Figure 12-21 Simulation of the interaction of propofol and remifentanil in preventing a somatic response at skin incision and time to recovery. Note that with remifentanil, the optimal combination is a propofol concentration of 2.5 µg/mL and a remifentanil concentration of 5 to 7 ng/mL and that increasing the duration of the infusion has minimal impact on recovery time if the optimal dose of remifentanil is not used. However, if the propofol dose is increased, recovery is prolonged. (Adapted from Vuyk J, Mertens MJ, Olofsen E, et al: Propofol anesthesia and rational opioid selection: Determination of optimal EC50-EC95 propofolopioid concentrations that assure adequate anesthesia and a rapid return of consciousness. Anesthesiology 87:1549–1562, 1997.)