All right, and welcome back to our next lesson in our series on hemodynamics. And in this lesson, we're going to talk about everybody's favorite working in the ICU, which is our invasive monitoring. So as we all know, Invasive monitoring is very common in the ICU. Especially these days, we have very sick, very complex patients.
And the various forms of invasive monitoring that we have available to us can really tell us a lot about what's going on with our patients, with their hemodynamics, how their hemodynamics are responding to the various treatments that we're putting in place. as well as how their blood flow is being impacted by other forms of treatments that we're doing for them. So there's a lot of valuable, great information that can come from the various invasive monitoring techniques that we have available to us.
But at the end of the day, just remember that it all goes back to the basics. So just because certain numbers are telling you certain things on the monitor, you still need to look at your patient and see. Does the patient line up with what you're seeing on the monitor?
You could have great numbers on the monitor and your patient not look so hot, and there's probably something going on. On the flip side, the numbers could look awful on the monitor, but look at your patient. Is your patient fine? Are they doing okay? And if so, it might not be telling you the full story.
All right, so we're going to talk about a few different types of invasive monitoring. The first one that we're going to talk about is our CVP. So our CVP is going to be giving us a representation of our right atrial pressure, or basically the venous return to the heart, essentially our preload.
And this is going to be the right heart preload. The nice thing about CVP is if you have a central line in place, You can simply use one of the lumens on your central line in order to obtain a CVP. And when you have a patient that you're monitoring their CVP up on the monitor, you're going to see a waveform that looks something like this. Now, when we talk about the normal values for CVP, it really depends on the source that you're looking at. But on average, typically, you're going to be looking for numbers to be between 2 and 10 millimeters of mercury.
Now like I said since the CVP is essentially measuring our preload and if we think about situations in which our CVP or our preload is going to be increased these would be things like fluid overload. So if you had too much fluid, you would have a high preload. Another situation in which you might see an increased CVP would be is if your patient is having cardiac tamponade.
So in this scenario here, the tamponade is preventing the heart from being able to beat effectively. So we are going to get a backup as blood is not passing through the heart. So this will increase our CVP.
And another situation in which you might see an increased CVP would be in right heart dysfunction. So similar concept with the cardiac tamponade, the right heart is not functioning appropriately, therefore it's not moving the blood. across to the lungs and into the left side of the heart.
Therefore, you're going to get a backup heading into it. Now on the flip side, some cases in which you might see decreased CVP or decreased preload would be things like dehydration, volume loss, and this can be either fluid or blood, and lastly, venodilation, and this is essentially dilation of the veins that cause pooling of the blood, not allowing it to be returned to the right atrium. All of these things are going to contribute to a decreased volume returning to the heart, therefore a decreased preload, and you will be able to measure this with a decreased CBP. All right, so moving on and talking about the different forms of invasive monitoring, the next one that we are going to talk about is the arterial line. So the arterial line, or A-line as it's commonly referred, is essentially a catheter that is sitting inside of an artery.
And typically our common spots are going to be either our radial, our femoral, sometimes you can do a brachial or even a pedal A-line. But it's going to give us a direct and more importantly a real-time representation of systolic and diastolic as well as giving us a calculated mean arterial pressure. And the real beauty of the A-line is... the fact that it is real time.
So this is great if you're on any sort of vasoactive medication that you need to see real time what are the effects of this medication and where is my pressure currently at. Now typically the waveform that you will see will look something similar to this. Now, not the greatest of drawings, but essentially this is going to be our systolic blood pressure right here. We're going to have our diastolic blood pressure.
And then here you're going to have your dichrotic notch. And it's going to be important that you evaluate this waveform to ensure that you're getting an optimal and accurate reading. If the waveform becomes underdamped or whipped, a lot of times you'll see a peaking. very high systolic that goes significantly above the rest of your waveform.
Sometimes you also see an even lower diastolic. So when you're comparing these numbers to your manual cuff, you'll see a higher systolic. systolic and a lower diastolic.
