Spectrogram and time domain electroencephalogram signatures of two patients receiving propofol for induction and maintenance of unconsciousness. (A) High slow-delta power after the 200-mg propofol bolus at minute 3 (green arrow) is evident between minutes 3 and 5. The electroencephalogram transitions to robust slow-delta and alpha oscillations maintained by a propofol infusion at 100 μg kg⁻¹ min⁻¹. The lower and upper white curves are the median and the spectral edge frequencies, respectively. (B) After bolus doses of propofol (green arrows), the patient’s electroencephalogram transitions between three different states: slow oscillations (minutes 5 to 8) after the 100-mg propofol bolus at minute 3; burst suppression (minutes 8 to 17) after two additional 50-mg propofol boluses; and slow-delta and alpha oscillations from minutes 17 to 25. Beginning at minute 24, the alpha band power decreases and broadens to the beta band. The slow-delta oscillation power decreases after minute 24. The dissipation of the slow-delta and alpha oscillation power as the patient emerges gives the appearance of a zipper opening. (C) Ten-second electroencephalogram traces recorded at minute 5.5 (slow-delta oscillations) and minute 24 (slow-delta and alpha oscillations) of the spectrogram in A. (D) Ten-second electroencephalogram traces showing slow oscillations at minute 7.1, burst suppression at minute 11.5, and slow-delta and alpha oscillations at minute 17 for the spectrogram in B. A–D were adapted, with permission, from Purdon and Brown, Clinical Electroencephalography for the Anesthesiologist (2014), from the Partners Healthcare Office of Continuing Professional Development.⁶⁹  Adaptations are themselves works protected by copyright. In order to publish this adaptation, authorization has been obtained both from the owner of the copyright of the original work and from the owner of copyright of the translation or adaptation.