Intracranial pressure and cerebral blood flow

Intracranial pressure (ICP) is determined by the volumes of brain, blood and cerebrospinal fluid within the skull, which is of course of fixed volume. The Monro–Kellie hypothesis states that an increase in volume of one of these components must be compensated for by a reduction in volume of one or both of the others. If this compensation is insufficient, then potentially fatal increases in ICP can occur. Maintenance of relatively constant ICP is essential for normal perfusion of the brain. Cerebral blood flow is regulated both globally, in order to prevent hypo- or hyper-perfusion resulting from changes in systemic arterial blood pressure, and locally, to meet the dynamic oxygen and substrate demands of different brain regions. Monitoring of ICP and the cerebral blood supply is possible through a variety of invasive and non-invasive techniques, and these techniques are already established in anaesthesia and intensive care medicine.