Background General anaesthesia reduces blood pressure, but cerebral autoregulation is considered to maintain its blood flow if mean arterial pressure (MAP) is between 60-150 mmHg. Thus, vasoactive medication is administered to treat anaesthesia-induced hypotension if MAP decreases to below approximately 60 mmHg. In young healthy adults, propofol anaesthesia, with limited reduction in blood pressure, decreases cerebral blood flow by approximately 50% by a decrease in neuronal activity. However, it is unknown whether the anaesthesia-induced reduction in cerebral blood flow is affected by a marked decrease in MAP and whether propofol anaesthesia affects the lower level of cerebral autoregulation.