Central venous catheterization is widely used for various purposes during surgery. For central venous catheterization, subclavian vein is selected because of the relatively low risk of infection, long-term patency and low patient discomfort. The cross - sectional area of the subclavian vein is an important factor to increase success rate. Several studies have reported that the Trendelenburg position increases the cross-sectional area of the subclavian vein, and the lateral tilt position can change the cross-sectional area of the subclavian vein. However, the impact of lateral tilt position to the cross-sectional area of the subclavian vein is not clear. The ipsilateral position can increase the cross-sectional area of the subclavian vein, and the contralateral position can decrease the cross-sectional area by gravity.

In the first stage of this study, we compare the cross-sectional area of subclavian vein using ultrasonography in supine, ipsilateral, and contralateral tilt position.

Inclusion Criteria:

- the patients who receive elective neurosurgical surgery and require central venous catheter

Exclusion Criteria:

• the patients who have puncture site infection
• the patients who have chemoport, pacemaker in right subclavian vein
• the patients who had received right mastectomy or right pneumonectomy
• other contraindications for subclavian venous catheterization (eg. mass, hematoma, vegetation, and anticoagulation)