Spectral Differences of Anesthetic Agents: Addressing Fundamental Problems With New Methods

BACKGROUND: Processed electroencephalography parameters are used to guide anesthesia to adequate levels for surgical procedures. Despite known spectral differences between anesthetics, studies often assume similar anesthetic states when titrating to the same target values, presupposing a reductive one-size-fits-all approach for all anesthetic agents. We hypothesize this may introduce bias and aim to characterize the differences using conventional and new approaches. METHODS: For this retrospective study, we included 108 patients undergoing surgery under general anesthesia with either fluranes or propofol. We analyzed steady-state frontal electroencephalography during surgery. Conventional approaches were compared with “fitting oscillations & one-over-f” and “variational mode decomposition” at clinically guided hypnotic and analgesic levels. After comparing the hypnotic drugs at the group level, we used 2 distinct ranges of spectral edge frequency (SEF) for further analyses (8–15 Hz vs 15–21 Hz). RESULTS: Sevoflurane and desflurane (“flurane”) demonstrated similar spectral patterns using both conventional methods and “fitting oscillations & one-over-f” and “variational mode decomposition.” “Variational mode decomposition” presented a 1.5 Hz higher central frequency (area under the receiver operating characteristic [AUC]: 0.88, 95% confidence interval [CI], 0.81–0.94, P < .001) in the propofol group (10.8 Hz [10.4–11.6]), compared to the flurane group (9.26 Hz [8.51–9.41]). “Fitting oscillations & one-over-f” produced a 2.04 Hz higher center frequency (AUC: 0.82, 95% CI, 0.72–0.91, P < .001) in the propofol group (10.6 [9.8–11.3]) compared to the flurane group (8.56 [8.02–9.69]). The exponent was 0.26 Hz − 1 lower (AUC: 0.76, 95% CI, 0.67–0.85, P < .001) in the propofol group (2.45 Hz − 1 [2.45–2.71]) compared to the flurane group (2.71 Hz − 1 [2.50–2.93]). At the lower SEF range, “variational mode decomposition” presented a 1.5 Hz higher central frequency (AUC: 0.83, 95% CI, 0.70–0.94, P < .001) in the propofol group (10.4 Hz [9.7–10.9]), compared to the flurane group (8.92 Hz [8.03–9.45]). “Fitting oscillations & one-over-f” produced a 1.5 Hz higher center frequency (AUC: 0.83, 95% CI, 0.68–0.95, P = .002) in the propofol group (10.3 [10.0–10.8]) compared to the flurane group (8.78 [7.63–9.66]). The exponent was 0.31 Hz − 1 lower (AUC: 0.79, 95% CI, 0.65–0.91, P = .002) in the propofol group (2.57 Hz − 1 [2.44–2.70]) compared to the flurane group (2.88 Hz − 1 [2.66–3.05]). Similar differences were found in the higher SEF group. However, no significant difference was found in the exponent between the groups. CONCLUSIONS: Differences between the electroencephalographic (EEG) spectral patterns under propofol anesthesia compared to anesthesia using fluranes were sensitively captured by 2 recent approaches to EEG analysis. This could potentially lead to establishing agent-specific anesthetic indices.