Intensivist and Emergency Medicine Bedside Ultrasound (INBU and EMBU) - SD

Introduction

Hello, I'm Anthony Dean.
I'm the Director of the Division of Emergency Ultrasound at the University of Pennsylvania in Philadelphia, Pennsylvania in the United States.
Today we're going to be talking about the assessment of the inferior cava for volume status in critically ill patients, either in the emergency department or the critical care unit.
Without further ado, let's get going on the lecture.

Alternatives to IVC Assessment

When we consider the use of the inferior vena cava for assessment of intravascular volume or hemodynamics, it's worth considering the alternatives.
Obviously the history is one.
We can ask patients about orthopnea, PND, progression of dyspnea on exertion, and so forth, which certainly will help us.
And physical exam, we can look at vital signs, capillary refill tissue turga, central venous pressure by internal jugular assessment.
There are some serologic markers, especially of poor perfusion due to hypovolemia or intravascular volume depletion, lactate.
And for volume overload, we can look at A BNP.
Invasive techniques include the pulmonary art artery and CV catheters.
Central venous catheters are more widely used in the emergency department, and obviously pulmonary artery for catheters in the critical care units.
But both of them come with the cost of a certain expenditure of manpower resources.
They have certain well identified complications, which everyone's familiar with, and the information they provide is not universally agreed upon and accepted as being accurate.
This cardiac sono, sonography, which we're not gonna focus on this lecture, the assessment of cardiac function in patients in shock.
And then as certainly, finally, there, as some people will consider as a components to the cardiac exam, there's assessment of the veic cava, and some people use the veic cava as well, which is technically a little bit more challenging.
So today's we're, today we're going to actually focus on the inferior veic cava.

Technique for IVC Assessment

And we'll start really by talking about technique.
And the i inferior cava is really something that should be quite easy to find, but in not all circumstances, is that the case.
And then once it's found, there's some details of technique which can really enhance the information that's obtained by the ultrasound scan.
So, first of all, as with all organs, there's a longitudinal transverse plane available.
But in the case of the IBC, there's actually two windows that are very useful for us.
The first is the subxiphoid, which tends to be more widely promulgated.
It's the traditional window used by the cardiologists, which they obtained by getting the subcostal subxiphoid view of the heart, and then just fanning down inferiorly to the inferior vena cava right below the right atrium.
But the alternative, which we find in our practice is underutilized and actually more often useful because so many of our patients either have prot, truant, abdomens, or gas filled abdomens making the subi fo view hard, and we actually find the intercostal, it's often the go-to window before trying the subxiphoid.
Now, obviously in each of these, there is a longitudinal and transverse plane available.
The probe ideally will have a small footprint.
So you can either use the cardiac phase array or a small footprint curved array probe, if you have those available.
If not, then the abdominal probe could be used in the pinch.
The widely curved array probe, the linear array probe is likely to be less useful for this purpose because most patients, except for pediatric ones, are too big for the be to be sufficient depth available to see the IBC.

