 Hi and welcome to nursing school explained and this video on mechanical ventilation. If you haven't already done so, I highly recommend watching my video on respiratory terms and physiology so that you have a better understanding of what some of these terms mean and a review of the physiology of normal inspiration, expiration ventilation, perfusion, oxygenation, all those things. I also recommend watching the video on artificial airways which are basically needed to to deliver this mechanical ventilation. So let's look at this. Indications for mechanical ventilation are apnea. Certainly if the patient is not breathing, they're going to need to be put on a machine to breathe for them. There can be acute respiratory failure and I also have a video on that with there might be a need to protect the airways. So if the patient is maybe sedated and they vomit frequently or they have a GI bleed and that now turns out that they are hyperbolemic and they maybe have altered level of consciousness, we might need to protect that airway and put them on a mechanical ventilator. Certainly for severe hypoxia, we need to help the patients with their oxygenation as well as respiratory muscle fatigue. So now the patient may be having an acute asthma exacerbation where they breathe so heavily for a long period of time, eventually they will tire out and require mechanical ventilation. So when we look at this, we basically have two types of different ventilation, which is negative pressure and positive pressure ventilation. Negative pressure ventilation is also called the iron lung. You might have heard that term before. And that basically is a specialized chamber that is applied around the patient's chest and it causes the air to rush into the patient's chest. So it's basically this machine that expands as almost like a second layer of the patient's chest wall and expands and causes the respiratory muscles to expand just like they would in normal inspiration and then the air rushes in. This is not used for purely ill patients. This is something that's typically used for patients with neuromuscular disorders, CLS disease or spinal cord injury. Now the other mode of ventilation is positive pressure ventilation or PPV. And this is where the ventilator pushes air into the lung. So now we have an artificial airway in place and the ventilator delivers that air through this artificial airway. And there are two types. Number one is volume and number two is pressure ventilation. And the two are just slightly different. Where volume ventilation is that there is a predetermined BT and the BT stands for tidal volume, which is basically the volume of air that the ventilator is going to deliver to the patient. So the tidal volume is delivered with each inspiration that the ventilator pushes the air in and then the expiration happens passively just like in normal respiration. During inspiration, we contract the diaphragm, expand the chest muscles, air rushes in and then expiration is more of a passive chest recoil. But the volume ventilation does not account for compliance and resistance of the chest or the patient's underlying lung conditions, which can certainly be a problem. Where pressure ventilation is a predetermined peak inspiratory pressure. So now we are delivering that volume with a certain amount of pressure and that pressure takes into account the compliance and resistance and the tidal volume varies depending on what the patient's underlying conditions are. So if the lungs are not very compliant or there's a lot of resistance in the airway, the tidal volume is adjusted to the needs of the patient and begin the provider will determine what ventilation is appropriate for the patient. Now the ventilator is a highly specialized machine and please keep in mind that this is all in conjunction with the respiratory therapists. Respiratory therapists are highly specialized in taking care of these patients and it's really all in collaboration with them so that we take care of these patients. Now nurses will typically know a basic, have a basic understanding of the ventilator settings but respiratory therapists go to school specifically to know about this, how to regulate that and all these things. So here's what the basic terminology and modes that we need to understand. So the ventilator regulates the tidal volume which is typically 6 to 10 milliliters per kilo of the patient's ideal body weight. And this is important to know because if this patient is obese, their lungs are still the same for their height, right? Their volume that the lungs contain is still normal. They don't miraculously get more lung volume because their body size has now increased. So it's always based on the patient's ideal body weight which a lot of times is determined by their height. And then it also regulates the FiO2 which is the oxygen concentration. So the ventilator can deliver anywhere from 21% of oxygen to 100%. And remember that 21% is basically room air. So the patient does not always require additional oxygen or additional FiO2 to be on the ventilator. So they can be on room air but there might be some other causes that require them to be on mechanical ventilation. And the goal usually is to achieve a PAO2 of greater than 60 or no two side of greater than 90. The ventilator also regulates the respiratory rate. And remember that