Quantification of Dynamic and Static Cerebral Autoregulation (CA) Under Anaesthesia

Inclusion Criteria: * ASA-I or ASA-II, willing and able to give written informed consent, scheduled for elective, non-cardiothoracic surgery under general anaesthesia and age 18 years and above. Exclusion Criteria: * Patient related * Unable/ unwilling to participate * ASA-III or higher * Age \< 18 years * History of: uncontrolled hypertension, diabetes, Parkinson's disease, uncontrolled cardiac arrhythmia, Pure autonomic failure (formerly called idiopathic orthostatic hypotension), Multiple system atrophy with autonomic failure (formerly called Shy-Drager syndrome), Addison's disease and hypopituitarism, pheochromocytoma, peripheral autonomic neuropathy (e.g., amyloid neuropathy, idiopathic autonomic neuropathy), known cardiomyopathy, extreme left ventricle hypertrophy or ejection fraction \< 30%, proven or suspected allergy for any of the medication used during induction of anaesthesia, malignant hyperthermia. * Unability to record transcranial Doppler ultrasound due to anatomical variance (\~5% of population) * Contra-indications for intravenous or inhalational anaesthesia. * Contra-indications for phenylephrine: severe hypertension, peripheral vascular illness, severe hyperthyroidism * Simultaneous use of MAO-inhibitors, dopaminergic or vasoconstrictor ergot alkaloids (bromocriptine, cabergoline, pergolide, ergotamine, methylergometrine, methysergide), linezolid, tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, digoxin, quinidine, oxytocin. * Surgery related * Day case surgery * Laparoscopy with CO2 insufflation * Extreme positioning during surgery (head-down/up tilt, lateral decubitus position, prone) * Surgery \< 60 minutes.