Identifying the Right Vessel

Now, the first thing to do, and I'm gonna emphasize this and reiterate it throughout the lecture, is to make sure you're looking at the right vessel.
And this actually is not an uncommon pitfall for people starting out with this.
But the very first thing is to identify in the transverse plane, the vert robotic, which can be seen right here.
And once you found the vertebral body, you can adjust your depth, because nothing that we're interested in is behind that.
So I usually suggest starting fairly deep, and then identify the vertebral body and then adjusting your depth.
And then obviously, there would be the two vessels right in front of it.
Here's an aorta with calipers on it already, and over here is the inferior vena cava.
If you're using the subxiphoid window, do not press too hard with your probe, or you might occlude the inferior vena cava.
Now, we're gonna talk a little bit about the difference between the two vessels.
The IVC as is ob intuitive to be obvious, is on the patient's, right, which means more to the left of the screen.
And the AOR should be on the left, patient's left the vena cava enters the abdomen much higher up, and above T 12, it's really the usually for most people, the lone vessel in the abdomen.
The venia cava is compressible.
It's usually ovoid, as opposed to the aar, which is not, the IVC has thinner walls and no anterior branches below the hepatic veins.
And if you look at this anatomy image here, you'll see that here, the hepatic veins right up here, which actually drain into the inferior cava right at the di level of the diaphragm.
Below that, there are no anterior vessels, whereas the aorta has the CX trunk and the superior mesenteric artery here.
So, if you're looking at a vessel that you see vessels arising from the front of, then you're looking at the aorta, not the IBC.
The size of the IBC is variable.
Obviously that's gonna be a major part of our assessment.
But in general, it it's potentially a larger vessel that has much lower flow.
So in order to be able to transmit the cardiac output in the same amount of time with this low pressure and low flow situation, it needs to have a bigger diameter than the aorta.
There's usually respiratory variation of which there's none.
If you're gonna put color flow on the two vessels, you'll see changes in flow, and you'll also see changes in size related to respiration.
Finally, the most important one, maybe to de-emphasize is that the impulse that some people have to try and distinguish the aorta and the IVC by positivity.
I frequently hear that the IVC is a non pulse star vessel, whereas the aorta is a pulse star vessel, and that is emphatically untrue.
IVC is also a pulse star vessel every time the heart contracts, every time the right atrium contracts, since there's no valve behind it, it pushes blood back into the IVC.
So there's B2B variation size of the inferior vena cava.
Here is a longitudinal picture of the inferior vena cava.
You can see a beating for sure.
You can see it has thin walls.
We just moved into the transverse plane, and you can see the classic view with it on the right, the patient's right, which is the left of screen here, we are longitudinal again as the clip loops, no anterior vessels.
And here we are now in transverse plane once again.
This let's we'll have a look at a couple of other images in this image here.
You can see the vertebral body, as we mentioned.
The aorta actually looking almost like it's a little bit ovoid.
Maybe there's a bit of extra pro pressure here.
Someone in low blood pressure.
And here's the inferior vena C over this side here, both pulsatile and with changes.
If you can see the movement of the other tissues around it, reflecting movement of the diaphragm respiratory variation, this vessel is changing in size.
With that movement.
Once again, just to convince the audience, here is a picture of the inferior cava right behind the portal vein.
Pulsatile right over here, we're above the level of the disc, catching a little bit of the ATA here, but sometimes above the level of the ATA in this clip in the abdomen.
So this is the lone vessel when you see this SAO disappear.
And over here, an image of the aar, another al vessel and transverse view.
It's hard to see the inferior vena caver right here, because there's some, looks like there's some gas here probably in the duodenum.
And two more images down here, longitudinal and a transverse picture of the IVC both showing pulsatility.

Measurement Technique

So moving on, once we found the inferior caver and definitively identified it, the transverse plane, you going to fan your probe in a cephalad direction, superior Northwoods direction to the highest point of the inferior ven cava that's free of the hepatic veins throughout the respiratory cycle.
And that's usually described as one to three centimeters below the level of the diaphragm or the hepatic pains, depending on which literature you're reading.
And then you're gonna actually do visual inspection, a qualitative inspection of both of the vessel of the inferior cava in both transverse and longitudinal planes, looking at size, shape, and collapse.
And we're gonna go into quite a bit of detail about what you're gonna be looking for when you do that.
If you're going to record this after you've done your visual inspection for measurement, which in most cases we do do.
Although being critical care physicians, we've been increasingly interested in the potential utility of qualitative estimates substituting for quantitative measurements because of the time involved in quantitative measurements being often prohibitive in the management of very sick people.
But nevertheless, the two options are either recording an entire cycle in M mode.
And right here you can see the EM mode sampling crystal, a dotted line going down here right through the vessel, staying right in the middle of the vessel throughout the cycle.
You can see the hepatic veins coming in and away from with the respirations, the inferior vena cava, and indicating that you're about the right level just below where the hepatic veins are throughout the respiratory cycle.
And right here is en mode image.
The frozen EM mode image from up here actually looks like this.
And you're going to measure between the widest place in expiration right here, and the narrowest place in inspiration right over here.
And there are measurements, which are a little bit hard to see on this screen, of 3.8 millimeters at the thinnest and 18.3 millimeters at the maximum transverse dimensions of the vessel.
The alternative tech technique is to freeze B mode images in inspiration and expiration or to just freeze, and then use your cine loop to obtain two different images, one at the maximum, one at the minimum, and then make measurements directly across like this without using the M mode feature.
This requires a little bit more time and because time is in the of the essence in our practice, it's used less frequently than the technique I just described before.

