Changes in Pulse Wave Transit Time and Its Variability After Placement of Interscalene Brachial Plexus Block

Inclusion Criteria: * American Society of Anesthesiologists status of 1 * Scheduled to receive interscalene brachial plexus block for arthroscopic shoulder surgery Exclusion Criteria: * Coagulopathy * Infection of the skin area for interscalene brachial plexus block * Peripheral neuropathy or neurologic sequelae in the upper limb ipsilateral to the surgery * Allergy to local anesthetics or a history of allergic shock * Contralateral vocal cord palsy, hemidiaphragmatic paresis/paralysis or pneumo/hemo thorax * Arrhythmias * Cardiac conduction abnormalities * A history of medication affecting cardiac conduction * Ischemic heart disease * Hypertension * Diabetes mellitus * Thyroid disfunction * Other medical conditions affecting autonomic nervous activity