially those with obstructive lung disease like COPD and asthma, um you have to be really careful cuz they need that more prolonged expatory phase. Maybe you guys have heard that you know someone with uh COPD exacerbation when you watch them breathing, they often have this prolonged expatory phase, right? So they and they have to breathe out for a lot longer to empty those lungs because they have obstruction going on. So if you don't provide them that prolonged expatory phase on the ventilator, what'll happen is they won't have enough time to empty. And let's say you give them 500 cc's a tital volume and the expatory phase isn't long enough. So they only empty 400 cc's. That means each breath they're holding on to 50 cc's. One breath that doesn't matter.

[00:56:19]But if you're making them breathe 20 times per minute and they um uh hold on to 50 cc's with every breath, you know, that's 20 * 50. That's 1,000 cc's of extra title volume that is building up in their lungs which can cause auto peep um hyperinflation, breath stacking, all that stuff u is one in the same um and that can be deadly right pumathorax uh hypotension they won't be able to ventilate um all that good stuff. So definitely check out that other episode on auto peep uh if that's an interest to you. So think about prolonging the expatory time in obstructive lung diseases like asthma and COPD which we have talked about a bunch. So, auto peep just to spell it out um we have mentioned it and uh hopefully it has registered but just to be more explicit auto peep is where air that cannot fully exhale um before the next breath gets trapped. So, it's trapped gas it's cause it causes intrinsic peep. Um, and we're not going to dive into it, but that's um, kind of like we mentioned, if you don't have enough time to ex exhale the full title volume and you hold on to a certain percentage of that title volume, it builds up over time, right? It's 50 cc's, it's another 50, another 50, another 50, another 50 with each breath.

[00:57:29]And then you get to a point where the lungs are so full of trapped gas that you can't even give the patient a breath. They have hugely increased pressures in their lungs. um it can compress vascular structures, affect the heart, affect ventilation, cause pneumthorax. So all that stuff is um from um uh breath stacking or auto peeping in patients with obstructive lung disease. And when it comes to the ID ratio, the causes of this are things that are going to shorten that expatory phase. Right? So if you increase the respiratory rate, remember the respiratory rate tells the ventilator how many seconds they have to give each breath. So if you increase the respiratory rate that is going to decrease the expatory time just inherently it's going to decrease the inspatory time too, but you've told the ventilator it has to give a certain amount of title volume already. So they're still going to get that title volume. They're just going to have less time to breathe it out. Okay. Um so if you shorten the expiratory time for any reason or you increase the respiratory rate, all that can contribute to auto peeping. Um and as we said it can lead to increased intrathoracic pressure, decreased venus return, increased work of breathing, bar trauma, all that good stuff.

[00:58:36]All right. So in some practical kind of clinical applications um so we can make this more graspable for use at the bedside. Um we'll start with obstructive lung disease because that is what this is really really super super relevant for. Um not to sound like a broken record, but if that's all you take out of this episode, that's a really really good learning point. So in obstructive lung disease you want to maximize expiration. So the strategy for your ID ratio you want to get it closer to 1:3 to 1:5 somewhere in that range. And remember normal is 1 to two. And to do that you can lower the respiratory rate or you can increase the inspatory flow right cuz that's the rate in which the ventilator is giving that inspatory breath. So increasing inspatory flow shortens the inspatory time. Some ventilators you can just directly shorten the inspatory time and that decreases the inspatory phase of that breath which then allows more time for exhalation. Um many ventilators the I to E ratio is something that um you don't directly change although some you can many ventilators you directly change this inspatory time. Okay so you shorten the inspatory time and then it tells you how that affects the ID ratio. Um so clinical clues for obstructive lung disease are normal stuff. Again, we won't belabor these things. Wheezing, prolonged exatory phase, peak pressures, um, flow not returning to baseline, all the stuff we talked about in that auto peep episode. All right, so that's one of the big applications of IDE ratio, prolong that expatory phase by decreasing the respiratory rate or increasing the inspatory flow or decreasing the inspatory time, anything to give the ventilator the ability to allow more time in expiration. All right, the other small application and you know this is highly variable. It's important to know um but not something we often do. Okay, so just be very careful if you're thinking about trying this. Um and it would be inverting Let us mute our computer. Apologies. It would be inverting the ID ratio. So instead of doing the normal of some like 1:2 going like 1 one um to increase the mean airway pressure to try to improve oxygenation.

