Association of different combination doses of remifentanil-propofol with transcranial motor-evoked potentials during skull base surgery

Abstract Background Monitoring of transcranial electrical motor evoked potentials (TceMEPs) is widely used in neurosurgery. The association of different combination doses of remifentanil-propofol in total intravenous anesthesia (TIVA) with TceMEPs during surgery remains uncertain. Methods In this prospective observational study, consecutive patients (aged 18–65 years) who underwent skull base surgery under general anesthesia at our clinical center between April 2021 and April 2023 were included. All patients were anesthetised with propofol-remifentanil TIVA and maintained at a Bispectral Index of 40–60. The association between different combination doses of remifentanil-propofol and the change in TceMEP amplitude from baseline was assessed using a multivariable model adjusted for confounders and a response surface model. Besides, anesthetic dose, extubation time, pain score at 24h postoperatively and unexpected body movements during surgery were recorded. Results A total of 240 patients (mean age, 49.3 [SD, 12.1] years; 107 [44.6%] women) who underwent skull base surgery were included in this study. Our study showed that an increase in propofol dose was significantly associated with a constant increase in the Log of the change in TceMEP amplitude (β = 0.29 [95%CI: 0.01 to 0.58], p = 0.046) after adjustment. Increasing remifentanil was not associated with Log (change in TceMEP amplitude) (β = 0.33 [95%CI: -2.1 to 2.76], p = 0.79) after adjustment. In addition, through the response surface analysis, we found that when the propofol infusion was less than 2.96 mg/kg/h and the remifentanil infusion was greater than 0.24 µg/kg/min, the more the remifentanil infusion was, the less impact it had on the changes in TceMEP. When the propofol infusion was greater than 2.96 mg/kg/h, as the propofol infusion increased, it had a greater impact on the changes in TceMEP. Pearson’s test showed a correlation between propofol and remifentanil dose at BIS 40–60 (γ= -0.4637, p < 0.001). Conclusions In this study, propofol reduced TceMEP amplitude in a dose-dependent manner. Due to the synergistic interactions between propofol and remifentanil, remifentanil could reduce the amount of propofol at the same anesthesia depth, a propofol infusion rate less than 2.96mg/kg/h and a remifentanil rate greater than 0.24 µg/kg/min is recommended in neurosurgery requiring TceMEP monitoring.