High Frequency Ventilation// Neonatologist explains the BASICs

He gave the example of a dog panting rapidly on a hot day like And welcome to tala talks nikki where we break down medical concepts And make them super easy for you to understand and to retain them forever Today we're going to go over high frequency ventilators We were going to take a break from the whole ventilators and gases and everything But so many of you have asked us to go over high frequency ventilation that we decided to throw one in early Before we continue, please remember to like and to subscribe to our channel And please let us know what you'd like us to review next at this point We're pretty much exclusively listening to your requests and taking it from there So we started going over this lecture and then we realized once again that it would be a lot more palatable If we broke it down into two parts So today we're going to go over one the generalities of high frequency ventilation Two the definition of high frequency ventilation Three gas exchange in conventional ventilation, which is really important for you to understand as well as four gas exchange in the oscillator Then in the next video we'll go over clinical applications of the oscillator As well as just some more kind of clinically relevant Aspects of it. So the settings that we start on how we wean how we escalate dependent on gases So make sure that you watch the follow-up video in a couple of weeks, right? So number one some general information about high frequency ventilation So when we talk about high frequency ventilation, we are talking about either really the oscillator or the jet ventilator Both of these ventilators use really rapid ventilatory rates So very very rapid breathing rates, which is why you hear them banging away like this They also use really small tidal volumes In fact, the tidal volumes that are generally used are smaller than the dead space of a baby or of a body Which is a very weird concept, but i'm going to come back to that in a bit When you examine babies on the oscillator The combination of the really high rates and the really tiny tidal volumes will make it look like the baby's chest is vibrating So just wiggling really really rapidly in fact that wiggle on the chest is something that we look for and We evaluate to see whether the settings are sufficient for the babies. And again, i'll come back to that in a bit Even though oscillators and jets use a very similar form of gas exchange The main difference with oscillators is that they use a constant distending pressure to keep the lungs open So the oscillators are very much considered an open system So they have a constant mean airway pressure keeping the lungs open rather than this constant up and down Between the pip and the peep the other big difference between oscillators and jet ventilators Is that oscillators use active inspiration as well as expiration for their gas exchange Jet ventilators are kind of like a hybrid between high frequency as well as conventional ventilators And they do use a pip and a peep as well So there is that constant opening and closing of the lungs jets deliver pulses of gas into the trachea With active inspiration and passive expiration as opposed to the active inspiration and expiration with the oscillator This talk is going to focus more on oscillators So i'm going to concentrate more on that right now in the future. I'll dedicate a whole separate video to jet ventilators Now let's go over number two the definition of high frequency ventilators the FDA Defines high frequency ventilators as any machine that delivers a rate of above 150 breaths a minute which is basically divide 150 divided by 60 Is about 2.5 breaths a second so for example on the jet we'll start babies anywhere about On a rate of about 360 and we go up all the way to 660 Breaths a minute the unit we use to describe the frequency is hertz which is cycles per second so for example if on the jet we are Putting the baby on a rate of 360 which is 360 breaths per minute Then that's 360 divided by 60 which is six breaths a second So that baby is on six hertz If the baby is on a rate of 420 breaths per minute, then that is equivalent to seven hertz We don't use hertz as much in the jet as we do on oscillators Normally when we put babies on the oscillators, we use slightly higher rates than we do on when we put babies on the jet so for example a preemie baby on the oscillator we would use Rates or frequencies somewhere between hertz of 12 to 15 for a full-time baby We may use anywhere between 8 and 12 hertz. Sometimes we go even lower than this, right? So number three And this is leading up to discussing exactly how oscillators work So I think that even though you probably definitely don't need to know this to be able to use an oscillator It will again help you understand the system a lot better and hopefully help you retain it better first Let's talk about the gas exchange during regular breathing or negative pressure ventilation Which is basically the same form of gas exchanges during a positive pressure ventilation, which is what we use on the conventional ventilator This would be a really good time to go back and watch the two videos on regular ventilators Just so that you can kind of remind yourself and so that you have that basis before we move onwards so during negative or positive pressure ventilation the two main forms of gas exchange are convection or bulk flow and then Diffusion during inspiration if the baby is on a breathing machine, then the air gets pushed into the lungs this is the convection part of gas exchange or basically the Bulk flow of the gas then as the air gets into the tiny bronchioles and the alveoli or the respiratory part of the lungs Then diffusion takes over as the main form of gas exchange Diffusion as you all know is the movement of a gas or a liquid from an area of higher concentration To an area of lower concentration what you need to realize with this type of gas exchange specifically with a convection or the initial bulk flow of the gas exchange is that Until the air reaches the alveoli Every single little area of the lung needs to be filled including areas that are considered dead space So what are the areas of dead space in the lungs? They're basically any area of the lungs that don't directly take part in gas exchange So those areas where the oxygen isn't going directly into the blood and we're not getting carbon dioxide directly out of the blood Obviously, there's the anatomical dead space. So the trachea or if you have an endotracheal tube the Larger bronchi the smaller bronchioles that are the respiratory bronchioles. These do not directly take part in gas exchange They're just there to provide a conduit for the air to reach the alveoli as well as obviously to greatly increase the surface area of the lungs as an aside That's why when babies are intubated and they have their endotracheal