Brain wave monitor may reveal hidden pain during surgery

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Adult patients aged 18-70 years undergoing elective craniotomy. * Patients classified as ASA 1-3 according to the American Society of Anesthesiologists (ASA) classification. * Patients scheduled for surgery under general anesthesia. * Patients who provide written informed consent to participate in the study. * Patients with normal cognitive function (i.e., no diagnosed dementia or severe cognitive impairment). * Patients with a preoperative BIS value within the normal range (i.e., no extreme baseline deviations). Exclusion Criteria: * Patients classified as ASA 4 or higher. * Patients with neurological disorders (e.g., Parkinson's disease, epilepsy, stroke history). * Patients with psychiatric disorders (e.g., severe depression, schizophrenia) that may affect pain perception and response. * Patients with known allergies to local anesthetics or opioids. * Pregnant or breastfeeding women. * Patients with contraindications to anesthesia, including but not limited to: * Severe cardiovascular disease (e.g., uncontrolled hypertension, recent myocardial infarction). * Severe respiratory disease (e.g., COPD, uncontrolled asthma). * Patients with any neurological or pharmacological condition that may interfere with BIS-DSA or EEG measurements. * Patients with preoperative chronic opioid use (≥3 months) due to potential tolerance affecting response to intraoperative analgesia. * Patients with a history of substance abuse that may alter the BIS response or anesthetic metabolism. * Patients with significant hearing or communication impairments, preventing them from understanding or responding to preoperative assessments. * Patients with significant scalp pathology (e.g., infections, scars, large vascular malformations) at the BIS electrode placement site, which may interfere with signal acquisition.