Decreased respiratory depression during emergence from anesthesia with sevoflurane/N2O than with sevoflurane alone

Purpose: To investigate ventilation and gas elimination during the emergenc e from inhalational anesthesia with controlled normoventilation with either sevoflurane/N2O or sevoflurane alone. Methods: Twenty-four ASA I-ii patients scheduled for abdominal hysterectomy were randomly allocated to receive either 1.3 MAC sevoflurane/N2O (n= 12) or equi-MAC sevoflurane (n= 12) in 30% oxygen (O-2) Expired minute ventilat ion volumes (V-E), end-tidal (ET) concentrations of O-2, carbon dioxide (CO 2), sevoflurane and N2O as well as purse oximetry saturation (SpO(2)) and C O2 elimination rates (VCO2) were measured. The ET concentrations of sevoflu rane and N2O were converted to total MAC Values and gas elimination was exp ressed in terms of MAC reduction, Time to resumption of spontaneous breathi ng and extubation were recorded and arterial blood gas analysis was perform ed at the end of controlled normoventilation and at the beginning of sponta neous breathing. Results: Resumption of spontaneous breathing and extubation were 8 and 13 m in less, respectively, in the sevoflurane/N2O than in the sevoflurane group . Spontaneous breathing was resumed in both groups when pH had decreased by 0.07-0.08 and PaCO2 increased by 1.3-1.5 kPa. Depression of V-E and VCO2 w ere less, and MAC reduction more rapid in the sevoflurane/N2O than in the s evoflurane group. Conclusions: Respiratory recovery was faster after sevoflurane/N2O than sev oflurane anesthesia. Changes in pH and PaCO2 rather than absolute values we re important for resumption of spontaneous breathing after controlled normo ventilation, In both groups, the tracheas were extubated at about 0.2 MAC.