Inhalation anaesthetic agents in neurosurgery

Of all the available halogenated anaesthetic agents, isoflurane appears to be the most advantageous for the neurosurgical patient. Concentrations which produce satisfactory anaesthesia for neurosurgical procedures cause little or no depression of myocardial function, and no increase in intracranial pressure. Cerebral perfusion pressure is maintained. Autoregulation remains effective at concentrations of up to 1.5 MAC. Vascular reactivity to carbon dioxide is also maintained. Cerebral metabolic rate is decreased in a dose-related fashion and a cerebral protective effect, maximal at clinical concentrations, has been demonstrated. Isoflurane produces predictable electroencephalographic changes as anaesthesia deepens. Because the metabolism of isoflurane in vivo is so low, the risk of interference with organ function after surgery or adverse drug interactions is reduced. The potency is such that adequate anaesthetic and surgical conditions for most intracranial procedures may be achieved with 0.5-1% isoflurane combined with hyperventilation with or without nitrous oxide. The rapid, precise adjustment of depth of anaesthesia made possible by the low blood/gas solubility of isoflurane is especially beneficial in neurosurgical procedures because of the great variability of surgical stimulation. Prompt elimination of isoflurane allows fast return to consciousness and permits early neurological examination after surgery.