What is the normal diameter of the Inferior Vena Cava (IVC) in adults?

Normal IVC Diameter in Adults

The normal inferior vena cava (IVC) diameter in adults is less than 2.1 cm when measured approximately 1-2 cm from the cavoatrial junction. 1

Measurement Technique

• Position the patient supine and use a phased array or curvilinear probe in the subcostal view to visualize the IVC as it enters the right atrium 2
• Measure the IVC diameter at end-expiration approximately 0.5-3.0 cm (or 1-2 cm per most guidelines) below its junction with the right atrium 1, 3
• The measurement should be taken in the long-axis view, perpendicular to the IVC long axis 3

Normal Values and Clinical Interpretation

• IVC diameter < 2.1 cm is considered normal 1, 3
• When the IVC diameter is < 2.1 cm AND collapses > 50% with a sniff maneuver, this suggests normal right atrial pressure of 3 mmHg (range 0-5 mmHg) 1, 3
• IVC diameter > 2.1 cm indicates distension and suggests elevated right atrial pressure, particularly when associated with decreased inspiratory collapse (< 50% with sniff or < 20% with quiet inspiration) 1, 2

Respiratory Variation Assessment

• Normal respiratory collapse is > 50% during a sniff maneuver in spontaneously breathing patients 1, 2
• The inspiratory response assessment often requires a brief sniff rather than normal inspiration, as normal breathing may not elicit adequate collapse 3
• Reduced collapsibility (< 50%) combined with IVC diameter > 2.1 cm suggests elevated right atrial pressure of 15 mmHg (range 10-20 mmHg) 1, 3

Important Clinical Caveats

• Normal young athletes may have dilated IVC in the presence of normal pressure, which can lead to overestimation of right atrial pressure 3
• Severe tricuspid regurgitation may affect IVC dynamics independent of volume status 2
• High intra-abdominal pressure can falsely suggest IVC distension despite normal right atrial pressure 2
• IVC assessment has limited reliability in mechanically ventilated patients due to altered intrathoracic pressure dynamics 2

Integration with Clinical Context

• A dilated IVC (> 2.1 cm) with minimal respiratory variation should prompt evaluation for conditions causing elevated right-sided pressures, including pulmonary hypertension, right ventricular failure, or tricuspid regurgitation 1, 2
• When evaluating for right ventricular pathology, combine IVC assessment with RV size (RV/LV ratio > 1.0 indicates enlargement), septal flattening, and TAPSE measurements 2
• Severe hypovolemia presents with small, collapsing IVC (often with > 50% collapse) and small cardiac chamber sizes 2