The Influence of Anesthesia on Corticocortical Evoked Potential Monitoring Network Between Frontal and Temporoparietal Cortices

BACKGROUND: Previous studies have reported the usefulness of intraoperative corticocortical evoked potentials (CCEPs) for preserving language function during brain surgery. OBJECTIVE: This study aimed to assess the influence of depth of anesthesia on CCEP to establish its clinical utility. METHODS: Twenty patients with brain tumors or epilepsy who underwent awake craniotomy were included in this study. Before resection, the electrode plates were placed on the frontal and temporoparietal cortices, and 1-Hz alternating electrical stimuli were delivered to the pars opercularis/pars triangularis in a bipolar fashion. Electrocorticograms from the temporoparietal cortices time-locked to stimuli were averaged to obtain CCEP responses from a state of deep anesthesia until the awake state. The correlation between CCEP waveforms and bispectral index (BIS) was evaluated. RESULTS: CCEP amplitude increased with the increase in the BIS level. CCEP latency decreased in 5 patients and increased in 15 patients under anesthesia compared with the awake state. CCEP amplitudes decreased by 11.3% to 75.2% (median 31.3%) under anesthesia with <65 BIS level. These differences were statistically significant (P < 0.01, Wilcoxon signed-rank test). With respect to CCEP latencies, there was no significant difference between the awake and anesthetic states. CONCLUSIONS: CCEP amplitudes were correlated with depth of anesthesia, whereas CCEP latencies were not affected by anesthesia. The influence of anesthesia should be considered when applying this technique to intraoperative monitoring.