Intravascular volume status is frequently an important issue in patient evaluation and treatment in the ED.  Direct measurement of central venous pressure, however is invasive and inconvenient.  Ultrasound is increasingly convenient and available in the emergency department for noninvasive bedside evaluation.  Imaging of the IVC by ultrasound has been used for estimating right atrial pressure.

The literature:

One specific population that has been studied is dialysis patients at outpatient dialysis centers.  Measurement of maximal IVC diameter (IVCmax) was taken within 2.5 cm of the IVC-RA junction.  The minimal IVC diameter (IVCmin) was measured during a “sniff.”  Two different parameters, indexed IVC size (VCDi) and IVC collapsibility index (IVCCI), were then used to evaluate volume.

VCDi = (IVCmax)/(BSA)
IVCCI = [(IVCmax – IVCmin) / IVCmax]

A second study compared IVC caval index (percent collapse with respiration) as well as diameter with RA pressure as determined by catheterization.  These measurements were also taken within 2cm of the right atrium using a subcostal view.  Caval index demonstrated the best correlation with RA pressures.

These criteria are similar to those in the previously discussed study, however more easily applicable particularly in the ED setting where BSA is not immediately available and rough estimates are more appropriate.  An important note however, is that IVC measurement does NOT accurately predict right atrial pressure in patients who are being artificially ventilated.

While certainly not the answer in every situation, volume assessment by IVC ultrasound is a quick and noninvasive method for initial evaluation and initial treatment decisions.  It may also be useful in determining which patients would benefit from more invasive monitoring.

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