Ultrasound-Guided Erector Spinae Plane Block Versus Modified Thoracoabdominal Block for Analgesia in Obese Patients

Patients will be randomly allocated into two groups: ESPB (n=20) and M TAPA (n=20).

1. ESPB group: This group will receive ultrasound guided erector spinae plane block.
2. M-TAPA group: This group will receive ultrasound guided modified thoracoabdominal nerve block.

Preoperative assessment:

The patient will enter the preparation room, he/she will be asked about his medical and surgical history in details and fasting hours (6-8 hrs) and full examination will be performed including airway examination. Lab investigations including complete blood count (CBC), coagulation profile, liver function tests and renal function tests will be checked.

The procedure will be explained to the patient and informed consent will be signed after his agreement then the patient will be classified into one of the groups.

The VAS will be explained to the patient in details as it will be used as a measurement tool for assessment of postoperative pain.

Operating Room preparation \& Equipment:

The ultrasound used will be Siemens ACUSON X300 Ultrasound System, the scanning probe was a linear probe 8-14 MHZ. A 50-mm block needle 22 gauge will be used. (SonoPlex Stim Cannula, Germany) All blocks will be given by one researcher using 40ml of drug 0.25% bupivacaine (20ml on each side)

Intraoperative management:

After that, the patient will be monitored with electrocardiogram (ECG), non-invasive arterial blood pressure, pulse oximetry, oxygen saturation (SpO2) and Capnography. IV access will be secured with 18-gauge cannula and Premedication (ranitidine 2.0 mg/kg IV and metoclopramide 0.1 mg/kg IV) will be given. Predicted body weight will be used for calculation of drug dose.

A) In ESPB group:

• The patient will assume the sitting position with an assisting nurse for support and to ensure patient's safety.
• A single anesthesiologist will perform ESPB on both sides of the body.
• The level of T10 will be determined by counting 3 spinous processes below T7 (which is at the level of the inferior angle of the scapula), and will also be double-checked by counting down from C7.
• Before applying the block, the spinous process of the spine and a spot 3 cm laterally from it are indicated.
• The probe will then be lateralized 2.5-3 cm into the parasagittal plane.
• The needle will be placed and advanced under sono-vision until it contacts the transverse process of the T10 vertebra after being visible to the Trapezius, Rhomboid Major, Erector Spinae muscle, and these structures.
• No sedation will be used.
• Utilizing aseptic methods, subcutaneous local apathetic infiltration of lidocaine will be performed using insulin syringe.
• After negative aspiration, LA will be deposited deep to the erector spinae muscle in the fascial plane.
• After that, a 22-gauge spinal needle will be used to inject 20 ml of bupivacaine 0.25% and 5 ml of lidocaine 2% as local anesthesia (LA) on each side.

B) M TAPA group :

• The patient will assume the supine position with an assisting nurse for support and to ensure patient's safety.
• A single anesthesiologist will perform M-TAPA on both sides of the body.
• Transversus abdominis, internal oblique and external oblique muscles will be located with a high-frequency linear probe on the costochondral angle in the sagittal plane under ultrasound guidance at the 10th costal margin.
• In order to see the lower surface of the costal cartilage in the midline, a deep angle will be made to the costochondral angle at the margin of the 10th costa.
• Utilizing aseptic methods, subcutaneous local apathetic infiltration of lidocaine will be performed using insulin syringe.
• After negative aspiration, using the in-plane approach, a 22-gauge spinal needle will be placed in the cranial direction, and the needle's tip will then be advanced to the posterior aspect of the 10th costal cartilage.
• The 10th costal cartilage's cranial edge will be never passed by the needle tip, and 20 mL of 0.25% bupivacaine will be injected into the chondrium's lower surface.
• For the other side, the identical procedure will be repeated.

C) After blocks, the onset of general anesthesia will be achieved after intubation, surgical sterilization, draping and positioning.

D) All patients will receive general anaesthesia (GA). Anaesthesia will be induced with propofol (2 mg/kg), fentanyl (2 μg/kg) and atracurium (0.5 mg/kg). The GA will be maintained by isoflurane (1.2 %) and atracurium (0.1 mg/kg/20 min).

E) Intraoperative vital signs as heart rate, blood pressure and intraoperative opioid requirements will be recorded every 15 minutes till patient recovery.

F) After skin closure, muscle relaxation will be reversed using neostigmine (0.04mg/kg) and atropine (0.01mg/kg) after the return of spontaneous breathing.

G) Patients will be transferred to the post-anesthesia care unit (PACU) for 60 min for complete recovery and monitoring H) If at any point hypotension occurred (defined as a decrease in mean arterial pressure > 25% from the baseline value or systolic arterial pressure of 100 mmHg), it will be treated with 5 mg of IV bolus ephedrine, which will be repeated every 3 min until the hypotension resolved. Bradycardia (defined as a heart rate (HR) of 40 beats/min) will be treated with intravenous atropine (0.5 mg).

I) Within the first 30 minutes, postoperative vital signs (heart rate and blood pressure) and VAS (static and dynamic) for pain will be recorded at 30 minutes, 2, 6, 12, 24 hours and if VAS ≥4 or when the patient asks for analgesia, nalbuphine IV (0.1mg/kg) will be given (rescue analgesia) targeting VAS ≤ 3. The time to first call for analgesia will be recorded. The patient will receive paracetamol (1gm/8hrs IV) as a regular analgesia. If the patient requires more than two doses of rescue analgesia in the first hour following surgery, the block will be deemed to have failed. The inappropriate analgesia will be considered when 120% increase in systolic blood pressure and/or heart rate from baseline in absence of other causes. The intraoperative analgesic management will be achieved using fentanyl bolus of 1 mcg/kg.