The goal of this observational study is to investigate the relationship between the response to skull pin fixation pain and the analysis of blood pressure, heart rate, and brain wave activity in adults undergoing brain surgery. The main questions it aims to answer are:

Does the analysis of blood pressure, heart rate, and brain wave activity indicate the patient's response to skull pin fixation pain during brain surgery? How do the methods used to reduce skull pin fixation pain in brain surgeries affect narcotic opioid consumption? The researchers will monitor the patients' response to skull pin fixation pain during surgery through the analysis of brain wave activity.

Adult patients undergoing elective craniotomy under general anesthesia will be evaluated. Methods used to manage pin-related pain will be categorized into three approaches: intravenous opioids, local Methods used to manage pin-related pain will be categorised into three approaches: intravenous opioids, local anaesthetic injection at the pin site, and scalp block. injection at the pin site, and scalp block. The patient's The patient's haemodynamic responses and reactions to painful stimuli recorded by the BIS-DSA monitor during skull clamp placement will be documented. responses and reactions to painful stimuli recorded by the BIS-DSA monitor during skull clamp placement will be documented. These records are automatically archived in the BIS-DSA device.Waveform data will be converted into numerical values using a predefined hue-based algorithm.

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.

"This study will include adult patients undergoing elective craniotomy under general anesthesia. Participants will be assigned to different pain management techniques (scalp nerve block, intravenous opioids, or local anesthetic injection) to evaluate their effects on BIS-DSA spectral analysis and hemodynamic responses.