Fig. 4. Response surface describing the interaction between propofol and remifentanil on probability of no response to laryngoscopy. The thick lines reflect to the 50% isobole. (A ) Probability of no response to laryngoscopy with the empirical model, based on target-controlled infusion (TCI) predictions. (B ) Probability of no response to laryngoscopy with the empirical model, based on individual post hoc Bayesian prediction of propofol and remifentanil concentrations. (C ) Probability of no response to laryngoscopy with the proposed hierarchical model, based on TCI predictions. (D ) Probability of no response to laryngoscopy with the proposed hierarchical model, based on individual post hoc Bayesian prediction of propofol and remifentanil concentrations.