Classical positioning decreases the cross-sectional area of the subclavian vein

Background: The classic position for subclavian venipuncture is the Trendelenberg position, with the head turned away and placement of a shoulder roll (SR). The purpose of this study was to determine whether this position results in the largest cross-sectional area (CSA) of the subclavian vein (SV). Methods: Adult volunteers underwent ultrasound imaging of the right SV in supine and Trendelenberg positioning in the following four head and shoulder positions: head neutral with the chin midline (NL), head turned away (TA), head neutral with an SR, and head TA with an SR (TA/SR). The mean CSA of the SV in each position was calculated. Statistical significance was determined using Student's t, Wilcoxon signed rank, and Bonferroni test. Results: Eighteen adults participated in the study. Trendelenberg positioning significantly increased the CSA of the SV in all positions except NL compared to supine positioning (P < .03). An SR significantly decreased SV CSA in all positions. The largest SV CSA was obtained in the TA/Trendelenberg position (1.41 ± .06 cm²). The classic positioning for subclavian cannulation, TA/SR/Trendelenberg, resulted in a significantly smaller CSA than TA/Trendelenberg position (1.27 ± .06 cm², 15% reduction, P < .01). Conclusions: The classic recommended maneuvers of turning the head and placing an SR significantly reduce the CSA of the SV. Positioning patients in Trendelenberg with the head turned away without an SR optimizes SV size. Positioning patients in this manner may serve to reduce the morbidity associated with percutaneous access of the SV.