Central venous access catheterization is one of the most common procedures performed by physicians. Site selection for access includes the internal jugular vein and subclavian vein. Trendelenburg position likely decreases the incidence of venous air embolism during these procedures. At least 25° of Trendelenburg position using the lateral approach and more than 20° of head rotation (maximum) results in the largest cross-sectional area of the internal jugular vein. The largest subclavian vein size is obtained when the patient is in moderate Trendelenburg position (15° head down) with the head straight up and the shoulders lying flat on the bed. The distance between the sternoclavicular joint and the point on the lower border of the clavicle at which the subclavian vein crosses, measured as overlap length (OL), increases with lower shoulder position. Lowering the shoulders facilitates needle entry into the subclavian vein, decreases the likelihood of an arterial puncture, and reduces the risk of excessive needle advancement. Shoulder neutral position produces maximal overlap of the medial third or more of the clavicle. The “bump” position (shoulder forward with head turned) increases the likelihood of successful central venous catheter placement.