that is very important in acid-base balance. And so ABGs will help us determine what the patient needs and how the ventilator settings may need to be adjusted. And so depending on hyper or hypoventilation it will help us regulate the patient's pH because we know that acidosis and alkalic states can be regulated by increasing or decreasing the amount of CO2 that we're either retaining or blowing off for this patient. So the ventilator regulates the respiratory rate. It also regulates the P, which is the positive end expiritorial pressure. And I'll explain a little bit later what that is, which is typically 5 centimeters of water. It also regulates PS, which is pressure support. And pressure support is the positive pressure to help the patient's inspiratory pressure. This usually 6 to 18 centimeters of water and again I'll get to that. The ventilator also controls the inspiration to expiration ratio. And that is basically the time frame it takes for the air to enter the lungs and to exit. And that again will depend on the patient's arterial blood gas results. And it can be anywhere from 1 to 2 to 1 to 5. And then the ventilator also has a high pressure limit. And this is important to know because when we pressure ventilate the patient, when we're pushing air into the lungs, if we deliver too much pressure too fast even, then we are running a risk of the alveolar bursting. And then we have another problem called the pneumothorax that can lead to attentional pneumothorax. And this is certainly a complication that we don't want. So the ventilator can help regulate the high pressure limit, which is basically the maximum of pressure the ventilator can generate to deliver the tidal volume for the particular patient that we've set it to. And that's usually a setting of 10 to 20 centimeters of water above the peak inspiratory pressure. As for ventilator modes, we have basically two modes, which is first, assist control and secondly, synchronized in the mandatory ventilation or SIMV. So assist control we have from our ventilator a preset tidal volume and a preset respiratory rate. And then the patient may take a spontaneous breath that's above the respiratory rate that we've set this ventilator at. And when the patient takes that additional spontaneous breath, the ventilator delivers the tidal volume. So the machine has the ability to detect when the patient is taking that extra breath and detects it and automatically delivers that tidal volume, which means that the patient can breathe faster but not slower than the set respiratory rate. And so the patient has some control over their breathing, not much, but some control. So for example, the tidal volume can be 650 and the respiratory rate, let's say, is 12. So at the minimum, the ventilator will deliver the respiratory rate of 12 per minute. But the patient may breathe at 14 or 15 or 24, whatever it might be. And so then when the respiratory rate that's above or these additional breaths that happen above the respiratory rate of 12 occur, the ventilator detects that and delivers that tidal volume. So the patient really is now breathing at 24, let's say, when the ventilator is only set at 12. And so certainly we have to look at the patient's, the whole patient picture and determine why this is happening. But what's important to know here is that there's a minimum that's required. And also keep in mind that the patient on a ventilator will need to be sedated, right? Nobody will tolerate a tube down the throat and air blowing into the lungs when they are fully awake in the lurch. These are critically ill patients. So sometimes the patient just needs to be heavily sedated where they don't have any spontaneous breaths. And so in this case, the patient's respiratory rate will be the 12, right, that we have set. But now the patient might be ready to or might be breathing a little bit faster than that. They will still with every spontaneous breath get that extra tidal volume that we have set the ventilator to deliver with every breath. So it allows the patient to have some control, but really not much. And then the second mode synchronized in the intermittent mandatory ventilation or SIMV. So let's look at this. It also has a preset tidal volume at a preset respiratory rate that occurs in synchrony with the patient's spontaneous breath. So now the patient is able to breathe between the respiratory rate that the ventilator is set at, but receives a preset FIO2 and also self regulates the respiratory rate and the tidal volume of the spontaneous breath. So the difference here is that when we have these spontaneous breaths in assist control, the ventilator delivers that tidal volume that we have set it to be at the 650 in our example with each one of those spontaneous breaths. Where in SIMV, the patient still gets the preset oxygen concentration, the FIO2 that we have set it to. But when they take that extra breath, the patient also determines how much volume of air they're taking in. So they are not getting this extra tidal volume pushed that the ventilator pushes in. They self regulate that air or the tidal volume that they're getting with those spontaneous breaths. And so SIMV is mostly used during weaning when the patient is getting ready to come off the ventilator. Because when we go from a heavily sedated patient to somebody who is starting to