Studies demonstrate CVP correlation with Caval Index.
- Caval Index (CI) = [(IVCexp - IVCinsp) / IVCexp] x 100%
Additionally, studies have shown that CVP is not a reliable indicator of fluid status and volume responsiveness (benefit from additional IVF).
The extremes of IVC diameter (complete collapse or plethora) in conjunction with cardiopulmonary pocus (EF, pulmonary edema) may be helpful in determining fluid tolerance (additional IVF will not cause harm).
*2 small (N 23, 39), single center studies (single operator only) in septic, ventilated patients showed correlation between fluid responsiveness and Distensibility Index (DI) & Variability Index (VI). Results have not been reproduced.
Utilize PLR with LVOT VTI (or possibly CFT/CBF - few small studies, needs more rigorous studies) to better assess volume responsiveness.
IVC plethora highly sensitive for etiologies of high right sided pressures (PE, CHF, Tamponade, PTX, etc). Lacks specificity.

*Barbier C, Loubiéres Y, Schmit C, et al. Respiratory changes in inferior vena cava diameter are helpful in predicting fluid responsiveness in ventilated septic patients. Int Care Med 2004; 30:1740–1746.

*Feissel M, Michard F, Faller JP, et al. The Respiratory Variation in Inferior Vena Cava Diameter as a Guide to Fluid Therapy. Int Care Med 2004;30:1834–1837.

Marik P, Cavallazzi R. Does the Central Venous Pressure Predict Fluid Responsiveness? An Updated Meta-Analysis and a Plea for Some Common Sense. Crit Care Med 2013;41(7):1774–1781.