Subcostal TAP Block and EEG Dynamics in Laparoscopic Cholecystectomy

This is a prospective, single-center observational study including adult patients scheduled for laparoscopic cholecystectomy under general anesthesia. The study will be conducted at Sancaktepe Sehit Prof. Dr. Ilhan Varank Training and Research Hospital.

Perioperative analgesic management will be determined by the attending anesthesiologist according to routine clinical practice and will not be assigned by the study protocol. Patients will subsequently be evaluated in two observational groups according to the analgesic technique received. One group will consist of patients receiving intravenous remifentanil infusion without a subcostal TAP block, while the other group will consist of patients receiving intravenous remifentanil infusion together with an ultrasound-guided subcostal TAP block.

General anesthesia will be maintained using sevoflurane and remifentanil according to routine clinical practice. Depth of anesthesia and cerebral electrical activity will be monitored using Bispectral Index (BIS) monitoring and electroencephalography (EEG). Intraoperative EEG characteristics, including changes in alpha-band activity and burst suppression, as well as BIS values, will be recorded and compared between the two groups.

Intraoperative analgesic consumption, including remifentanil and additional fentanyl use, will be recorded from anesthesia records. Hemodynamic responses and other routinely monitored parameters will also be documented.

Postoperative pain will be evaluated using the Numerical Rating Scale (NRS) at rest and during activity at 0, 1, 4, 8, 12, and 24 hours after surgery. Routine postoperative analgesia includes intravenous paracetamol and tenoxicam. When clinically indicated for inadequate pain control, rescue analgesia with intravenous tramadol may be administered according to routine clinical practice, and additional analgesic consumption will be recorded.

Postoperative recovery will additionally be assessed using the 15-item Quality of Recovery questionnaire (QoR-15). Mobilization time, length of hospital stay, and patient satisfaction will also be recorded.

The primary objective of the study is to evaluate the association between subcostal TAP block use and intraoperative analgesic requirements, anesthetic depth, EEG dynamics, and burst suppression. Secondary objectives include comparison of postoperative pain, additional analgesic consumption, quality of recovery, mobilization time, length of hospital stay, and patient satisfaction between the two groups.

• Remifentanil (Drug): Intravenous remifentanil infusion administered as part of routine general anesthesia and perioperative analgesic management.
• Ultrasound-Guided Subcostal Transversus Abdominis Plane Block (Procedure), also known as subcostal TAP Block: Ultrasound-guided subcostal transversus abdominis plane block performed as part of routine perioperative analgesic management according to the attending anesthesiologist's clinical decision.

Primary outcomes

• Total Intraoperative Remifentanil Consumption [From induction of general anesthesia until the end of surgery]: Total amount of intravenous remifentanil administered during laparoscopic cholecystectomy will be recorded from the anesthesia record and compared between the remifentanil-only group and the remifentanil plus subcostal TAP block group.
• Intraoperative Bispectral Index Values [From induction of general anesthesia until the end of surgery]: Bispectral Index (BIS) values recorded during general anesthesia will be evaluated to assess anesthetic depth and compared between the two observational groups.
• Intraoperative EEG Alpha-Band Activity [From induction of general anesthesia until the end of surgery]: Changes in electroencephalographic alpha-band activity during general anesthesia and surgical stimulation will be recorded and compared between the two observational groups.
• Intraoperative Burst Suppression [From induction of general anesthesia until the end of surgery]: Burst suppression observed on intraoperative EEG monitoring during general anesthesia will be recorded and compared between the two observational groups.

Secondary outcomes

• Total Intraoperative Fentanyl Consumption [From induction of general anesthesia until the end of surgery]: The total dose of intravenous fentanyl administered during laparoscopic cholecystectomy will be recorded from the anesthesia record and compared between the two observational groups.
• Postoperative Pain at Rest [At 0, 1, 4, 8, 12, and 24 hours after surgery]: Pain intensity at rest will be assessed using the Numerical Rating Scale (NRS), ranging from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Measurements will be recorded at 0, 1, 4, 8, 12, and 24 hours after surgery.
• Postoperative Pain During Activity [At 0, 1, 4, 8, 12, and 24 hours after surgery]: Pain intensity during activity will be assessed using the Numerical Rating Scale (NRS), ranging from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Measurements will be recorded at 0, 1, 4, 8, 12, and 24 hours after surgery.
• Total Postoperative Rescue Tramadol Consumption [During the first 24 hours after surgery]: The total dose of intravenous tramadol administered as rescue analgesia for postoperative pain with an NRS score of 4 or greater will be recorded.
• Quality of Recovery-15 Score [At 24 hours after surgery]: Postoperative quality of recovery will be assessed using the 15-item Quality of Recovery questionnaire (QoR-15). The total score ranges from 0 to 150, with higher scores indicating better quality of recovery.
• Time to First Mobilization [Up to 24 hours after surgery]: The time from completion of surgery to the patient's first postoperative mobilization will be recorded.
• Length of Hospital Stay [From completion of surgery until hospital discharge Up to 7 days]: The duration of postoperative hospital stay will be recorded and compared between the two observational groups.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Age 18 years or older
* American Society of Anesthesiologists (ASA) physical status I-III
* Scheduled to undergo laparoscopic cholecystectomy under general anesthesia
* Written informed consent provided by the participant or, when applicable, the legally authorized representative

Exclusion Criteria:

* Refusal to participate in the study
* American Society of Anesthesiologists (ASA) physical status IV-V
* Known allergy or hypersensitivity to medications used during perioperative anesthetic or analgesic management

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