Ultrasound is an imaging xof sound waves, which are transmitted into the body and are then reflected, back again from the structures being examined. Every ultrasound image is composed of a discrete number of lines of echo data placed side by side to appear continuous. Ultrasound imaging has a huge variety of applications for patients on intensive care units. Ultrasound can be used to guide an extremely wide range of procedures including guided central line insertion, pleural aspiration, regional anaesthesia, marking sites for safe insertion of chest drains, solid organ or tumour biopsy and various abdominal work. The best reflection from the shaft of an interventional needle is obtained when it is perpendicular to the direction of the ultrasound beam. Medical ultrasound has been used for more than 40 years, but its use in anaesthesia has only developed recently.