The Cardiac Caval Index: Improving Noninvasive Assessment of Cardiac Preload

Objectives: Inferior vena cava (IVC) pulsatility quantified by the Caval Index (CI) is characterized by poor reliability, also due to the irregular magnitude of spontaneous respiratory activity generating the major pulsatile component. The aim of this study was to test whether the IVC cardiac oscillatory component could provide a more stable index (Cardiac CI-CCI) compared to CI or respiratory CI (RCI). Methods: Nine healthy volunteers underwent long-term monitoring in supine position of IVC, followed by 3 minutes passive leg raising (PLR). CI, RCI, and CCI were extracted from video recordings by automated edge-tracking and CCI was averaged over each respiratory cycle (aCCI). Cardiac output (CO), mean arterial pressure (MAP) and heart rate (HR) were also recorded during baseline (1 minutes prior to PLR) and PLR (first minute). Results: In response to PLR, all IVC indices decreased (P <.01), CO increased by 4 ± 4% (P =.055) while HR and MAP did not vary. The Coefficient of Variation (CoV) of aCCI (13 ± 5%) was lower than that of CI (17 ± 5%, P <.01), RCI (26 ± 7%, P <.001) and CCI (25 ± 7%, P <.001). The mutual correlations in time of the indices were 0.81 (CI-RCI), 0.49 (CI-aCCI) and 0.2 (RCI-aCCI). Conclusions: Long-term IVC monitoring by automated edge-tracking allowed us to evidence that 1) respiratory and averaged cardiac pulsatility components are uncorrelated and thus carry different information and 2) the new index aCCI, exhibiting the lowest CoV while maintaining good sensitivity to blood volume changes, may overcome the poor reliability of CI and RCI.