Dexmedetomidine (DEXM) is a highly selective α2-adrenoceptor agonist that has been used increasingly in pediatric anesthesia. This prospective double blinded randomized comparative study is designed to evaluate the analgesic effect of caudal increasing doses of DEXM 0.5 , 1 , 1.5 , 2µg/kg combined with Levobupivacaine (Levob) 0.125% (ED95% =125%=least effective concentration) in providing pain relief over a 24-h period and lowest surgical stress peak. Study hypothesis: Levobupivacaine 0.125 %( ED95) combined with different increasing doses of dexamedatomedine >1 µg/kg could not add more analgesic & stress response obtundation outcome, but increase side effects (sedation and hemodynamic depression). The peak cortisol level during urology surgery was at the end of the 1st postoperative (PO) hour. Aim of the Study: To detect the optimal analgesic and safe caudal adjuvant DEXM dose associated with the least side effects& stress response modulation, guided by PO Cortisol peak difference in between the study groups during pediatric hypospadias surgery.

Background: Dexmedetomidine (DEXM) is a highly selective α2-adrenoceptor agonist that has been used increasingly in pediatric anesthesia. This prospective double blinded randomized comparative study is designed to evaluate the analgesic effect of caudal increasing doses of DEXM 0.5 , 1 , 1.5 , 2µg/kg combined with Levobupivacaine (Levob) 0.125% (ED95% =125%=least effective concentration) in providing pain relief over a 24-h period and lowest surgical stress peak. Study hypothesis: Levobupivacaine 0.125 %( ED95) combined with different increasing doses of dexamedatomedine >1 µg/kg could not add more analgesic & stress response obtundation outcome, but increase side effects (sedation and hemodynamic depression).The peak cortisol level during urology surgery was at the end of the 1st postoperative (PO) hour. Aim of the Study: To detect the optimal analgesic and safe caudal adjuvant DEXM dose associated with the least side effects& stress response modulation, guided by PO Cortisol peak difference in between the study groups during pediatric hypospadias surgery.

Optimal effective dose defined as; the least caudal DEXM dose which produce the best analgesic outcome [least time to 1st analgesic request and lowest rescue analgesic dose (24Hs)] associated with the least stress response (cortisol PO. first One hour peak), least PO sedation, and hemodynamic stability IO. &PO. HR & MAP. The peak cortisol level during urology surgery was at the end of the 1st postoperative (PO) hour.

. Material & Methods A prospective randomized double blinded (drug injector and PO assessor) comparative study will be conducted in Mansoura university hospital after obtaining ethics committee approval and written informed parental consent 164 boys (age 1-6 years, ASA I) scheduled for hypospadias surgery. Exclusion criteria; (Operative time exceeding 3 hours, bodyweight >25kg, bleeding diathesis, infection at the site of block, pre-existing neurological or spinal disease or abnormalities of the sacrum, inability to palpate the sacral hiatus by anatomic landmark palpation technique) or those with a history of allergic reactions to local anesthetics were excluded from the study. Patients will fast for solids 6h and water and 2 hours before surgery. After Patient Preoperative preparation, General anesthesia induction, caudal block and caudal drug injection (Levob plus DEXM) bolus will be injected according to each group as follow;

• Group A will take Caudal Levob 0. 125%+ DEXM 0.5µg/kg.
• Group B will take Caudal Levob 0.125%+ DEXM 1µg/kg.
• Group C will take Caudal Levob 0. 125%+ DEXM 1.5 µg/kg.
• Group D will take Caudal Levob 0. 125%+ DEXM 2µg/kg.

The study outcomes recording:

1ry outcome: Time to (1st analgesic request OPS >4). Secondary outcome: Total 24hours PO. Rescue analgesic dose IM pethidine 0.5mg/kg [2,3] based on local policy and protocol, Patients demographic data [age, weight, end tidal Sevoflurane (volume %) prior starting skin closure, intraoperative fentanyl total dose, recovery time (time from discontinuation of anesthesia to spontaneous eye opening)], Serum Cortisol level at basal before anesthesia and 1hour postoperative in between groups [1] , Apnea incidence (NO&%), and desaturation (NO&%), Objective pain score, Sedation score, Behavioral score for Agitation assessment, and Modified bromage score (residual Lower limb muscle weakness) recorded every 15 minutes for 1st hour then every 30 minutes for next 3 PO hours then at next 6th, 12th, 18th, 24th PO hours, hemodynamics, HR&SBP the incidence of bradycardia and hypotension per 50% percentile. Recorded every 10 minutes IO for maximum operative time 3 hours and every 30 min PO for next 2h in the recovery room until the child was discharged to the ward.

Inclusion Criteria:

• 164 boys (age 1-8 years, ASA I) scheduled for hypospadias surgery

Exclusion Criteria:

• Operative time exceeding 3 hours, bodyweight >25kg, bleeding diathesis, infection at the site of block, pre-existing neurological or spinal disease or abnormalities of the sacrum, inability to palpate the sacral hiatus by anatomic landmark palpation technique) or those with a history of allergic reactions to local anesthetics were excluded from the study