Mechanical Ventilation Explained Clearly – Ventilator Settings & Modes (Remastered)


welcome to another MedCram lecture we’re going to talk about mechanical ventilation and this is meant to be a introduction to mechanical ventilation so if you’ve never done mechanical ventilation before we’re going to introduce you to the basics so you can go in and actually feel competent about managing a patient on the ventilator this is often a daunting task because typically these patients are critical but actually the basics are fairly graspable and this is a series that’s going to actually go through a number of different lectures and we’re gonna start with the basic starting right now the first thing you’ve got to know is you’ve got another definition of some of these things okay so you’ve got the patient then you’ve got this thing coming out of their mouth that’s the endotracheal tube we’re gonna show this a little bit more later and then you have it hooked up to a big machine with a bunch of knobs on it and dials and output this is what we know as the ET tube that’s the endotracheal tube and then finally you’ve got the actual ventilator that’s important to know because sometimes people are intubated that means we put a tube down into their mouth because they need airway protection in other words because they can’t protect their airway they can’t protect liquids and solids from going down their airway work that stuff shouldn’t go and because of this it’s not too comfortable we’ve got to sedate them and when we sedate them we’ve got to put them on a ventilator so that might be one reason why we would have to do this the other reason is because they can protect their airway okay but they just can’t breathe on their own they’re struggling to breathe and so we help them out with the mechanical portion of breathing and that’s where the ventilator comes in and the way we deliver that is through the endotracheal tube so it’s kind of important to know what an endotracheal tube looks like and the basic is pretty much the same all the way around it’s this long tube kind of looks like this and that’s the part that connects to the ventilator this is the part that goes inside the patient and actually you’ll see that there is a balloon on the end of that endotracheal tube the thing that allows you to blow it up it’s a little thing that goes up the pilot part comes out and it’s like a little pilot balloon that you can kind of feel what the pressure is and then there’s a little port where you can inject air into it so when this goes down and you intubate somebody goes into their mouth past their vocal cords specifically and down into the trachea so the vocal cords usually end up about right here and so this is going down into somebody’s trachea okay and then usually it branches off you’ve got the left and the right mainstem bronchus okay so here you have the endotracheal tube going down now this balloon gets inflated here so that stuff that might make it down here doesn’t go past and go into the lung this is called airway protection and we blow up the balloon here after we intubate them to make sure that that happens now in some versions of this they’ll have like a little device right here that also comes out the purpose of that is to suck secretions that might come up and go out and that’s subglottic suctioning that’s kind of an option but this is the basic anatomy of an endotracheal tube now of course we just talked about the ventilator that’s got a bunch of buttons and whistles and things and we’re gonna talk about them a little bit okay so going back to our patient again we’ve got our endotracheal tube we’ve got our ventilator so what’s the purpose of this ventilator the purpose of the ventilator is to maintain homeostasis between the dew gas concentrations that we’re talking about here which is carbon dioxide and oxygen okay so oxygen is being put into the patient and carbon dioxide is coming out and for the most part we want to keep those close to normal there’s some exceptions to that here’s the point though there’s many different ways to put air into somebody okay we can say we’re gonna put air into somebody based on volume so we’re going to put a certain X amount of volume into somebody and then let it come back out that’s one way of doing it another way of ventilate somebody is saying we’re going to inflate them to a certain pressure so we’re gonna have this ventilator put a certain amount of pressure into the patient and then when that pressure is released then it’s gonna come back out so we can do that now we can do it at a certain rate we can do this fast and we can do it slow okay so in other words how many breaths per minute we could also adjust the flow rate so in other words yes we can port a certain volume in but we can give that volume slowly or we can give that volume very quickly the other thing that we can do is we can decide how much pressure to leave in there at the end of when we put the air in and then we can decide how much pressure to leave in there after we’re done putting the air in finally we can decide how much oxygen we want to put in there we can put a lot or we can put a little now just to further complicate this just to kind of see where we’re going with this we can have the ventilator be in charge of when the patient gets a breath or we can have the patient be in charge of when they want to get a breath so think about all of these different variabilities and now you can quickly see how there are so many different ways that you can ventilate somebody and each one of these ways is a different mode of ventilation you may have heard of these before like AC or simv or pressure support or CPAP these are all different modes and we’re going to go through some of these modes and show you how this is working okay so here’s our system over here we’ve got the ventilator here we’ve got the tubing that goes