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NEUROSURGICAL ANESTHESIA

The Effect of Sevoflurane and Isoflurane Anesthesia on Interictal Spike Activity Among Patients with Refractory Epilepsy

Andrew D. J. Watts, MD, FANZCA^*, Ian A. Herrick, MD, FRCPC^*, Richard S. McLachlan, MD, FRCPC, Rosemary A. Craen, MBBS, FANZCA, FRCPC^*, and Adrian W. Gelb, MB, ChB, FRCPC^*

Departments of *Anaesthesia and Clinical Neurological Sciences, University of Western Ontario and London Health Sciences Centre, London, Ontario, Canada

Address correspondence to Dr. Ian A. Herrick, Department of Anaesthesia, London Health Sciences Centre, 339 Windermere Rd., London, Ontario, Canada N6A 5A5.

The electrophysiologic effects of sevoflurane are not well characterized in humans. Among patients with refractory epilepsy, this study compared 1) electroencephalographic (EEG) interictal spike activity during wakefulness and sevoflurane anesthesia, and 2) electrocorticographically (ECoG) recorded interictal spike activity during sevoflurane and isoflurane anesthesia. We studied 12 patients undergoing insertion of subdural electrodes. Before commencing anesthesia, awake (baseline) EEG recordings were obtained. After inhaled induction, EEG interictal spike activity was evaluated during stable, normocapnic, and hypocapnic (PaCO₂ = 28–30 mm Hg), sevoflurane anesthesia administered at 1.5 times the minimum alveolar anesthetic concentration (1.5 MAC). Immediately after surgery, ECoG recordings were obtained from subdural electrodes during 1) 1.5 MAC isoflurane, 2) 0.3 MAC isoflurane, and 3) 1.5 MAC sevoflurane anesthesia. EEG spike frequency increased in all patients during sevo- flurane anesthesia compared with awake recordings (P = 0.002). Compared with 0.3 MAC isoflurane anesthesia, ECoG interictal spike frequency was higher in all patients during 1.5 MAC sevoflurane anesthesia (P = 0.004) and in 8 of 10 patients during 1.5 MAC isoflurane anesthesia (P = 0.016). Under sufficiently rigorous conditions, both sevoflurane and isoflurane can provoke interictal spike activity at near burst-suppression doses. This property is more prominent with sevoflurane than isoflurane.

Implications: The results of this study suggest that the capacity to modulate neuroexcitability is a dose-dependent feature of volatile anesthetics that is manifested most prominently at near burst-suppression doses (i.e., 1.5 times the minimum alveolar anesthetic concentration) and is minimal or absent at low doses.

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