The minimum alveolar concentration (MAC) of sevoflurane with and without nitrous oxide in elderly versus young adults

Study Objective: To determine the minimum alveolar concentration (MAC) of sevoflurane with and without 65% nitrous oxide (N2O) in non-Asian patients at least 70 years of age, and in patients aged 18 to 35 years. Design: Randomized open-study design. The Dixon up-down method determined the target sevoflurane concentration for each patient. Setting: Operating rooms of a large university hospital. Patients: 27 ASA status I and II patients aged 18 to 35 years and 26 patients at least 70 Tears of age, who were free of any conditions or diseases that would interfere with MAC determination. Interventions: Unpremedicated patients breathed savoflurane until the predetermined target end-tidal sevoflurane concentration was reached for at least 15 minutes before skin incision. Up-down sevoflurane increments were 0.25% after an initial target concentration of 2%. This continued until there were at least three crossover pairs in each of the four groups. Measurements and Main Results: Patients were observed for purposeful movement in response to a skin incision. End-tidal sevoflurane, N2O and oxygen (O-2) concentrations were measured by a calibrated infrared analyzer. MAC was determined by logistic regression analysis. The MAC of sevoflurane in O-2/air for the mean age in each group was 2.6% in the younger group (age = 25 yr) and 1.45% in the elderly group (age = 76 yr). Nitrous oxide 65% decreased MAC about 50% in each group at any age studied. Conclusions: The MAC of sevoflurane determined in this study is similar to that determined in previous studies, including the MAC determined in an elderly Asian population. Increasing age and N2O decrease sevoflurane MAC similarly to that determined with other volatile anesthetics.