Transthoracic echocardiography (TTE) has major application in the intensive care unit (ICU). Proficiency in TTE allows the intensivist to determine the diagnosis of cardiopulmonary failure, develop management strategies, and follow the results of therapeutic interventions with serial examinations. By definition, critical care echocardiography (CCE) is performed by the intensivist in the ICU. The clinician acquires and interprets the image at the bedside, and uses the information to guide management. It follows that the intensivist must have a high level of skill in image acquisition, which requires a working knowledge of ultrasound physics, machine controls, and transducer manipulation. This chapter will review important elements of image acquisition with emphasis on transducer manipulation. The reader is referred to Chapters 2 and 3 for a comprehensive discussion of physics and machine controls.
Proficiency in CCE can be separated into basic and advanced levels. Basic CCE is performed as a goal-directed examination using a limited number of views. It is designed to answer very specific clinical questions at the bedside. Proficiency in advanced CCE requires a high level of skill in all aspects of image interpretation and acquisition. Advanced CCE allows a comprehensive evaluation of cardiac anatomy and function using TTE and Doppler echocardiography. Both basic and advanced CCE require skill in image acquisition.
The performance of TTE has challenges that relate to the fact that the heart is surrounded by lung and ribs, both of which block ultrasound transmission. Since ribs block ultrasound waves, cardiac transducers are designed with a small footprint to scan through the small rib interspace. During scanning, left arm abduction may increase the size of the interspace. Aerated lung also block ultrasound, so that positioning the patient in the left lateral decubitus position may be helpful because in this position the heart is moved from behind the sternum, and the left lung moves laterally, thus exposing more of the heart for examination. While the left lateral decubitus view improves visualization from the parasternal and apical views, the supine position is best for the subcostal examination.
The critically ill patient may be difficult to place in a favorable scanning position. Patients on ventilatory support, particularly when hyperinflated, may have very poor parasternal and apical windows. Very often, the subcostal view yields the only acceptable image. Transthoracic echocardiography image quality may be poor in the edematous or muscular patient. Obesity presents a special challenge for two reasons. It attenuates the penetration of ultrasound. In addition, abdominal obesity elevates the diaphragm, particularly when the patient is supine and when passive on ventilatory support. The heart is then rotated into a more vertical position. This makes it difficult to obtain properly oriented parasternal views. The presence of chest dressings, wounds, or subcutaneous air also degrade TTE image quality. Transesophageal echocardiography (TEE) is always an alternative in the patient who fails TTE. Artifacts in echocardiography relate, in part, to the fact that the heart is a ...