The aim of this clinical trial is to evaluate the difference of analgesic potency of sevoflurane and desflurane at equi-minimum alveolar concentration using a surgical pleth index.

Volatile anesthetics vary in their relative hypnotic potencies. Recent studies demonstrated that equi-minimum alveolar concentration of various volatile anesthetics produced different EEG-derived indices such as bispectral index. However, there was no controlled study that demonstrates the difference of analgesic potency. The aim of this clinical trial is to evaluate the difference of analgesic potency of sevoflurane and desflurane at equi-minimum alveolar concentration using a surgical pleth index.

Inclusion Criteria:

• patients undergoing arthroscopic shoulder surgery
• 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 who have not received interscalene approach brachial plexus block (refusal or failure)
• pregnant women