Sonographic Safety Margins of Subclavian Vein: Effect of View and Arm Position

Central venous catheterization via the subclavian vein (SCV) is clinically favored due to its lower infection and thrombosis rates. However, traditional landmark-guided approaches carry the risk of mechanical complications, including pneumothorax and inadvertent arterial puncture. While real-time ultrasound guidance is strongly recommended to minimize these risks, there is an ongoing debate regarding the optimal probe position-specifically, the supraclavicular (SC) versus the infraclavicular (IC) view. Furthermore, clinical practitioners frequently utilize arm abduction to facilitate venous access, yet its dynamic effect on the anatomical safety margin (the distance between the SCV and adjacent vulnerable structures like the subclavian artery \[SCA\] and pleura) remains insufficiently quantified. This prospective, non-invasive observational study aims to address this knowledge gap. The study will enroll 55 adult patients scheduled to undergo Study Protocol: Timing: Immediately following the induction of general anesthesia, during the standard pre-procedural preparation period, a brief (approximately 3 to 5 minutes) ultrasound assessment will be conducted. Imaging: An investigator will obtain short-axis ultrasound views of the SCV from both the SC and IC positions. Positioning: In each ultrasound view, measurements will be recorded under two different patient arm positions: neutral (adducted alongside the torso) and 90-degree abduction. Data Acquisition: All ultrasound images will be captured at the end-expiratory phase and saved for offline analysis. Safety: The study involves solely non-invasive sonographic observation; no research-specific needle puncture, cannulation, or catheterization will be performed. Routine scheduled clinical care and procedures will proceed immediately after the brief image acquisition is complete. By analyzing sonographic parameters such as the SCV-SCA distance, vessel cross-sectional areas, depth to the pleura, and the SCV-SCA overlap index, this study seeks to elucidate the most secure anatomical window. Ultimately, the data will establish safer, evidence-based guidelines for patient positioning and ultrasound probe placement during SCV access.