wake up and be able to interact with the environment, with the nurse, we can explain, we are on a mechanical ventilator, we're getting ready to take you off. And certainly we will have to deal with the patient's anxiety and nervousness and all that's going on there. But because the patient slowly starts to self regulate, it will help during that weaning process. Because we can't go from heavily sedated patients to extubation, right? That sedation medication is not going to wear off. So it needs to be a process that we're slightly and carefully slowly weaning the patient off the ventilator. So that they can eventually be extubated and regulate their breathing on their own again. And so SIMV allows for better synchrony with the patient's breathing. And it also causes decreased muscular atrophy. Because remember that the patient or the ventilation occurs because our chest wall contracts. The diaphragm contracts and all the muscles of the chest wall expand, the air rushes in. And then the expiration, like with it happens passively. But if we're completely controlling the ventilation, there is no spontaneous effort, which means that these respiratory muscles get tired, get weak, and they can atrophy. But now in SIMV, when we allow the patient to take these spontaneous breaths at their own rate, with their own tidal volume, we kind of train these respiratory muscles to take over again and strengthen them so it results in decreased muscular atrophy of those respiratory muscles. Now let's look at some of those additional terms that apply to mechanical ventilation. So number one is pressure support or PS that I already mentioned in the ventilator settings. So that is a positive pressure again here that's delivered only during inspiration. The patient must be able to initiate a spontaneous breath. And then the patient's level of inspiration determines the respiratory length, tidal volume, and their respiratory rate. And their tidal volume depends on the pressure level and their airway compliance. Now the benefits of this pressure support is there's increased patient comfort because they're really almost in charge of their breathing. There's decreased work of breathing because the ventilator pushes the air in so there's less of a need to work for that inspiration. There's decreased oxygen consumption and then there's increased endurance conditioning preventing the muscular atrophy. And then we have peak positive and expiratory pressure. And this is the positive pressure that's applied during exhalation. So now when the patient exhales was still pushing in a little bit of volume or a little bit of pressure so that the alveoli stay open. So the difference between pressure support is that occurs during inspiration and then peak is the end expiratory pressure happens during exhalation. And the benefits of that is it improves the oxygenation because the alveoli have a longer period of time where they stay open and get aerated. It prevents an electricis because we know collapse of the alveoli causes an electricis and therefore it improves gas exchange because now the alveoli are held open longer and there's one room for that gas exchange to occur. And it also decreases the need for increased FIO2 so the patient might need a lower level of oxygen to have the same oxygen saturation or PA02. Now this is a classic setting in ARDS. This is where the lungs are completely drowning you can call it in that extra fluid that's accumulating because the cytokine storm and all these inflammatory markers and peep will help push that fluid out of the alveoli and keep the alveoli open to allow for the gas exchange. But we have to be cautious if the patient has increased intracranial pressure if they have decreased cardiac output aka low blood pressure or if they are hyperbolemic which also means that they have low blood pressure. And the reason for that is because now that end expiratory pressure that we're applying takes up space in the patient's just cavity and there's only so much space available. Now if we take up that space with this extra peep with this extra pressure there is less pressure or less room available for anything else that happens which can affect the blood return from the inferior vena cava and therefore cause hyperbolemia or cause hypotension. Therefore if the patient already has low cardiac output or is hyperbolemic peep is really contraindicated because then we don't have to help the patient's blood pressure because that peep is taking up the space in their thoracic cavity. So really we need to stabilize the blood pressure first and then apply the peep or apply the peep first and then worry about fixing the hyperbolemia and the cardiac output again depending on the patient's individual status and what is going on what is the need reason for the mechanical ventilation. And then over here let's look at a few more other terms and you've probably heard of CPAP which stands for Continuous Positive Airway Pressure and that is very similar to peep and it is a continuous delivery of oxygen during spontaneous breathing. So now we might have a ventilator setting where there's no set respiratory rate there might be a set tidal volume but the respiratory rate is not really given although the ventilator will always have a preset respiratory just as a backup. But this is a continuous delivery of oxygen