Effect of Adding Dexmedetomidine to Bupivacaine in US- Guided Erector Spinae Plane Block for Post-operative Pain Management in Pediatric Patients Undergoing Lower Abdominal Surgeries

• Preoperative setting:

• A careful history taking will be done from the parents of the child for any medical disorder such as congenital coagulation disorders or therapeutic anticoagulants.

• A complete physical examination of the child will be done, including the central nervous system for signs of mental disturbance, the chest for any deformities or chest infection, the heart for congenital heart disease, and the back for any spinal deformities or infection at the site of injection.

• Routine preoperative investigations will be done to all patients, including laboratory investigations (complete blood picture, liver and kidney function tests, prothrombin time and partial thromboplastin time) and other as needed by the patient condition.

• Written informed consent will be obtained from all participants' parents or legal guardian prior to the study.

• Intraoperative setting:

• All children will be premedicated orally with midazolam (0.05-0.1 mg/kg over 2-3 minutes, maximum 6 mg) 30 minutes prior to surgery. On arrival of the patients to the operative room, routine monitoring with 5-leads electrocardiogram (ECG), non-invasive blood pressure (NIBP) and pulse oximetry will be instituted, then anesthesia will be induced with 8% sevoflurane in 100% oxygen. After an adequate depth of anesthesia is reached, an intravenous access will be placed under aseptic condition, then all patients will receive intravenous (IV) fentanyl (1 µg/kg) and atracurium (0.5 mg/kg), and orotracheal endotracheal intubation will be performed. Anesthesia will be maintained with a mixture of oxygen-air (50% - 50%) and isoflurane

1. -1.5%). Muscle relaxation will be sustained during the procedure with incremental doses of IV atracurium (0.1 mg/kg) every 25 minutes.

In group A: US guided ESPB will be performed with aseptic precautions using a (6- 19) MHz linear probe in a sterile cover with sterile jelly (GE LOGIQ 5, USA).

• Technique of US guided ESPB block: The block will be performed by a trained anesthetist in regional anesthetic techniques while the patient in lateral position, the ultrasound transducers will be placed in a parasagittal plane 2-3 cm away from the midline at the level of first lumbar vertebra (L1) (The L1 level will be identified by counting upwards from the sacrum). Sliding the transducer medially till identifying the transverse process which appear as flat acoustic shadow and after identification of erector spinae muscle (ESM) and transverse process, a 22-gauge 50 mm echogenic block needle (Sono Plex® PAJUNK®, Germany) will be introduced in cranio-caudal direction with in-plane technique and after confirming the position of the tip of the needle over the transverse process with negative aspiration to blood or air, Bupivacaine 0.25% (with a maximum dose 2 mg/kg) plus Dexmedetomidine (0.5µg/kg), putting into consideration that the total volume to be 0.3 ml/kg on each side, will be injected. The spread of local anesthetic in a plane below the erector spinae muscle will be visualized.
• The skin incision will be made 15 min after the block.
• Baseline values of heart rate (HR) and mean blood pressure (MAP) will be recorded before skin incision and then recorded at 5, 30, 60 minutes after skin incision and at the end of surgery. Also, patients will be monitored for sign of local anesthetic toxicity.
• Any complications related to the block given will be recorded including hematoma, intravascular injection, and allergic reactions.
• If local anesthetic toxicity occurred, cardiovascular and respiratory support and 20% intralipid bolus of 1.5 ml/kg over 2-3 min will be given.