Vascular POCUS

Could you throw me a line?

Vascular POCUS for the internist focuses primarily on line placement. Central and arterial lines are important tools that many patients need, not only those who need to spend time in the intensive care unit. The ability to safely perform these procedures, identify your structures, follow your needletip, and confirm placement are all vital to this process. Here we review the ultrasound techniques primarily, with additional teaching on other vascular POCUS topics including IVC assessment, with plans for more (including Aortic U/S, and DVT evaluation) in the future.

Central Lines

There are 3 main locations for placement of a central line.

  1. Internal Jugular
  2. Femoral
  3. Subclavian

Location is chosen based on a variety of factors, but typically preferred in the order listed above. Some other considerations are reviewed for each in their respective sections.

Typical Indications
Shock requiring vasopressors
Acute dialysis (trialysis catheter) in those without fistula/graft
Placement of Transvenous Pacer or Pulmonary Artery Catheter (Swan)
Inadequate peripheral access (unable to obtain or maintain)
Other medications that require central access

General Site Contraindications
Distorted local anatomy (trauma, malformations)
Infection overlying the tissue
Thrombus in the target vessel

Probe Positioning
Use the vascular probe, looking for a cross-section of vessel (perpendicular to it’s course)
Apply pressure to distinguish arteries from veins, veins are much more easily compressible

Internal Jugular

The internal jugular vein is probably the most popular site for central line access due to its anatomy, and presumably a lower risk of infection. As above, it is not a good choice for patients with distorted local anatomy (due to trauma, malformations), infection in the overlying tissue, or thrombus in the target vessel.

Normal Anatomy

Here is a cross-sectional image of the left IJ (and Carotid) using the vascular probe. You can see the thin layers of skin/soft tissue at the very top of the image, with the thick darker layers of sternocleidomastoid muscle beneath. Telling the Carotid and IJ apart can be down a few different ways. As mentioned above, the IJ is compressible, and can be completely obliterated with pressure, whereas the carotid will not be easily compressed or obliterated. This image also shows that valsalva reduces venous return to the heart, leading to backup of venous blood and distention of the IJ. Finally, the vein tends to be more amorphous in shape as you can see, whereas the carotid artery takes a more circular, regular shape in cross-section.

Compressible vein without Carotid artery visualized. Minimal pressure is usually enough to compress veins unless there is significant distention.

For some additional teaching, this youtube video is a helpful resource: https://www.youtube.com/watch?v=_RHRy64jQ6s. If you’re interested in reviewing the steps of the actual procedure, and contents of the central line kit, you can check out this additional video: https://www.youtube.com/watch?v=qJaP6hd3qPc. However, it’s always best to review the steps with your fellow (or senior/co-seniors) before attempting the procedure.

Femoral

The femoral vein is another popular site for central line access due to its ease of access, and lower risk of pneumothorax (although it theoretically has a higher risk of infection with the location).

Normal Anatomy

Here is a cross-sectional image of the femoral vasculature using the vascular probe. There are several layers of skin/soft tissue above the vessels. Telling the femoral artery & veins apart is a bit easier than the Carotid & IJ, as sliding the probe distally will show the femoral artery split into the superficial and deep femoral arteries. Again, the vein should be compressible, while the artery(ies) are significantly less so. Ideally you want to find a view where the vein/artery(ies) are not overlying one another, so that your needle can most safely approach it’s target.

For some additional teaching regarding the procedure and technique, this youtube video is a helpful resource: https://www.youtube.com/watch?v=qStwKmk6w1M.

Subclavian

The subclavian vein is a less frequently used site of central access, due to a higher risk of pneumothorax, and the challenges of using ultrasound to visualize the vessel given the visually-obstructing clavicle.

While we do not commonly perform subclavian lines, sometimes these are necessary based on challenging anatomy, or significant access needs. You can learn more about this, and how you can even use ultrasound to assist you in placement of these lines here: https://www.youtube.com/watch?v=_VYHj4sRlkc.

