A central venous catheter or central line is an intravenous line that is inserted into a large vein such as the internal jugular vein, the subclavian vein, the axillary vein, the femoral vein or a large vein in the arm. They can be temporary or can be implanted if they will be used several times. They are used when medication that can't be administered by mouth would also be harmful to a smaller vein. They are also used for direct measurement of blood gases and venous blood pressure.