Longitudinal vs. Transverse Views

Now, why do we want to look at both longitudinal and transverse planes of the IVC?
The reason is because both of them taken alone can have fatal potential fatal flaws, and both of 'em provide additional information that the other one cannot provide.
Starting first with the transverse plane.
The advantage of this is that you can definitely identify the a, the aortas we've mentioned before, if once you've seen the two vessels and know which one, if you need to look at, you're not gonna make any mistake of which vessel you're gonna look at and analyze and measure.
You can see the entire IVC throughout the respiratory cycle.
And it turns out that the inferior cable oftentimes actually swings a little bit from side to side with respirations, not just it doesn't just move north and south.
And since that's the case, if you're only looking at a longitudinal plane, and the vessel is swinging from side to side, you'll actually think that it's getting thinner with the respirations and thicker through the respiratory cycle, where in fact, you're just swinging off the plane and onto the plane, again, of the out sound probe.
And going along with that, you can make sure that your sampling bar right here is going right through the vessel throughout the respiratory cycle.
The bad thing about the transverse plane is that sometimes there are extrinsic things compressing on the vessel, either in the liver or behind the IVC, or most commonly, the diaphragm itself.
And if you're just in the transverse plane, the area of constriction caused by one of these extrinsic things appears just like a narrowing or a collapse of the vessel with respiratory variation.
And since that's the case, without looking longitudinally, you can be given the mistaken impression that the IVC, the vessel, the inferior cava, has severe collapse with respiratory variation.
And sometimes it's hard to know at your level because the if the hepatic veins are very collapsed and you're not certain that you're just below the hepatic level of the hepatic veins.
Here's a loop of the longitudinal image.
And the advantages and disadvantages of the longitudinal inferior vena cava are really the exact corollary of what we mentioned previously and for the transverse plane.
So this is an example showing extrinsic compression, which can only be seen in the longitudinal plane, right here.
This area here, which I'm not exactly sure what it is, it's most likely to be the piece of the diaphragm.
Right below the you see the movement of the heart here is really impacting right below this hepatic vein.
Here is the level we'd be measuring the diameter of the vessel.
And although this is a fairly thin inferior vena cava here, you can see how measurement here, indeed here is another extrinsic compression, would give you the sense that the inferior vena cava was completely collapsed those points, and had no volume in his tool, whereas there actually is some volume in the inferior cava.
The pitfall of the longitudinal one, as we mentioned, is that the longitudinal plane is that you can slide right off the longitudinal view of the vessel.
And this in this view here, you can see how this inferior ven cava appears like it's got a hundred percent collapse at various parts of the respiratory cycle.
Fortunately, when we viewed this had already looked transversely, and so we weren't fooled, and we got another view of the vessel as follows on plane.
And here you can see that there's almost no collapse at all of this vessel.
This is a well filled vessel with some pulsitile, some B2B, as well as respiratory variation, but far less than we've seen in the previous image.

Subxiphoid vs. Intercostal Windows

So what about the subxiphoid versus the intercostal windows?
The subxiphoid window is the traditional views, as we mentioned, but mainly to compression of the IVC.
And especially if you have a small liver window, bowel gas, you're trying to move those out of the way, you're more likely to cause some compression.
And if you have a patient with abdominal pain or abdominal trauma, then obviously this window is almost precluded from use the intercostal window.
Avoids the problem with IVC compression and sometimes may give you a truer AP diameter because the IVC, as you can see in this schematic here, actually sort of tends to hang out over on the side of the vertebral body.
And really you want to measure the IVC in the dimension that it's going to expand and collapse.
The IBCs as it collapses, becomes more and more lemon shaped from being a round thing to lemon shaped and ends up finally as a slit.
But that dimension there the is really not the one that's reflecting its volume the volume of fluid in it.
The dimension that's gonna reflect that best is the one that goes across the short axis here of the lemon or the football, or whatever you choose to call this the shape right here.
So, and furthermore, when the IBC rises and falls with respiratory variation and beat tope variation, it does so along this short axis here.
So changes are gonna be much more significant in this direction than they are in the long axis direction of the vessel.
The big disadvantage to the intercostal is it requires a little bit more skill because of the technical challenge of scanning between ribs, especially some older people have quite a lot of calcification in their intercostal muscles, and that can either be challenging or preclude scanning in that window.

