Inferior vena cava (IVC) ultrasound is undoubtedly popular, but it’s not without its share of misconceptions and knowledge gaps—like the common myth that IVC ultrasound directly measures volume status, which we’ve debunked in a previous post. In this post, let’s dive into the practical side of IVC imaging, exploring views and nuances that often don’t get enough attention in POCUS workshops.

Let’s begin with the standard subxiphoid long-axis view – see examples below. To obtain this view, we position the transducer in the subxiphoid space with the orientation marker pointing toward the patient’s head. This is the conventional view for measuring the anteroposterior diameter and assessing respiratory variation, typically at a point about 1 cm below the IVC-hepatic vein junction. However, this view comes with its own challenges—it is susceptible to the cylinder effect, as previously discussed. Additionally, novice users often mistake the aorta for the IVC, a common issue I encounter when performing quality assurance on ultrasound images. This topic has been covered in a previous post as well.

The second view is the subxiphoid short axis, or transverse view, obtained by rotating the transducer 90 degrees from the long axis. One major advantage of this view is that it avoids the cylinder effect, allowing for measurement of the maximal diameter by visualizing the vessel’s cross-section. In this orientation, the IVC appears on the left side of the image/right of the body (assuming the transducer marker aligns with anatomical conventions—right in the abdominal preset, left in the cardiac preset), surrounded by the liver. Adjacent to it, and anterior to the vertebral shadow, lies the aorta, although the latter may be obscured by bowel gas and not well-visualized.

Interest in this view is growing, and promisingly, one study demonstrated that the short-to-long diameter ratio (S/L), or sphericity index, derived from this view correlated better with central venous pressure (CVP). Practically speaking, this means that as the IVC becomes more circular rather than oval, CVP is likely increasing, as illustrated in the figure below.

That said, always remember the golden rule of POCUS: “One view is no view.” Relying solely on the transverse (short axis) view comes with two significant pitfalls:

1. Site Ambiguity: In the long axis view, it’s easier to pinpoint where you’re measuring the diameter and assessing collapsibility. However, in the short-axis view, this can be more challenging. You need to find a location slightly distal to the IVC-hepatic vein (HV) junction. Ideally, the image where you measure the diameter should show the IVC along with partial cuts of the three hepatic veins converging toward the IVC but not the junction itself. The image below demonstrates how the IVC diameter changes as the transducer is swept distally. The yellow lines overlaid on the long axis image reflect ‘approximate‘ scan planes to illustrate the point.

Below is another example demonstrating different diameters in long and short axis views. Basically, these views don’t correspond to the same point. This can cause problems during follow ups.

2. Confusion with the Right Atrium (RA): The RA is another circular, anechoic structure that the IVC drains into, and novice POCUS users frequently mistake it for the IVC’s cross-section. This confusion is particularly common when the hepatic vein appears to almost join the RA in images, as their insertion points are close. Even experienced users may occasionally misidentify these structures, especially if the IVC is very small. The key is to look for the bright diaphragm between the liver and the RA and, when in doubt, increase the depth and confirm using the subxiphoid 4-chamber view (and of course look at the IVC in long-axis).

The third view is the subxiphoid bicaval, or “snail” view, which we’ve discussed in detail previously. When obtainable, it is a nice view to directly visualize a central venous catheter in the superior vena cava (SVC) and perform a pulsed Doppler assessment of the SVC (e-VExUS). However, when using this view to measure the IVC diameter, keep in mind that the vessel may be visualized obliquely (foreshortened), which can result in underestimating its maximum diameter.

The fourth view, often called the “rescue view,” involves imaging the IVC from the lateral aspect (right mid to anterior axillary line, with the orientation marker pointing toward the head). This view is commonly used when the subxiphoid window is inaccessible or produces non-diagnostic images, such as in cases of abdominal distension. In this view, the aorta is frequently visible beneath the IVC (“double barrel shotgun” sign) as the ultrasound beam passes from the right lateral side to the midline of the body. Remember that structures closer to the transducer appear at the top of the image, while those farther away are displayed at the bottom, placing the aorta below the IVC.

It’s important to note, however, that this view measures the lateral diameter of the vessel in its long axis, not the standard anteroposterior diameter, as illustrated in the accompanying CT image. Therefore, these measurements are not interchangeable (see this study), though this view can provide a general sense of whether the IVC is significantly enlarged or small. However, by rotating the transducer 90 degrees, you might be able to obtain a transverse view. If the vessel appears round, it’s likely that the lateral and anteroposterior diameters correlate. This view can be particularly useful in pregnant patients, where other windows may be challenging (Positioning is crucial in these patients – check out this study).