Performance of transesophageal echocardiography

Transesophageal echocardiography is technically easy and generally safe to perform in intubated critically ill patients. Nevertheless, it should be done only by specially trained physicians. Guidelines for appropriate training have been recommended by the American Society of Echocardiography ( Pearjman,.etiia/ 1992). In the

ICU, the examination is usually undertaken with the patient in the supine position. Before examination, the history is taken with emphasis on gastrointestinal-tract-related symptoms, such as dysphagia, hematemesis, and esophageal varices, and upper gastrointestinal surgical procedures. The mean duration of a transesophageal echocardiography examination is about 20 min. One transesophageal echocardiography daily is generally sufficient, but the procedure can be repeated if necessary. Echocardiographic images are recorded on videotape, together with an ECG lead and respiratory flow obtained using a pneumotachograph, the signal of which is amplified and displayed on the video screen. Thus precise timing of cardiac beats within the respiratory cycle can be obtained. Because non-invasive hemodynamic monitoring is often the main objective of transesophageal echocardiography in the ICU and the study may have to be interrupted early, we focus on the transgastric short-axis view first. The probe is raised to the mid-esophageal position to obtain a four-chamber view and to the upper esophageal position which allows imaging of basal short-axis views of the heart. Finally, the ascending arch and descending thoracic aorta are systematically explored.

The transgastric short-axis view

This view, which is the cornerstone of non-invasive hemodynamic monitoring, allows an accurate two-dimensional and M-mode echographic assessment of the left ventricle giving areas, diameters, and thicknesses (Fig 1). It also allows qualitative evaluation of the regional wall motion of the left ventricle. Transesophageal echocardiography is of greater sensitivity in this setting, permitting a more complete examination of the left ventricular free wall.

Fig. 1 Short-axis view of the left ventricle obtained using a transgastric approach. In this patient, who was being managed for septic shock, repeated measurement of the area of the left ventricle at end-diastole (ED) and end-systole (ES) allowed the adequacy of left ventricular filling to be checked and assessment of the beneficial effect of hemodynamic support (epinephrine (adrenaline) infusion on day 1, replaced by dobutamine infusion on days 2 and 3, after some improvement).

The four-chamber view

The four-chamber view, which is readily obtained 30 to 35 cm from the dental arches, is ideal for estimating both right and left atrial and ventricular dimensions and kinetics (Fig 2). Unfortunately, left ventricular dimensions are consistently underestimated and accurate measurements on this view are not recommended. The morphological features of native or prosthetic mitral valves are best visualized using transesophageal echocardiography. In the absence of tachycardia, color and pulse-wave Doppler are extremely useful in searching for valvular heart diseases, abnormalities of left ventricular diastolic function, and hypovolemia. Tricuspid regurgitation, which is frequent in mechanically ventilated patients, is also revealed on the four-chamber view and can be quantified by color Doppler.

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