Ultrasound Teaching Atlas
Draft — not yet peer-reviewedcoreAbdomen / RetroperitoneumRUSH

IVC — Volume Status

Assess the inferior vena cava's size and collapsibility to estimate volume status and filling pressures.

This module is a content/teaching-structure draft. Images shown are illustrative schematics — real, de-identified, license-verified ultrasound clips replace them before peer review.

Learning objectives

  • Obtain a long-axis subxiphoid view of the IVC entering the right atrium.
  • Assess IVC diameter and respiratory collapsibility.
  • Interpret a flat collapsing vs. a plethoric non-collapsing IVC.

Maps to

  • Resident: ACEP Emergency Ultrasound — Cardiac/IVC: Acquisition
  • Resident: ACEP Emergency Ultrasound — Volume assessment
  • Tech: Critical care POCUS — volume status

Acquisition — getting the view

Probe
phased-array
Patient position
Supine.
Orientation convention
radiology
Probe placement
Subxiphoid, rotated to a sagittal plane along the IVC
Marker direction
Indicator toward the head (longitudinal)

Probe placement (3D)

Subxiphoid, rotated to a sagittal plane along the IVC

Structures in the imaging plane (near → far): Abdominal wall · Left lobe of liver (window) · Inferior vena cava · Hepatic vein inflow · Right atrium junction

Step by step

  1. From the subxiphoid 4-chamber view, rotate the probe so the indicator points cephalad to bring the IVC into long axis.
    Why: Shows the IVC entering the right atrium through the liver window.
  2. Measure the IVC diameter ~2 cm from the RA junction (or just distal to the hepatic vein inflow).
    Why: Standard location for reproducible measurement.
  3. Observe the change in diameter with quiet respiration (and a sniff).
    Why: Collapsibility reflects filling pressures.

Troubleshooting

Confusing the IVC with the aorta.
The IVC is thin-walled, compressible, drains into the RA, and shows respiratory variation; the aorta is pulsatile and thick-walled.
IVC out of plane / cylinder effect.
Keep the vessel in true long axis to avoid underestimating the diameter.

Findings: normal

Normal IVC

A roughly 1.5–2.5 cm IVC with moderate respiratory collapse correlates with a normal central venous pressure.

Schematic of a normal IVC in long axis
Schematic: IVC entering the RA with respiratory variation.
Original schematic, dedicated to the public domain (CC0).

Findings: pathology

Flat vs. plethoric IVC

A small IVC (< ~1.5 cm) collapsing > 50% suggests low filling pressures (hypovolemia/distributive). A plethoric IVC (> ~2.5 cm) with minimal collapse suggests elevated pressures (cardiogenic/obstructive/overload).

Signs: < 1.5 cm + > 50% collapse → low CVP; > 2.5 cm + minimal collapse → high CVP

Schematic comparing flat and plethoric IVC
Schematic: flat collapsing vs. plethoric IVC.
Original schematic, dedicated to the public domain (CC0).

Interpretation practice

A hypotensive patient has a small IVC that nearly fully collapses with each breath. What does this suggest?

Small collapsing IVC
Small, > 50% collapsing IVC — interpret.
Original schematic, dedicated to the public domain (CC0).

Measurement practice

Measure the maximal IVC diameter ~2 cm from the right atrial junction.

IVC diameter measurement
Calipers across the IVC, 2 cm from the RA.
Original schematic, dedicated to the public domain (CC0).
cm

Check your understanding

A plethoric IVC with minimal respiratory collapse suggests…

How is the IVC distinguished from the aorta?

References

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