Fig. 5. Results of computer simulations designed to identify optimal target concentration pairs of remifentanil and sevoflurane that minimize the time to responsiveness.  A shows the predicted decline in effect site and alveolar concentrations for remifentanil and sevoflurane after stopping drug administration regimens targeted to reach the EC⁹⁵isobole for tetanic stimulation for 1 h. The EC⁹⁵isobole is on the “floor” of the cube; the vertical axis represents time elapsed since stopping the administration of the drugs. The isobole representing an 80% probability of the return of responsiveness (Observer's Assessment of Alertness/Sedation score ≥ 4) is shown by a  dotted line that is superimposed on the concentration decay curves. The  highlighted curve is the sevoflurane and remifentanil target concentration pair that resulted in the fastest return of responsiveness.  B shows the time in minutes to the return of responsiveness after a 1-h procedure in which sevoflurane and remifentanil were administered to target concentration pairs on the EC⁹⁵isobole for tetanic stimulation. The  highlighted trace on the panel on the left is shown topographically. The minimum time to regain responsiveness represents the target concentration pairs for a 1-h procedure.