The purpose of this observational study is to evaluate and compare the anatomical safety margins of the subclavian vein using ultrasound. Medical professionals commonly use the subclavian vein to insert central venous catheters, but nearby vulnerable structures, such as the lung and artery, can be at risk during the procedure.

This study investigates two different ultrasound probe positions: supraclavicular (above the collarbone) and infraclavicular (below the collarbone). It also examines how changing the patient's arm position (from resting in a neutral position to being raised at a 90-degree angle) affects the distance between the vein and these vulnerable structures.

Participants are adult patients scheduled for surgery under general anesthesia who already require ultrasound-guided vascular access. Immediately after falling asleep from anesthesia, researchers will perform a brief 3 to 5-minute ultrasound scan of the collarbone area. This is a strictly non-invasive imaging study; no research-related needle punctures or catheter insertions will be performed. The findings aim to provide robust anatomical evidence to make future vascular procedures safer for patients.

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.

Inclusion Criteria:

• Patients requiring ultrasound-guided vascular procedures.
• Age between 20 and 79 years.
• Patients who have voluntarily provided written informed consent for this clinical study.
• American Society of Anesthesiologists (ASA) physical status classification I, II, or III.

Exclusion Criteria:

• Anatomical variations of the clavicle (e.g., history of clavicle fracture).
• Suspected thrombosis at the target site.
• Known anatomical abnormalities of the subclavian vein or artery.
• Inability to abduct the arm (e.g., due to shoulder joint abnormalities).
• Patient refusal to participate.

Need for ultrasound-guided vascular access for general anesthesia

Individual participant data (IPD) will not be shared to protect patient privacy and confidentiality, in accordance with the Institutional Review Board (IRB) regulations. Only aggregated and anonymized data will be presented in the final publication.