Objective To explore the effects of different initial concentration of sevoflurane vaporizer (Fd) on the "washing" time and anesthetic depth in combined intravenous-inhalation anesthesia.

Methods A total of 80 patients who underwent pelvic or abdominal surgery in Tumor Hospital Affiliated to Nantong University from February 2020 to May 2022 were selected and treated with combined intravenous-inhalation anesthesia. According to the different Fd, the patients were randomly divided into high concentration group (group H, n=40) and low concentration group (group L, n=40). After induction of intravenous anesthesia, the sevoflurane vaporizer was opened and the fresh gas flow (FGF) was adjusted to 2 L/min. According to the patient's age, Fd was adjusted to 3 minimum alveolar concentration (MAC) and 2 MAC, respectively in group H and group L. The BIS, body temperature, mean arterial pressure (MAP), heart rate (HR), vaporizer opening time (T1), time of end-expiratory sevoflurane concentration (C_ETSev) reaching 0.7 MAC (T2), "washing" time (time from T1 to T2) and regulation times of vaporizer were compared between the two groups.

Results The "washing" time in group H was (102.8±8.6) s, which was significantly shorter than that in group L (198.0±16.4 s, P＝0.010). There was no significant difference in MAP, HR, body temperature, P_ETCO₂ and BIS between the two groups at T1 and T2 time. There was no significant difference in the regulation times of vaporizer (3.6±0.3 times vs 3.4±0.3 times) and sevoflurane consumption (11.95 mL/h vs 12.02 mL/h) between the two groups.

Conclusions In combined intravenous-inhalation anesthesia, sevoflurane Fd setting of 3 MAC and 2 MAC can reach enough anesthetic depth before the effect of intravenous anesthetic wearing away. To shorten the "washing" time of sevoflurane, vaporizer setting at 3 MAC is a good choice.