The influence of passive leg elevation on the cross-sectional area of the internal jugular vein and the subclavian vein in awake adults

The aim of this study was to evaluate the influence of passive leg elevation and Trendelenburg position on the cross-sectional area (CSA) of the internal jugular (IJ) and subclavian veins (SCV). Ultrasound imaging was used for the following measurements of both the IJV and SCV: baseline in the supine position (control); Trendelenburg position 15°; reverse Trendelenburg position 15° and passive leg elevation 50°. Twenty healthy male volunteers were studied. Mean CSA of the IJV was 1.12±0.57 cm² in control, 1.66±0.67 cm² in the Trendelenburg position (P <0.0001 vs. control), 0.38±0.23 cm² in the reverse Trendelenburg position (P <0.0001 vs. control), and 1.40±0.64 cm ² during passive leg elevation (P <0.0001 vs. control). Mean CSA of the SCV was 0.92±0.23 cm² in control, 0.98±0.17 cm² in the Trendelenburg position, 0.86±0.21 cm² in the reverse Trendelenburg position and 0.93±0.18 cm² during passive leg elevation. The results indicate that passive leg elevation increases the CSA of the IJV, but has little effect on the SCV. The CSA of the IJV appears to be influenced more by gravitational factors than the SCV.