Intravenous Regional Analgesia of Dexmedetomidine

Dexmedetomidine is a highly selective α₂-adrenergic receptor agonist that exerts its effects by inhibiting the release of norepinephrine at presynaptic nerve terminals, leading to reduced sympathetic activity; This mechanism results in analgesia, sedation, and anxiolysis without significant respiratory depression

Inclusion Criteria: * Age 18-60 years * American Society of Anesthesiologists (ASA) Physical Status Classification System I or II * Scheduled for elective knee surgery under spinal anesthesia * Body mass index (BMI) 18-30 kg/m² * Able to provide informed consent Exclusion Criteria: * Pregnant or lactating women * Hypersensitivity to dexmedetomidine * Chronic kidney diseases serum creatinine \>1.5 mg\\dl or Patient has known renal disease * Chronic opioid or sedative use * Any cardiac conduction abnormalities * Uncontrolled arterial hypertension * Neuropathy * Diabetes mellitus * Impaired perfusion of the operative limb (Edema, Peripheral vascular Disease e.g "Raynaud Phenomenon") * History or recent lower limb deep venous thrombosis (DVT) or Phlebitis * Infection or vascular access limitation in the operated lower limbs * Any contraindication of spinal anesthesia e.g "Coagulopathy" * Any contraindications for tourniquet e.g "sickle cell anemia"