Volume Control vs Pressure Control - Settings, Scalars, and Clinical Application Explained

Ajouté : 2026-05-22

[00:00:00]All right, everybody. Welcome back to another episode here at Whiteboard Medicine. We appreciate you checking it out. Today's topic is a foundational fundamental topic in critical care medicine and that is volume control and pressure control on mechanical ventilation. Volume control or pressure control, which one should you be using and why? In real clinical practice, it's not just about the mode. It's about understanding what you are controlling for and what you are not. If you've ever had a patient with things like rising peak pressures, worsening compliance, or title volumes that don't make sense, the answer is often hidden within the mode, the scalers, and the waveforms. So, what we're going to do in this episode is we're going to break this down. We'll first dive into volume control. We'll talk about what it is, what the settings are, what's guaranteed, and also how to interpret the scalers at the bedside.

[00:00:55]We'll then do the same thing in pressure control, focusing on pressure delivery, how that affects volume, patient interaction, and then we will actually do a head-to-head direct comparison of the two, talking about when to use each mode in clinical scenarios. By the end of this episode, we hope you'll have a clear practical framework for interpreting these different ventilator modes, their scalers, and how to choose between them. If you want a full ICU curriculum, you want to go past passively digesting these videos with study guides, question banks, medical education posts, clinical reviews, even full mini courses, we would love for you to check out our Patreon page. It is whiteboard medicine, emergency critical care. It is all things emergency critical care medicine. It's probably one of the biggest collections of medical education content on emergency critical care out there. Um, and it's ever growing. We've been super excited, super interested. It's been growing like mad and we'd love for you to check it out. So, if you're interested, it's linked in the episode description as well as the pin comment in YouTube. But no further ado, let's dive into today's episode. So, assist control volume controller or ACVC or assist volume control AVC or simply volume control.

[00:02:10]And this is what it's often referred to in the clinical arena. And that's what we're going to use for the rest of the video is just call it volume control. Um although we're talking about assist control volume control and we're going to use scalers to understand this but before we dive into that we wanted to just talk about volume control what that meant. So this is a mode of ventilation.

[00:02:28]Uh when you intubate someone and put them on a ventilator you can select the mode the way in which the ventilator is delivering that patient's ventilation.

[00:02:37]And when we talk about mode modes of ventilation for most modes and you know most primarily being the two we use most often volume control and pressure control. Volume control which we're talking about in this video and as the name implies is where you control the volume. Makes sense. Pressure control is where you control the pressure. So in these two different modes of ventilation, the difference in what you set is in volume control, you set a title volume and in pressure control, you set an inspatory pressure. And what this means is the thing you're not setting in that mode is the uncontrolled variable. So in volume control, you're controlling the tital volume the patient is getting with each breath or the cc's of oxygen that the ventilator is pushing into the lungs with each breath. That's the title volume. But what you're not controlling the uncontrolled variable that results from this is the pressure.

[00:03:41]The inspatory pressure, the peak pressure in this case in pressure control, you're controlling the pressure. You're saying, "Hey, ventilator, with each breath, I want you to give a set pressure." What is uncontrolled though is then the title volume. And we'll put uncontrol for these um cuz that's that's uh the uncontrolled variable that results from the pressure you set. So, what this means is there's kind of four main settings on a ventilator. There's certainly many more, lots of complexity there, but the four main settings, three are shared between these two modes of ventilation. And that is PEEP or the positive end expiratory pressure. That is the FiO2 or the fraction of inspired oxygen. And that is the respiratory rate or how many breaths per minute the ventilator is delivering. And these three are on both volume control ventilation and pressure control ventilation. And you're choosing these.

[00:04:32]You're saying I want a PEPA 5, an FO2, a 60%, a respiratory rate of 20, or whatever you choose. And we're not going to be talking about each one of these in this video, although we certainly will in a future video. So definitely subscribe and stick around for that. The fourth setting on the ventilator is what's going to be different between volume control and pressure control. And for the sake of this video, again, we're going to do a video on pressure control, but this video we're talking about volume control. So, what you're setting here is the title volume. And the title volume is the cc's or milliliters of air that the ventilator is going to deliver per breath.

