Effect on nitrous oxide on the anaesthetic requirement of enflurane

The effect of nitrous oxide on the minimum alveolar concentration of enflurane required to prevent movement in response to skin incision in 50% of subjects (MAC) has been investigated in two groups of 16 patients. The end-tidal enflurane concentration was held constant for 25-36 min in order to equilibrate the brain with the alveolar anasthetic partial pressure. When nitrous oxide (30%) was present in the inspired mixture the MAC of enflurane was 1.17%; the value decreased to 0.57% when 70% nitrous oxide was used.