From a recent study:
The purpose of this study is to evaluate the utility of IVC diameter, using echocardiography as a marker of volume overload and the relationship between these parameters and N-terminal pro-B natriuretic peptide (NT-proBNP) in patients with systolic heart failure (HF).
We included 136 consecutive patients with systolic HF (left ventricular ejection fraction, less than 50%), including 80 patients with acutely decompensated HF and 56 patients with compensated HF as well as 50 subjects without a diagnosis of HF. All patients underwent transthoracic echocardiography to assess both their IVC diameters and the degree of inspiratory collapse (greater than or equal to 50%, less than 50%, and no change [absence] groups); NT-proBNP levels were measured, and these data were compared between the 2 groups.
Inferior vena cava diameter and NT-proBNP were significantly higher among the patients with HF than among the control subjects (21.7 ± 2.6 vs 14.5 ± 1.6 mm, P less than .001 and 4789 [330-35000] vs 171 [21-476], P less thatn .001). The mean IVC diameter was higher among the patients with decompensated HF than among the patients with compensated HF (23.2 ± 2.1 vs 19.7 ± 1.9 mm, P less than .001). The values of NT-proBNP were associated with different collapsibility of IVC subgroups among HF patients. The NT-proBNP levels were 2760 (330-27336), 5400 (665-27210), and 16806 (1786-35000), regarding the collapsibility of the IVC subgroups: greater than or equal to 50%, less than 50%, and absence groups, P less than .001, respectively, among HF patients. There was a significant positive correlation between IVC diameter and NT-proBNP (r = 0.884, P less than .001). A cut off value of an IVC diameter greater than or equal to 20.5 mm predicted a diagnosis of compensated HF with a sensitivity of 90% and a specificity of 73%.
Inferior vena cava diameter correlated significantly with NT-proBNP in patients with HF. Inferior vena cava diameter may be a useful variable in determining a patient's volume status in the setting of HF..
What's interesting here is that these echocardiographic parameters are nothing more than surrogates for CVP measurements, which have, deservedly or not, fallen into disfavor in evaluating patients with shock. Nevertheless it seems to perform well in the setting of heart failure.