[00:05:10]So I'm, you know, if you're in the clinical arena and you're sitting at title volume, it might be I want the patient to get 400 cc's per breath, 400 cc's of air or 500 or 350 or what have you. Um, and that is volume control ventilation. What makes it different?

[00:05:27]Many things, but in the settings, what makes it different pressure control is that you're setting a title volume that you want the patient to get with each breath. Now, ventilators are smart.

[00:05:34]There's lots of algorithms these days.

[00:05:36]Let us mute that. Um, and the ventilator is not just going to give this title volume every time. The patient has some control over this. Um, because the ventilator is not just going to push this in no matter what, right? There's going to be some variability from breath to breath depending on if the patient is, you know, accepting that breath or if they're not very accepting of that breath. But about this title volume the patient will get with each breath. And that affects our scalers. So when we're talking about volume control, you're going to see the front of a ventilator.

[00:06:08]So let's say you got a patient here, stick figure human, and they are intubated. Unfortunately, they have bad pneumonia. So they have a breathing tube coming out of their mouth and that breathing tube is, you know, hooked up to a ventilator and you have the ventilator screen. And every ventilator is different, but a lot of ventilators have these four settings on the bottom of the ventilator. All right? They have the PEEP, the FiO2, the respiratory rate, and then this fourth setting if we're in volume control. So if this is ACVC, this is going to be the title volume.

[00:06:45]And as we said, the uncontrolled variable here is the pressure. So often in the top right corner you'll have a peak pressure which is the pressure that the ventilator is experiencing each time it pushes in this title volume or the cc's per breath of air that you're setting.

[00:07:03]And on the front of the ventilator oftent times they show scalers. And these scalers are usually pressure over time, flow over time and volume over time. And these scalers are going to look different depending on what mode of ventilation you're in. And it is important to understand how they differ with each mode of ventilation. And you can also identify the mode of ventilation a lot of times looking at the scalers. Um so that's what we're going to talk about next in the video is the scalers that you will see in volume control or assist control volume control. The first one here is pressure versus time. So pressure on the y axis, time on the x- axis. The second is flow over time and the third is volume over time. And in volume control, the scalers you see are determined by how the ventilator is delivering the breath. All right, the volume scaler is the easiest to understand. So that's what we'll start with. So what you have with each breath, this is a single breath here. So this is one breath and as you can see the volume goes up for half the breath as the ventilator is delivering that breath and then it goes down for the other half. Right? That's as the patient is expiring. So this is inspiration. This is expiration.

[00:08:30]And this volume should be about what you set on the ventilator. It should be about that title volume. So if you set 400 cc's, each one of these breaths should be about 400 cc's of air. And you can see that repeated, right?

[00:08:43]Inspiration, expiration, inspiration, expiration, right? And this should be about 400 each time. And this would be three breaths, right? One breath, two breath, three breath. And this looks similar between volume control and pressure control. uh you get about you know the title volume is going to be different but the the scaler itself the shape of it inspiration and expiration is about the same right because the volume goes up when they inspire the volume goes down when they expire and it goes hopefully to zero right cuz you hopefully breathe out all the air you breathe in and then when there's no air going in when they're between breaths you just have this volume at zero cuz they're between breaths right breath one in breath one out no breath breath one breath two in breath two out no breath breath three in breath three out. So that makes sense, right? That's an easy one to understand. What about these other two scalers though? You have flow and pressure. So as we said, when the ventilator delivers a certain volume, the ventilator is going to experience a pressure, right? Cuz if you push air into the lungs, there's going to be a pressure that develops that the ventilator senses while it's pushing that air in. All right? And that's going to vary depend on the cycle of the breath. But something to know about volume control is even though you're setting a title volume, the ventilator is actually targeting a flow. And this is going to make sense in a second. So if we talk about ventilators, often times there's three things we think about with each breath.

