Dexmedetomidine Added to Bupivacaine for ESP Block in Children 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.

In group B: This group will receive ESPB using Bupivacaine 0.25% (with a maximum dose 2 mg/kg) alone 15 min before skin incision with the same protocol and precautions.

* In both group an increase in heart rate to 20% above the baseline values at any time during the procedure will be defined as insufficient analgesia and fentanyl 0.5 µg/kg will be given and the total amount of intraoperative opioid will be recorded. * At the end of the surgery Isoflurane will be discontinued and neostigmine 0.05 mg/kg plus atropine 0.02 mg/kg will be administered to reverse the effect of atracurium. After awakening from anesthesia and achieving an appropriate level of consciousness, the patient will be discharged from the operating room to be transferred to the PACU (Post Anesthesia Care Unit), and pain assessment will be done immediate post extubating.

Postoperative setting:

* Postoperative pain score will be assessed using FLACC scale immediately after transfer to the PACU, at 1, 2, 4, 6, 8, 12 hours postoperatively and before discharge from hospital. * If the FLACC score was ≥ 4, analgesia in the form of Paracetamol 15 mg/kg IV will be administered as the first rescue analgesia. The time for the first rescue analgesic administration will be recorded. If this analgesia will not be adequate, intravenous pethidine at 1mg/kg will be given as the second rescue analgesia and the total analgesic requirements of paracetamol and pethidine will be recorded. * FLACC is a behavioral pain assessment scale used for nonverbal or preverbal patients who are unable to self-report their level of pain. Pain is assessed through observation of five categories including face, legs, activity, cry, and concealability.

• Postoperative Pain Scores [Time frame: At 1, 2, 4, 6, 12, and 24 hours after surgery]
• Total intraoperative analgesics [Time frame: During the operation from the induction of anesthesia until the recovery.]
• Total Postoperative Analgesic Consumption [Time frame: Within 24 hours postoperatively]
• Incidence of Adverse Effects [Time frame: Within 24 hours postoperatively]