[01:00:45]Okay? because you spend more time in inspiration. So, you have more time with that positive pressure breath that can sometimes help oxygenate, but it depends a lot on what's going on with the lungs and it's really risky. So, it makes us a little nervous. Um, so definitely definitely if you're going to try this, do this with a lot of caution. Um, but it is something that you could try uh in the right clinical scenario.

[01:01:08]All right. So, in the default ICU patient, the normal ID ratio is going to be right around 1:2. You can adjust it based on the clinical scenario, waveforms, gas exchange, humanamics, underlying physiology. And to adjust it in volume control, you'll increase the inspatory flow rate or decrease the inspatory time depends on the ventilator. This will shorten inspiration and as a result, it will prolong expiration. In pressure control, you'll just directly adjust the inspatory time. Go down on it. That will shorten inspiration cuz it's less time inspiration, which then will prolong or increase expiration. always consider the respiratory rate because you can only do so much to the I to E times um if you're at higher respiratory rate. So decreasing respiratory rate will certainly give you more time in each breath.

[01:01:55]Uh waveform interpretations. We probably aren't going to go much into this um because this is really focused in our auto peep episode uh and I think it might end up just being more confusing if we try to just do a brief discussion on it. Um but just shout out again to that auto peep episode if you have an interest. So getting towards the end year here, high yield clinical pearls.

[01:02:15]The ID ratio is really about that expatory time. Most ventilator problems in obstructive lung disease is that there's not enough time to exhale. Post intubation hypotension, consider auto peep. Um we were out first, but you know, maybe that's too aggressive cuz pneumthorax and other things are certainly important as well. Um but at least think about auto peep. In ARDS, inverting ratios can at times improve oxygenation, but you got to be really careful if you're going to try this.

[01:02:39]There's a lot of risks there. And then always think about your waveforms and physiology to adjust the ID ratio.

[01:02:44]Common pitfalls are ignoring the respiratory rate because you can make the IDE ratio as nicel looking as you want, but if it's got a high respiratory rate, you still will not have a lot of time in expiration, right? Because that respiratory rate drives how many seconds you have for each breath. Uh, another common pitfall is not looking at the waveforms. A ventilator often will show you the problem. And the third is treating numbers instead of physiology.

[01:03:07]ID ratio is a tool. Um it's not just a goal. It's not a set it and forget it as with everything. Adjust and then re-evaluate after that. Okay. So always re-evaluate.

[01:03:20]That is so critical um in patients who are quite sick. So quick bedside summary. Obstructive lung disease target ID ratio of 1:3 to 1:5 ARDS. You could consider doing an ID ratio 1:1 but this is very risky. The default the normal ID ratio is 1:2. All right. Let's end with some practice questions, shall we? If you've not done practice questions on this channel before, what we do is we read the question stem, we read the answer options, then we go right into the answer. Um, so if you want more time to think about it, just pause the episode cuz we're just going to jump right into the answer. Uh, we'll do a beginner, intermediate, advanced question, and then that'll wrap things up. So, beginner, a 65-year-old with COPD is intubated for respiratory failure. The ventilator shows breath stacking and excy flow that does not return to baseline. What is the best initial adjustment? A, increase the respiratory rate. B, decrease the inspatory flow. C, increase the expatory time, or D, increase the title volume.

[01:04:15]Pause here if you need to. The correct answer is C, increase the expatory time.

[01:04:20]Right? The whole goal here, what's happening? Auto peep or breath stacking.

