The aim of this clinical trial is to evaluate the ratio of hypnotic to analgesic potency of sevoflurane and isoflurane at equi-minimum alveolar concentration using EEG analysis.

Anesthetic agents vary in their relative hypnotic potency. Recent studies demonstrated that equi-minimum alveolar concentration of various volatile anesthetic agents may produce different spectral entropy or bispectral index values. However, there is no study that demonstrate the difference between analgesic potency of volatile anesthetics. The aim of this clinical trial is to evaluate the ratio of hypnotic to analgesic potency of sevoflurane and isoflurane at equi-minimum alveolar concentration using EEG analysis.

Inclusion Criteria:

• patients undergoing general anesthesia using volatile anesthetics and intubation
• patients with american society of anesthesiologist physical status I, II
• patients obtaining written informed consent

Exclusion Criteria:

• patients with a history of any psychiatric or neurological disease
• patients who had received any medication affecting the central nervous system
• patients who had received medication affecting the sympathetic or parasympathetic nervous systems
• patients undergoing supraglottic airway for airway management
• pregnant women