IVC and Filling PressureIVC

Name: IVC and Filling Pressure (IVC) — POCUS Tips
Creator: Yonathan Daniel, MD

A gauge of right atrial pressure — useful at the extremes, easy to over-read, and never a fluid-responsiveness test on its own.

Open the interactive view with the loop and quiz →

IVC and Filling Pressure ultrasound frame — Still frame from the IVC and Filling Pressure loop. Loop: Pocus 101.

Where to put the probe

Window: Subxiphoid, IVC in long axis as it enters the right atrium
Marker: Patient’s HEAD (12 o’clock)
probe: phased or curvilinear
preset: cardiac / abdominal
depth: 15–20 cm

Get the view

Start from the subcostal four-chamber view, then rotate the marker to the patient’s head.
Confirm it is the IVC, not the aorta: it enters the right atrium, has thin walls, and a hepatic vein joins it.
Measure 1–2 cm caudal to the hepatic vein confluence, perpendicular to the vessel wall.
Watch two full respiratory cycles, or run M-mode with a slow sweep to see the variation cleanly.

What you are looking at

Inferior vena cava: Thin-walled, non-pulsatile, changes caliber with respiration.
IVC–right atrium junction: Proves the vessel’s identity; the measurement is referenced from just below it.
Hepatic vein confluence: The landmark for where to measure — 1–2 cm distal to it.
Aorta (do not confuse): Deeper, to the patient’s left, thick-walled and pulsatile, with no hepatic vein and no atrial connection.

On the screen

The do-not-confuse pair in transverse: the IVC (screen left, patient’s right) changes calibre with breathing and flattens with pressure; the aorta (screen right) stays round and pulsatile. Follow the IVC into the right atrium before you measure it. Image: The POCUS Atlas

Numbers that matter

Diameter and collapse	Estimated RAP	Reading it
< 2.1 cm with > 50% collapsespontaneously breathing, with a sniff	≈ 3 mmHg	low filling pressure — a fluid challenge is reasonable in shock
> 2.1 cm with < 50% collapsespontaneously breathing, with a sniff	≈ 15 mmHg	high filling pressure — look for RV failure, tamponade, obstruction
Discordant findingsone criterion met, not the other	≈ 8 mmHg	intermediate; the IVC is not going to decide this case
Virtually collapsed IVC in shockany respiratory phase	very low	strongly favors hypovolemic or distributive shock

Don’t be fooled — pitfalls

Aorta mistaken for IVCThe aorta is pulsatile, thick-walled, to the patient’s left, and never joins the right atrium. Follow the vessel before you measure.
Off-axis measurement under-reads diameterThe IVC is a cylinder — a tangential plane makes it look narrow. Rotate until the walls are parallel and the lumen is at its widest.
Positive pressure ventilation inverts the physiologyCollapse indices are validated in spontaneously breathing patients. On a ventilator the IVC distends rather than collapses with each breath, and PEEP and tidal volume drive the number. A distensibility index above roughly 12–18% has only been studied in fully passive, sinus-rhythm patients at tidal volumes of 8 mL/kg or more.
Standardize the breathThe ASE cut-offs use a sniff. A forced deep inspiration or labored breathing exaggerates collapse and will talk you into fluids the patient does not need — note which manoeuvre you used.
Plethora is not always a volume problemTamponade, massive PE, RV infarction, severe tricuspid regurgitation and tension pneumothorax all dilate the IVC; raised intra-abdominal pressure makes it unreliable in either direction, and a young athlete can run a large IVC that still collapses normally.

Bad image? Fix it

Bowel gas blocks the windowSlide right and angle through more liver; the hepatic window is more reliable than the midline.
Cannot find the vesselFind the right atrium first and follow it caudally — working backwards from the heart is faster than hunting a tube.
Vessel drifts in and out of planeRotate a few degrees until both walls stay crisp through the whole respiratory cycle.
Want a defensible numberM-mode through the measurement point with a slow sweep, then measure max and min on the frozen trace.

So what — what the finding changes

Small collapsing IVC + shockGive a defined fluid bolus and rescan — the trend matters more than the single measurement.
Plethoric IVC + B-linesStop fluids. Move to afterload reduction and diuresis as clinically appropriate.
Plethoric IVC + clear lungs + dilated RVThink obstructive: PE, tamponade, tension pneumothorax. Look for each before giving volume.

Keep going

Educational use only. Not for diagnosis or treatment decisions — confirm findings with formal imaging and your own judgment. By Yonathan Daniel, MD · Pathways · Quiz on this view · About · Last reviewed 2026-10-04.