From the Guidelines
The normal inferior vena cava (IVC) diameter is less than 2.1 cm, and a decrease of more than 50% in diameter during inspiration suggests normal right atrial (RA) pressure of 0-5 mm Hg. A normal IVC typically measures between 1.5 to 2.1 cm in diameter when measured at end-expiration, as stated in the recommendations for cardiac chamber quantification by echocardiography in adults 1. The IVC should demonstrate respiratory variation with a decrease in diameter of at least 50% during inspiration when right atrial (RA) pressure is normal. This respiratory variation occurs because during inspiration, negative intrathoracic pressure increases venous return to the right heart, causing the IVC to collapse partially.
Some key points to consider when evaluating IVC diameter and collapse include:
- The diameter of the IVC 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 measurement should be made perpendicular to the IVC long axis for accuracy.
- Evaluation of the inspiratory response often requires a brief sniff, as normal inspiration may not elicit this response.
- If the IVC diameter is larger than 2.1 cm and/or shows less than 50% collapse with inspiration, this may indicate elevated right atrial pressure, which can be seen in conditions like heart failure, pulmonary hypertension, or fluid overload states.
It is essential to note that in normal young athletes, the IVC may be dilated in the presence of normal pressure, as mentioned in the study 1. Therefore, the combination of an IVC diameter less than 2.1 cm with greater than 50% collapse during inspiration strongly suggests normal right atrial pressure.
From the Research
Normal IVC Diameter
- The normal IVC diameter is less than 1.2 cm is not supported by the provided studies, however, study 2 suggests that the mean IVC diameter is around 1.9 cm.
- A 50% decrease in the diameter when the RA pressure is normal (0–5 mm Hg) is not directly mentioned in the provided studies.
IVC Diameter Measurement
- Study 2 compared different acquisition techniques for IVC measurement by point-of-care ultrasonography (POCUS) and found that the sub-xiphoid transabdominal long axis (LA) view had the highest intra-class correlation coefficient (ICC) for B-mode measurements.
- Study 3 used a handheld ultrasound device to measure IVC diameter and found that an increase in IVC diameter was associated with an increased risk of heart failure admission.