Clinical Validation of Algorithms for Mean Systemic Filling Pressure and Automated Cardiac Output

Background of the study: Volume-state in critically ill patients is a difficult parameter to determine, and knowledge about it could make the difference between life or death concerning proper treatment. Determination of volume state starts with adequate 3D transesophageal echocardiography (TOE) in the operation room, including with non-invasive doppler carotid artery measures. TOE is a standardly used method in cardiac surgery. Because echocardiography only gives information about volume status at a certain timepoint, a real-time continuous value reflecting volume-status is needed. "Mean systemic filling pressure (Pms)" appears to be a promising value reflecting volume status. There is a reliable, but cumbersome method available which to date serves as a gold standard to determine Pms (Pms calculated by constructing venous return curves during incremental levels of airway pressure, thereby simulating a decrease in preload --\> Pms-Insp). However, this method cannot be used in daily clinical practice because it is laborious and cumbersome. Therefore there is a need for a non-invasive methods measuring Pms, which could now be determined by a computerized algorithm with the Navigator-device (Pms-Nav). It is key to compare this Pms-Nav with its gold standard (Pms-Insp) in order to establish a clinical validation for Pms-Nav. Objective of the study: 1. Is there a good correlation between Pms-Nav and Pms-Insp? 2. Is there a good correlation between invasive continuous cardiac output measurement (by thermodilution and pulse-contour analyse detected by the PiCCO-device) and 3D transoesophageal echocardiography (TOE) and carotid echo doppler?