Transesophageal Doppler devices: A technical review

Monitoring of aortic blood flow, conducting large portions of the cardiac output (CO), allows conclusions on the global hemodynamic status of patients. For this purpose, transesophageal Doppler (TED) devices have been developed, which interrogate the descending aorta and calculate aortic blood flow velocity using the Doppler principle. The recorded velocity-time curve can be used to estimate CO as well other advanced hemodynamic parameters such as preload, afterload and myocardial contractility. Clinical studies in perioperative patients have demonstrated a reduced postoperative morbidity and shorter length of hospital stay when TED is used to guide fluid management. However, several assumptions are needed to translate the measured Doppler frequency shift to hemo- dynamic variables and discrepancies between the assumed and the actual condition may introduce a considerable risk for erroneous calculations. A correct interpretation of the displayed parameters requires profound knowledge on the technical basis of this method as well as its technical limitations. Our review focuses on these technical aspects which the clinician should be familiar with to allow proper use of TED monitoring devices.