**1. An introduction to ultrasound**

Ultrasound was first introduced in the early 1950s; however, individual units were not available for use until the 1960s. Its initial application was primarily experimental, and it did not enter a clinical role until the 1970s. The first ultrasound machines were large, complex and required the subject to be immersed in water. The images were difficult to interpret, requiring extensive training. Technological improvements led to a more compact device and better software that decreased the delay from signal acquisition to image display. This optimized real-time scanning and opened the door for widespread clinical use to develop [1]. In the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1970s, studies were performed to evaluate the utility of bedside ultrasound to detect artificially instilled fluid into a cadaver's peritoneal cavity, and within 1 year of this research, the first case of ultrasound used to detect hemoperitoneum was published. The first publication on ultrasound use by an emergency medicine physician appeared in 1988, and research into its use in bedside trauma evaluation began in multiple centers across the globe [1].

There are also various ultrasound modes that allow us to address specific questions related to movement or flow. "B" mode (brightness mode) is primarily used for diagnostic imaging with two-dimensional displays in gray-scale based on the tissues echogenicity. "M" (motion) mode depicts the motion through time of structures along a single vertical line within the B-mode image. This mode is frequently used to look for subtle movement in images or better characterize the degree of movement experienced by a structure like as a heart valve [12]. Color flow mode depicts direction and flow velocity of fluids, such as blood within the heart or vessels. Power Doppler mode emits short bursts of waves, allowing more accurate localization of echo

The Evolving Role of Ultrasound in Emergency Medicine http://dx.doi.org/10.5772/intechopen.74777 147

The phased array probe is typically used in cardiac evaluation, and four basic views are obtained. Parasternal long view visualizes the mitral valve, left ventricle and right ventricle. Apical four view is demonstrated just infero-lateral to the nipple, and demonstrates both atria and ventricles. A pericardial effusion can be easily demonstrated using ultrasound. An acute pericardial effusion of as little as 50 mL can lead to tamponade and requires immediate intervention [14, 15]. Small effusions usually occur in the posterior and inferior areas, and as they grow they extend to the apex. Moderate effusions are defined as 10–20 mm (anterior plus posterior) separation from the pericardial sac and the myocardium, and a large effusion is >20 mm [12]. The effusion will appear as a dense anechoic or hypoechoic area surrounding the heart, between the muscle and the hyperechoic pericardial sac [12]. It is important to determine if an effusion is causing tamponade, a condition when fluid accumulation in the pericardial sac increases the pressure enough to overcome the diastolic pressure of the right heart and prevent sufficient filling [14, 16]. Using ultrasound, visualization of right ventricle (RV) collapse during diastole is more reliable to determine the presence of tamponade, with a sensitivity of 48–100% and specificity of 72–100%. Right atrial collapse has a sensitivity of 50% in early tamponade and 100% in late tamponade, but a poor specificity of 33–100% [14, 17]. If the effusion has pus, blood or fibrin, it can appear less hypoechoic than expected. It is important to differentiate these more obscure pericardial effusions from the "epicardial fat pads" that some patients will have, and performing the ultrasound in a supine position will help as fluid should collect posteriorly and a hypoechoic layer only apparent anteriorly most likely represents fat [12].

The FOCUS (focused cardiac ultrasound) exam was created to protocolize a comprehensive exam looking for pericardial effusion, relative chamber size, global cardiac function and volume status (via left ventricle size, ventricle function or inferior vena cava size and change with respirations) [15]. In the hands of skilled practitioners, this exam can lead to decreased

In determining the left ventricle (LV) function, there are three parameters used to give a rough estimate of "good," "moderate" or "poor" ejection fraction. All parts of the ventricle wall should contract equally and symmetrically toward the its center, the myocardia must

morbidity and mortality in blunt and penetrating trauma [15].

sources and is more sensitive in measuring flow velocity in low-flow states [12, 13].

**3. Diagnostic ultrasound**

**3.1. Cardiac ultrasound**

In the 1990s, additional advancements included color Doppler mode, the transvaginal transducer and multifrequency probes. The American College of Emergency Physicians (ACEP) offered its first emergency ultrasound course in 1990 and, along with the Society of Academic Emergency Medicine, published the first supporting position paper regarding emergency ultrasound in 1991 [2, 3]. ACEP then published the *Emergency Ultrasound Guidelines* in 2001, defining the scope of practice for emergency ultrasound and included recommendations for credentialing, quality assurance and standards for the examinations [4].

An emergency medicine ultrasound examination, also termed point-of-care ultrasound (POCUS) should be quick, focused, and performed for a specific condition for which it has proven utility. POCUS should be easily learned and attempt to demonstrate only a few easily recognizable findings at the bedside [1]. POCUS has continued to gain popularity due to the significant value it adds in decision-making, the immediate availability to imaging and the advancing technology with further device miniaturization and greater resolution [1]. In prehospital medicine, it is being investigated for its utility in expediting care prior to arrival and has demonstrated the ability to accurately assess trauma patients, allowing early communication of necessary resources to hospitals [5, 6]. It has also demonstrated significant utility in aeromedical evacuation and field assessment of remote-access trauma [7–10]. However, the remainder of this chapter will focus on the utility of POCUS in the hospital and its developing role in emergency department evaluation.
