Inferior Vena Cava Eval

Physiologically on spontaneous ventilation,  the diameter of the IVC decreases in response to inspiration when the negative intrathoracic pressure leads to an increase in RV filling from the systemic veins. The opposite happens with expiration. The diameter of the IVC and the percentage decrease in the diameter during inspiration correlate with RA pressure. Keep in mind that the IVC is commonly dilated and may not collapse in patients on ventilators, so its use to estimate RA pressure is not recommended.

Although FoCUS does not require you to make any measurement, we will take two measurements of the IVC since they correlate specifically with right atrial pressure. This pressure can then be used for determination of systolic pulmonary artery pressure using CWD (beyond FoCUS). In all likelihood you will be asked to determine if the CVP is high or not and low or not by visual estimation alone.

Measurement technique

The diameter of the IVC should be measured in the subcostal view with the patient in the supine position at <2.0 cm from the junction with the right atrium. We ask the patient to perform a sniff on interrogating the IVC. The diameter of the IVC decreases in response to inspiration when the negative intrathoracic pressure leads to an increase in RV filling. Note that the IVC is commonly dilated and may not collapse in patients on mechanical ventilators and so this estimating CVP based on IVC is not routinely used in such cases.

Nml IVC 02.gif

/

IVC Size
Changes w respiration or sniff maneuver
Estimated CVP
> 2.1 cm
< 50%
15 mmHg
< 2.1 cm
> 50%
3 mmHg
< 2.1 cm
< 50%
8 mmHg
> 2.1 cm
> 50%
8 mmHg

IVC measurement. On the left, IVC measurement. Red arrow head indicating approximate location. On the right, estimated RA or CVP based on size and collapsibility of the IVC. Blue arrow indicating low CVP and red indicating high CVP. In short, a >2.1cm measurement and minimal collapsibility is high CVP, a <2.1cm measurement and major collapsibility is low CVP and anything is between is a CVP of 8mmHg. 

 

Examples

High CVP

This patient's IVC is dilated >2.1cm and does not collapse when performing sniff test.

 
 

Not high or low CVP ("Normal CVP")

The IVC appears more than 2cm. It does collapse more than 50% on inspiration. Thus his CVP is estimated at 8mmHg without having a specific measurement

High CVP

This patient's IVC is dilated >2.1cm and does not collapse when performing sniff test.

 

Low CVP

Small IVC <2.1cm with more than 50% collapsability

 

Error in measurement

The image on the left displays a pulsatile structure, the aorta, and vertebral bodies posterior to it. On the right the liver encases the IVC so you see tissue anterior and posterior to it. 

Lets try distinguishing these two windows again since one will effectively visualize the aorta and the other, the IVC.

References

1.  Lang RM, Badano LP, Mor-Avi V, et al. Recommendations for cardiac chamber quantification by echocardiography in adults: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiogr. 2015;28(1):1-39.e14.

2.  Via G, Hussain A, Wells M, Reardon R, ElBarbary M, Noble VE, Tsung JW, Neskovic AN, Price S, Oren-Grinberg A, Liteplo A, Cordioli R, Naqvi N, Rola P, Poelaert J, Guliĉ TG, Sloth E, Labovitz A, Kimura B, Breitkreutz R, Masani N, Bowra J, Talmor D, Guarracino F, Goudie A, Xiaoting W, Chawla R, Galderisi M, Blaivas M, Petrovic T, Storti E, Neri L, Melniker L; International Liaison Committee on Focused Cardiac UltraSound (ILC-FoCUS); International Conference on Focused Cardiac UltraSound (IC-FoCUS). International evidence-based recommendations for focused cardiac ultrasound. J Am Soc Echocardiogr. 2014 Jul;27(7):683.e1-683.e33. doi: 10.1016/j.echo.2014.05.001. PMID: 24951446.

3. Gudmundsson P, Rydberg E, Winter R, Willenheimer R. Visually estimated left ventricular ejection fraction by echocardiography is closely correlated with formal quantitative methods. International Journal of Cardiology,
2005; Vol 101: Issue 2: 209-212. ISSN 0167-5273.