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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

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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. 

Measuring CVP

Examples

High CVP

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

High CVP
Normal CVP

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.