That will be one indication that you are underdamped or not accurate. You can also be overdamped or beginning to flatten. And this is then going to, you're going to lose the nice picture of your waveform.
You may lose seeing your dichrotic notch. Your systolic is going to lower. Your diastolic may come up.
And again, it's not going to be an accurate number. which if you're titrating vasoactive medications, it's going to be important that you do have an accurate waveform. Now, if the waveform is accurate and you have discrepancies between your A-line and your manual cuff, first, you obviously want to troubleshoot your A-line and your transducer and all of that is fine and taken into account. Then the A-line is going to be a more accurate representation of your blood pressure because it's directly in the artery. It's giving you a direct representation of actual pressures into a waveform and numbers that we can see on our monitor, whereas opposed to the automatic blood pressure cuffs that most monitors use are actually calculated values.
And I won't go into the complex nature of how they work, but know that It's not like when you listen or you auscultate with a manual blood pressure. It works in a different manner, and it's calculating out your systolic and your diastolic and your mean arterial pressure. So again, if your A-line waveform is good and those numbers differ from your manual blood pressure cuff, you want to be going off of your A-line because it is going to be the truer, more accurate number. All right, now moving on, the next form of monitoring that we're going to talk about is a system called the flow track. Now this is a proprietary system that is developed by Edwards Life Science.
It does require its own transducer to be used in place of the typical ones that are often used, as well as its own monitor setup. But in my opinion, it is a pretty neat form of monitoring that we have available to us. And the nice thing about it is it's...
simply uses A-lines and the setups that we use for A-lines minus the transducer, just like we do with any other patient. So we can actually get a lot more information and a better picture about our patient's hemodynamics simply from the arterial line, which before was only giving us our systolic, diastolic, and our mean arterial pressure. Now the purpose of this lesson isn't to go through all the bells and whistles of what the flow track can and can't do.
But I do want to give you a basic understanding of some of the numbers and the information that it can give to you. So this is going to be a representation of the newer model flow track. You might be familiar with the older model.
It's referred to as the Vigileo. It will give you all the same numbers, just not in as newer of a user interface. But this is our screen that we have here. On the side, you've got a series of...
options and buttons that you can select and this is all on a touch screen and there's different screens that you can flip through and everybody sort of seems to like their own particular setup and you can certainly customize things as you wish but one of the screens will kind of show you some of your values right along here and it will give you numbers through here that correspond with different values and whatever the value is that you are monitoring. And so with the Vigileo or the FlowTrack, there's really three additional hemodynamic values that you are going to be able to get from the FlowTrack above and beyond just your normal pressures that you would get with an arterial line. And those are going to be your stroke volume. or your stroke volume index. It's going to be your cardiac output and cardiac index, and then another value that we're going to talk about here in a minute, which is called stroke volume variance.
Now for the stroke volume and stroke volume index, obviously with these index numbers, you enter in the patient's height and weight, and that will give a body surface area and allows us to calculate out these index values. But the way that the FlowTrack is able to determine what your patient's stroke volume is, is they have their own proprietary algorithm that the computer and their monitor uses, and it sits there and it assesses points and values along the arterial line tracing. And what they've done is they've found a relationship between your pulse pressure and stroke volume.
And so by constantly assessing the tracing of the arterial line and looking at the patient's pulse pressure, they're then able to do calculations and determine what the patient's stroke volume is. Now on to the cardiac output and cardiac index. Now once again, we know our cardiac output is equal to our heart rate times our stroke volume. And since now we know our stroke volume...
Based on our relationship with the pulse pressure, which the flow track is able to determine, and it can also determine a heart rate based off the arterial line tracing, we now can determine what our patient's cardiac output or cardiac index is, again, all just off of an arterial line. And so the final hemodynamic value that we're able to get from the flow track is what we call the stroke volume variance. And basically, stroke volume variance is another form of monitoring that can give us an idea of a patient's preload. So just as we talked about the CVP being an indication for preload, a stroke volume variance on a patient can also tell you about their preload.
