IVC
Indications
Undifferentiated hypotension
Fluid responsiveness assessment***
***The IVC alone is not a reliable way to assess for fluid responsiveness! The decision of whether to give fluid is a clinical decision based on patient symptoms, the physical exam, ultrasound findings, and clinical gestalt.
Acquisition
The Views
Long axis
The Patient
Supine
The Probe
Curvilinear
Long Axis
Nestle the probe midline in the epigastric space with the indicator pointed to the patient’s head
If you are having difficulty visualizing, there may be bowel gas in your view. Sweep downward with gentle pressure (graded compression) to push bowel gas out of the way.
Identify your landmarks
Aorta: anechoic to the patient’s left
IVC: anechoic to the patient’s right
Hepatic veins: anechoic, draining into the IVC
Protip: If you place the probe left to midline, you can sweep to the patient’s right to pass the aorta and confirm that you are looking at the IVC!
Approach to evaluating for fluid responsiveness
As the patient breathes in and out, the diameter of the IVC will change. Inspiration causes the right atrial pressure to decrease, pulling fluid from the IVC forward.
The variation is termed “respiratory variation”
Measure the IVC at its maximal diameter and minimal diameter
hOthThe caval diameter is used to help judge whether a patient may be responsive to fluid based on the IVC’s respiratory variation alone
Caval diameter = (max diameter - min diametermax diameter )* 100
If caval diameter is >40-50% in a spontaneously breathing patient, the patient may be fluid responsive (use other exam features and clinical gestalt)
If caval diameter is >14-18% in a mechanically ventilated patient, the patient may be fluid responsive (use other exam features and clinical gestalt)
Why does this make sense? When a spontaneously breathing patient breathes in, pressure in the right atrium will drop due to increased intrathoracic volume. In a patient that is mechanically ventilated, they are constantly experiencing high intra-abdominal pressures, and so the change in right atrial pressure will be smaller.
Examples
Collapsible IVC suggestive of volume depletion
Plethoric IVC suggestive of volume overload or obstructive or cardiogenic shock
Ultrasound G.E.L. Podcast
Want to learn more? Take a listen to a review of the literature!
