3 The technology
3.1 Ultrasound technology has long been used in interventional radiology to guide percutaneous procedures at sites such as the kidneys, liver, arterial and venous circulation, pleural cavity, gallbladder and joints. Real-time ultrasound guidance of CVC insertion provides the operator with visualisation of the desired vein and the surrounding anatomical structures before and during the insertion. The advantages of ultrasound-guided central venous catheterisation include the identification of the precise position of the target vein and the detection of anatomical variants and of thrombosis within the vessel, together with the avoidance of inadvertent arterial puncture. Ultrasound guidance therefore has the potential to reduce the incidence of complications related to initial venous puncture, which is the first stage of CVC insertion.
3.2 Two types of real-time ultrasound guidance are described: two-dimensional (2-D) imaging ultrasound guidance and audio-guided Doppler ultrasound guidance. Two-dimensional imaging ultrasound, which is the more commonly used method, provides a real-time grey-scale imaging of the anatomy. Audio-guided Doppler ultrasound generates an audible sound from flowing venous blood, which helps the operator localise the vein and differentiate it from its companion artery. The portable ultrasound machines can be used in operating theatres, accident and emergency departments, ITUs, HDUs and radiology suites, as well as at the bedside on the hospital ward.
3.3 Operators need to be trained to use ultrasound-guided techniques. Training involves not only acquiring the necessary manual skills, but also having a basic understanding of ultrasound principles and being able to interpret ultrasound images.