'Stop sign' position for subclavian ultrasound: a single-blinded observational study of subclavian vein dimensions.

Objective: Right subclavian vein (SCV) dimensions were evaluated on ultrasound and whether these change when the right upper limb is in a neutral position compared with the 'stop sign' position (shoulder abducted and externally rotated to 90°, elbow flexed to 90°), and when patients were positioned 30° head-up compared with lying supine.

Methods: Images of transverse and longitudinal views of the right SCV in patients ≥18 years, presenting with a range of conditions to a Regional Hospital Emergency Department, were recorded by two physicians in a randomly assigned, nonsequential order and measured blinded. Data were analysed with paired Student's t tests. N = 62.

Results: Primary outcome: cross-sectional area (CSA) of the right SCV in transverse images.

Secondary Outcomes: depth of SCV to skin and diameter of SCV on longitudinal images. There was no significant difference in CSA of the SCV in supine patients when the arm was in the stop sign position compared with neutral (mean CSA: 1.20 ± 0.42 and 1.15 ± 0.39 cm, respectively; P = 0.3). In patients positioned 30° head-up, the stop sign position significantly increased CSA from 0.65 ± 0.33 to 1.00 ± 0.38 cm (P < 0.0001).

Conclusions: Utilizing the stop sign position does not change SVC dimensions when patients are supine, however, may improve dimensions when lying supine is contraindicated.