Neuro anaesthesia--a review of the basic principles and current practices

The changes in intracranial pressure which occur following a change in one of the constituent volumes within the skull are governed by the Monro-Kellie doctrine, stated in the late 18th century and describes how an increase in one of the constituent volumes must be reflected by a reciprocal decrease in another volume to avoid any change in pressure and that if this does not occur, there is a rapid rise in intracranial pressure. Cerebral blood flow is affected by many physiological and pharmacological factors, and is relevant as a change in cerebral blood flow results in a similar alteration in cerebral arterial volume which will affect intracranial dynamics. Another important concept to be understood is cerebral perfusion pressure, how it is related to intracranial and arterial pressures and its relevance during the conduct of any neuroanaesthetic. Both carbon dioxide and the volatile agents are potent vasodilating agents and will cause a catastrophic rise in intracranial pressure and fall in cerebral perfusion pressure if hypercapnia develops in the presence of more than one MAC of a volatile agent. The volatile agents are reviewed and it is stressed that while isoflurane may have advantages over the older volatile agents it is not without complication and nitrous oxide which has always been regarded as an innocuous agent may also have some significant intracranial affects. The use of propofol, as an infusion and the neuromuscular blocking agents and narcotics are described. Recently the use of induced hypotension during clipping of cerebral aneurysms has been questioned and this view and the treatment of vasospasm is discussed in some detail.(ABSTRACT TRUNCATED AT 250 WORDS)