The aim of the study is to investigate the accuracy of a new semi-invasive cardiac output monitoring system in patients undergoing elective cardiac surgery. The investigators hypothesize that the semi-invasive device may be affected by mean arterial pressure and systemic vascular resistance.

A recently introduced semi-invasive monitoring system consists of an algorithm that provides beat-to-beat measurement of CI by analysis of the arterial blood pressure tracing. By using the autocalibration mode this software calculates the individual aortic compliance and systemic vascular resistance by taking patient data like age, height, weight and gender into account. After estimation of beat-to-beat stroke volume, a subsequent multiplication by the heart rate delivers pulse contour cardiac index. Furthermore, this device offers the opportunity for external calibration by a reference technique, e.g. pulmonary or transpulmonary thermodilution.

The aim of the present study was to investigate the accuracy and trending ability of autocalibrated semi-invasive CI by a new arterial waveform analysis compared with transpulmonary thermodilution before and after cardiopulmonary bypass (CPB).

Inclusion Criteria:

Patients undergoing elective coronary artery bypass grafting Personal declaration of consent to the study

Exclusion Criteria:

Patients <18 years of age A left ventricular ejection fraction ≤0.5 Emergency procedures Patients with haemodynamic instability requiring continuous pharmacologic support Patients with intracardiac shunts Severe aortic-, tricuspid- or mitral stenosis or insufficiency Mechanical circulatory support.