RECOVERY AND KINETIC CHARACTERISTICS OF DESFLURANE AND SEVOFLURANE INVOLUNTEERS AFTER 8-H EXPOSURE, INCLUDING KINETICS OF DEGRADATION PRODUCTS

Background: Desflurane and sevoflurane permit speedier changes in anes thetic partial pressures than do older halogenated anesthetics. The au thors determined the kinetic characteristics of desflurane and sevoflu rane and those of compound A [CH2F-O-C(=CF2)(CF3)], a nephrotoxic degr adation product of sevoflurane. Methods: Volunteers received 1.25 mini mum alveolar concentration of desflurane or sevoflurane, each administ ered for 8 h in a fresh gas inflow of 2 1/min. Inspired (F-I) and end- tidal (F-A) concentrations of anesthetic and compound A were measured during administration, and F-A relative to F-AO (the last end-tidal co ncentration during administration) during elimination. The indices of recovery mere also measured. Results: The ratio F-I/F-A rapidly approa ched 1.0, with values greater for sevoflurane (desflurane 1.06 +/- 0.0 1 vs. sevoflurane 1.11 +/- 0.02, mean +/- SD). The ratio F-A/F-I for c ompound A was approximately 0.8. The F-A/F-AO ratio decreased slightly more rapidly with desflurane than with sevoflurane, and objective mea sures indicated faster recovery with desflurane: The initial response to command (14 +/- 4 min vs. 28 +/- 8 min [means +/- SD]) and orientat ion (19 +/- 4 vs. 33 +/- 9 min) was quicker, and recovery mas faster a s defined by results of the Digit Symbol Substitution, P-deletion, and Trieger tests. Desflurane produced less vomiting (1 [0.5, 3]; median [quartiles] episodes) than did sevoflurane (5 [2.5, 7.5] episodes). Th e F-A/F-AO ratio for compound A decreased within 5 min to a constant v alue of 0.1. Conclusions: These anesthetics have kinetics consistent w ith their solubilities. Sevoflurane's greater biodegradation probably increases FI/F-A differences during anesthetic administration and decr eases F-A/F-AO differences during elimination. The F-A for compound A differs from F-I by 20% (F-A/F-I = 0.8) because of substantial degrada tion. Recovery from anesthesia proceeds nearly twice as fast with desf lurane than with sevoflurane. Differences in ventilation, or alveolar or tissue elimination, do not completely explain the slower recovery w ith sevoflurane.