Effect of Inhalational Anesthetics on Myocardial Deformation Indices - A Dose-Response Cross-over Study

The primary research activity will be: baseline transthoracic echocardiogram (TTE) views taken upon the patient entering the operating room by one of the cardiothoracic anesthesiology fellows or attendings, TEE views taken by the echocardiography fellow or attending in the mid-esophageal 4C, 2C and LAX views once the patient has reached sevoflurane end-tidal minimum alveolar concentration (MAC) of 0.5, 1.0, and 1.5. Following this, sevoflurane will be changed to isoflurane and wait till complete washout of sevoflurane (i.e. end-tidal sevoflurane concentration reaches zero). Isoflurane concentration will be adjusted according to bispectral index and hemodynamics to maintain anesthesia during this period. Once complete sevoflurane wash-out has been achieved, isoflurane concentration will be adjusted and repeat images taken at the 0.5, 1.0, and 1.5 MAC values.

Investigators will establish stability at each MAC level (0.5, 1.0 and 1.5) for 5 minutes before obtaining TEE images. The whole study is done during pre- cardiopulmonary bypass(CPB) period while surgeon spending time dissecting internal mammary artery or other parts of surgical dissection before heparinization. The entire study duration will be a maximum of 35-40 minutes and this will not prolong the operating time. The adjustment of the anesthetic will be performed by the cardiac anesthesiology fellow or senior resident involved in this research along with the faculty officially performing the case. All images will be acquired prior to the initiation of cardiopulmonary bypass by the echocardiography rotating resident or research resident, cardiac anesthesiology fellow or cardiac anesthesiology attending anesthesiologist (all received extensive training in TEE to obtain those required images). Following the completion of the case and the uploading of images to a central echocardiography server, one of the study personnel will perform analysis of the images in the anesthesiology offices on a computer with post-processing software to determine strain.

MAC up to 1.5 is very well tolerated in cardiac surgical patients and is routinely used to achieve hemodynamic conditions during surgery. Use of vasopressor and inotrope to allow maintain depth of anesthesia with inhalation anesthesia agents is also routine in cardiac surgical patients and not in any way different from routine clinical care.

Hemodynamic information (heart rate, blood pressure, central venous pressure, cardiac index or pulmonary artery pressure) will be obtained after stabilization with each MAC and will be recorded immediately or extracted from the electronic medical records.