To determine the superior vena cava (SVC) collapsibility index (CI), I use transesophageal echocardiography (TEE) to obtain a midesophageal bicaval view of the superior vena cava (SVC) in the long axis. I’ll then apply M-mode through the SVC to determine the maximum and minimum diameters (Dmax and Dmin, respectively) over the respiratory cycle.
CI = 100 x (Dmax – Dmin) / Dmax
>36% is the threshold the literature cites to indicate fluid responsiveness in patients with sepsis receiving mechanical ventilation.