[01:04:23]Right? The patient, we tell you in the question stem, is breath stacking, and their expatory flow does not return to baseline, meaning they're not exhaling all of the air that you're delivering them. Um, so the thing you need to do is give them more time to exhale. Um, and in these answer options, that would be increasing the expatory time. Other things you could have done, you could decrease the respiratory rate. That would be a fair answer. You could also increase the inspatory time. You also could increase the inspatory flow. All of these things would also increase the expatory phase, right? Anything that's going to either decrease restor rate, shorten the inspatory time, or increase the flow.

[01:05:07]Um, and I think we put increase in time.

[01:05:09]We meant decrease the inspatory time.

[01:05:11]Shorten it. Okay. Next question.

[01:05:14]Intermediate. A patient with severe ARDS remains hypoxic despite high PEEP and FI2. You consider adjusting the ID ratio. What is the primary physiologic benefit of using an inverse IDE ratio?

[01:05:25]A. Decreases airway pressure. B increases expiratory time. C. increases mean airway pressure. D reduces dead space. Pause if you need to. The correct answer is C. Increases mean airway pressure. Okay, this is that maneuver that you can try but is risky, right? So the ID ratio normally is 1:2. If you were to change it to one one and give a lot more time and inspiration, inspiration is when you're getting your positive pressure breath. So this increases the mean airway pressure and sometimes can improve alvolola recruitment and oxygenation. But it's highly dependent. It's very risky. It's not something that is commonly done. So, um obviously be very very thoughtful if this is something you're considering.

[01:06:04]Okay, last question. A mechanically ventilated patient becomes acutely hypotensive after increasing the respiratory rate. The ventilator waveform shows incomplete exhalation.

[01:06:13]What is the most likely mechanism? A increased veagal tone, B decreased cardiac contractility, C increased in thoracic pressure from auto peep or D decreased systemic vascular resistance.

[01:06:24]Correct answer is C. We actually are just realizing we made all the answers.

[01:06:28]See, um increase in thoracic pressure from auto peep, right? So they increase the respiratory rate. We know that that inherently means you're going to have less time in exhalation and by doing so you risk auto peep because that patient might need that time to exhale all their breath and that's what you're seeing happening.

[01:06:49]They become hypotensive after increasing the respiratory rate. They have incomplete exhalation. This is auto peep. So higher respiratory rate, shorter expiratory time, air trapping, auto peep, all that good stuff. So going back down on the respiratory rate would be reasonable or decreasing the inspatory time or increasing the flow rate would all be things you could do to try to improve this auto peep situation.

[01:07:11]All right, that's all we have for you today. If you want to stick around, we have a full kind of deep dive on all the things our Patreon page has to offer at the end of the episode. Um, otherwise, let us know what thoughts, comments, questions you have down below. Um, we've been working really hard and we're really proud of our YouTube members um, page and our Patreon page. So, definitely check those out if you have an interest. And either way, stay well, keep learning. We hope to see you next time.

[01:07:35]If I could borrow a quick 60 seconds of your time, I wanted to introduce you to a community we're really excited about building, and that is our Patreon community. In this community, you will get access to high yield medical education posts, ad free videos, study guides, practice questions, mini courses, book chapters, and much more.

[01:07:55]You will see that by joining this community, you will get access to the PDFs, the study guides for every single YouTube video. Here's an example of one of those right now. In addition to that, you will get access to many courses. In these courses, we will have videos, study guides, practice questions, bedside tips and tricks, and 30 practice questions at the end to test your knowledge. In addition to that, we have collections on every major emergency critical care topic that contains videos, medical education post, practice questions, study guides, all categorized. And lastly, we have book chapters. These book chapters are high yield clinical reviews such as this one on the basics of mechanical ventilation.

[01:08:37]Beyond that, we have ad- free videos, we have practice questions, and we are constantly innovating and integrating new resources for you all. If you have a passion for emergency critical care medicine like us, consider joining this community today. In it, we hope that you will find all the resources necessary to push your knowledge to the next level and really improve the bedside care of these critically ill patients.