[00:10:22]The trigger or when the ventilator decides to give a breath. the target or what the ventilator is targeting cuz it needs to target something, right? Um it's a ventilator. It's not a human. It can't think. So, you have to tell the ventilator, I want you to target X with this breath. And then the cycle or when the ventilator stops the breath. So, the trigger when the ventilator decides to start a breath, the target or what it targets during that breath, and then the cycle when it decides to stop a breath.

[00:10:53]And in volume control, the trigger is time. Makes sense, right? We said we set a respiratory rate. If we set the respiratory rate at 20, that means that every minute, every six 60 seconds, the ventilator is saying that that patient needs to get 20 breaths every 60 seconds or about one breath, right, per every 3 seconds. And ventilators are smart now. And this is assist control, meaning the the patient can also take their own breaths and that counts towards the 20. But if the patient is not taking their own breaths, every 3 seconds the v uh the ventilator says I need to give a breath or that's my trigger. If there's not been a breath in 3 seconds that triggers me to give a breath. So time is what triggers the ventilator to start a breath.

[00:11:41]We're going to skip target and come back to it and go with cycles. So what then causes the ventilator to stop a breath is the title volume and what the ventilator targets is the flow. And this is where things get confusing. But if you understand this, you'll understand the scalers or possibly vice versa. So let's pause. I told you in volume control, you're setting a title volume for the ventilator to give with each breath.

[00:12:08]Right? But I just then told you that the ventilator is targeting a flow. Well, what's that about? Why wouldn't it target a title volume? Right? If I said give it a certain title volume, why wouldn't it just target the title volume? Well, it is in a way, but it's in an indirect way because what causes the ventilator to stop a breath is the title volume. So, if I tell the ventilator I want that person to get 400 cc's of air with each breath, the ventilator says okay, I get that. I get that. I am going to target a flow. So flow is the amount it's like uh cc's per of air per unit of time. So if I say I want the patient to get 400 cc's let's just do 500 because it's an easier number.

[00:12:55]The ventilator goes no problem. I know that if each breath that I'm giving I'm just making up numbers here. Each breath that I'm giving is going to be 1 second long and I need to give 500 cc's. I know how much air to flow in in that second.

[00:13:12]It's 500 cc's per second. Let's just say the breath is going to be 2 seconds long. Right? So if the breath is 2 seconds long, the ventilator says no problem. 500 over 2 seconds is going to be 250 cc's of air per second. And that's what I'm going to flow in because this is you know air cc's per unit time seconds. So what the ventilator actually targets is this flow. It's the cc's of air per second because it knows then that it will give the title volume I'm setting over the duration of that breath. So it will give 250 cc's per second for the 2 seconds until it gets to the title volume I set of 500 cc's.

[00:13:52]Right? 250 * 2. And then it will cycle.

[00:13:55]It will say stop the breath. That's the title volume they wanted. Breath is over.

[00:14:00]And this then translates into why our pressure and flow scalers look the way they do. Because if you look over here and start with flow, what you see is flow is flat on the top whereas pressure ramps up at the top. Now why would that be?

[00:14:23]Because we are targeting a set flow. So over time, right? So the ventilator says, "Okay, 250 cc's per second of flow. I'm going to just ramp up immediately to that set flow of 250 cc's over, you know, 1 second time." And then the flow just immediately goes to zero.

[00:14:44]This is inspatory flow. And then this is negative because the patient's starting to expire. So this portion here, the positive portion is inspiration.

[00:14:54]This portion here goes all the way down to the negative portion is expiration because this here is zero flow, right?

[00:15:03]So now there's no flow when the breath is done being expired out until they inhale. You get your set flow rate. It holds that flow 250 cc's per second.

[00:15:11]Okay, I got my title volume. I got to my 500 cc's of title volume. I'm going to just drop the flow, right? It just shoot goes all the way back down to zero. But then the patient starts to breathe out and expire until it goes back to zero when the patient's breathed all the air out. Right? And that's why in volume control, this top area is flat on top because the target is a flow rate. It's a constant flow rate until you get to the title volume that you set and at which point the ventilator stops flow and the breath is over. And that's also why you get this ramped up pressure because if you give a set flow rate, it's going to slowly build up the pressure in the lungs, right? You got two lungs here. You got a trachea that goes into these lungs and I'm pushing air in. And that air has to expand the lungs. But the lungs, you know, aren't they have a compliance, right? It takes effort to expand those lungs and overcome the lungs compliance.

