Echocardiography in Intensive Care: The Basics. Part I

OBJECTIVE: To review the current status of echocardiography in critically ill patients with special reference to the advantages and disadvantages of the transthoracic and transoesophageal approaches. DATA SOURCES: A review of articles published in peer reviewed journals from 1976-1999 and identified through a MEDLINE search on echocardiography. SUMMARY OF REVIEW: Echocardiography uses the reflection of high frequency sound waves at tissue boundaries to construct a two-dimensional image of cardiac structures. Two-dimensional echo-cardiography is the cornerstone of cardiac ultrasound, although Doppler techniques (pulsed wave, continuous wave, and colour flow) form an integral part of every modern echocardiographic study. The Doppler effect is based on changes in sound frequency that occur when a sound source moves towards or away from an observer. Blood flow velocities measured by Doppler can be used to estimate pressure, valve area and stroke volume. The standard imaging positions of the probe are either outside the thorax (i.e. transthoraracic echocardiography or TTE) or inside the oesophagus (i.e. transoesophageal echo-cardiography or TOE) both of which provide information that can be helpful in managing critically ill patients. CONCLUSIONS: Echocardiography is a rapidly developing technology. Cardiac structures can be imaged in 'real time'. Image quality continues to improve. The use of transoesophageal probe positioning has also widened the potential of this bedside technique in critically ill patients.