Interaction of carbon monoxide and cyanide on cerebral circulation and metabolism.

Significant elevations of carboxyhemoglobin and blood cyanide have been found in fire victims. The nature of the interaction of acute exposures to these agents is unclear. This study was undertaken to describe the of cyanide and carbon monoxide--alone and in combination--on the circulation and metabolism of the brain in anesthetized dogs. Cerebral blood flow increased to 130 and 200% of control with elevations in carboxyhemoglobin to 30 and 51% or with elevations in blood cyanide to 1.0 and 1.5 microgram/ml, respectively. Cerebral oxygen consumption remained unchanged until the higher level of carbon monoxide or cyanide was reached. When carbon monoxide and cyanide were administered simultaneously, cerebral blood flow increased in an additive manner, but significant decreases in cerebral oxygen consumption occurred at the combination of the lower concentrations. These data suggest that carbon monoxide and cyanide are physiologically additive on producing changes in cerebral blood flow, but may act synergistically on cerebral metabolism.