Inferior vena cava ultrasound

Provides an assessment of intrvascular volume status.

Useful in hypotensive states and to determine intravascular volume in patients with sepsis, CHF, dehydration and with hemorrhage.

The diameter and degree of collapse of the IVC reflects changes in the intravascular volume and can estimate central venous pressure.

The IVC contracts and expands with respirations: negative pressure created by inspiration increases venous return to the heart and collapses the IVC temporarily. while exhalation decreases venous return and causes the IVC to return to its baseline dimension.

In the presence of a low intravascular volume, the percentage collapse of the IVC will be proportionally higher than in intravascular volume overload states.

This process is quantified as the caval index:: IVC expiratory diameter – IVC inspiratory diameter, divided by IVC expiratory diameter × 100 = caval index (%).

A high caval index reflects volume depletion, while a low percentage indicates volume overload.

With volume depletion the diameter of the IVC is decreased and the percentage collapse will be greater than 50%.

With volume overload here is a large IVC diameter and minimal collapse on inspiration.

Engorged IVC may occur in settings other than intravascular volume overload, such as cardiac tamponade, mitral regurgitation, or aortic stenosis, and results of IVC sonogram may be invalid.

Intubated patients receiving positive pressure ventilation will have a reversal of IVC changes with respiration.

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