[Effect of fresh gas flow on isoflurane pharmacokinetics during anesthesia induction]

To investigate the effect of different fresh gas flow (FGF) rates on isoflurane pharmacokinetics during anesthesia induction.

Sixty female patients (ASA class I-II, age range of 18-49 years) scheduled for gynecological laparoscopic surgery were randomly divided into groups I, II, and III (n=20) for isoflurane inhalation with FGF rate of 1, 2, and 3 L/min, respectively. Each group was further divided into two equal subgroups according to the setting concentration of the isoflurane vaporizer at 1% (groups I 1, II 1, and III 1) and 2% (groups I 2, II 2, and III 2). Isoflurane with different setting concentrations was administered under different FGFs in the patients after tracheal intubation following anesthesia induction, and the inspiratory concentration (CIiso) and expiratory concentration (CEiso) of isoflurane in the airway were monitored and recorded every 3 min for totalling 18 min, with the observation time points marked as T1 to T6, respectively.

CIiso and CEiso varied significantly at different time points and between different subgroups (P<0.05). In each subgroup, CIiso and CEiso increased along with time and reached a relatively stable stage at 9 min, but failed to reach the setting concentration during the observation period. At different observation time points, CIiso and CEiso in the subgroups with setting isoflurane concentration of 2% were almost twice as much as that in the subgroups with setting isoflurane concentration of 1%.

CIiso and CEiso increase along with time lapse in all the groups and reach a relatively stable stage at 9 min after inhalation initiation, but can not reach the setting concentration. The larger the FGF and setting concentration, the faster CIiso and CEiso increase.