Spinal anaesthesia. Ultrasound probe being prepared for use in placing a central line during surgery. Central line placement, the insertion of a central venous catheter, also called CVP insertion, is where surgeons place a catheter into a large vein in a patient's neck, chest or groin. This enables them to inject drugs or fluids, take blood samples, and monitor the central venous pressure. The ultrasound probe emits high-frequency sound waves, using the reflected echoes to build up a picture of internal body structures. This enables the surgeons to place the catheter accurately. Here, a gel is used to improve sound transmission, but the gel is placed inside a plastic covering to prevent cross-contamination. For a sequence showing central line placement, see clips K003/3590 to K003/3594.