This study aims to propose a strategy for controlling the depth of anesthesia based on continuous and non-invasive monitoring of exhaled breath: BIS value during intravenous-inhalation combined anesthesia is predicted according to the real-time exhaled concentrations of sevoflurane and propofol, so as to achieve the depth of anesthesia management for patients who cannot use standard BIS. Furthermore, the relationship between anesthetic concentration and depth of anesthesia was analyzed in different subgroups.

Inclusion Criteria:

• Age ≥18 years old
• ASA I-III
• Expected duration of surgery > 1 hour
• Radial artery catheterization was performed
• Patients requiring BIS monitoring.

Exclusion Criteria:

• Patients with contraindications to general anesthesia
• mental disorder, unable to answer
• long-term use of antiepileptic drugs and psychotropic drugs
• pregnant patients
• patients refused to participate
• the investigator thought that the study was not suitable for inclusion
• patients who did not wake up in PACU

Patients who underwent general anesthesia for the first time and combined intravenous and inhalational anesthesia