The Cardiac Caval Index: Improving Noninvasive Assessment of Cardiac Preload

Area of Science:

• Cardiovascular Physiology
• Medical Imaging Analysis
• Hemodynamics

Background:

• Inferior vena cava (IVC) pulsatility, quantified by the Caval Index (CI), suffers from poor reliability due to inconsistent respiratory variations.
• Existing indices like CI and respiratory CI (RCI) are influenced by spontaneous breathing patterns, limiting their clinical utility.

Purpose of the Study:

• To evaluate a novel index, the averaged cardiac CI-cardiac component (aCCI), derived from IVC oscillations.
• To compare the stability and sensitivity of aCCI against traditional CI and RCI in response to fluid loading via passive leg raising (PLR).

Main Methods:

• Long-term monitoring of the IVC in nine healthy volunteers using automated edge-tracking.
• Calculation of CI, RCI, and aCCI before and during a 3-minute passive leg raising (PLR) maneuver.
• Measurement of cardiac output (CO), mean arterial pressure (MAP), and heart rate (HR) during baseline and PLR phases.

Main Results:

• The aCCI demonstrated the lowest Coefficient of Variation (CoV) at 13±5%, significantly lower than CI (17±5%), RCI (26±7%), and the overall cardiac CI-CCI (25±7%).
• Indices showed decreased values post-PLR, with CO increasing slightly (4±4%, P=.055), while HR and MAP remained stable.
• Temporal correlations revealed low agreement between respiratory and cardiac components (RCI-aCCI: 0.2), suggesting distinct physiological information.

Conclusions:

• Respiratory and cardiac pulsatility components of the IVC are largely uncorrelated, providing complementary information.
• The aCCI exhibits superior reliability (lower CoV) and maintains sensitivity to blood volume changes, potentially overcoming the limitations of traditional CI and RCI.