[00:16:09]But that in turn creates pressure pushing back, right?

[00:16:13]Cuz those lungs are expanding and kind of pushing back as they expand. And that's what causes the pressure that is created. And you know, peak and plateau pressures and things is going to be a different video. But when you set a set flow rate, that's going to slowly as it flows air down and pushes those lungs out, build up an increasing pressure as more air is delivered into the lungs until you get to that point where the breath is done. You can see these line up, right? Breath is done. In which point the patient expires and the pressure drops back down to this set pressure, which if you watched our original video, this is the PEEP, the positive and expatory pressure, which we won't go into here. Definitely check out that other video. And as you'll see, and we're going to link all these in the video description when we talk about pressure control scalers. This looks different than a pressure control scaler. This ramp up is characteristic of volume control because you have a set flow rate and as that flow over a period of time. Let's just again make it up.

[00:17:12]Say it's 2 seconds. For every 1 second, it's kind of pushing in 250 cc's per second or you could break this down even further into milliseconds. but it's flowing a certain volume of air in per millisecond and that is slowly filling up the lungs increasing the pressure until that breath is over at which point the patient expires and the pressure goes back to the end expatory pressure that we set on the ventilator. All right. So this is very characteristic of volume control. You get this flat top at your flow scaler. You get this ramped up pressure scaler. Uh and then volume uh the volume scaler is pretty constant between pressure control and volume control. It's pretty constant. So today we're going to be talking about assist control. Pressure control. Um also known as ACPC or assist pressure control. Um or many people in the clinic are going to just refer to it as pressure control.

[00:18:05]And that's what we're going to refer to it as uh for the rest of this video. and we're going to talk about it in relation to the pressure time scaler, the flow time scaler, and the volume time scaler.

[00:18:16]Before we do that though, we wanted to talk a little bit about pressure control. So on a ventilator, there's lots of different things you can set, but the main four things that you can set are the PEEP or the positive and expatory pressure, the FiO2 or the fraction of inspired oxygen, the respiratory rate, and these three, we uh have done this exact same video for volume control. Again, we'll link it in the video description. Um these three are all present in both pressure control and volume control. Right? Volume control being you control the volume and the uncontrolled variable is the pressure.

[00:19:00]Whereas pressure control you control the pressure and the uncontrolled variable is the volume. And we'll talk more about this in a second. But in both of these modes of ventilation, these three settings are the same. the PEEP, the FiO2, and the respiratory rate. The setting that is different between the two is the fourth. And in pressure control, you're setting the inspatory pressure, whereas in volume control, you're setting the title volume or the cc's of air that is being pushed into the lungs with each breath. So, this is volume control. In pressure control, you're setting the inspatory pressure. And what you're saying, what you're telling the ventilator is you're saying, "Listen, with every breath, I want you to give this pressure, right? This millimeters of mercury." And that pressure is going to create a title volume. The title volume is the cc's or milliliters of air the patient gets with each breath.

[00:19:58]That's the title volume. So, the inspatory pressure you're setting is going to create a title volume, but the title volume created is going to be very patient dependent, right? right? It's going to be based on the patient's anatomy, physiology, their lung compliance, all these different things.

[00:20:13]So, this is the uncontrolled variable.

[00:20:15]This is the result of the inspatory pressure you set. The nice thing about pressure control though is that the ventilator, it won't go above this inspatory pressure usually. So if you're worried about, you know, barot trauma or certain damages from high inspatory pressures in volume control, because in volume control, you're setting the volume here. And the pressure that results from that volume is uncontrolled. You're saying, I want the patient get 500 cc's per breath of title volume, and whatever pressure that takes is what that pressure takes. In pressure control, you're saying, "I want the patient's lungs to just get this pressure." And whatever tital volume that pressure creates is the amount of title volume they'll get with each breath. All right? So, the title volume is a result of the inspatory pressure you set. So, there's no nothing in here where you're setting a title volume.

