Ultrasound Case 015

Image 1: Longitudinal view of the IVC deep to the liver: The IVC is flat with complete collapse on inspiration and very little filling seen only during atrial systole on expiration.

Image 2: Transverse view of the IVC: The IVC again is flat with complete collapse on inspiration and minimal pulsatile filling on expiration reflecting atrial systolic IVC flow reversal.

Hypovolaemia.

Using the IVC as the sole determinant of volume status is fraught with difficulty. Complete collapse of the IVC with associated hypotension however correlates well with volume depletion and should prompt fluid administration.

The IVC AP diameter and its variation through the respiratory cycle can be used as a rough guide to volume status. In the euvolaemic spontaneously breathing patient the IVC generally partially collapses during inspiration. This is because during inspiration negative intrathoracic pressure draws more blood into the right heart; at the same time the diaphragm descends, increasing abdominal pressure and blood from the upper abdominal IVC is propelled upwards and out of the IVC. Whilst precise measurements are quoted as being useful (greater that 50% collapse with inspiration and maximal diameter less than 2.1cm associated with hypovolaemia and less than 50% inspiratory collapse and AP diameter greater than 2.1cm associated with hypervolaemia) errors can occur. Consider cardiac tamponade as just one example where a large IVC does not necessarily correlate with hypervolaemia.

Despite the many limitations a flat IVC in the supine patient with associated hypotension is a very useful finding which does reflect volume depletion and should prompt rapid and appropriate fluid administration.