during spontaneous breathing which is also why it's used during what patients with sleep apnea. So it's this continuous oxygen that is being delivered and it can be used as a mode for a patient with an endotracheal tube or a tracheostomy or via a face mask such as we see in patients with sleep apnea. Now the problem here is that it increases the work of breathing because the patient now exhales against this continuous pressure that is being applied. So it's almost as if you are blowing out air and somebody is pushing air in at the same time. So there's increased resistance, increased work needed from the chest muscles and the diaphragm to push the air out during the exhalation. And then we have another set of positive airway pressure which is bi-level positive airway pressure also known as BiPAP. And these two levels basically mean that there is different positive pressure levels during inspiration and during expiration. So here it's continuous airway pressure but here we can set it to where the patient receives a different positive airway pressure during inspiration and expiration. And this is a non-invasive machine. It can usually be done via a face mask but it has to have a tight seal that usually means it almost looks like a BVM that is applied around the patient's mouth and nose or there are now machines where there's a nasal mask only in case the patient cannot tolerate the face mask. Now there is no control of the respiratory rate so the patient must be able to cooperate and spontaneously breathe. The machine detects the inspiration and expiration and then delivers this positive pressure during inspiration and expiration that the machine is set for. This is usually indicated in patients with COPD, heart failure, who might be in pulmonary edema but would need to again push that fluid out of the alveola to allow for gas exchange. It might be used in acute respiratory failure almost as a precursor or when the patient starts to maybe get a little bit into that respiratory failure state it might be something that we want to try before mechanical or ventilation or in the tracheal intubation and also is often used after extubation. So if the patient has been intubated for a while we want to support them with a little bit of positive pressure so that they can kind of get used to their spontaneous breathing and maybe their chest wall muscles are tired so that pressure will help with the chest recoil. But it is contraindicated if there is altered level of consciousness right because now the patient is not really in control over their breathing and we're running a risk that they become apnoic. We need a spontaneous breath to be able to initiate the biopap and if the patient is altered we can't really guarantee that. The other reason that biopap is contraindicated is there's a lot of secretions because now we don't have the airway protected and we're at risk if there are a lot of secretions and that positive airway pressure is blowing air into the patient's mouth and nose at the same time that the secretions could be pushed down into the lungs and then we have aspiration and a whole set of other problems. And then one more term that happens it's called extra corporal membrane oxygenation also called ECMO that's exactly what it means. It's extra corporal outside of the body membrane oxygenation so it's basically a machine that now filters the patients or oxygenates the patient's blood. It's like a cardiac bypass so but now we are not removing the blood because we're doing physical work on the on the heart such as in creating a bypass graph but the machine partially removes blood infuses oxygen just like the lungs would removes the CO2 just like the lungs would and then returns the blood back to the patient. It requires systemic anti-coagulation because the blood is pumped out of the body and there's a high risk for clotting. Now this is basically almost kind of like a last-ditch effort this is somebody who is severely severely ill who's had acute respiratory failure for a while who's been on a ventilator but nothing none of these positive pressure modalities are helping with their oxygenation. Their alveoli are completely congested and no air exchange is happening with the patient's own lungs. Now we need to use this machine to basically bypass the patient's lungs and use the machine to help with the gas exchange in the hopes that then the lungs can recover and then the patient can come off this machine. Now this is a highly specialized machine that you need special training for of course and usually a perfusionist is involved in caring for these patients because they're so critically ill and require a lot of critical care and attention. So thank you for watching this video on mechanical ventilation. I know it's a long one but I hope it's helped you understand the different modes of ventilation the ventilator settings and so forth. Now by no means this is designed for any kind of critical care nurse or respiratory therapist but it's just to help you gain a better understanding of the basis of how mechanical ventilation works so that you can apply it to your nursing school and your clinicals and maybe have a better understanding if you get a rotation in the ICU or any of those units where you might encounter patients like that. Thanks for watching Nursing School Explained. See you soon.