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

Inclusion Criteria:

• patients undergoing general anesthesia using volatile anesthetics and supraglottic airway (I-gel™)
• patients with american society of anesthesiologist physical status I, II
• patients aged 19-65 years
• 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 tracheal intubation for airway management
• pregnant women