Clinical Research Directory

Inclusion Criteria: * Age between 18 and 70 years * American Society of Anesthesiologists physical status I or II * Scheduled to undergo elective breast surgery with an estimated surgical duration of 45 to 180 minutes * Planned anesthesia technique is total intravenous anesthesia * Able to understand Turkish and communicate verbally * Able to read and write and provide written informed consent * Clinically normal hearing function and no ear, nose, or throat condition that prevents headphone use Exclusion Criteria: * Diagnosed unilateral or bilateral hearing loss or use of a hearing aid * Current psychiatric disease or regular use of psychotropic medication, including antidepressants, antipsychotics, anxiolytics, or hypnotics * Diagnosis of chronic pain syndrome or chronic use of opioids, pregabalin, or gabapentin * Neurological disease that may affect BIS interpretation, such as epilepsy, dementia, stroke sequelae, or Parkinson disease * Known allergy or contraindication to propofol, remifentanil, or rocuronium * Morbid obesity, defined as body mass index greater than 40 kg/m² * History of active alcohol or substance dependence * Pregnancy or breastfeeding * Emergency surgery or reoperation * Planned addition of regional anesthesia in the preoperative period * Refusal to participate in the study or refusal to sign the informed consent form