The Effects of Horner's Syndrome Developing After Interscalene Brachial Plexus Block on Autonomic Nervous Activity

Inclusion Criteria: * American Society of Anesthesiologists physical status 1 * Arthroscopic shoulder surgery under interscalene brachial plexus block Exclusion Criteria: * Coagulopathy * Infection at the site of brachial plexus block * Peripheral neuropathy or neurologic sequelae on the operative limb * Allergy to local anesthetics or history of allergic shock * Psychiatric diseases * Patient refusal * Difficulty communicating with medical personnel * Arrhythmias * Ischemic heart disease * Hypertension * Diabetes mellitus * Thyroid dysfunction * Conduction abnormalities on electrocardiogram * Electrolyte imbalance * Medications affecting cardiac conduction * Contralateral vocal cord palsy * Contralateral hemidiaphragmatic paresis or paralysis * Contralateral pneumothorax or hemothorax