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

Approach to evaluating for fluid responsiveness

1. 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. 

2. The variation is termed “respiratory variation”

3. Measure the IVC at its maximal diameter and minimal diameter

4. hOthThe caval diameter is used to help judge whether a patient may be responsive to fluid based on the IVC’s respiratory variation alone

5. Caval diameter = (max diameter -  min diametermax diameter )* 100

6. If caval diameter is >40-50% in a spontaneously breathing patient, the patient may be fluid responsive (use other exam features and clinical gestalt)

7. If caval diameter is >14-18% in a mechanically ventilated patient, the patient may be fluid responsive (use other exam features and clinical gestalt)

8. 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