[00:21:07]You're setting an inspatory pressure.

[00:21:08]Whatever volume results from that with each breath is the volume that results with each breath. And you can go, let's say they're getting too much tidal volume. You set the inspatory pressure at 30 millm of mercury and it's resulting in a title volume of 700 cc's per breath. And you're like, that's way too high. Well, you can go down, right?

[00:21:26]Maybe you'll decrease the inspatory pressure to 20 millm of mercury. And that pressure being lower, you could picture, right? If you're pushing in less pressure, the title volume is going to be lower. Maybe the patient then gets 500 cc's per breath. And most of the time, this is ventilator dependent. Most of the time, this is the pressure above the PEEP. So, let's say I set this at 15 and the PEEP is at five. That means the total pressure they're getting with each breath is 20. 15 + 5. Um, again, a little ventilator dependent. Okay? So, you're setting an inspatory pressure in pressure control. You're controlling the pressure.

[00:22:04]How do we understand that with the scalers? Well, the scalers look different in pressure control than they do in volume control or a different mode of mechanical ventilation. And that is based on three different things. Right?

[00:22:17]Anytime we're thinking about a mode of mechanical ventilation, a way we can help to understand it is based off of what the ventilator does with each breath. And what creates a breath? Well, for the ventilator to create a breath, there has to be something that triggers the ventilator to give a breath. Right?

[00:22:36]So that's how the ventilator decides it needs to start a breath because this is a machine. It's not thinking for itself.

[00:22:42]Um you need something that triggers the ventilator to give a breath. You also need the ventilator to target something, right? It can't just push in air randomly, right? It has to target something. And then you need the ventilator to cycle or to end the breath, right? And all these are things that the ventilator isn't thinking about. It's not, you know, you need to set this. And in pressure control, this these three things differ than volume control. So in pressure control, the thing that triggers a pressure is the time. And this is actually the same as volume control. So you set a respiratory rate at 20 and the patient can take breaths that count towards that 20. But let's say the patient isn't taking any breaths. 20 breaths per minute. That means one breath every 3 seconds. And if the patient doesn't breathe in 3 seconds, that triggers the patient or the ventilator to give the patient a breath. So time is the trigger. Every 3 seconds, that patient should get a breath because I set the respiratory rate to 20 breaths per minute.

[00:23:41]And in pressure control, the target is the pressure you're setting. So you're setting a pressure. Again, let's say it's 20.

[00:23:49]And you're telling the ventilator that you want them to give 20 millm of mercury with each breath. And that's what the ventilator is going to target.

[00:23:56]It's going to target 20 mm of mercury.

[00:23:59]All right. So then how does it cycle?

[00:24:00]How does it end the breath? Well, time as well because each breath, and this is a more advanced setting, but each breath only lasts a certain amount of time, right? So let's just say I'm just making this up for the sake of easy numbers, but let's say that you said the breath can last for 2 seconds, right? The ventilator will cycle or end that breath at that 2 seconds that you set it. And ventilators are smart. They let the patient also contribute to some of these things. If the patient wants a longer breath or a shorter breath, but not to too much because this is ventilator desynchrony, which we talked about in some of these other videos that we'll link in the video uh video description, um it can cause ventilator desynchrony or the patient not cooperating with the ventilator. But in pressure control, the target is what you set, right? It's going to target a certain inspatory pressure. So if we think about the scalers then if we go down to the scalers um this is the pressure on the y-axis verse time scaler this is zero pressure and then this is all time this is the flow verse time scaler this is zero flow and this is the volume vers time scaler and this is zero volume versus time scaler is very similar for all intents and purposes is pretty much the same uh it has the same look between volume control and pressure control. All right, it looks the same.

[00:25:22]And what it is is this is a single breath. Every triangle is one breath.

[00:25:27]And what happens in this breath is the volume goes up, right? It's positive.

[00:25:30]This is inspiration or this is when the ventilator is giving a breath. And you get to whatever you set, right? 400 cc's, 500 cc's the title volume. And then the volume starts to go down.

