Abstracts

Rationale: Previously, the usefulness of intraoperative cortico-cortical evoked potentials (CCEP) was reported for preserving subcortical fibers during brain surgery. However, the influence of anesthesia on CCEP waveforms has not been elucidated. This study aims 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 electrodes were placed on the frontal and temporo-parietal cortices and 1-Hz alternating electrical stimuli were delivered to the pars opercularis/pars triangularis (pO/pT) in a bipolar fashion. Electrocorticograms from the temporo-parietal 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 was increased in accordance with the increases in BIS level in all patients. On the other hand, CCEP latency was decreased in 5 patients and increased in 15 patients under anesthesia compared with awake state. CCEP amplitudes were 11-75% decreased under anesthesia with < 65 BIS level and these differences were statistically significant. With respect to CCEP latencies, there was no significant difference between awake and anesthetic states. Conclusions: CCEP amplitudes were correlated with depth of anesthesia, whereas CCEP latencies were not affected by the anesthesia. The influence of anesthesia should be considered to apply this technique to intraoperative monitoring. Funding: KAKENHI 16K10795 from the Japan Ministry of Education, Culture, Sports, Science, and Technology (MEXT)