Qualitative and Quantitative Assessment

What needs to be measured when you assess the IVC?
So first of all, we're considered qualitative ones, but to get the technical issues outta the way, the inferior cava has a minimal diameter on inspiration, during the actually due to the negative effect of the in thoracic pressure and inspiration.
And in case people have trouble remembering, the maximal diameter is in expiration, the two Xs go together just like the two minimal and the inspiration go together.
Maximal diameter on expiration.
So we actually looked at measurement of the IBC in different planes and different and windows, and really found that there was relatively little consistent difference.
There was some statistical difference, but it did not amount to a clinically significant difference.
It was a matter of a few millimeters, which is probably within the normal limits of operator ability to resolve this organ.
So in terms of the qualitative assessment of the IVC, first of all shape, the words that frequently used are slit like, or flat versus plethoric, or round or full.
Another qualitative assessment is if your inferior cava collapses a hundred percent at any time, that is something that visually is easily identified and is obviously not right.
You're always supposed to have enough blood in your IVC to fill your heart and diastole.
So a hundred percent collapse is something that is physiologically not sound, especially if you're treating a patient in shock.
And the patient needs some volume.
We actually looked at people's ability to make gross visual estimates of inferior cava shape.
We asked 'em to look at it before they measured it, and circle one of these shapes, which were basically progressed in on, they were shown to the operators in this order from flat, very thin slit like, to sort of a flat rugby ball or American football here to a rounder rugby ball, or American football up to a circular soccer ball or basketball shape right here.
And what we found was that the agreement between a measured and visual estimated sizes was pretty tight at the extremes for very flat or very round.
But for the intermediate shapes the level of agreement was much wider.
And I think the important thing to take home from this is that this really is useful to us, but only useful at the extremes.
But at the extremes of a flat or very plethoric IVC, in critical care medicine, that's where issues really matter to us.
If we're in here and we choose to give more fluid or not to give more fluid, or if we choose to diaries the patient a little bit, or not diaries them, it probably is not gonna be so critical for the patient because they have some give in their system right here with some fluid in the vessel.
The extremes we want to be more consistent and more accurate.
And the extremes is where patients tend to be when they're critically ill.
We also assessed the correlated people's estimation of the IVC diameter sort the estimation of the IVC as being small, medium, or large, or small, normal or large, and then correlated it with the measured maximum diameter of the IBC.
And again, at least in the lower extreme, found that it was pretty tight correlation.
When people were saying medium or large, there was really not nearly such close correlation with actual size.
Although the there's was very little overlap between the medium and large sizes in any patients, and a size of less than one centimeter.
So for small IBCs, it's probably a visual estimate of it being small probably does relate to a maximum di of less than 10 millimeters, which is in many studies, is one of the thresholds that kind of emerges of a somewhat underfilled IVC.
We also assessed inter agreement, two different people using visual estimates, and measured estimates of the or, or measurements of the collapse index.
And found there wasn't great correlation in respect to collapse index, but interestingly, there was quite a good correlation with respect to maximum and minimum diameters.
And one of the things about the collapse index that emerges when you use it very much is that any errors are multiplicative with the collapse index because of the nature of the calculation that comes up with it.
So any differences are multiplied when you get to the collapse index, which is probably why there is such poor correlation.