[00:25:41]That's when the patient is expiring or breathing that air out, right? And this is going to be your whole breath, your title volume, 400 cc's. They inspire to 400 cc's and they breathe it out and it should go back to zero after each breath because you are expiring the same amount of title volume that you inspired. And if this doesn't happen, you can get breath stacking and some of these other things. We actually made a video on it.

[00:26:04]We'll link it in the video description.

[00:26:05]Uh auto peep breath stacking air trapping where we talk about uh what happens when you're not expiring all the air each time. Yeah. And that's each breath, right? This is breath one, breath two, breath three. You inspire, right? Breathe. Ventilator gives the breath. Then you expire or breathe out all that air. It goes back to zero. And this is your title volume or how many cc's of air you're getting with each breath. Same thing, inspiration, expiration.

[00:26:32]And these again look the same between volume control and pressure control. The pressure and flow scalers look different between the two though. And this is what pressure controls looks like. And it's all about the target, right? In pressure control, you're targeting a pressure. So you get this flat top because you're saying, "I want it to be 20, right?" So the ventilator says, "Great. This here 20." So the ventilator cranks up the pressure with each breath to 20 and it just leaves the pressure at 20. So you get this flat top and that's just sitting at an inspatory pressure of 20.

[00:27:07]Then when the breath's done, it drops back to not quite zero here because this is the peep which we talked about in uh that other video that we mentioned the introduction. Um so we won't go into it here as much. Um but every breath, right? So that's breath one. Breath two, it goes straight back up to that inspatory pressure of 20 you set. It leaves it there for the whole breath and then it drops back down to the peep.

[00:27:31]That's breath two. Same thing for breath three. And that's why you get this flat top because it's a constant pressure that you set, right? You're like, I want this pressure to be 20 mm of mercury for the whole breath. That's what the ventilator targets and that's what it keeps it at for the duration of the breath. There's no in between, you know?

[00:27:48]It doesn't ramp up and ramp down. It just goes straight up to 20 cuz that's what you set. It stays at 20 for the breath. When the breath's done, it goes back down, right? Breath starts again, straight up to 20, stays at 20 for the whole breath, back down.

[00:28:02]The flow that results from that looks different in pressure control than volume control as well. Right? Um the flow here is going to be dependent on how that pressure was given. Right? So the pressure just ramps up to the pressure of 20. So flow starts at zero, right? This is when there's no breath being delivered. There's no inspiration or expiration going on. And all a sudden the ventilator gives the 20 mm of mercury and the flow goes way up, right?

[00:28:31]and then it stays at 20. So if you picture what this looks like because this is the pressure doesn't slowly ramp up. The pressure just goes to 20 and keeps it there. So that initial up to 20 creates this steep up slow for flow. And then as it holds it at 20, the flow actually starts to slowly decrease. It's still positive. You're still getting flow into the lungs, but it starts to decrease up until that breath is done. Right. So this here lines up with when the breath ends. So at this point there's no more inspiratory pressure being given. So it drops down to negative flow because the patient starts to breathe out. So this here is inspiration. This here is expiration cuz the patient is breathing that air out. So there's negative flow.

[00:29:20][gasps] Inspiration. And then I'm blowing out expiration. So there's negative flow up until the breath is over. And then there's zero flow cuz there's no inspiration or expiration. And same thing, the pressure starts, it gives a pressure to 20. So the flow shoots up quick. The pressure then stays at 20. So you're still getting a breath in, but it's not you initially get a [snorts] and then you start to keep that pressure constant. So the flow slowly decreases while it's still going in until the breath is done. And then you start to expire. [sighs and gasps] >> [sighs] >> Right. So, inspiration, expiration, inspiration, expiration. And that's why you get this triangle flow for pressure control because you're getting the set pressure that's cranking up to the pressure you want. And then it's staying there, right? That's the pressure scaler staying there. And as it stays there, you don't get this huge increase. The flow is still positive, but it's kind of ramping down until that pressure is done. All right? So, this is characteristic of pressure control. Um, you get the flat pressure top because that's what's targeted and the flow does this huge increase and then slopes back down towards zero. 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. 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.

