Postoperative pain is a common manifestation in orthopedic patients, mainly due to intraoperative tissue damage and inadequate intraoperative pain assessment and management .Axillary brachial plexus block provides motor and sensory block with the distribution of the median, radial, ulnar and musculocutaneous branches so can be conducted with upper limb orthopedic surgery in hand, rest and elbow surgery distal to the cubital fossa . In this study the investigators will investigate (0.19%) and (0.25%) bupivacaine for postoperative motor power recovery and post-operative analgesic efficacy in ultrasound guided axillary brachial plexus block among pediatric patient undergoing below elbow orthopedic surgery.

Patients meeting inclusion criteria will be randomly assigned to receive either:

(Group A: n=30)will receive 0.25% bupivacaine plus 1 µg/kg dexmedetomidine . (Group B: n=30) will receive 0.19% bupivacaine plus 1 µg/kg dexmedetomidine. Using computer generated number and concealed using sequentially numbered, sealed opaque envelope technique. There will be no restrictions or stratifications in the randomization process. The allocation envelope will be opened by the assistant lecturer at the time of anesthetic preparation.

All children will be anaesthetized in accordance with the local policy of the Abu El-Reesh pediatric hospital-Cairo university's pediatric anaesthetic unit. Except for oral clear liquids intake 2 hours before surgery, all children will fast for 6 hours. Patients will attend in the preparation room one hour before the operation to get a preoperative checkup, as well as their age and body weight will be recorded. Premedicated by intramuscular injection of atropine 0.02 mg/Kg and midazolam 0.2 mg/Kg . On arriving the operating room, heart rate (HR) ,oxygen saturation and non-invasive blood pressure will be continuously recorded, using standard monitor (Dräger infinity vista XL).

All patients will be induced with inhalational anesthetic using (100%) O2 + Sevoflurane. After deepening of the anesthesia, I.V. line will be inserted and atracurium 0.5mg/kg and fentanyl 1μg/kg patients will be given, then the patients will be intubated by appropriate size of endotracheal tube volume control ventilation (VCV) 5-7 ml/kg and respiratory rate will be adjusted to keep and PaCO2 levels between 30-35 mmHg using (G.E-Datex-Ohmeda, Avance CS2, USA) anesthesia machine. Anesthesia will be maintained with an isoflurane 1 MAC with 50% oxygen in air, with the goal of keeping the bispectral index (BIS) measurement between (40-60), and atracurium top-ups of 0.1mg/kg will be given every 30 minutes for neuromuscular blockade.

Axillary brachial plexus block will be conducted with the patient in supine position under general anesthesia.

In Group A:(0.25 %bupivacaine group) ultrasound guided Axillary brachial plexus block will be conducted using a total volume of 0.5ml/kg of bupivacaine 0.25% + 1 µg/kg dexmedetomidine.

In Group B:(0.19%bupivacaine group)ultrasound guided Axillary brachial plexus block will be conducted using a total volume of 0.5ml/kg of bupivacaine 0.19% + 1 µg/kg dexmedetomidine.

The surgical procedure will be start after 15-20 min. If there is an increase in heart rate or mean arterial blood pressure of more than 20% of the baseline value after skin incision then it will be considered as block failure and these patients will be excluded from the study. 1-2ug/kg intravenous fentanyl will be given to failed block.

At the end of surgery, residual neuromuscular block will be antagonized with IV neostigmine 0.05 mg/kg and atropine 0.02mg/kg. All patients will receive 15mg/kg paracetamol IV.

At recovery room motor power will be assisted using Modified Bromage scale by attending anesthesiologists who will be blinded to the study groups, then each 30 min till full recover of motor power .

The post operative pain assessment in the PACU and the ward, patient will be assessed immediately postoperatively and then at 1st, 4th, 8th, 12th hour post-operatively using (FLACC score) for Pain assessment.

Inclusion Criteria:

1. American society of Anesthesiologists (ASA )class I-II
2. Duration of surgery less than 1 hour.

Exclusion Criteria:

1. Parent refusal.
2. Prolonged procedure exceeding 1 hour.
3. Patients with apparent infection at site of needle insertion.
4. Patients with any coagulation disorder(Platelets ≤ 50,000 and/or international normalized ratio INR> 1.5)
5. Patients with known neuropathy or brachial plexus injury.
6. Patients with any cardiac, hepatic, renal failure.
7. Patient with known sensitivity to local anesthetic drugs.

Double blinded