IVC and Aorta Assessment (Doniger)

Question 1

What are the possible methods of determining hydration status using POCUS? (3)

Answer 1

1. IVC diameter measurement 2. Degree of collapsibility of IVC on inspiration vs. expiration 3. IVC/aorta diameter index

Question 2

What are predisposing factors to aortic dissection in pediatric patients (4)?

Answer 2

1. Trauma 2. Congenital cardiovascular anomalies 3. Connective tissue disorders 4. Hypertension 5. Trauma

Question 3

What is the objective of the IVC evaluation via POCUS?

Answer 3

Assess for dehydration/hypovolemia

Question 4

What are the objectives of the aorta evaluation? (2)/

Answer 4

1. Assess for aortic aneurysm 2. Assess for aortic dissection

Question 5

What happens to the IVC during inspiration vs. expiration?

Answer 5

During inspiration = increased negative intrathoracic pressure so blood is pulled from the IVC into the right atrium = IVC collapses During expiration = positive intrathoracic pressure pushes blood back into the low pressure IVC system = IVC expands ****Overall, IVC reaches maximum diameter during expiration and minimum during inspiration

Question 6

In trauma patients, how does IVC diameter measurement compare to blood pressure, heart rate or base deficient for predicting fluid response in adult trauma patients?

Answer 6

IVC diameter measurement is BETTER compared to all these things

Question 7

What is the caval index?

Answer 7

Caval index = AP diameter of the IVC and its percentage of collapse -the higher the caval index, the more hypovolemic the patient is -used in adult patients

Question 8

How does IVC diameter/caval measurements compare with central venous pressure in adult patients?

Answer 8

Very high correlation! :)

Question 9

What is the main limitation with IVC measurements in pediatrics? -how do you account for this limitation?

Answer 9

IVC changes with age and size/BMI -to combat this: use IVC/Aorta ratio!!! -easier to obtain in pediatric patients and the ratio corrects for changes in patient size and age

Question 10

What is the IVC/Ao ratio and why do we use it instead of caval index or IVC diameter measurements in children?

Answer 10

Compare the IVC to the Aorta and they should be 1:1. If the IVC < aorta, then there is dehydration or hypovolemia

• we use IVC/Ao ratio to account for the differing IVC sizes in children of different weights/BMIs
• overall: low IVC/Ao ratio means dehydration!
• aorta diameter remains constant despite intravascular volume depletion AND the aorta corrects for size and age of the patient

Question 11

How sensitive/specific is the IVC/Ao ratio based on previous studies for dehydration?

Answer 11

Sensitivity 86%, specificity 56% when using an IVC/Ao cutoff of < 0.8. -another study actually showed that the IVC measurements when compared to CVP in children can be unreliable in PICU population -further research needs to be done to determine further the reliability and utility of t`he IVC evaluation in kids

Question 12

What blood vessels make up the IVC?

Answer 12

Formed by the union of the common iliac veins around the level of the umbilicus -this is also the location where the abdominal aorta bifurcates to form the common iliac arteries

Question 13

Where is the IVC located in relation to the aorta?

Answer 13

Runs anterolateral to the spine and to the RIGHT of the abdominal aorta

-the abdominal aorta starts at the level of the diaphragm and runs caudally, lying anterolateral to the spine and to the left side of the IVC

Question 14

What are the point of care questions for whether a pediatric patient is dehydrated/euvolemic/fluid overloaded?

Answer 14

1. Is there > 50% inspiratory collapse of the IVC?
2. Is the IVC/Aorta ratio < 1:1?

Question 15

What are the 2 point of care questions you can ask using aorta POCUS?

Answer 15

1. Is an aortic aneurysm present?
   a. Is the aorta > 3 cm?
   b. Are the iliac arteries > 1.5 cm?
2. Is an aortic dissection present?

Question 16

What is the preferred transducer for IVC and Aorta assessment?

Answer 16

Low frequency (2-5 MHz) curvilinear abdominal transducers are the best for scanning most pediatric abdomens as they give the highest resolution pictures

• possible to use phased-array transducers
• in very small thin children, linear transducers can also identify the relevant structures

Question 17

How do you obtain the transverse view of the IVC and where should you expect to see the different structures?

Answer 17

Place the transducer just caudal to the xiphoid process with the indicator oriented towards the patient’s right side

• this will give you a cross-section of the IVC
• depth should be deep enough to see the vertebral body shadow
• anterior to the vertebral shadow (ie. in the near field), you should see the IVC to the right and Aorta to the left

Question 18

How do you obtain the longitudinal view of the IVC?

Answer 18

After obtaining the transverse view, rotate the transducer 90 degrees with the indicator towards the patient’s head

• Sliding from side to side, you can move from IVC to aorta
• in order to follow the IVC along it’s long axis to where it enters the right atrium, need to angle the transducer slightly towards the patient’s right shoulder

Question 19

How do you obtain the transverse and longitudinal views of the aorta?

Answer 19

Same as with the IVC!

• transverse: place transducer caudal to the xiphoid process with indicator towards patient’s right
• longitudinal: place transducer caudal to the xiphoid process with the indicator towards the patient’s head

Question 20

What are the common pitfalls in POCUS of the IVC and Aorta?

