Prospective combined clinical validation of an algorithmic calculated mean systemic filling pressure (Pms-Nav) with the gold standard for Pms (Pms calculated from venous return curves during inspiratory hold procedures with incremental airway pressures; Pms-Insp). Secondary correlation between invasive cardiac output measurement versus 3D TOE and carotid echo doppler measured 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?

Inclusion Criteria:

• Good left and right ventricular ejection fraction
• No significant valvular insufficiencies/stenoses
• No significant comorbidity
• Signed informed consent
• Elective coronary artery bypass surgery
• Postoperative mechanically ventilated admitted to the PACU

Exclusion Criteria:

• Withdrawal informed consent
• History of pneumonectomy of lobectomy
• Mechanical support of circulation
• COPD Gold 3 or 4
• Complications during surgery
• Postoperative bleeding >50mL/15 minutes after admission to PACU - No thoracic drain in pleura
• Postoperative pneumothorax
• Participation in other research studies/trials
• Elevated intra-abdominal surgery (>12 mmHg)

Patients undergoing coronary artery bypass grafting with a good left and right ventricular ejection fraction, no significant valvular insufficiencies/stenoses and no significant comorbidity.

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