Canine cerebral oxygen consumption during enflurane anesthesia and its modification during induced seizures

Abstract

The effects of enflurane at <0.1, 2.2, and 4.2% (end expired) concentrations on cerebral metabolism and circulation were studied in 6 dogs. A 34% decrease in cerebral oxygen consumption (CMR(02)) occurred at 2.2% (approximately MAC) and no further decrease was observed at 4.2%. Cerebral blood flow (CBF) was increased at each of the higher concentrations despite progressive significant decreases in arterial pressure. In 4 additional dogs, anesthesia was maintained at 1.5 MAC enflurane (3.4% end expired) and seizures were induced by hyperventilation (Pa(CO2), 20 mm Hg) and intermittent hand clapping. Typical electroencephalographic (EEG) seizure patterns were accompanied by a 48% increase in CMR(O2) (mean) and gross skeletal muscle activity. Control conditions were reestablished and seizures were again induced by pentylenetetrazol (30 mg/kg). These seizures could not be differentiated from those previously induced by hypocapnia and hand clapping. It is concluded that enflurane generally resembles other halogenated anesthetics in its effects on CMR(O2) and CBF but differs in producing seizures similar to those produced by a known convulsant.