When placing the central line catheter in the left internal jugular vein under short-axis ultrasound guided, an operator should be stand around the lying patient's head. The investigators are going to evaluate to effects of the operator's location. (Above the midline of patient's head versus above the left extended axillary line)
When the left internal jugular vein catheterization under short-axis ultrasound guided, an operator should be stand around the lying patient's head. The investigators are going to evaluate to effects of the operator's location.