What is the most commonly used view to assess inferior vena cava (IVC) size and collapse?

Subcostal View Is the Recommended View for Assessing IVC Size and Collapse

The subcostal view is the most commonly used and recommended view for assessing inferior vena cava (IVC) size and collapse in clinical practice. 1

Rationale for Using the Subcostal View

The subcostal view offers several advantages for IVC assessment:

• The American Society of Echocardiography and European Association of Cardiovascular Imaging explicitly recommend that "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
• This view provides optimal visualization of the IVC as it enters the right atrium
• The measurement should be made perpendicular to the IVC long axis for accuracy 1
• The subcostal view allows assessment of both IVC diameter and respiratory variation (collapsibility)

Proper Technique for IVC Assessment

When assessing the IVC using the subcostal view:

1. Position the patient supine
2. Place the ultrasound probe in the subxiphoid region
3. Obtain a long-axis view of the IVC as it enters the right atrium
4. Measure the IVC diameter 1-2 cm from the junction with the right atrium
5. Measure both maximum (expiration) and minimum (inspiration) diameters
6. Calculate the collapsibility index to estimate right atrial pressure

Clinical Significance of IVC Assessment

IVC assessment provides valuable information about:

• Right atrial pressure estimation
• Volume status assessment
• Evaluation of right heart function
• Response to respiratory variation

According to guidelines, an IVC diameter < 2.1 cm that collapses > 50% with a sniff suggests normal right atrial pressure (approximately 3 mmHg), while an IVC diameter > 2.1 cm that collapses < 50% suggests elevated right atrial pressure (approximately 15 mmHg) 1

Alternative Views and Their Limitations

While the subcostal view is preferred, alternative approaches may be necessary in certain situations:

• The transhepatic view can be used when the subcostal view is not obtainable 2, 3
• However, studies show wide limits of agreement between subcostal and transhepatic measurements, with variations up to 4 mm in both directions 2
• The percentage variation in IVC size with respiration is more reliable than absolute diameter when using alternative views 2
• The transhepatic view tends to underestimate IVC collapsibility compared to the subcostal view 3

Common Pitfalls and Considerations

When assessing the IVC, be aware of:

• The IVC collapses asymmetrically into an elliptical form during respiration, which can affect measurements from different views 3
• Normal young athletes may have a dilated IVC despite normal right atrial pressures 1
• In mechanically ventilated patients, the relationship between IVC measurements and volume status is altered
• Measurements should be made perpendicular to the long axis of the IVC to avoid oblique measurements that can overestimate diameter

In conclusion, while alternative views may be used when necessary, the subcostal view remains the gold standard for IVC assessment due to its reliability, standardization in guidelines, and optimal visualization of both IVC diameter and respiratory variation.