Cardiac Output Measurement by TEE

Overview

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.

The measurement of the LV performance, as reflected by measuring cardiac output (CO), is an important component of hemodynamic assessment during cardiac (and non-cardiac) surgery. It has become standard of care in guiding fluid management and inotropic therapy in both the operating room (OR) and the intensive care unit (ICU) in most centres, and is considered by far the most understood and commonly communicated parameter of cardiac performance, in addition to being consistently shown as a predictor of patients' outcome. Several methods have been used to measure CO. The most commonly used is via thermodilution (PAC), but its invasive nature and potential for serious complications led to the utilization of the non-invasive methods, such as those based on TEE. Since the establishment of the role of TEE in the setting of hemodynamic monitoring during cardiac surgery, various ways of quantifying LV function have been utilized. The method recommended by current guidelines is a volumetric calculation via the method of disks (modified Simpson's method, MOD). Recent advances in ultrasound technology and software development allow the utilization three-dimensional (3D) volumetric assessment and speckle tracking for cardiac deformation.