Collapse Index Calculation and Interpretation

Just to review the math that goes behind the collapse index.
The collapse index is the diameter of this level here, collapsed distance here, divided by the total diameter of the vessel.
And that is actually calculated by measuring.
Since we can't measure this distance right here, we actually measure the inspiratory, the smaller diameter, and we subtract that from the big diameter in expiration.
So we end up with this number here, and we divide that by the big number D expiration.
So collapse index is D expiration, diameter expiration, minus D diameter on inspiration divided by D diameter on expiration.
A high IVC collapse index studies show no consistent threshold for hypovolemia using 50% as a cutoff.
KERCHER atel obtained an 81% sensitivity and an 89% specificity for CVP less than or equal to 10.
Other people have found this un insensitive, other investigative find that is insensitive with hypovolemic patients, and stable hypovolemic patients.
But when people become unstably hypovolemic, then it becomes more useful.
So really, I think the bottom line as we should take from this, is that as the collapse index approach is a hundred percent as it gets, the IVC has an inspiratory size that's closer and closer to zero, the it's increasingly likely the patient is hypovolemic.
The big pit forward.
The collapsed index is that clinicians who've used it realize pretty quickly that it's quite possible, have an extremely dry pa patient who has a maximum IBC diameter of four millimeters, and a minimum IBC diameter of two millimeters, both of which represent an extremely underfilled vessel.
But the mathematics would just make that a collapse index of 50%.
So really, the qualitative assessment and the overall diameter should probably be weighed equally with the collapsed index in many of our sicker patients.
And I think the collapse index may be of more use to people who are looking at somewhat stable patients whose volume needs to be assessed, for example.
It's widely used in clinics, in dialysis clinics for assessment of dialysate volume removal, or maybe in congestive heart failure clinics, where doctors are looking for optimal diuresis of their patients with chronic congestive heart failure.
Similarly, a low IVC collapse index.
In other words, the exact number for when you call someone volume overloaded is also not clear from the literature.
Less than 20% suggest conditions causing increased CVP, which include volume overload, congestive heart failure, but also you should consider right ventricular failure, right ventricular infarct, acute pulmonary hypertension either from pe, or chronic pulmonary hypertension, tricuspid stenosis or regurgitation tamponade.
All of these things will cause a more dilated IVC and a decreased collapse index.
Similar bottom line is previously, the closer you get to zero collapse index, no collapse at all.
The more confident you are that the patient is either volume overloaded or has a high CVP, or certainly adequately volume resuscitated if you're in the process of resuscitating someone.
There is one textbook that actually does lay out numbers, range of numbers, otto's textbook of echocardiography.
But I've searched extensively for the scientific basis of this, and there's really no reference in the text.
And I've not seen this supported by the literature anywhere else.
It's presumably sort of a consensus expert opinion of the authors of the textbook.
But I I've warned practitioners who work in the Emergency Department of critical care units that these numbers seem pretty high for what we're used to seeing.
We've we find many of our normal patients have IBCs with D is less than 15, which we would not call small.
And these very large numbers of IBCs represented here with fairly low collapses probably reflect a cardiologist's experience with large numbers of patients with chronic congestive heart failure, and not the same as typically encountered in emergency medicine, to bear that out.
Lion Blaid al did a study of patients before and after phlebotomy for as blood donors.
And they found that the IVC was quite a sensitive reflector of blood loss.
Obviously 450 ccs not a huge volume, but the IVC uh diameter consistently went down by about five millimeters, both for minimum maximum diameters.
But as you can see, the maximum diameter went from 17 to 12, which would not be an unusual pair of numbers for many normal patients without any symptoms and without significant volume derangement.
One other study looked at absolute diameter and found that in trauma patients less than nine millimeter diameter, maximum diameter, that was sensitive and specific for shock in trauma patients.

