Different Propofol-Remifentanil or Sevoflurane-Remifentanil Bispectral Index Levels for Electrocorticographic Spike Identification during Epilepsy Surgery

Background: Medical therapy, the cornerstone of managing epilepsy, still fails a substantial portion of patients. Little information is available regarding the potential impact of different bispectral index (BIS) levels on electrocorticographic spike identification for surgical epileptic foci resection. Methods: Twenty-two intractable epilepsy subjects were randomly allocated to the propofol-remifentanil or sevoflurane-remifentanil groups, and were further randomized to four BIS85 (BIS 71-85), BIS70 (BIS 56-70), BIS55 (BIS 41-55), and BIS40 (BIS 40) sequence order. Results: Two-way ANOVA revealed no differences between groups in spike frequency (P = 0.720), spike amplitude (P = 0.647), or number of spiking leads (P = 0.653). In the propofol and sevoflurane groups, decreasing BIS levels increased mean +/- SD spike/min frequency (P < 0.001 and P < 0.001) at BIS85 (10 +/- 12 and 10 +/- 8), BIS70 (19 +/- 17 and 17 +/- 15), BIS55 (22 +/- 17 and 18 +/- 8), and BIS40 (25 +/- 15 and 23 +/- 17). Furthermore, in the propofol and sevoflurane groups, decreasing BIS levels increased spike microvolt amplitude (P = 0.006 and P = 0.009) at BIS85 (1,100 +/- 400 and 750 +/- 400), BIS70 (1,200 +/- 460 and 850 +/- 490), BIS55 (1,300 +/- 560 and 940 +/- 700), and BIS40 (1,400 +/- 570 and 1,300 +/- 700). Whereas, in the propofol and sevoflurane groups, there was no difference in the location or number of spiking leads (P = 0.057 and P = 0.109) at the four BIS levels. Compared with BIS85, spike frequency in the propofol and sevoflurane groups increased 100 and 170% at BIS70, 116 and 180% at BIS55, and 132 and 230% at BIS40. Compared with BIS85, spike amplitude increased 108 and 113% at BIS70, 121 and 125% at BIS55, and 128 and 170% at BIS40. Conclusion: Decreasing BIS levels in the propofol and sevoflurane groups enhanced epileptogenic spike frequency and amplitude with the same location and number of spiking leads.