Figure 11-7 Time course of spectral edge and serum opioid concentration. Fentanyl (top panel) and alfentanil (middle panel) were infused at 150 µg/minute and 1500 µg/minute, respectively. Remifentanil (bottom panel) was administered at 3 µg/kg/minute for 10 minutes. The spectral edge changes lag behind the serum concentration changes in the case of fentanyl, whereas the spectral edge and serum concentrations are closely parallel in the cases of alfentanil and remifentanil. (From Scott JC, Ponganis KV, Stanski DR: EEG quantitation of narcotic effect: The comparative pharmacodynamics of fentanyl and alfentanil. Anesthesiology 62:234–241, 1985; and Egan TD, Minto CF, Hermann DJ, Barr J, Muir KT, Shafer SL: Remifentanil versus alfentanil: Comparative pharmacokinetics and pharmacodynamics in healthy adult male volunteers. Anesthesiology 84:821–833, 1996.)