The normal value for your SVV is going to be less than 13. So there's a saying, high and dry. So if they are 13 and above. It tells us that the patient has decreased preload, decreased volume. They probably would respond to volume. And the concept behind how this is able to tell us about volume status is because of a thing called pulsus paradoxus.
And this is essentially a variation in your pulse with respiration. Essentially, with the less volume that you have in your vasculature, this will lead to a... greater variance in your blood pressure with each breath.
And to essentially draw this out, this may be something that you may have noticed on an A-line tracing on the monitor before, but Didn't think anything about it. But sometimes, and as an exaggerated example with your A-line, and these waveforms aren't going to be the greatest, but with your A-line, sometimes you'll notice variation as you're going. And you'll kind of see this up and down movement.
And these ups and downs will correspond with breaths being delivered by a ventilator. So if you think about a vent is delivering positive pressure. So as a breath is being delivered to the patient, this is going to increase.
the intrathoracic pressure. This is going to put pressure on the superior and inferior vena cava, which is going to decrease venous return to the heart, which is going to impact your cardiac output. So you're going to see a decrease in your blood pressure. Then as expiration happens, that pressure is released. The vena cava is able to expand.
The blood is able to get back to the heart and you're going to see your blood pressure rise. And the concept of Pulsus paradoxus is as you have more fluid in your vasculature, you see less variation. So if you then are depleted or low on volume, you're going to see more of this variation, which is why on our SVV, if the variation is high, it means that they are low on their preload.
Now, as great as SVV is, It does have some limitations, especially in terms of using the flow track to monitor it. And some of these limitations are going to be spontaneous breaths. So if a patient is taking spontaneous breaths, that that is going to render our SVV inaccurate.
If the patient has an open chest. Also, if they have. any arrhythmias, commonly atrial fibrillation, in which we have an irregular heart rate that is going to yield our stroke volume variance as inaccurate.
And if any of these cases do exist, there is a simple little trick called passive leg raise that you're able to do in which you raise the patient's legs up at a 45 degree angle. And this essentially gives a mini bolus temporary effects that only last until you raise the legs back down. And if in doing so you see your stroke volume and your cardiac output improve, it may be an indicator that your patient may be responsive to fluid.
All right, so that just about sums up everything that we're going to talk about with the flow track. It has the potential to provide a lot of insight into your patients, but do know that it does have some limitations. But you do get a lot of information for you.
No more invasive of a line than an arterial line, which oftentimes many of our patients have already. So moving on, we're going to move to the last form of invasive monitoring that we are going to talk about, and that is going to be our SWAN or our PA or pulmonary artery catheter. Now, the SWAN or the PA cath has had its ups and downs over the years when it comes to studies in terms of whether it is an effective form of...
monitoring our patients'hemodynamics or not, but they certainly are something that are used in a lot of environments, particularly in cardiovascular ICUs and with open heart patients. So they definitely still have their place in the practice that we can provide for our patients. And essentially what the SWAN is, or the PA catheter is, is it's a very long catheter that is inserted through an introducer. that will go in through the vena cava.
It will pass through the right atrium of the heart into the right ventricle and come out and sit into the pulmonary artery. At various points along the catheter, there are ports that enable us to either infuse medications or to get pressure readings, which can give us different pressures at different locations throughout the anatomy of the heart and the vasculature, which can give us more of a picture of the hemodynamics of our patient. So with the swan catheter, there's going to be four main values that we are able to obtain from the catheter itself.
The first one is going to be our right atrial pressure, or our CVP. The next one is going to be our pulmonary artery pressure. The next one after that will be our pulmonary capillary wedge pressure.
And finally, the last one will be our cardiac output and cardiac index. So for our right atrial pressure, or our CVP, again, the waveform is going to look just like we talked about with the CVP already, and the same normal values are going to apply to this as well, 2 to 10 millimeters of mercury. All right, now so for our pulmonary artery pressure, essentially the tip of the catheter is sitting in the pulmonary artery, and at the very tip of the catheter, there is a port in order for us to be able to measure pressure.
