Effect of Nitrous Oxide and of Narcotic Premedication on the Alveolar Concentration of Halothane Required for Anesthesia

Sixty-eight surgical patients were divided into three groups and anesthetized with either halothane and ogygen, halo thane-oxygen following narcotic premedication, or halothanc-oxygen and 70 per cent nitrous oxide. The minimum alveolar concentration of halothane required to prevent movement in response to surgical incision was 0.74 per cent. Addition of narcotic premedication decreased this value to 0.69 per cent and addition of nitrous oxide (without narcotic premedication) allowed a reduction in the alveolar halothane concentration to 0.29 per cent. Advantages of administering nitrous oxide with halothane are: (1) decreased cost of anesthesia, (2) increased speed of recovery, and (3) possible decreased hepatotoxicity. We believe that these advantages outweigh the disadvantage of decreased percentage of oxygen administered. The narcotic premedication resulted in only a slight decrease in required alveolar halothane concentration. We believe this decrease is insignificant relative to the possible cardiovascular depression that may accompany narcotic premedication.