From the Guidelines
Yes, this is normal. An inferior vena cava (IVC) diameter of 1.2 cm with a 50% decrease in diameter during respiration is consistent with normal right atrial (RA) pressure in the range of 0-5 mm Hg, as suggested by the American Society of Echocardiography and the European Association of Cardiovascular Imaging 1.
The IVC is a large vein that returns deoxygenated blood from the lower body to the right atrium of the heart. During normal respiration, the negative intrathoracic pressure during inspiration causes the IVC to collapse partially, which is reflected as a decrease in its diameter. A normal IVC typically measures less than 2.1 cm in diameter, and a respiratory variation (collapse) of greater than 50% correlates with normal right atrial pressures, as stated in the guidelines 1.
Key points to consider include:
- The IVC diameter should be measured in the subcostal view with the patient in the supine position at 1.0 to 2.0 cm from the junction with the right atrium, using the long-axis view 1.
- 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 1.
- Evaluation of the inspiratory response often requires a brief sniff, as normal inspiration may not elicit this response 1.
- IVC diameter < 2.1 cm that collapses > 50% with a sniff suggests normal RA pressure of 3 mm Hg (range, 0–5 mm Hg), whereas IVC diameter > 2.1 cm that collapses < 50% with a sniff suggests high RA pressure of 15 mm Hg (range, 10–20 mm Hg) 1.
This finding suggests normal cardiac function without evidence of right heart failure or volume overload. If the IVC were dilated with minimal respiratory variation, it would suggest elevated right atrial pressures, which could indicate conditions like heart failure, pulmonary hypertension, or volume overload.
From the Research
IVC Diameter and Collapsibility
- A normal IVC diameter is typically considered to be less than 2 cm 2.
- The IVC diameter can decrease by 50% or more with inspiration in patients with normal right atrial pressure 2.
- A study found that the IVC diameter decreased significantly during simulated blood loss, with a maximum IVC diameter in the long axis view decreasing from 1.5 ± 0.4 cm to 1.0 ± 0.3 cm at -20 mmHg of LBNP 3.
- The collapsibility index of the IVC, which is calculated by measuring the difference in IVC diameter between inspiration and expiration, can be used to estimate right atrial pressure 4.
Relationship between IVC Diameter and Right Atrial Pressure
- The IVC diameter has been found to correlate modestly with right atrial pressure, with a correlation coefficient of 0.41 in one study 5.
- However, changes in intravascular volume appear to correlate better with IVC diameter rather than with right atrial pressure 5.
- A decrease in IVC diameter has been found to be associated with a decrease in intravascular volume, even in the absence of changes in right atrial pressure 3.
Clinical Significance of IVC Diameter
- A dilated IVC without collapse is associated with poor survival, independent of other clinical and echocardiographic characteristics 2.
- The IVC diameter can be used as a marker of hypovolemia, with a decrease in IVC diameter indicating a decrease in intravascular volume 3, 6.
- The physical examination of the IVC diameter can be used to assess for anemia and hypovolemia, particularly in patients with suspected blood loss or dehydration 6.