Studies on IVC Measurement Accuracy

So moving on to the meaning of the IBC measurements and the IVC test characteristics, at our center, we investigated the accuracy of ultrasound used by intensive intensivists and emergency physicians with assisting the volume status of patients in the critical care unit that were completely unknown to them.
And we compared that with the treating attending physicians expert clinical judgment on the volume status of the patient.
We also compared it with invasive monitoring.
These were fairly challenging group patients.
They were all in the surgical intensive care unit.
Many of them were post-op with numerous dressings, abdominal dressings.
They had many of them were immobilized, unable to certainly cooperate it all with the exam.
And obviously that actually creates some limitations in somewhat artificial model for the emergency department, but it's a very good model for intensivists.
It was a prospective convenience sample.
And the physicians doing the ultrasounds had basic ultrasound skills plus a three hour structured didactics and practice session to hone their skills in assessment, both of the heart and the inferior vena cava, both of which were used.
The IVC was qualitative and quantitatively evaluated.
The heart was evaluated for ejection fraction filling.
And the sonologist at the end of that based on nothing else.
They were not they were blinded to any hemodynamic data from the patient or any clinical data were asked to give an impression the patient's volume status as hypovolemic or not hypovolemic.
And this bedside ultrasound assessment were compared and contrasted with CVP measurements to the expert clinical judgment, which was the gold standard as mentioned.
And it turns out that none of the modalities worked particularly stellar fashion against the expert clinical judgment as can be seen here.
The degree of agreement was slightly higher with the cardiac ultrasound, very similar between the IVC ultrasound and CVP, and similar with the IVC collapse.
And then when each of these were compared with expert clinical judgment and CVP together, the cardiac outstanding was found to be the closest thing to being significantly better than the CVP measure.
And in a one-tailed test, it actually very close, very nearly attained clinic statistical significance as can be seen here.
For intubated patients.
This there was even better concordance.
This was a small sample.
And certainly there are many other problems with intubation and the assessment of IIVC.
A couple of studies have looked at the IVC and assessment of children.
Initially nephrologists did the studies, and found that there's good correlation with weight change for expiratory inspiratory and mean as well as collapse index in patients getting dialysis.
More recently the as a result of the fact that the children's IVC changes with age in a similar way to the aorta, an IVC aorta ratio has been explored as the best technique for assessment of dehydration in children.
The in this study, the optimum ratio was found to be around one 1.01, and as a cutoff between intravascular volume depletion and adequate hydration, the using that number, they obtained a sensitivity of 97% with a 58% specificity for dehydration.
And a clinical standard was used as a clinical judgment was used as a reference standard in that particular study in 2010, using a criterion for dehydration of greater than 10% weight gain after the illness, this group, Levi Atal, found that a ratio of 1.22 was the best cutoff with sensitivity specificity, very similar to what we just mentioned, 90, a little over 90% and 60% for dehydration using this this is a FA fairly severe or moderately severe degree of D dehydration here.
The two are two curves they had here, and the curve that is the best of them all was actually the aorta IVC ratio.
And the IVC inspiratory collapsed the world Health Organization Vidia Hydration Score were did not perform as well.
Another study that appeared in 2010 actually looked at dehydration in children with acute symptoms of or symptoms or signs of dehydration, and the ratio weights were measured and after their acute illness, they returned for REM measurement.
And in this case, the dehydration was defined as a 5% weight gain, was gain, 72 children who completed the entire study.
And they actually found on the other side of the one mark sensitivity and specificity, the same very similar numbers, with an area under the curve of 73% for using the aorta.
So the IVC aorta ratio this was not significantly better than the expert opinion of a pediatric emergency medicine attending using the golic method of assessment for dehydration.
So if you're an expert pediatrician, then you can probably do this as well, at least according to this study.
It's an ultrasound machine.
And so it it'll really depend on your clinical skills and your clinical practice.
If you're very experienced with children, maybe the ultrasound doesn't add very much to your evaluation.

