Focused Echocardiography in the ICU
Technological advancements in portable ultrasound units have helped bring high-quality imaging to the bedside of the critically ill patient. The ability to obtain images of a quality that approaches traditional echocardiography imaging systems, including Doppler measurements, has enabled clinicians to obtain dynamic information about cardiac function and cardiopulmonary interaction that was not previously possible. Ultrasound examination, including focused echocardiography, has now become an integral part of care in many critical care units. The availability of transesophageal transducers for portable units has extended the utility of this diagnostic tool in critically ill patients.
KeywordsInferior Vena Cava Right Ventricle Stroke Volume Variation Right Ventricle Function Inferior Vena Cava Diameter
see B-mode imaging.
a measure of the resistance of tissue to the propagation of ultrasound. It is largely dependent on the density of the tissue and the speed of sound propagation through the tissue.
Insonation window located at the apex of the heart, approachable from the transthoracic and transesophageal modalities.
two dimensional imaging based on scanning over an area and mapping intensity in two dimensions. By repeating the imaging at a sufficiently fast scan rate, a real-time image can be obtained.
A form of imaging in which Doppler velocity signals are measured over an area, converted to a color map, and overlaid onto the corresponding 2D image.
refers to the longitudinal waves associated with sound traveling through a medium. Longitudinal waves consist of alternating pressure deviations.
A form of Doppler interrogation in which a continuous ultrasound is transmitted, with continuous receiving of the reflected waves and calculation of velocity. This mode is sensitive to velocities all along the beam, and thus is useful for finding the maximum velocity only but not where it is located.
A location on the surface of the body or in the esophagus/stomach that is free of interfering structures, allowing acquisition of an image.
an imaging mode consisting of a one-dimensional view recorded against time.
Transthoracic insonation window located to the left of the sternum, about the fourth intercostal space.
In pulsed Doppler or B-mode imaging, represents the rate at which the transducer is pulsed. Imaging of deeper structures requires more time for the ultrasound signal to be reflected from the deep structures, requiring a lower PRF, and less information that can be recorded.
A form of Doppler interrogation in which a pulse of ultrasound is transmitted, with the signal received during a specified time window corresponding to a known depth. This mode allows recording of velocities at a particular intracardiac location.
A mechanism of ultrasound signal loss that occurs when a wave is reflected away from a tissue interface of differing acoustic impedances.
The anatomic area that can be imaged at one time. For linear transducers, the scan area is a square below the transducer. For phased-array sector transducers such as that used in echocardiography, the scan area is pie-shaped, with the narrow angle directly under the transducer.
Transthoracic insonation window located in the epigastrum below the xyphoid process.
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