Basic principles of ultrasound and the use of lung ultrasound in the COVID-19 pandemic

Given that ultrasound use is increasing in healthcare, operators must be familiar with its physics in order to optimise the image and interpret potential artifacts. Ultrasound are sound waves at frequencies above the range of human hearing, that are transmitted from and received by an ultrasound transducer with piezoelectric properties. As it propagates through tissues, some of the ultrasound waves are reflected at tissue boundaries, leading to its detection by the ultrasound transducer. These are processed by the ultrasound machine and result in the generation of an image. Various settings can be adjusted to optimise the image, such as the frequency of the transmitted ultrasound wave, depth of the focal zone and the gain. Artifacts are presentations on the monitor of the ultrasound machine which are added, omitted, or are of improper brightness, location, shape, and size compared with true anatomical features. It can result in falsely perceived objects, missing structures or degraded images. The presence or absence of such artifacts in lung ultrasound can be valuable in the interpretation of the resulting image. In the setting of COVID-19, lung ultrasound has become increasingly useful in evaluating disease progression and providing a point-of-care radiological adjunct in clinical decision making. © World Federation of Societies of Anaesthesiologists 2022.