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Neal F. Kassell, Patrick W. Hitchon, Mary K. Gerk, Martin D. Sokoll, and Todd R. Hill

been assuming a wider role in the management of neurological disorders characterized by cerebral ischemia and/or brain swelling and increased ICP. 8, 13, 16, 17, 21, 23 Beneficial effects of this modality have been postulated in the prevention of infarction, by virtue of an antioxidant effect 4, 5 and by decreasing cerebral metabolism 11, 19, 24 and thus allowing the brain to survive with decreased CBF. However, the most thoroughly documented action of this agent is in decreasing ICP and thereby increasing cerebral perfusion pressure. High-dose barbiturates

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Michael N. Diringer, Tom O. Videen, Kent Yundt, Allyson R. Zazulia, Venkatesh Aiyagari, Ralph G. Dacey Jr., Robert L. Grubb Jr., and William J. Powers

or mass lesions; therefore further studies are needed in these subgroups of patients with TBI. Conclusions In patients with severe TBI, we found no evidence that early moderate hyperventilation to a PaCO 2 of 30 mm Hg or hyperventilation to 25 mm Hg during periods of elevated ICP produced global or regional cerebral ischemia. This finding was robust: even in regions where CBF during hyperventilation fell below the CBF threshold for energy failure defined during acute ischemia, there was no reduction in cerebral metabolism. This indicates that there was no

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Albert N. Martins and Thomas F. Doyle

surrounding focally traumatized brain. We also wished to learn if focal brain injury is accompanied by a global reduction in CBF and cerebral metabolism, as reflected by oxygen consumption. Materials and Methods Animal Preparation Young adult macaques ( Macaca mulatta and Macaca fascicularis ) of both sexes, weighing between 3 and 5 kg, were initially anesthetized with 50 mg of ketamine and 0.2 mg atropine sulfate, both given intramuscularly. After being intubated with a cuffed endotracheal tube, they were placed on a volume respirator and paralyzed with an

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Koji Yoshida, Kuniaki Ogasawara, Hiroaki Saura, Hideo Saito, Masakazu Kobayashi, Kenji Yoshida, Kazunori Terasaki, Shunrou Fujiwara, and Akira Ogawa

C arotid endarterectomy (CEA) is an effective means of preventing stroke in appropriately selected patients. 3 It also improves cerebral hemodynamics through the surgical repair of carotid stenosis, which can lead to a recovery in the reduced cerebral metabolism seen before surgery. 4 In contrast, blood flow in the cerebral hemisphere ipsilateral to the CEA sometimes substantially increases above the metabolic demands of the brain tissue immediately after surgery. 30 This phenomenon is defined as “postoperative cerebral hyperperfusion.” 27 , 30

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Claudia S. Robertson, Raj K. Narayan, Ziya L. Gokaslan, Rajesh Pahwa, Robert G. Grossman, Pedro Caram Jr., and Elizabeth Allen

hypervolemic therapy guided by monitoring pulmonary wedge pressure. Routine medications included phenytoin, morphine for sedation, and antibiotics. Intracranial pressures greater than 20 mm Hg were treated with hyperventilation (pCO 2 25 to 30 mm Hg), cerebrospinal fluid drainage, sedation and paralysis, mannitol, and (if necessary) barbiturates. Because of the marked effect of barbiturates on cerebral metabolism, CBF measurements obtained while patients were in barbiturate coma are not included in this analysis. In the first group of patients, the presence of cerebral

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Daniel F. Kelly, Neil A. Martin, Rouzbeh Kordestani, George Counelis, David A. Hovda, Marvin Bergsneider, Duncan Q. McBride, Ehud Shalmon, Dena Herman, and Donald P. Becker

surprising given the decline in blood flow that normally occurs with aging, presumably as a result of reduced cerebral metabolic demands. 27, 32 The strong correlation between age and outcome seen in this and other studies, although likely to be multifactorial, may be related to a global reduction in cerebral metabolism. 46 Regarding the increased incidence of evacuated subdural or intracerebral hematomas in Groups 1 and 2, a similar correlation between evacuated intradural hematomas and low blood flow has been reported by Bouma, et al. 6 Salvant and Muizelaar 42 also

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Leslie N. Sutton, Alan C. McLaughlin, Stephen Dante, Mark Kotapka, Teresa Sinwell, and Elizabeth Mills

. McMillian V , Siesjö BK : The influence of hypocapnia upon intracellular pH and upon some carbohydrate substrates, amino acids and organic phosphates in the brain. J Neurochem 21 : 1283 , 1973 McMillian V, Siesjö BK: The influence of hypocapnia upon intracellular pH and upon some carbohydrate substrates, amino acids and organic phosphates in the brain. J Neurochem 21: 1283, 1973 15. Michenfelder JD , Thege RA : The effects of profound hypocapnia and dilutional anemia on canine cerebral metabolism and blood flow

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Jan Plougmann, Jens Astrup, Jens Pedersen, and Carsten Gyldensted

flow is increased then cerebral metabolism must also be increased. The latter possibility accords with many studies indicating an increase in CBF by xenon. 4, 6, 7, 9, 11, 15 The lack of correlation between AVDO 2 and the effect of xenon on ICP points toward the ability of xenon to enhance blood flow as well as metabolism. The reliability of AVDO 2 values may be questioned as part of this argument. Because oxygen partial pressures were very high and changed from 100% to 70% when switching to xenon, the amount of dissolved oxygen in blood is significant and must be

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Walter D. Obrist, Thomas W. Langfitt, Jurg L. Jaggi, Julio Cruz, and Thomas A. Gennarelli

blood flow (CBF) (p < 0.02, chi-square test). Arteriovenous Oxygen Differences The difference between arterial and jugular venous O 2 content provides a means of assessing the overall balance between cerebral metabolism and blood flow, thereby indicating the presence of global ischemia or hyperemia. This is evident from rearrangement of the Fick equation: AVDO 2 = CMRO 2 /CBF. 27 Thus, when CBF is low relative to the brain's metabolic needs (ischemia), a wide AVDO 2 is obtained. Conversely, when CBF is high relative to metabolism (hyperemia), a

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Richard Klementavicius, Edwin M. Nemoto, and Howard Yonas

Physiol 229: 113–118, 1975 7. Greeley WJ , Ungerleider RM , Quill T , et al : The effects of hypothermic cardiopulmonary bypass and total circulatory arrest on cerebral metabolism in neonates, infants, and children. J Thorac Cardiovasc Surg 101 : 783 – 794 , 1991 Greeley WJ, Ungerleider RM, Quill T, et al: The effects of hypothermic cardiopulmonary bypass and total circulatory arrest on cerebral metabolism in neonates, infants, and children. J Thorac Cardiovasc Surg 101: 783–794, 1991 8. Hagerdäl M