Figure 11-6 Electroencephalography (EEG) stages for fentanyl and alfentanil. Representative 3-second tracings of EEG recordings from fentanyl and alfentanil are shown. Awake = mixed α (8–13 Hz) and β (>13 Hz) activity. Stage 1 = slowing with α spindles. Stage 2 = more slowing, theta activity present (4–7 Hz). Stage 3 = maximal slowing, δ waves present (<4 Hz), with high amplitude. (From Scott JC, Ponganis KV, Stanski DR: EEG quantitation of narcotic effect: The comparative pharmacodynamics of fentanyl and alfentanil. Anesthesiology 62:234–241, 1985.)