Perioperative Analgesic Effect of Different Volumes of Modified Thoracoabdominal Perichondrial Approach on Patients Undergoing Sleeve Gastrectomy: Prospective Randomized Trial

This prospective randomized controlled trial will include patients scheduled for elective laparoscopic sleeve gastrectomy at Menoufia University Hospitals following approval by the institutional ethics committee.

Written informed consent will be obtained from all participants. Randomization and Grouping

Participants will be randomized into three groups using dark closed envelopes. Each group will receive a different volume of local anesthetic for M-TAPA after induction before the surgical procedure:

• Group A: 20 mL: 20 mL of 0.25% bupivacaine per side (40 mL total).
• Group B: 30 mL: 20 mL of 0.25% bupivacaine + 10 ml normal saline solution per side (60 mL total) .
• Group C: 40 mL: 20 mL of 0.25% bupivacaine + 20 ml normal saline solution per side (80 mL total) .

Sample size: 60 subjects Intervention All patients will receive standard general anesthesia, followed by bilateral ultrasound-guided M-TAPA.

Monitoring Standard monitoring with electrocardiography, non-invasive blood pressure, capnography, a multi-gas analyzer, and peripheral oxygen saturation will be performed on all patients in the operating room (BIS, muscle relaxation, and TOF).

Anesthesia induction and endotracheal intubation will be performed intravenously using propofol 2 mg/kg, fentanyl 1-2 µg/kg, and atracurium 0.4-0.5 mg/kg. Anesthesia will be maintained with isoflurane.

A qualified anesthesiologist administering the block in the anatomical plane of M-TAPA will be excluded from the data collection procedure and will not be informed of the precise volume of the solution used.

Inclusion Criteria

Patients will be eligible for the study if they meet the following criteria:

1. Adults aged > 20 years to 60 years. 2. Scheduled for elective laparoscopic sleeve gastrectomy. Exclusion Criteria

Patients will be excluded from the study if any of the following conditions apply:

1. American Society of Anesthesiology (ASA) ASA > class 2.
2. History of chronic pain or opioid use for more than 3 months before surgery.
3. Previous major abdominal surgery (which may affect M-TAPA efficacy).
4. Known hypersensitivity or allergy to local anesthetics (e.g., bupivacaine).
5. Coagulopathy or ongoing anticoagulant therapy that could increase bleeding risk.
6. Local infection at the injection site.
7. Neuromuscular disorders affecting pain perception.
8. Patient with mental or psychiatric disorders.

M-TAPA Technique Following tracheal intubation and prior to the start of the surgical procedure, the transversus abdominis, internal oblique, and external oblique muscles will be visualized using Digital Ultrasonic Diagnostic Imaging System: Mindray Model (DP-15), 75-L 38EB linear probe in the sagittal plane at the costochondral angle. The probe will be positioned at the 10th costal margin and angled deeply at the costochondral angle to view the inferior surface of the costal cartilage at the midline. A 21-G, 80-mm block needle will be inserted in the cranial direction using the in-plane technique, advancing the needle tip towards the posterior aspect of the 10th costal cartilage. Care will be taken to ensure the needle tip does not cross the cranial edge of the 10th costal cartilage. Once properly positioned, 0.25% bupivacaine will be injected beneath the costal cartilage. The same process will be repeated for the other side.

Measuring Outcomes

• Primary:
• Time to First Rescue Analgesia:
• This is the key primary outcome. It measures the duration from the end of surgery until the administration of the first rescue analgesic.
• A longer time to first rescue analgesia indicates prolonged postoperative pain relief and higher efficacy of the M-TAPA block.
• Secondary:
• During surgery, the patients' vital signs (heart rate, blood pressure) will be measured to assess the effectiveness of the M-TAPA block in controlling pain without causing significant hemodynamic instability.

After completion of the surgical procedure \& reversing the muscle relaxants and extubated, patients will be transferred to the postanesthetic care unit (PACU) for 30 minutes after the block, patients will be discharged to ward for first 24 h.

Assessment:

1. Intraoperative Assessment:

• Hemodynamic Monitoring:
• Continuous monitoring of heart rate, blood pressure, and time interval of recovery throughout the surgery to assess the physiological response to pain.
• Intraoperative Fentanyl consumption: (50 ml of Fentanyl \& be repeated)
• The need for additional intraoperative analgesics will be recorded, including any increase in anesthetic requirements due to inadequate analgesia from the M-TAPA block With 20% elevation in hemodynamic or increase anesthetic requirements to achieve satisfactory BIS.

1. Postoperative Assessment:

• Time to First Rescue for Analgesia: The interval between initial pain relief treatment and the need for an additional dose to maintain pain control, indicating the duration of analgesic effectiveness.
• Pain Intensity Measurement (VAS Score): . Pain will be assessed using the Visual Analog Scale (VAS) at specific intervals after surgery, where: . VAS 0 = No Pain, and VAS 10 = Worst Possible Pain. . The overall VAS score will be calculated as the mean of all recorded VAS scores over the 24-hour postoperative period. . Patients reporting VAS ≥ 4 will receive Nalbuphine (3 mg IV) as rescue analgesia.
• Total Analgesic Consumption:

The total amount of analgesics (nalbuphine in mg) administered over 24 hours postoperatively will be recorded.

• Hemodynamic Changes (Postoperative): Vital signs such as heart rate and blood pressure will be monitored regularly to detect any hemodynamic changes related to pain or analgesic administration.
• Adverse Events or Side Effects: Any side effects of the analgesia (e.g., nausea, vomiting, respiratory depression) or adverse reactions to the M-TAPA block or analgesics will be recorded during the 24-hour postoperative period.