I653 and isoflurane produce similar dose-related changes in the electroencephalogram of pigs

I653 is a new volatile anesthetic structurally similar to enflurane and isoflurane. Since enflurane can induce convulsions, whereas isoflurane progressively depresses cortical electrical activity, the authors believed it important to assess the effect of I653 on the EEG (in both the "time" and "frequency" domain). The EEG was assessed visually and quantitatively, and a new EEG parameter was introduced. The burst-suppression ratio (percentage of time the EEG was isoelectric) quantified the extent of burst suppression phenomena. Eight swine were anesthetized with I653 or isoflurane in oxygen and in random sequence, exposed to approximately 0.8, 1.2, or 1.6 MAC with normocapnea and to 1.2 MAC with hypocapnea (PETCO2 of 25 mmHg). Four animals were also anesthetized with 3.2% (1.2 MAC) enflurane in oxygen. Both I653 and isoflurane produced a dose-related depression of cortical electrical activity. At 0.8 and 1.2 MAC of either agent, occasional sharp waves occurred singly, were apparently not related to external (auditory) stimuli, and probably represented normal variation in the EEG. No electrographic or gross motor seizures occurred with either I653 or isoflurane. In contrast, all pigs given enflurane developed seizures during hypocapnea. At equipotent concentrations, I653 and isoflurane had the same effect on EEG parameters. Increasing doses of either I653 or isoflurane caused decreasing amplitude and frequency and increasing suppression. Hypocapnea during either agent slightly increased high-frequency activity, and slightly decreased burst suppression.