Arterial Lines

There are 3 main locations for placement of an arterial line.

  1. Radial
  2. Femoral

Location is again chosen based on a variety of factors, but typically preferred in the order listed above. Some other considerations are reviewed for each in their respective sections.

Typical Indications
Need for consistent, accurate hemodynamic monitoring, such as:
– Titrating vasopressors or vasodilators
– Non-invasive BP monitoring is inaccurate due to altered anatomy, arrhythmia, or obesity
Frequent lab draws (e.g. q6 ABGs)
Procedures (such as cardiac catheterization, arterial stenting)

General Site Contraindications
Distorted local anatomy (trauma, malformations, AV graft/fistula, aneurysms)
Infection overlying the tissue
Absence of collateral circulation
Thrombus in the target vessel
Poor perfusion distal to the target site

Probe Positioning
Again, use the vascular probe, looking for a cross-section of vessel (perpendicular to it’s course)
Apply pressure to distinguish arteries from veins, veins are much more easily compressible

Radial

The radial artery is best visualized on the lateral, ventral aspect of the wrist, proximal to the thenar prominence. As with all other access sites, it is not a good choice for patients with distorted local anatomy (due to trauma, malformations), infection in the overlying tissue, or thrombus in the target vessel. For arteries, particularly the radial artery, ensuring there is adequate alternate supply (Allen’s test) is vital prior to any attempt to cannulate the vessel.

Normal Anatomy

Here is a cross-sectional image of the radial artery using the vascular probe. There is mostly skin/soft tissue above the vessels. Telling the artery & veins apart is again, easiest with compression (veins should be compressible, while the artery(ies) are significantly less so).

Allen’s Test

Being able to adequately palpate the ulnar artery is also helpful, but not sufficient on its own!!

Femoral

The femoral artery is your best alternative site for arterial line insertion (although it theoretically has a higher risk of infection with the location).

Normal Anatomy

Here is a cross-sectional image of the femoral vasculature using the vascular probe. There are several layers of skin/soft tissue above the vessels. Telling the femoral artery & veins apart is a bit easier than the Carotid & IJ, as sliding the probe distally will show the femoral artery split into the superficial and deep femoral arteries. Again, the vein should be compressible, while the artery(ies) are significantly less so. Ideally you want to find a view where the vein/artery(ies) are not overlying one another, so that your needle can most safely approach it’s target.

For some additional teaching regarding the procedure and technique, this youtube video is a helpful resource: https://www.youtube.com/watch?v=qStwKmk6w1M. Just target the artery (with the correct kit!) rather than the vein!!

Other Vascular POCUS

IVC Assessment

Typical indications
Differentiate causes of shock
Differentiate causes of shortness of breath
Establish likelihood of fluid responsiveness
Assess response to interventions

Probe Positioning
Use the phased array probe, in the same position as you would to get the subxyphoid cardiac view (epigastric). Fan probe laterally (90 degree turn clockwise) to view the IVC and identify it draining into the right atrium.

Normal Anatomy

Here you can see the Liver in the center/middle of the view, with the heart on the left, and the IVC and the large anechoic (black) band feeding in to the right atrium on the left, and curving upwards on the right.

It can be hard to tell the IVC and Aorta apart. The IVC will dump straight into the right atrium, this is the most reliable way of identifying it. It should also vary with respiration (unless the CVP is too high!), and you can have the patient ‘sniff’, causing rapid forcefully negative intrathoracic pressure, collapsing the IVC >50% in normal patients.

Central Venous Pressure Measurements

IVC (cm)Respiratory ChangeCVP (cm H2O)
<1.5Total collapse0-5
1.5-2.5>50% collapse6-10
1.5-2.5<50% collapse11-15
>2.5<50% collapse16-20
>2.5No change>20

Remember, these are just estimations. But this can be helpful in determining the cause of shock, as mentioned above, and for estimating volume in patients with unclear volume status. Like all volume assessments, it is imperfect, and should be taken as a piece of information within the complete clinical picture, rather than as sufficient alone to determine volume status.