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

In the context of intravenous regional anesthesia (IVRA), dexmedetomidine has been employed as an adjuvant to local anesthetics like lidocaine to improve block characteristics; Clinical studies have demonstrated that adding dexmedetomidine to lidocaine in IVRA accelerates the onset of sensory and motor blocks, extends the duration of postoperative analgesia, and reduces the incidence of tourniquet pain

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"

An anesthetist, not involved in the study , was responsible for randomization list construction, in blocks, opening the sealed envelopes and so, the preparation of the study drug