Abstract

Background: The electroencephalogram (EEG) may be useful for monitoring anesthetic depth and avoiding overdose. We aimed to characterize EEG-recorded brain oscillations during increasing depth of anesthesia in a real-life surgical scenario. We hypothesized that alpha power and coherency will diminish as propofol dose increases between loss of consciousness (LOC) and an EEG burst suppression (BS) pattern. Methods: This nonrandomized dose-response clinical trial with concurrent control included EEG monitoring in 16 patients receiving slowly increasing doses of propofol. We assessed 3 intraoperative EEG segments (LOC, middle-dose, and BS) with spectral analysis. Results: Alpha band power diminished with each step increase in propofol dose. Average alpha power and average delta power during the BS step (-1.4 +/- 3.8 and 6.2 +/- 3.1 dB, respectively) were significantly lower than during the LOC step (2.8 +/- 2.6; P=0.004 and 10.1 +/- 5.2 dB; P=0.03, respectively). Peak alpha power was significantly higher during the LOC (5.4 +/- 2.6 dB) compared with middle-dose (2.6 +/- 3.6; P=0.04) and BS (0.7 +/- 3.2; P=0.0002) steps. In addition, as propofol dose increased, alpha band coherence between the F7 and F8 electrodes decreased, whereas delta band coherence exhibited a biphasic response (initial increase between LOC and middle-dose steps and decrease between middle-dose and BS steps). Conclusion: We report compelling data regarding EEG patterns associated with increases in propofol dose. This information may more accurately define "therapeutic windows" for anesthesia and provide insights into brain dynamics that are sequentially affected by increased anesthetic doses.