Maintenance of Anesthesia

Anesthesia is maintained by inhalational agents or by an infusion of an intravenous agent such as propofol. Rapid awakening is desirable after neurosurgery to allow neurological assessment of the patient, and is best achieved with short-acting drugs. Opioid analgesics and muscle relaxants are given as needed and the patient's lungs are ventilated. Moderate hyperventilation is used for craniotomies in order to reduce CBF and brain volume, thereby providing good operating conditions. However, extreme hyperventilation may be associated with critical reduction in flow to compromised areas and focal ischemia, and is best avoided [13].

Mannitol, frusemide, steroids and CSF drainage can all be used to decrease brain swelling. In patients at risk of cerebral ischemia, mild hypothermia may be achieved by passive cooling. A core temperature of 34°C provides some degree of cerebral protection without exposing the patient to the risks of more severe hypothermia. Patients should be actively warmed to 36°C by the end of surgery if they are to be wakened and extubated.

Cardiovascular parameters are kept as near as possible to physiological in order to ensure good cerebral perfusion. Normovolemia is the ideal, with a hematocrit of about 30%. Normal saline is the intravenous fluid of choice and 5% dextrose should be avoided [14]. Occasionally, deliberate hypotension is indicated for surgical reasons.

In a number of centers, surgery that requires total circulatory arrest is undertaken. In order to minimize ischemic cerebral damage, this is accomplished after the establishment of profound hypothermia by femoral-femoral cardiopulmonary bypass. Barbiturates or propofol are administered beforehand.

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