[00:31:36]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. So if you watch those other videos, this is all going to sound very familiar. If you haven't, uh, this might sound not as familiar, but hopefully you have a good foundation. So this is part of our ventilator ventilator series. As we've me as we've mentioned, we have done a handful of ventilator videos including VC and PC scalers in different videos.

[00:32:22]We also, this is our pulmonology playlist. Also have talked about auto peep breath stacking, air trapping.

[00:32:28]We've talked about double triggering, premature cycling, breath stacking, flow starvation, uh introductory concepts.

[00:32:34]So, uh again, we'll link all this in the video description. Uh super interesting videos and we'd love for you to check them out and let us know what you think.

[00:32:40]Uh today though, volume control and pressure control scalers side by side.

[00:32:46]So, these two modes of ventilation give breaths to the patient in different ways, right? So if you're on a ventilator, you were intubated, you have to select a mode of ventilation that the patient is going to receive. In adults, many times that mode is volume control. Not all the time, um, but many times, at least in the United States, I guess I can't speak for other countries, um, that is going to be volume control or VC. And it's usually assist control, volume control.

[00:33:17]Again, we'll just call it volume control uh, for the sake of brevity in this video. Another type of ventilation though is pressure control. And in the pediatric world, uh, sometimes pressure control is the go-to. And in the adults, uh, sometimes you'll find adults on pressure control as well, depending on the clinical scenario going on. But these two modes of ventilation give different scalers, right? And these are scalers. It's pressure over time, flow over time, and volume over time. And you can often identify the mode of ventilation based on their scalar. And understanding the mode of ventilation and the scalers helps you understand exactly how you're delivering that breath to the patient on the ventilator, when to use each different mode, and what might be causing different ventilator desynchrony or ventilator problems. Apologies. Um, so here we have the scaler side by side.

[00:34:06]We talked in these other videos about three different ways or things that the ventilator needs to decide every time it gives a breath. And those are the trigger.

[00:34:19]Again, this might sound familiar. The trigger, the target, and the cycle. And again, just in brief, the trigger is uh the ventilator is not a thinking person, right? It needs these start points and end points. Um it needs to know what we want it to do. And the trigger is when the ventilator decides to start a breath. What is triggering the start of a breath? And the trigger for both pressure control and volume control is time. Which makes sense, right? Because we're setting a respiratory rate on the ventilator. And that respiratory rate is going to be given over 1 minute. And if we set that respiratory rate at 20, that's 20 breaths every 60 seconds or one breath, right? Every 3 seconds. And in assist control, right, this is assist control, volume control, assist control, pressure control. In assist control, the patient can also take their own breaths. And that counts towards the 20. But if the ventilator, let's just say the patient isn't breathing, every three seconds that ventilator is going to give a breath because we said 20 breaths per minute. And that's the trigger. Every 3 seconds that go by, the p the ventilator is going to be triggered to give a breath. The target is what the end point is during that breath. What we want the ventilator to target during that breath.

[00:35:37]And in pressure control, that target is the pressure we set. We told the ventilator that we want it to give a certain pressure each breath. So that's what it's going to target, right? We set, let's say it's pressure control, and we set the inspatory pressure at 20 mm of mercury. That ventilator says, okay, every breath I'm going to target 20 mm of mercury of pressure. That's what I'm pushing in. And whatever volume that creates is the volume that creates.

[00:36:02]In volume control, that target is actually the flow. And we'll come back to why this makes sense after we go over the cycle. The cycle is when the ventilator ends the breath or cycles the breath. And in pressure control, that's time. That's time again, right? The ventilator gives we tell the ventilator that it's going to give this pressure.

[00:36:22]It's going to target this pressure over a certain amount of time. And when that time is done, the ventilator stops giving the breath. All right. In volume control, that cycle is actually the volume, the title volume, how many cc's or milliliters of air the patient is getting with each breath. And that's why flow makes sense, right? Cuz flow is cc's over unit time. Let's just say second, cc's per second. So, if we set a title volume, if we say we want the patient to get 400, let's say 500 cc's per breath, and we're just making up numbers here, but let's just say that breath uh is going to be over 2 seconds.

