Cardiac Output Measurement by TEE

Transesophageal echocardiography (TEE) has become a standard monitoring tool during cardiac surgery. It allows continuous accurate assessment of heart structures and function without interfering with the surgery and the anesthetics. The imaging of cardiac structures is used to direct optimal surgical intervention and assess surgical results. Cardiac output (CO) is the result of stroke volume (SV) multiplied by the heart rate. Measurement of cardiac output (CO) is used to quantify the performance of the left ventricle. It is commonly achieved using a pulmonary artery catheter (PAC) (also known ad Swann-Ganz catheter). A known amount of saline solution is injected in the proximal part of the catheter and the variation of blood temperature detected at the tip. Cardiac output is measured based on the duration and degree of temperature change. This method remains an accepted gold standard. TEE allows measurement of cardiac output using a number of different 2D and 3D imaging modalities. Although current guidelines identify the Method of the Disks(MOD) as the gold standard other technique could potentially be more precise. In this study, the investigators want to assess the accuracy of four different TEE methods to measure cardiac output compared with Thermodilution as a standard of care.