10015- STMO-1 EXPRESSION OF ANESTHETIC FADE IN INTRAOPERATIVE MEP MONITORING DURING BRAIN TUMOR SURGERY

Abstract We retrospectively examined whether anesthetic fade (AF) occurred in brain tumor surgery with direct motor field stimulation motor evoked potential (dMEP) and transcranial stimulation MEP (tcMEP), and whether it could have been avoided by compound muscle action potential (CMAP) after peripheral nerve stimulation normalization, and examined the causes of AF. In 108 muscles in 40 patients where tcMEP was performed and 24 muscles in 24 cases where dMEP was performed, and whether AF could be avoided by CMAP normalization was examined. In 108 muscles where tcMEP was performed, the relative amplitude of surgery with an operative time of 190 minutes or more was 1.07±0.88, which was significantly lower than the relative amplitude of surgery with an operative time of less than 190 minutes (1.67±2.69) (P=0.0447, Student’s t-test). The relative amplitude values under CMAP normalization were also 1.29±1.62 over 190 minutes and 1.24±1.48 under 190 minutes, indicating no significant difference (P = 0.4430).The relative amplitude of surgery with an operative time of 360 minutes or more was 0.56±0.26 in the 24 muscles where dMEP was performed, and a significant difference was observed between the relative amplitude of surgery with an operative time of less than 360 minutes (1.43±0.75) (P = 0.0045). The relative amplitude values under CMAP normalization were 0.57±0.25 over 360 minutes and 1.48±0.72 under 360 minutes, which was also significant (P = 0.0038). AF was also more intense in dMEP and could not be avoided by CMAP normalization. Although there were few cases and it required consideration of direct invasion of the pyramidal tract in brain tumor surgery, it is suggested that a decrease in the transmissibility of neuromuscular junctions is considered to be a cause of AF that and a decrease in excitability of motor field pyramidal cells may be more active at 6 hours or more.