Effect of isoflurane and enflurane on the electrocorticogram of epileptic patients

We studied the effect of inhaled anesthetic agents on the electrocorticogram (ECoG) in four epileptic patients during nondominant right hemisphere temporal lobectomy while they received 70% nitrous oxide in oxygen (70% N2O/O2) alone, 70% N2O/O2 with 0.5 to 1.5% isoflurane, or 70% N2O/O2 with 2% enflurane. The mean frequency of epileptiform spikes decreased during use of isoflurane, but not enflurane, compared with use of 70% N2O/O2 alone. Enflurane produced paroxysms of synchronous high-voltage spikes. The mean number of electrodes exhibiting spike activity decreased with isoflurane use and increased with enflurane use compared with use of 70% N2O/O2 alone. This preliminary study suggests that isoflurane can suppress epileptogenic tissue and that both isoflurane and enflurane can distort the ECoG, confounding accurate identification of the seizure focus. When used judiciously, however, enflurane may be a potent synchronizer and activator of the epileptogenic focus, making it easier to identify.