Cerebral metabolic depression and brain protection produced by midazolam and etomidate in the rat

Midazolam and etomidate have been shown to depress cerebral metabolism and may protect the brain during ischemia. However, it has been reported that etomidate may produce EEG spiking activity and seizures, which could adversely affect outcome. We compared the effects of midazolam and etomidate on EEG, cerebral blood flow (CBF), and cerebral cortical oxygen consumption (CMRO2) as well as neurologic outcome following incomplete cerebral ischemia in the rat. CBF was measured with radioactive microspheres and cortical CMRO2 was calculated by multiplying cortical CBF by the arterial-sagittal sinus oxygen content. Incomplete ischemia was produced by unilateral carotid artery occlusion combined with hemorrhagic hypotension. In low doses (0.02 mg/kg/min i.v.), both midazolam and etomidate depressed EEG, decreased CMRO2, and improved outcome from ischemia compared to nitrous oxide control rats. At a higher dose (0.2 mg/kg/min i.v.), midazolam further depressed EEG and CMRO2 and again improved outcome compared to N2O controls. In contrast, high dose etomidate (0.2 mg/kg/min) produced spiking EEG activity without further depression of CMRO2 and a worsening of outcome following cerebral ischemia. These results support previous reports that midazolam and etomidate may protect the brain from incomplete cerebral ischemia but suggest that EEG spiking activity associated with high dose etomidate may be associated with a worse outcome.