BLOOD-CONCENTRATIONS OF SEVOFLURANE AND ISOFLURANE ON RECOVERY FROM ANESTHESIA

We studied 16 healthy ASA physical status I patients (aged 13-71 yr for sevoflurane and 22-74 yr for isoflurane) to determine maximum blood concentrations on awakening (MBC(awake)) from sevoflurane and isoflurane anaesthesia, and determined if age and duration of anaesthesia significantly influenced MBC(awake). After operation, the end-tidal concentration of anaesthetics was decreased gradually. During recovery from anaesthesia, patients were asked repeatedly to open their eyes. We obtained blood samples to measure the anaesthetic concentration when patients first opened their eyes. MBC(awake) of sevoflurane and isoflurane (ml of anaesthetic gas per ml of blood) were 0.40 (SE 0.04) % and 0.53 (0.04) %, respectively. MBC(awake) values of sevoflurane and isoflurane correlated significantly with age (P < 0.05) but not with duration of anaesthesia. Blood:gas partition coefficients of sevoflurane and isoflurane were 0.65 (SD 0.05) and 1.36 (0.09), respectively. There was no significant correlation between age and blood:gas partition coefficient for sevoflurane and isoflurane. Awakening alveolar concentrations (MAC(awake)) calculated from MBC(awake) were 0.61 (SE 0.05) % for sevoflurane and 0.39 (0.02) % for isoflurane, and correlated significantly with age. The ratios of awakening alveolar concentration to MA C were reasonably constant - 0.33 for sevoflurane and 0.33 for isoflurane.