Associations Between Age and Dosing of Volatile Anesthetics in 2 Academic Hospitals

BACKGROUND: The inverse relationship between age and dose requirement for potent volatile anesthetics is well established, but the question of whether anesthetic providers consider this relationship in practice remains unanswered. We sought to determine whether there is an association between patient age and the mean dose of volatile anesthetic delivered during maintenance of anesthesia. METHODS: This was a retrospective cross-sectional study of patients receiving a single potent volatile anesthetic at 2 academic hospitals using data recorded in an anesthesia information management system. Multivariate linear models were constructed at each hospital to examine the relationship between age and mean minimum alveolar concentration (MAC) fraction delivered during the maintenance of anesthesia. RESULTS: A total of 7878 cases at the 2 hospitals were included for analysis. For patients aged < 65 years, we observed decreasing doses of volatile anesthetics as age increased. Per decade, mean delivered MAC fraction decreased by an estimated 1.8% (95% confidence interval, 1.5-2.2, P < 0.0001), smaller than the 6.7% decrease suggested by previous studies of human anesthetic requirements. At age > 65 years, the magnitude of the inverse association between age and MAC fraction was higher (3.8% decrease per decade; 95% confidence interval, 2.9-4.7). CONCLUSIONS: Increasing age is associated with decreased absolute doses of potent volatile anesthetics, an association that seems to strengthen as patients enter the geriatric age range. The observed decreases in absolute anesthetic dose were less than those predicted by previous research and therefore represent an overall increase in age-adjusted dose as patients grow older.