Answer 20

1. Wrong position of the transducer with the indicator to the patient’s left instead of right - then you see the IVC and aorta switch positions and you’ll get confused!
   - ALWAYS ALWAYS ALWAYS have indicator either to patient’s right or to their head
2. Applying too much pressure during scanning can compress the IVC and give a false AP diameter measurement
3. If you are scanning too superficially, other hollow structures like the gallbladder and other blood vessels in the abdomen can be confused with the IVC and aorta - always use the vertebral shadow!!! The great vessels lie just anterior to the spine. Finding the vertebral shadow is the most important imaging landmark to ensure you are scanning correctly!!!!
4. Using size, shape and pulsation to differentiate between IVC from aorta can be misleading since in small children, they can be so close together. SO instead, you need to look at the thin vs. thick walls, compressibility, and change with respiration to help you differentiate

Question 21

In order to thoroughly evaluate the aorta, where do you need to scan?

Answer 21

Need to visualize and measure in 3 places while in transverse view:

1. Proximal: bounded by the diaphragm and SMA
2. Mid: between the proximal and distal segments
3. Distal: just proximal to the bifurcation into the iliac arteries
4. Branching into the iliac arteries
   - need to perform the scan from the xiphoid down to the umbilicus for a complete scan

Then also need to visualize in the longitudinal view as well

****NEED TO DO THIS TO RULE OUT AAA THROUGHOUT THE COURSE OF THE AORTA

Question 22

What position should the patient be in for IVC and aorta POCUS?

Answer 22

Supine position

Question 23

What are the 3 most common views for visualizing the IVC?

Answer 23

1. Subxiphoid transverse view
2. Subxiphoid longitudinal view = make sure you fan from side to side to get the widest AP diameter
3. Anterior midaxillary line longitudinal view

Question 24

How can you differentiate the IVC from the aorta sonographically? (4)

Answer 24

1. Thinner walls
2. No pulsations
3. Compressible
4. Respiratory variation
5. Courses through the diaphragm in its longitudinal view to enter the right atrium

***keep in mind that in smaller children, aortic pulsations may be transmitted to the IVC, giving the appearance that the IVC has pulsations since they run so closely together

Question 25

How do you measure the IVC/Ao ratio?

Answer 25

• Transverse view at the level of the left renal vein (subxiphoid region) = measure the AP diameter of the IVC and Aorta in a single still image
• if IVC/Ao ratio is <1 = dehydrated
• should improve to equal or greater than 1 after fluid challenge

Question 26

How do you measure the caval index?

Answer 26

The IVC exhibits changes in size during respiration

• During expiration, IVC expands while during inspiration, it contracts
• Caval index is measured in the LONGITUDINAL view
• First, measure the diameter of the IVC during inspiration 2 cm away from the diaphragm - this will be your MINIMUM IVC volume
• Second measure the diameter of the IVC during expiration 2 cm away from the diaphragm (aka in subxiphoid view) = this will be your MAXIMUM IVC volume
• then:

Caval index = (Max IVC - Min IVC) / (Max IVC) x 100

-caval index of greater than 50% is strongly associated with a low central venous pressure (aka dehydration) aka there is greater than 50% collapse during inspiration

Question 27

How do you measure the IVC on M mode?

Answer 27

In the longitudinal view, obtain the image of the IVC and then place the M mode cursor on the longitudinal view of the IVC at the level of the hepatic veins or approximately 2 cm distal to the diaphragm and measure the AP diameter of the vessel over time

-this is tricky since the curved abdominal probe creates a pie shaped image so getting the true AP diameter of the IVC can be tricky!

Question 28

When measuring the walls of the aorta, where do you put your distance marker?

-what are the criteria for aortic aneurysm at any point in your scans?

Answer 28

Outer wall to outer wall

-aortic aneurysm = aortic diameter > 3 cm anywhere in proximal/mid/distal regions OR iliac measurement of > 1.5 cm

Question 29

Can you view the IVC and aorta from the flanks or in left lateral decubitus and how useful are these views?

Answer 29

Yes you can - BUT this approach has not been studied as extensively or validated in volume assessment

Question 30

A 6 yo patient with a history of VSD presents with vomiting and diarrhea x 4 days. On exam, she is febrile, tachycardic and irritable. Her mucous membranes are dry and she has a delayed cap refill time. Her cardiac exam reveals a 3/6 systolic ejection murmur heard throughout the precordium. She is given a 20 ml/kg bolus of IV fluids but is still tachycardic. How can POCUS help you differentiate between clinical dehydration vs. congestive heart failure in her case?

Answer 30

Can ultrasound for cardiac function and IVC measurements

• cardiac function = can tell you whether the heart has good contractility
• IVC POCUS = measure the caval index (is there > 50% collapse with inspiration?) and measure the IVC:aorta ratio (if less than 1, patient is dehydrated)
• doing this will tell you whether you need to keep going with fluids or whether you should worry about other causes of tachycardia aside from dehydration

Question 31

What do you see in aortic dissection on POCUS of the aorta?

Answer 31

See a dissection flap = a piece of tissue within the lumen of the aorta on both transverse and longitudinal views

• should not rely on POCUS solely to diagnose or exclude aortic dissection!
• need other diagnostic studies to evaluate for presence of aortic dissection including MRI or angiography