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A concern is that seizure activity may go unrecognized in an anesthetized and paralyzed patient and may result in neuronal injury if substrate demand (CMR) exceeds supply for a prolonged period.204 A second concern is that the epileptogenic effect will persist in the postanesthesia period when seizures may occur in less well-controlled circumstances than those that exist in the surgical unit.
However, by con- trast with SAH, routinely administering nimodipine or any other CCB after neurologic stroke that has occurred in the surgical unit or in any other environment has not yet become standard practice.
In addi- tion, the patient can be easily rewarmed in the surgical unit after the risk of ischemia has subsided.
of 30%-35% is the theoretic optimum) in patients in whom focal ischemia might occur in the surgical unit.317 An increased hematocrit, because of viscosity effects, reduces CBF.14 In anticipation of a procedure wherein incomplete ischemia might occur, such as CEA, preoper- ative phlebotomy should be considered when hematocrit is in excess of 55%.
Propofol reduces CBF in regions of the brain surrounding the tumor, and quantitatively, the reduction in CBF is similar to that in the contralateral normal hemisphere.347 Measurement of regional CBF in the area of the tumor might also be a useful predictor of the grade of intracranial gliomas; both regional CBF and regional CBV are greater with high-grade gliomas.348 Considerable edema is often associated with intracranial tumors, and the radiologic extent of the edema, which presumably represents the extent of abnormal vessel leaki- ness, correlates with the severity of the elevation in ICP that occurs in association with intubation-related hyper- tension.349 Edema formation in the peritumoral region can be characterized as vasogenic with leakage of plasma proteins from the vascular space, hydrocephalic secondary to obstruction of CSF flow, or static as a result of venous obstruction by tumor.350 Although the precise mechanisms by which edema formation occurs are not clear, the loss of integrity of the tight junctions of components of the BBB, an increased permeability induced by vascular endothe- lial growth factor expressed by tumors, and an increased expression of leukotriene C4 in peritumoral fluid probably play a role.351 Osmotherapy with mannitol will effect a reduction in edema; however, with a permeable BBB, man- nitol can diffuse into the peritumoral space and lead to rebound edema formation.350 For acute reduction of ICP in the surgical unit, this concern is not significant.
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