IVC Collapsibility → RA Pressure
Estimation of right atrial pressure from inferior vena cava diameter and its inspiratory collapse on echocardiography (ASE/Rudski criteria).
Right atrial pressure is estimated non-invasively from the diameter of the inferior vena cava and the degree to which it collapses during a sniff, measured subcostally on echocardiography. RAP is then used to complete tricuspid-regurgitation-based pulmonary artery systolic pressure estimates.
📐 Formula
RAP ≈ 3 mmHg (IVC ≤ 21 mm, > 50% collapse); ≈ 15 mmHg (IVC > 21 mm, < 50% collapse); ≈ 8 mmHg intermediate
🎯 When to Use
- Estimating right atrial (central venous) pressure during a transthoracic echo.
- Deriving pulmonary artery systolic pressure (adds RAP to the TR-jet gradient).
- Assessing volume status and right-heart filling pressures.
⚙️ How It Works
- The IVC is imaged in the subcostal long axis and its maximal diameter measured ~1–2 cm from the right atrial junction at end-expiration.
- The patient sniffs and the percentage reduction in diameter (collapsibility) is assessed.
- A small, briskly collapsing IVC implies low RAP; a dilated, non-collapsing IVC implies high RAP.
📊 Interpreting the Result
- IVC ≤ 21 mm with > 50% collapse → RAP ~3 mmHg (range 0–5).
- IVC > 21 mm with < 50% collapse → RAP ~15 mmHg (range 10–20).
- Discordant findings (one criterion only) → intermediate RAP ~8 mmHg (range 5–10).
⚠️ Limitations & Pitfalls
- Unreliable in mechanically ventilated patients, where IVC dynamics are reversed/blunted.
- Trained athletes may have a dilated IVC with normal pressures; poor subcostal windows limit assessment.
- Provides a category estimate, not a precise pressure; invasive measurement remains the reference standard.
📚 References
- Rudski LG, et al. Guidelines for the echocardiographic assessment of the right heart in adults (ASE). J Am Soc Echocardiogr. 2010;23:685–713.
- Lang RM, et al. Recommendations for cardiac chamber quantification by echocardiography in adults. J Am Soc Echocardiogr. 2015;28:1–39.
⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.