Pearls and Pitfalls

Finally, some pearls and pitfalls about this.
There are some non intravascular volume causes of increased IVC diameter.
We've mentioned some of them already.
Tricuspid stenosis of regurgitation, ponic regurgitation, right heart failure, including acute causes such as pulmonary embolus, right ventricular infarct or tamponade.
And then non intravascular volume causes of decreased IVC diameter in increased intraabdominal pressure, stenotic things on the IBC, or they'll hopefully be able to recognize them for the longitudinal view.
And focal lesions or liver masses again should be recognized in the longitudinal view of the IBC.
Lots of studies have tried to use IVC or assessed its accuracy with intubated patients.
And really the data's all over the map, but if you think about it, the IVC mechanics of the respiratory mechanics get almost completely reversed in the setting of positive pressure ventilation leading to certainly the collapse index being a much less use with the increased in thoracic pressure of PO positive pressure ventilation.
The IVC should appear larger on the other side, on the cord add side of the diaphragm, the side of the diaphragm where we're looking at it.
And so clinically, certainly, and according to this one study here, which is somewhat older now, a raw diameter of less than 10 millimeters is an indication of low central venous pressure in intubated patients.
The IVC, if you have someone who's is any question about hypovolemia when they're intubated, they should have be tanked up to having a nice plush plethoric IVC to be sure that they're getting adequate filling pressures to allow their heart to work in the thorax with its increased positive pressure throughout the respiratory cycle, Mr.
Misidentification of other fluid fill structures, the IBC is another pitfall.
The aorta is probably the commonest one.
You can sometimes the gallbladder is mistaken if it's very long, sometimes the superior mesenteric vein, sometimes the portal vein.
And we've certainly seen pleural effusions down in the costophrenic angle posteriorly to be mistaken for these in still images.
I think we have a an example of that just coming up positively identified both TR vessels and transverse and longitudinal before measuring, as we mentioned before, in dry patients.
There's two classic pitfalls.
The first is that the IC is not found, that's the less serious.
The other is mistaking the aorta for the IVC and measuring the aorta instead.
If you can only find one vessel down there, it's the ata, because that's always there.
And it's the patient's dead and got no volume in on either side.
But make sure you identify two vessels in that transverse plane.
So to be sure that you're looking at the IVC, we've mentioned the danger of calling extrinsic compression collapse, coming off plane.
This example here is an example of a person who used this vessel here for measurements.
And this is actually the aorta it's not that easy to see.
This is a person who has a thin person.
Sometimes you see the aorta way up quite high behind the liver.
And the diaphragm coming across right here.
You can see the heart moving right here.
So since this person had an aorta that's visible, probably behind the crew of the diaphragm, which will extend right down here, but there's not a lung interposing between the aorta and the liver.
It's been mistaken for the IVC.
One of the features of IVC pulsation, which is demonstrated nicely here versus aortic pulsation, is that the aorta has a sharp upstroke.
So that there is beginning of systole, there's a sudden shoulder here, and then the ATA slowly collapses through the rest of the cardiac cycle until the next aortic valve opening right at dislocation here.
The IVC has the opposite.
It has a sharp downstroke and then slowly fills up with some undulations during the rest of the cardiac cycle.
Something that your eye learns to pick up after you've been doing this for a little while.
But initially this might be overlooked.
And there's one more way that you can make sure you're looking at the right vessel.
This here is a view of the correct vessel, the IVC.
And actually, you can see this, how the collapse component of the cycle is much more rapid here as opposed to the expansion component, as we just saw in the aorta.
Another Pitfall, again when you freeze an image, you get two black lines like this, and you're not sure which one you should be doing.
You have to make sure before you freeze and measure which ones which.
It turns out that this is the inferior vena cava right here, and behind here is the pleural effusion.
But they both look in the M mode frozen image right here.
They both look very similar, and in the transverse view, they also, this is sort of an oblique view of the IVC, but the two of them look quite similar.
This almost could be mistaken for a vessel back here, another series of vessels that could be mistaken.
Here we have the portal vein coming in.
But the bigger problem here is that this is way too low.
Way below the paddock pains.
'cause we're seeing the portal vein here.
So if you're looking at this image, you know that the measurement has been made too low.
Here is a good example of what it looks like when you're dealing with a very dry patient.
Here is our vertebral body.
The only vessel that jumps out at use this one here, which turns out is the ATA right here, is a slit like inferior caver.
And you can see that there's almost no hepatic veins here identifiable.
A couple of them every now and then are scene, which are also very collapsed dropping down into this collapsed IVC here.
So this is a sort of situation where it'd be easy to overlook the IVC.
Here's another longitudinal image of a very dry patient.
Again, it's showing how easy it would be to miss the IVC.
This is the IVC scene right along here.
Suddenly we went transverse on it, right here.
Here it is, right here.
We're back to the longitudinal right now.
And this is a very collapsed IVC, and you can see how easy it'll be to overlook it completely and not realize it's the vessel.
Here it is in the transverse plane right there, just for a very brief moment at the end of that clip.
Remember to look at your visual gestalt of the vessel.
Not to depend just on numbers.
Be careful about measuring beat to beat variation.
That's not what we're interested in.
We're interested in respiratory variation.
Make sure you put a slow sweet speed on your M mode in order to do that, and try and develop a sense of both cardiac and respiratory movement.
Once again, this is that the image that we saw before of the aorta, which was mistakenly taken as an IVC because of the IVC over here was so collapsed.
And not only is the mistake of demonstrate the mistake of using the wrong vessel, but it also shows the mistake of using beat to beat variation right here between sly and diastole.
That's not what we're interested in.
Even if this were the IVC, we're interested in a variation that occurs with the respiratory rate.
Okay?
So here we have a transverse view of the IVC, which again shows the tendency to use a some kind of beat to beat variation with this very rapid sweet speed sweep.
Speed.
This is very unlikely to be caused by a respiratory variation.

Summary

In summary, the use of the IVC does require some experience and skill for both technique and interpretation.
But actually is one of our is a completely non-invasive bead on the biggest and most important capacitance vessel of the body.
And considering the alternatives of invasive monitoring, I think that that IVC assessment should be a useful and well used tool in the armamentarium of any doctor who's taking care of patients in whom excess or lack of intravascular volume might be an issue.
I think it certainly can help guide both in diagnosis and therapy of these patients.
I'd like to express my thanks to Sona World for hosting this lecture, and I hope it's been helpful to everybody who listens to it.
Thank you very much.