Figure 5-4 In patients, administration of 65% nitrous oxide produces a more rapid rise in the alveolar concentration of anesthetic/concentration of inspired anesthetic (FA/FI ratio) for nitrous oxide than administration of 5% (i.e., concentration effect, two solid lines). The FA/FI ratio for 4% desflurane rises more rapidly when given with 65% nitrous oxide than when given with 5% (i.e., second gas effect, two dotted lines). (Adapted from Taheri S, Eger EI II: A demonstration of the concentration and second gas effects in humans anesthetized with nitrous oxide and desflurane. Anesth Analg 89:774–780, 1999.)