this prospective parallel group double blinded study will be conducted over 50 pediatric patients ASA (American Association of Anesthesiologists) I and II between the age of 8-13 years old, ASA physical status I and II, who will be scheduled for laparoscopic pyeloplasty and performed by the same surgical team. This study will be carried out at Ain Shams University hospitals. Written informed consent will be obtained from the parents. Exclusion criteria will include: History of developmental delay or mental retardation, parent refusal, history of allergic reactions to local anesthetics, rash or infection at the injection site, anatomical abnormality, bleeding disorders, history of cardiac, neurological, impaired renal function defined by s-creatinine \>150 μmol/L and impaired hepatic function. Preanesthetic evaluation and routine investigations will be carried out on the night of surgery and patients shall be fasting for 6 hours. After an intravenous (IV) cannula (22G) is secured , and midazolam 0.02 mg/kg iv will be administered to all patients before transfer to the operating room. Standard monitoring devices as ECG, Non- invasive blood pressure, nasopharyngeal temperature probe and pulse oximetry will be placed then baseline systolic and diastolic blood pressures and heart rate will be recorded. Induction of general anesthesia (GA) will be accomplished using propofol 1-2mg/kg, fentanyl will be administered intravenously at 1μg/kg, Intubation will be facilitated by atracurium (0.5 mg/kg) then an appropriately sized endotracheal tube will be placed.All patients will be mechanically ventilated with volume controlled mode with targeted EtCO2 (30-35 mmHg) and anesthesia will be maintained with 1.2% isoflurane in a mixture of 50% air and oxygen in all patients throughout the procedure which will be adjusted according to the adequacy of anesthesia. Intraoperative hypothermia will be prevented by warm intravenous fluids (15 ml/kg lactated ringer solution in the first hour then completed according to fluid chart) and warm mattress.

A total of 50 patients will be randomly allocated into 2 study groups: Quadratus lamborum dexmedetomidine intravenous group(QD IV group) and Quadratus lamborum dexmedetomidine perineural group(QD PN group) using concealed envelope method, physicians assigned participants to interventions according to allocation: Patients in both groups will receive quadratus lamborum block on the same surgical side , first the patients will be placed in the lateral position then turned to supine position after completion of the block. Under aseptic conditions,a high-frequency linear probe (SonoSite HFL50x, 15- 6 MHz, 55-mm broadband linear array) will be placed on the lateral abdomen, between the costal margin and iliac crest. The three abdominal muscles, external oblique (EO), internal oblique (IO), and transversus abdominis muscle (TA), will be identified then the probe will be moved posteriorly and QL muscle (QLM) will visualized. A 22-G block needle (Stimuplex D, Braun, Hongo, Bunkyo-ku,Tokyo) will be oriented in plane, from anterior to posterior direction, and the needle tip will be positioned between the anterior border of QLM and its fascia: In QD IV group a bolus of 0.5 ml/Kg bupivacaine 0.25% in addition to 2ml normal saline will be injected then dexmedetomidine (precedex 200 micrograms per 2ml, Abbott laboratories, Abbott park, IL, USA) which will be prepared in concentration 1μg/ml. 1ml/kg loading dose will be given over 10 min followed by 0.5 ml/kg/h infusion maintenance dose till the end of surgery. In QD PN, patients will receive perineural dexmedetomidine of 1μ g/kg diluted to 2 mL with 0.9% saline added to 0.5 ml/kg of 0.25% bupivacaine in addition to saline infusion 1ml/kg IV loading dose followed by by 0.5 ml/kg/h infusion maintenance dose till the end of surgery. Drug packs will be prepared before commencement of the study by a pharmacist unaware of the nature of the study, after 15 minutes of the block, surgical incision will be allowed but in case of conversion to open surgical procedure (laparotomy) patients will be excluded from the study.The average end-tidal isoflurane, total intraoperative fentanyl dose and incidence of intraoperative complications as hypotension, If the blood pressure dropped more than 30% of the baseline values, it will be managed by 10 ml/kg normal saline and ephedrine injection and/or bradycardia is defined as drop of heart rate more than 20% of the baseline values which will be managed by atropine 0.02mg/kg, all will be recorded. Inadequate analgesia is defined as more than 20% increase in mean blood pressure and heart rate after skin incision and during surgical procedure which will be managed by administration of 0.5 μg/kg fentanyl. At the end of surgical procedure, muscle relaxation will be reversed with neostigmine 50 μg/kg and atropine sulfate 20 μg/kg. Patients will extubated and shifted to the post-anaesthesia care unit.

The recovery time (The elapsed time for the patient to open his eyes upon command after discontinuation of Isoflurane) will be recorded. In postoperative anaesthesia care unit, postoperative monitoring of the hemodynamics will be undergone by a well trained nurse. when pain score \>4 on Wong-Baker FACES Pain Rating Scale (8) (fig.1), patients will be given morphine 0.05 mg·kg-1 6 hourly and acetaminophen IV 15mg/kg 6 hourly will be administered by a physician blinded to the nature of the study as first and second rescue analgesics respectively. Time to first analgesic requirement ( primary outcome) , Wong-Baker FACES Pain Rating Scale scores will be recorded at 2, 6, 8,12, 18 and 24h postoperatively, the degree of sedation will be assessed by Ramsay sedation scores(fig.2)(9) at the same time points, hemo-dynamics as systolic and diastolic blood pressures and heart rates will be recorded at PACU discharge then 4 hourly, total dose of morphine consumption, , the length of hospital stay, incidence of postoperative complications as hypotension, bradycardia, vomiting, pruritis and respiratory depression, which is defined as respiratory rate less than 10 breathes/min will be recorded. If the blood pressure dropped more than 30% 0f the baseline values, it will be managed by 10 ml/kg normal saline and ephedrine injection. Bradycardia is defined as drop of heart rate more than 20% of the baseline values. It will be managed by atropine 0.02mg/kg. Attacks of vomiting will be managed by ondansetron 0.1 mg/kg iv.