[00:37:00]That means we want that ventilator to flow. Flow is the um cc's per second of air the ventilator's pushing in. So, we want that ventilator to give 250 cc's per second of air with each breath because we know then that it'll get to 500 cc's and then it will cycle. It'll end the breath, right? It'll say, "I got to 500 cc's. I'm ending the breath." But what it's targeting is actually the flow. Um, but it bases the flow on the title volume that you set for the patient.

[00:37:31]And again, if this may doesn't make a lot of sense or if these this is all foreign concepts to you, definitely check out those two other videos linked in the video description. So the what it is targeting and how it is cycling determines the scalers that you're seeing. So if we go up here, right, we said that the target for each breath in pressure control, so this is going to be pressure control uh on the left and on the right is going to be volume control. So he said the target in pressure control is actually the pressure that we're setting. So this is the target. That's not how you spell target. Good enough. This is the target.

[00:38:11]In volume control, we said the flow is the target, right? If you remember target, we said the flow is the target.

[00:38:19]So in volume control, this is the target. And you might know, I don't know why we keep spelling that wrong. You might notice um something and that is that the target in each mode of ventilation, and we're going to erase this just so this doesn't confuse people cuz it's not related. Um you can see the target in each mode of ventilation creates this flat top, right? In pressure control, you get the flat top for the target because it's targeting the pressure. and volume control, you get the flat top and flow because it's targeting flow. And why that makes sense is the target that the ventilator is going to, it targets that and then it just holds it constant for the breath. So in pressure control, let's just say you set the pressure, the inspatory pressure, we'll just say IP, you set it at 20 mm of mercury, and that is what the ventilator is targeting. So each breath, it just shoots up to 20 mm of mercury, right?

[00:39:11]This is pressure versus time. So this is 20 mm and it just holds it there for the duration of the breath and then just releases the pressure and it goes back down. In volume control, you're setting a title volume and the ventilator is doing some math to figure out the flow it needs to give that title volume and then with each breath it ranks ranches up to that flow. Right? So this is flow and let's just say just making stuff up is 250 cc's per second and it just holds the flow there and then when the breath is done it releases the flow and it shoots back down. And as we talked about in the other videos this is expiration when it's going uh back to uh uh when expiring out off all the air.

[00:39:53]So the target of each mode creates the flat top scaler and then that means the other one isn't flat topped. It's a it's a uncontrolled variable that results. So in volume control you can see that the pressure scaler ramps up because this is an uncontrolled variable. The ventilator is going up to a certain flow and it's leaving the flow there. And as that flows into the lungs, the pressure in the lungs get higher, higher, higher until the flow stops at which point that pressure drops way back down until the next breath. All right? So that's why the pressure scaler in volume control ramps up. Whereas the pressure scaler and pressure control is that flat top because in pressure control that's the target.

[00:40:38]All right. Same thing for flow and pressure control. Right? So the pressure is the target. Thus the flow ramps up when it gets to that pressure. When the pressure is ramping up then it holds the pressure constant in pressure control.

[00:40:54]So the flow is still positive, right?

[00:40:56]you're still getting positive flow into your lungs, but um it holds it constant.

[00:41:00]So that flow isn't as um robust. It starts to slowly decrease until expiration. And again, we go into more detail um in those other two videos. And then the volume scalers for both pressure control here and volume control, you can see are pretty much equal because you're getting uh inspiration and expiration for each breath. Inspiration, expiration.

[00:41:23]uh and that volume that goes in and out should be the same right the same volume that goes in should come out independent of the mode of ventilation. So the big differences in scalers for mode of ventilation are the pressure scaler and the flow scaler and what to remember is the target that the ventilator does for each different mode. So in pressure control remember the target is pressure.

[00:41:49]So you get the flat top for the pressure scaler. In volume control, that target is flow. So you get the flat top for flow. And if we go up here, pressure control, you get the flat top for pressure. Uh volume control, you get the flat top for flow. Hey everybody, and welcome to Whiteboard Medicine. We appreciate you checking out the video.

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