Patients were anesthetized with dexmedetomidine (0.5 µg·kg loading, followed by infusion at 0.4 µg·kg·h) and propofol through target-controlled infusion for general anesthesia with tracheal intubation. The surgeon conducted the online scoring of the background signals, spiking frequency, amplitude, and pattern of single-unit activities by using a 0-10 verbal numerical rating scale (NRS; 0, maximal suppression; 10, minimal suppression), and responses were grouped into suppression (NRS ≤ 6) and nonsuppression (NRS > 6). The median inhibitory concentration (IC50) of propofol (as target effect-site concentrations: Ceprop) was determined using modified Dixon’s up-and-down method (UDM). Probit regression analysis was further used to obtain the dose-response relationship, and IC05 and IC95 were calculated.
Twenty-three adult patients participated in this study. Under the concomitant infusion of dexmedetomidine, the predicted IC50 value (95% confidence interval; CI) of Ceprop for neuronal suppression during MER was 1.29 (1.24-1.34) µg·mL as calculated using modified Dixon’s UDM. Using probit analysis, the estimated IC05, IC50, and IC95 values (95% CIs) were 1.17 (0.87-1.23), 1.28 (1.21-1.34), and 1.40 (1.33-1.85) µg·mL, respectively.
Our data provided reference values of propofol for dosage adjustment to avoid interference on MER under GA when anesthetics have to be continuously infused during recording.