tube in we generally cut the endotracheal tube to a shorter length Because we want to decrease the amount of dead space that the air has to travel through before it reaches the alveoli In addition to the anatomic dead space There is also alveolar dead space so this happens when for example You have the oxygen that goes through the trachea the bronchi the bronchioles and then reaches the alveoli But for whatever reason that alveolus is not perfused So there's no blood supply going to that airspace So that oxygen is just like sitting in that alveolus and it's got nowhere to go So basically this is kind of a type of dead space because gas exchange can't happen here Altogether the anatomic as well as the alveolar dead space is considered the physiologic dead space And again as air is being pushed in during positive pressure ventilation or sucked in during normal breathing then every single tiny area of dead space needs to be filled as part of either the convection and the bulk flow of the gas at the beginning or Unfortunately at the end where the air just kind of ends up in alveoli that aren't necessarily being perfused This is just a necessary byproduct or kind of a waste of the gas exchange in regular breathing In adults the anatomic dead space is about 2.2 milliliters per kilo In babies that number is larger and in micro preemies It may even be larger than that, but in babies the average is about 3 mls of dead space per kilogram So logically based on everything that i've said you would expect that the tidal volumes that we give a baby or that the baby is naturally breathing and remember Again, the tidal volume is the amount of air that goes in and out of the lung with each breath So you would expect that tidal volume by definition to be higher than the dead space volume Because logically if you give a baby a tidal volume of 2 mls per kilo Then all you'll be doing is filling the dead space just filling up the trachea and the larger bronchi And actually not ending up with any gas exchange So that is why generally when babies are on the ventilator We'll give tidal volumes anywhere between 4 to 6 mls per kilo Sometimes we go all the way up to 10 mls per kilo Right, so now let's talk about gas exchange and oscillators and this is where it becomes really difficult to understand Because as we said at the beginning of the tour, we generally use absolutely tiny tidal volumes in oscillators The tidal volumes are actually smaller than the dead space volumes of babies So how is gas exchange possibly working? well In 1915 I mean over a hundred years ago during world war one Yandel Henderson published a paper called the respiratory dead space In it, he discussed that there may be a possible mechanism for gas exchange in humans Where humans are breathing a tidal volume that's less than the anatomical dead space He gave the example of a dog panting rapidly on a hot day like So if you think about it a dog breathing very rapidly and very shallowly Is actually a very good model for an oscillator And he argued that if dogs are able to breathe so quickly and with such tiny tidal volumes And still manage to breathe successfully Then there must be a different type of gas exchange happening The way that Henderson showed that gas exchange can happen differently and this is brilliant Is by getting a long tube about a meter long a transparent tube and a couple of centimeters circumference or diameter rather he showed that if he Had was blowing smoke down the tube if he gave little very rapid Puffs of smoke down the tube the smoke doesn't completely fill the entire tube But rather there's a sharp cylinder down the center of the tube and the tip of that smoke cylinder Will come out before the entire tube is filled with smoke Whereas he showed that if he allows the smoke to be breathed out a lot slower Then the entire tube is filled with smoke before it comes out at the other end A lot more research as you can imagine has been done into the physics of gas exchange And As it transpires not everything that henderson postulated was completely right A more recent article was published in the new england journal in 2002 And it details all the different possible mechanisms of gas exchange during high frequency ventilation The references below so please go check that out if you're kind of interested in the whole physics of medicine But in the meantime Just realize that what henderson showed was that there is a way for gas exchange to occur with absolutely tiny tidal volumes Okay, the other huge concept you need to understand to get high frequency ventilation Is that for all these alternative methods of gas exchange to occur? most ideally The rate or again the frequency that the tidal volumes are deliver at Should depend on the size of the body If you can catch the natural frequency or vibration of that body Then the gas exchange is going to be a lot better so each body has its own natural vibration frequency a natural frequency is The frequency that a body tends to oscillate at Without any external pressures on it That sounds kind of ridiculous. But if you think about it, you instinctively know this So for example think about stringed instruments and realize that we use the word pitch To refer to the audible noise that a frequency makes so frequency and pitch are basically kind of referring to the same thing So think of a huge double bass like that huge stringed instrument and think how low that pitch or that frequency is like Compare that to a much smaller instrument like a violin which obviously as you all know functions at a much higher pitch or frequency That's because the natural frequency of a smaller object is higher than the natural frequency of a larger object Which is why when we use oscillators the smaller the size of the baby the higher the frequencies that we use So for example, if you have a 500 gram micro preemie, you're going to be using frequencies of 12 to 15 hertz Whereas if you have a big term baby who had a meconium aspiration syndrome or something You're much more likely to use a hertz of 8 to 10 In older kids and adults they'll use obviously with even bigger bodies Then their bodies are going to have a lower natural frequency So having a lower hertz on the oscillator will enable that gas exchange to happen more efficiently That's why and we're going to talk about this more in the next lecture We don't really change the frequency a lot when we are on the oscillator So you are just basically trying to optimize the gas exchange Okay, that was a lot of physics But again, I like talking about it and I really hope it will help you understand what high frequency ventilation is all about So absorb that and then stay tuned because in the next video We're going to talk a lot more about the specifics of when and how an oscillator is used In the meantime, please remember to like and to subscribe and let us know what you'd like to hear about next. Thank you