Figure 12-10 Interaction of isoflurane and remifentanil in preventing a somatic response at skin incision (i.e., minimum alveolar concentration reduction of isoflurane). The solid line represents the concentrations of isoflurane and remifentanil, when administered together, that are required to prevent purposeful movement in 50% of patients at skin incision. From Lang E, Kapila A, Shlugman D, et al: Reduction of isoflurane minimal alveolar concentration by remifentanil. Anesthesiology 85:721–728, 1996.)