Figure 31-17 Percent reduction in enflurane minimum alveolar concentration (MAC) as a function of plasma concentrations of fentanyl. Each point represents the mean concentration (±SEM) for fentanyl in plasma and the average percent (±SEM) reduction in enflurane MAC. Numbers of dogs below the vertical standard error bars indicate the numbers per data point. (Redrawn from Murphy MR, Hug CC Jr: The anesthetic potency of fentanyl in terms of its reduction of enflurane MAC. Anesthesiology 57:485, 1982.)