Femoral Vein Diameter Measurement Protocol

For the purpose of standardization, right femoral vein measurements were used in the study. The FV was visualized with B-mode US, 2–5 cm below the level of the inguinal ligament, just above the inguinal canal, from where the femoral artery was best palpated, without applying any pressure that could affect the diameter of the FV [10 (link)]. Next, FV diameter variation during the respiratory cycle [maximum FV diameter (FVD_max), minimum FV diameter (FVD_min)] was measured in the transverse view using a high-frequency linear array transducer [(VF 13–5; 4.1–12.1 MHz), Siemens, USA] on M-mode, and images were saved for reevaluation after the procedure. Using the values obtained, the FV collapsibility index (FV-Ci) was calculated with the following formula: FV-Ci = [(FVD_max–FVD_min)/(FVD_max)] × 100 [10 (link)] (Figure 1).