Typically on the monitor, you will see a waveform that looks something similar to this, and similar to an arterial line, you are going to have a systolic and a diastolic pressure with this. And the normals for that are going to be 20 to 30 over 10 to 20. And really you can think about the pulmonary artery pressure as almost being like an A-line for the right side of the heart. And if you do have an increase in your pulmonary artery pressure, it could be an indication of a few different things.
The first one could be some sort of atrial... or septal defect. You would also have an increase in patients with pulmonary hypertension. You would also see an increase if your patients were having left ventricular failure.
And similarly to when you have an increase in your CVP when the right heart is failing, if the left heart is failing, you're again going to have that backup of fluid and volume and blood that is going to create more resistance and the right heart is going to have to beat stronger in order to eject blood against that pressure. And finally, you may have an increased pulmonary artery pressure if your patient has either mitral stenosis or regurgitation. And now with this, you have either an incompetent valve to where blood is filling backwards out of the left ventricle and going back into the pulmonary vein, or in the case of mitral stenosis, enough blood is just not able to pass through that valve and causing that backup as well.
All right, so moving on to our pulmonary capillary wedge pressure. This pressure is an intermittent pressure that we are able to achieve by inflating a small balloon that sits at the end of the catheter. What this will do is this will occlude the pulmonary artery with the tip that we use to monitor pressure being distally to the balloon. This will prevent any flow coming from the right side of the heart and will give us an indirect measurement of preload on the left side of the heart. So if you think of a CVP for the left side of the heart, that is what the pulmonary capillary wedge pressure is going to be.
Once you inflate the balloon, you're going to see a pressure that looks very similar to a CVP with the waveform looking like this. The values are going to be a little bit different, and your normal range on this is going to be 8 to 12, and again, that's millimeters of mercury. And based on what your wedge pressure is, you can either be in a state where you have a normal pressure, an elevated pressure, or a decreased wedge pressure. If it's elevated, this could be things like fluid overload, could be aortic stenosis or aortic regurgitation, could be mitral stenosis, left ventricular failure, could be cardiac tamponade, or constrictive pericarditis.
Cases where you might find a low wedge pressure would be hypovolemia or vasodilation. Now, not all facilities nor all physicians will want you to get a pulmonary capillary wedge pressure, but it is important to note that if you are getting wedge pressures, that you don't leave the balloon inflated. You need to inflate the balloon, get your numbers, and then deflate it.
Because when the balloon is inflated, you are essentially creating an obstruction in part of the pulmonary artery. All right, finally, the last hemodynamic value that we are going to be able to get from the SWAN or the PACATH is going to be our cardiac output or cardiac index. Now, depending on the equipment that is being used, you can either get a continuous or intermittent cardiac index or cardiac output. The continuous cardiac output tends to be the more common types, but there are usually some of the older swans or PA caths, which you used to do boluses of fluid in order to get your cardiac output reading.
Lastly, you may come across some catheters that do have a pulse oximetry light that can give you your venous oxygen saturation, but that is something that's going to be beyond the scope of this hemodynamics lesson. Now one last important thing to note is that with all of these values that you're able to plug that information into calculations, which can give you your SVR and your PVR. Now your SVR and your PVR, which is your systemic vascular resistance and your pulmonary vascular resistance, these are going to be numbers that give you indications or clues as to your patient's afterload. Now some monitors and some setups will take all the information and you plug in any additional information that's missing into their calculations and it will spit out all sorts of values to you.
But with your SVR, you're looking for a number that's going to be between 800 and 1200. If it's below 800, this is telling you that your vessels are very dilated and you have very low resistance. And usually in these cases, you're also going to have a low blood pressure. As opposed to if you are greater than 1200, this is telling you that those vessels are very clamped down. So you have greater resistance.
And typically you're going to find... a greater blood pressure, but this is also creating greater force for the heart to beat against, which may impact your cardiac output. But this just about covers all the information that you will get from the SWAN and PACATH, as well as this concludes this lesson covering the different forms of invasive monitoring. For our next lesson, we're going to look at how we optimize treatment in order to manipulate our patient's hemodynamics.