The longitudinal subcostal view on bedside ultrasound can be very helpful at addressing a patient's fluid status. Take a look at the diameter of the IVC 2 cm proximal to the hepatic vein on this view and ask the patient to quickly sniff. If the patient has normal fluid status, the diameter of the IVC will collapse approximately 50%.
If you notice that the IVC completely collapses during the sniff, the finding is highly accurate at predicting hypovolemia and a low CVP.
If, on the other hand, the IVC doesn't appear to collapse much at all, the finding is highly accurate at predicting a high CVP and elevated right atrial pressure. This may occur in the presence of fluid overload from decompensated CHF, cardiac tamponade, and conditions associated with RV failure (e.g. massive pulmonary embolism).
