Postischemic cerebral blood flow and oxygen utilization rate in rats anesthetized with nitrous oxide or phenobarbital

The present experiments were undertaken to measure postischemic regional cerebral blood flow (rCBF) and oxygen utilization rate (CMRo2) in rats anesthetized with either 70% N2O or phenobarbital (150 mg x kg-1). In previous studies we have found that extensive restitution of cerbral energy metabolites occurs after 30 min of complete cerebral ischemia irrespective of the type of anesthesia used. Following 30 min of pronounced, incomplete ischemia, however, a comparable restitution of cerebral energy state was obtained in deeply anesthetized (phenobarbital 150 mg x kg-1) but not in superfically anesthetized (70% N2O) rats. The objectives of the present investigation were (1) to study whether postischemic cerebral blood flow was higher in barbiturate-anesthetized animals during the initial recirculation period, and (2) to investigate if the protective effects of phenobarbital previously observed could be attributed to a decrease in CMRo2. In both groups of animals a considerable variability in postischemic rCBF was observed between different animals. However, no signs of gross inhomogeneity in blood flow were found and no consistent differences in flow values between the two groups of animals were observed. Since the measured postischemic CMRo2 were identical in both groups of animals and since cerebral venous oxygen contents were above normal the results leave little support to the assumption that, in the present model of transient, incomplete cerebral ischemia, failure of recovery of cerebral metabolism (N2O group) is primarily due to impaired recirculation, nor do they indicate that the protective effects of barbiturates is due to their ability to reduce rate of cerebral energy utilization.