Nitrous Oxide Markedly Increases Cerebral Cortical Metabolic Rate and Blood Flow in the Goat

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Abstract
Two determinations of the effects of 1 h of N2O (70% via a mask) on cerebral O2 metabolism (CMRO2) and total and regional CBF [cerebral blood flow] (rCBF) were performed in goats. Following introduction of N2O, PaCO2 [arterial CO2 tension] and arterial blood pressure did not change, but arterial epinephrine levels declined over the 60-min period. Total CBF increased in the first 5 min of N2O exposure, reached a maximum of 165% control at 15 min, and then decreased to 143% control at 60 min. rCBF evaluations showed that much of this CBF increase was confined to cerebral cortical structures (188-246% control at 60 min). Over the same period cortical CMRO2 increased to 170% of control. No appreciable changes in the levels of high-energy phosphates or glycolytic intermediates were found at 60 min of N2O. The described changes are apparently attributable solely to the presence of N2O and not to sympathoadrenal influences, altered ventilation or anything related to the experimental preparation. Evidently, N2O (at least in goats) is associated with a marked cerebral cortical activation.