IVC POCUS is often misapplied in attempts to assess volume status and/or volume “responsiveness.” Here are some important concepts to understand when using IVC POCUS to guide management:
IVC measurement is not a reliable predictor of fluid responsiveness
Venodilation and obstructive pathology can decrease and increase (respectively) IVC size without any change in actual blood volume or “volume status”
IVC size/variation is affected by multiple factors including spontaneous breathing vs. mechanical ventilation (AND actual ventilator settings), and degree of respiratory effort (in both spontaneous and mechanically ventilated patients) so there are no true “cut off” points that determine volume responsiveness
Attempting to maximize cardiac output/oxygen delivery (macrocirculation) through IVF can actually cause venous congestion and worsen microcirculation and organ function
Some patients with a plethoric IVC (tamponade or tension pneumothorax) may actually benefit from IVF in the acute setting
Examine the entire IVC (cephalad and distal portion) and in the short and long axis (the IVC is actually elliptoid, rather than a true cylinder)
Interpret IVC size in relation to RA/RV function (pts with chronically elevated RA pressures may have a chronically dilated IVC)
References
Rola P, Haycock K, Spiegel R. What every intensivist should know about the IVC. Journal of Critical Care. Published online November 2023:154455.
