Emergency medicine ultrasound has the basic goal of improving patient care. This chapter strives to provide a "visual blueprint" for the reader who uses emergency medicine ultrasonography in his or her practice. It is intended to serve as a practical imaging reference when an emergency screening ultrasound examination (EUS) is being performed and assumes a basic knowledge and experience base in ultrasound examinations. For practitioners without this prerequisite body of knowledge, it may provide useful information about the scope of the EUS examination.
Success in performing an EUS is dependent on the physician's goal-directed approach to each examination. This demands that the physician uses ultrasound to identify, confirm, or exclude specific sonographic findings that are consistent with specific disease states or life-threatening conditions.
Basic ultrasound information—including transducer recommendations, scanning protocols, anatomic schematics, and ultrasound images—are presented throughout the chapter. Applicable protocols are patterned after imaging guidelines of the American Institute of Ultrasound in Medicine as well as the authors' collective experiences. The issues of the efficacy, accuracy, and/or sensitivity of this modality are not debated. Once again, this chapter is not presented as a primary instructional tool, but rather as a rapid visual review for the physician trained in EUS applications.
Sonography is performed using transducers of varying frequencies and configurations (Fig. 24.1). Lower or higher frequencies are selected for more or less depth of penetration. Many manufacturers produce multifrequency transducers available with small or large footprints. Different crystal orientations and phased array technologies allow for purpose built probes that emphasize detail (linear) or maximize the viewing area (curved). The various transducers recommended for use in the EUS include:
- Microconvex: This transducer has the advantage of a tight curvature and small footprint that allows for easy access between ribs and for subxiphoid imaging. This is an excellent transducer for the E-FAST, especially for the beginner who may have difficulty scanning or interpreting images with rib shadowing present. This probe is also helpful in the thin patients with a high-positioned gallbladder requiring intercostal windows for optimal imaging. These transducers are generally more expensive than the standard curve-linear transducer.
- Convex Array: Considered a standard abdominal transducer, it provides wide near and far fields of view (ideal in evaluating the aorta in long axis). The large footprint of this type of transducer may make subxiphoid cardiac imaging difficult, as will the noted presence of "rib shadowing" which is inevitable with this transducer in scanning the right/left upper quadrants in the coronal plane. This is the transducer of choice for abdominal imaging and is used by many vascular laboratories in evaluating the abdominal aorta.
- Phased Array: This transducer is the transducer of choice for cardiac ultrasound. Whereas a typical probe's imaging sector is determined by physical orientation of its crystals, phased array technology allows for electronic steering of the ultrasound beam. This results in a narrow, near field of ...