to the endotracheal tube down into the lungs and we’ve got our balloon here filled with air to make sure nothing else gets down there and we’re ventilating our right lung and our left lung so let’s talk about the first mode of ventilation and this will become important later the first mode that I want to talk about is AC okay the other way we call it as assist control the other name for it also is continuous mandatory ventilation or CMV now this is the most common mode of ventilation that you’ll see especially on a medicine floor or medicine units the key here is that the patient triggers the vent how does that happen well the patient takes a breath in and therefore there’s a negative pressure here which causes a negative pressure to be sensed here at the ventilator the other way you could sense it is by flow if there is a flow that actually goes through here by the negative pressure now as soon as the ventilator picks up on that negative pressure it’s going to deliver a specific volume and so there’s an actual dial on here where you can actually turn the knob to a specific volume or you can enter it in and that volume can be anywhere from 500 CC’s all the way up to 600 cc’s usually the ideal way of ventilating somebody would be around eight milliliters per kilogram ideal body weight anyway whatever that volume is it’s good to liver that specific volume in AC mode ventilation now the patient can trigger it you could also set up a backup mode or a rate what does that mean if I set the rate to for instance 12 because there are 12 five-second intervals in one minute that means every five seconds the ventilator will give a breath to the patient of a specific volume only if the patient does not take a breath if the patient is breathing above 12 then the ventilator will only give breaths when the patient triggers it by trying to take a breath in in other words if you set the mode to AC set in a volume and set a rate of 12 the patient can never breathe less than 12 times per minute now there’s something that you should understand about this which is very important you may recall from chemistry an equation that says P V equals n R T now in this system temperature is constant R of course is always a constant n is a constant and so the thing that you must realize is that pressure and volume are inversely proportional to themselves in other words as the volume of a gas goes up the pressure goes down if you have the same amount of gas however the other way of looking at this is compliance which I’ll abbreviate as a/c compliance is equal to the change in volume over the change in pressure which means to say that if the pressure changes a little bit and the volume changes a lot then you have a very compliant lung if you don’t have a very compliant lung it’s gonna take a lot of pressure to make just a small amount of change here’s the point the point is is that these set of lungs have a specific compliance and if you are delivering a specific volume into these lungs you are going to get a specific pressure after you deliver that volume that pressure can change depending on the compliance the point of this is is that you need to have a readout that tells you what the pressure is in that lung so you can know what the compliance is so in other words in this mode of ventilation you set the tidal volume and the ventilator will tell you what the pressure is so you’re setting the tidal volume you’re setting how much volume of gas is going to go into the lung and based on the compliance of the lung it will tell you what the pressure is if the compliance of the lung goes down then typically you’ll have higher pressures if the compliance of the lung is very high in other words a very compliant lung then your pressures are going to tend to be on the lower side now let’s make this converse to pressure control in pressure control what we’re doing is we’re setting a pressure in other words we’re going to decide how much pressure we’re going to ventilate this patient with and so as you can imagine if we’re setting a pressure there is a specific compliance to this lung depending on what state it is in and if we set a certain pressure if the compliance of this lung is very low then you can imagine we’re gonna have lower volumes however if the compliance of this lung is very high then we’re gonna have higher volumes because you remember compliance is equal to the change in volume over the change in pressure so in pressure control you can also have the patient or time triggering a set change in pressure and depending on the compliance the volume can change and so the key here is that you need to have alarm setup and you need to know and understand what those alarms mean what could happen here let’s for instance say in a pressure control situation where you’re giving a specific pressure if the compliance of these lungs somehow drop precipitously all of a sudden because of some pathology which we’ll get into you will notice that the volumes will drop you would want to know that and so you could set a alarm on the lower side of the volume so that if the volumes did go down an alarm would go off saying that you’re not ventilating conversely if you were back in our previous mode which was assist control and you’re setting a certain volume if the compliance of the lung dropped in that situation then as you would realize the pressure would start to go up because you’re trying to put a set amount of volume in to a low compliant lung and when that happens the pressure goes up the pressure would then trigger an alarm so the point here is in pressure control you’re setting a pressure and your output to read is your volume in AC it’s the flip of this so when we come back we’ll talk about the pressure volume relationship and a few more modes of mechanical ventilation

Leave a Reply

Your email address will not be published. Required fields are marked *