Dixon's up-and-down technique Dixon's up-and-down technique is a commonly used method to define MAC (27-30). The anesthetic concentration applied to the first patient is estimated by clinical experience. If there BIS values below 50, the concentration of inhalational anesthetic in subsequent patient is decreased by 20%. If the BIS show values greater than or equal to 50 for a period ≥ 1 minute steadily, the concentration is increased by 20% in the next patient. In each series of patients, the pairs of independent cross in order measurements are identified. A pair of cross consists of two consecutive patients where there is a BIS value below 50 in the first but not the second patient, or vice versa. Each patient was considered only for one single cross-over pair in order to assure independent test data. Six independent cross-over pairs and +/- 10 changes in direction are required to obtain reliable results (26).