THE USE OF MANNITOL IN NEUROANAESTHESIA A ND NEUROINTENSIVE CARE

Mannitol, the osmotic diuretic used in neuroanaesthesia and neurointen sive care, has, in addition to its osmotic properties, various effects upon haemodynamics, cerebral blood flow and cerebral blood volume. Th ree factors are proposed to contribute to mannitol's capacity to lower intracranial pressure and to improve cerebral compliance : cerebral d ehydration, and two forms of autoregulation-mediated vasoconstriction, In the case of viscosity autoregulation, it is admitted that changes in blood viscosity after mannitol result in reflex vasoconstriction to maintain cerebral blood flow constant. It has also been proposed that when mannitol administration results in increased cerebral perfusion pressure, vasoconstriction may occur in vascular beds in which autoreg ulation to perfusion pressure is preserved. On the basis of its effect s on cerebral blood flow and free radical scavenging properties, manni tol has recently been investigated as a cerebral protective agent, wit h the capacity to reduce or prevent damage due to cerebral ischaemia. Finally, mannitol may be injected into a carotid or a vertebral artery to produce blood-brain barrier breakdown, thus improving the brain pe netration of chemotherapeutic agents.