For nearly two decades, acute care surgeons have successfully performed, interpreted, and taught bedside ultrasound examinations of patients who are injured or critically ill.1–13 Real-time imaging allows the surgeon to receive instantaneous information about the clinical condition of the patient and, therefore, helps to expedite the patient’s management, which is important in patients with time-sensitive diagnoses. In many centers, ultrasound machines are owned by surgeons or surgical departments and are part of the standard equipment in the trauma resuscitation area as well as in the intensive care unit (ICU). While diagnostic peritoneal lavage (DPL) and computed tomography (CT) scanning are still valuable diagnostic tests for the detection of intra-abdominal injury in patients, ultrasound is not only faster but also noninvasive and painless.
As an extension of the physical examination, acute care surgeons routinely use ultrasound in the trauma setting to augment their physical examination in patients with suspected torso and extremity trauma, not only within the standard hospital resuscitation area but also in a variety of other locales. Additionally, ultrasound may be used to supplement the history and physical examination of nontrauma patients presenting with acute abdominal pain and a variety of other time-sensitive diagnoses in the emergency department. Finally, ultrasound may be used in the ICU in a variety of ways to facilitate procedures, detect complications, and augment a surgeon’s physical examination.
As such, this chapter begins with a basic introduction to select principles of ultrasound physics and then covers the components, indications, and pitfalls of the common, focused ultrasound examinations used by acute care surgeons who are evaluating trauma patients, nontrauma patients presenting with acute symptoms, and, finally, critically ill patients in the ICU.
Ultrasonography is operator dependent and, therefore, an understanding of select principles of ultrasound imaging is necessary so that images may be acquired rapidly and interpreted correctly. Knowledge of some of these basic principles enables the acute care surgeon to select the appropriate transducer, optimize resolution of the image, and recognize artifacts. Some basic terms and principles of physics relative to ultrasound imaging in the acute setting are defined in Tables 16-1 to 16-3.
Table 16-1 Ultrasound Physics Terminology Relevant to Ultrasound Imaging |Favorite Table|Download (.pdf)
Table 16-1 Ultrasound Physics Terminology Relevant to Ultrasound Imaging
|Ultrasound||High-frequency (>20 kHz) mechanical radiant energy transmitted through a medium|
- Diagnostic ultrasound: 1–30 MHz
- Medical diagnostic ultrasound: 2.5–10 MHz
|Frequency||Number of cycles/s (106 cycles/s = 1 MHz)|
- Increasing frequency improves resolution
- Higher-frequency transducers (e.g., 7.5 MHz) provide better resolution of tissues
|Propagation speed||Speed with which wave travels through soft tissue (1,540 m/s). Propagation speed (determined by density and stiffness of medium) is greater in solids than in liquids and greater in liquids than in gases
- To image an organ, the ultrasound wave must be emitted from the transducer, travel through a medium (soft tissue or liquid), ...