Minimum Alveolar Concentration of Desflurane in Patients Older Than 65 Yr

BACKGROUND: The minimum alveolar concentration (MAC) of desflurane/oxygen is 7.25% in the 18-30-yr age group, and 6.0% in the 31-65-yr age group. The addition of 60% N2O reduces MAC to 4.0 and 2.83%, respectively. Because MAC of other inhaled anesthetics is less than that for younger adults, we determined MAC of desflurane in adults aged 65 yr and older. METHODS: Thirty-nine patients, 21 of whom received 60% N2O/O2/desflurane, and 18 of whom received desflurane/oxygen, scheduled for surgery, were enrolled. They received no premedication, intravenous induction agent, opioid, or neuromuscular blocking agent for intubation. After 10 min or more at a steady end-tidal desflurane concentration, the incision was made. In both groups, six crossover pairs of patients responses (movement-no movement) provided a mean end-tidal concentration. Minimum alveolar concentration was defined as the average of the six crossover midpoints in each subgroup. RESULTS: MAC was 5.17 +/ 0.6% (mean +/- SD) in the desflurane/oxygen group. It was 1.67 +/- 0.4% in the desflurane/nitrous oxide/oxygen group. CONCLUSIONS: In the geriatric patient, MAC of desflurane, with or without nitrous oxide, is less than that reported in patients aged 18-65 yr. This is in agreement with results with all other inhalation agents.