The purpose of this clinical trial is to compare hypnotic effect of sevoflurane and desflurane at equal minimum alveolar concentrations using power spectral analysis of the electroencephalogram.

Volatile anesthetics 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 were no studies that demonstrate the difference of hypnotic potency using power spectral analysis of electroencephalographic signals (e.g., spectral edge frequency 95%, total power, % value of each bandage). The purpose of this clinical trial is to compare hypnotic effect of sevoflurane and desflurane at equal minimum alveolar concentrations using power spectral analysis of the electroencephalogram.

Inclusion Criteria:

• patients undergoing arthroscopic knee surgery under general anesthesia using volatile anesthetics
• 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