Figure 31-12 Minimal alveolar concentration necessary to prevent movement in 50% of subjects receiving a noxious stimulus for halothane combined with (1) oxygen, (2) oxygen and morphine premedication (0.15 mg/kg intramuscularly), and (3) 70% nitrous oxide. The anesthetic requirement for halothane is greatly decreased by nitrous oxide and less so by premedication with morphine. (Modified from Saidman LJ, Eger EI II: Effect of nitrous oxide and of narcotic premedication on the alveolar concentration of halothane required for anesthesia. Anesthesiology 25:302, 1964.)