Superior Vena Cava (SVC) Collapsibility Index (CI)

To determine the superior vena cava (SVC) collapsibility index (CI), I use transesophageal echocardiography (TEE) to obtain a midesophageal bicaval view of the SVC in the long axis. I’ll then apply M-mode through the SVC to determine the maximum and minimum diameters (D_max and D_min, respectively) over the respiratory cycle.

CI = 100 x (D_max – D_min) / D_max

>36% is the threshold cited in the literature to indicate fluid responsiveness in patients with sepsis receiving mechanical ventilation.