The risk associated with arterial hypotension during anesthesia for intensive care sedation has been demonstrated, but the threshold at which consequences for perfusion of one or more organs appear varies according to the mechanism of hypotension, associated abnormalities (HR, cardiac output and oxygen transport) and the patient's terrain. Currently, a mean arterial pressure greater than 60 mm Hg (1) and a reduction of less than 30-50% from the value measured before sedation are commonly used to ensure good perfusion of all organs. In intensive care, it is recommended to maintain a MAP between 60 and 70 mmHg and a Cerebral Perfusion Pressure (CPP) \> 50 mmHg for neurocompromised patients with Intra Cranial pressure (ICP) measure. Normally, cerebral blood flow is self-regulated, allowing adaptation of cerebral blood flow to oxygen requirements at different levels of high and low blood pressure. However, this protective mechanism may fail for a degree of hypotension that depends on several factors such as the age or vascular status of the patient. The aim of the study is to measure non-invasively, easily and reliably the variations of cerebral perfusion in patients with or without cardiovascular risk factors during controlled variations performed during routine care to set the blood pressure level within the recommended safety standards during sedation in intensive care unit. What is the tolerable target BP level for a patient under continuous sedation in the ICU? Is there a simple and non-invasive way to measure the level of cerebral blood flow autoregulation and especially the adequacy of the brain's oxygen requirements?