The beginning of ultrasonography can be traced to the development of sonar in World War II. Applications in the field of medicine became apparent as early as the 1950s. Although ultrasonography was initially considered a tool of radiologists, its use has spread to different subspecialties, notably cardiology and obstetrics, where it is now a routine and required skill. More recently, its benefits have been demonstrated for specific applications within emergency medicine. The American College of Emergency Physicians (ACEP) has issued position papers endorsing the 24-hour availability of ultrasound technology within the emergency department (ED) and its use by appropriately trained, experienced, and credentialed emergency physicians (1). In addition, a report by the American Institute of Ultrasound in Medicine agreed that ultrasound examinations may be performed by appropriately trained emergency physicians in (a) certain immediate or life-threatening situations in which ultrasound examination is needed and other ultrasound physicians are not available, (b) certain urgent conditions in which ultrasound physicians cannot provide timely service on a 24-hour-a-day, 7-day-a-week basis, and (c) situations in which ultrasound guidance may enhance the performance of certain procedures (2).

Emergency medicine residency programs are required to provide formal training in the emergent use of ultrasound as part of the core curriculum (1,3,4). Fellowships specializing in the use of ultrasound by emergency physicians already exist. It is now clear that the use of ultrasonography in the ED for specific indications is rapidly becoming a necessary skill.

The role of ultrasonography in the ED differs significantly from its previously recognized roles in other areas of medicine. For diagnostic purposes, ultrasound is generally used in the ED to answer a specific question, such as whether products of conception are clearly identifiable in the uterus. Its uses are limited to specific areas, and it is not intended to replace the more complete ultrasound studies typically performed by other specialists. Diagnostic ultrasonography has distinct advantages in the ED, where rapid, immediately available studies are crucial. It is possible to obtain adequate examinations even during the performance of cardiopulmonary resuscitation (5).

Ultrasound not only functions as a diagnostic tool in the ED but also provides guidance in the performance of various invasive procedures. It improves success rates and decreases complications in procedures commonly performed blindly (6,7,8,9,10,11,12). Ultrasound facilitates these procedures by allowing the clinician to visualize a needle or probe as it approaches the target, mark the skin surface above the target, or measure the distance from the skin surface to the target.

Uses of ultrasound in the ED have been studied in a number of applications specific to pediatric patients. Benefits have been demonstrated in all pediatric age groups, including neonates (13). Investigators have evaluated its usefulness
in cases involving pediatric trauma, removal of foreign bodies, adolescent pregnancies, pulseless electrical activity, and vascular line placement (10,11,12,13,14,15,16,17,18).

The chapters in this section are intended to serve not as a comprehensive instructional aid in the use of ultrasound technology but as an introduction to and review of the various techniques. As in the use and interpretation of any diagnostic procedure, routine standards must be applied. The clinician must develop understanding and competency in the areas of application, visualization, and interpretation of ultrasound images. Specific indications must be developed to avoid overuse of this technique. Definitive expertise in ultrasonography requires several years of subspecialty training. This is clearly not the goal for emergency physicians. However, training emergency physicians to perform and interpret ultrasound examinations for specific indications is possible in a reasonable period of time (18,19,20,21). ACEP has recommended minimum numbers of studies to be performed for proficiency in specific applications, and other authorities have suggested minimum hourly requirements in formal instruction, hands-on training, review of the literature, and formal review of studies with skilled sonographers (1,22,23). These suggested requirements are consistent with those currently recommended in other nonradiologic specialties utilizing ultrasound (23). Ongoing review and quality assurance are a necessary part of maintaining proficiency in ED ultrasonography.

Ultrasonography, like sonar, is based on the generation of sound waves and relies on the ability of tissues within their path to propagate and reflect these waves in order to produce a two-dimensional image of objects in its field. The ultrasound transducer converts electrical energy to sound energy, which propagates through body tissues (Fig. 132.1A). The denser the tissue, the better the sound waves are propagated. Sound waves propagate poorly through gas and do not reach structures separated from the transducer by a gas interface. This presents a problem for the unprepped patient with intestinal air who requires an abdominal scan. Wave propagation through bone is so rapid that ultrasound units are unable to accommodate it, and therefore objects behind bone cannot be detected.