Inclusion Criteria:  Age 18-80 years written informed consent scheduled major abdominal surgery  Exclusion Criteria:  Age <18 or >80 years pregnancy SIRS or sepsis any kind of cardiac arrhythmia known valve disease known heart failure any kind of known carotid stenosis carotid doppler peak velocity >182 cm/s before baseline measurement (expected stenosis) missing indication for invasive arterial blood pressure monitoring (IBP) not related to the study peripheral artery disease (PAD) BMI > 35 kg/m2 intraabdominal hypertension ASA-PSC of 4 severe lung disease (e.g. COPD grade 3, fibrosis) esophageal disease of any kind participation in another clinical study