ABSTRACT
Ultrasound is an imaging modality that utilises high-frequency sound waves in order to image structures within the body. Use of ultrasound has become routine in the theatre environment to aid vascular line insertion, guide peripheral nerve blockade, e.g. interscalene nerve blocks, and in some centres to also guide catheter placement within the epidural space. In the critical care setting, ultrasound is routinely used for vascular line insertion, cardiac output monitoring, echocardiography, transcranial Doppler, pleural aspiration, ascitic drainage, assessment of hepatic portal vein flow and detection of venous thromboembolism. Doppler effect is a commonly observed phenomenon whereby sound waves reflected from a moving target are altered and have a different frequency from the incident sound wave. A good example of this is the noise of a racing car where the pitch of the car increases as it approaches the observer and then abruptly drops as it races past the observer.
