Effects of nitrous oxide on the cerebrovascular tone, oxygen metabolism, and electroencephalogram of the isolated perfused canine brain.

Nitrous oxide has been reported to act both as a stimulant and as a depressant of cerebral oxygen metabolism (CMRO2) and blood flow under a variety of experimental conditions in the intact animal. The isolated brain preparation is advantageous because it permits direct measurement of blood flow and allows the study of drug effects without interference from other organ systems or drugs. In this study, six isolated perfused canine brain preparations were used to compare the CMRO2, cerebral vascular resistance (CVR), and the EEG of brains perfused with normocapnic, normoxic blood equilibrated with either 70% N2O or 70% N2. There was no significant change in CMRO2. Cerebral vascular resistance fell [16.4% +/- 3.4% SEM (P less than 0.015)] during exposure to N2O. The EEG pattern was reduced in amplitude, but showed an increase in both low-voltage beta activity (14-40 Hz), and 3-5 Hz activity. In the isolated brain, N2O reduced cerebral vascular tone while exhibiting no effect on cerebral oxygen metabolism.