Clinical Comparative Study Aiming to Evaluate Postoperative Effect of Using Intrathecal Dexmedetomidine and Fentanyl as an Adjuvant to Heavy Bupivacaine in Lower Limb Vascular Surgeries on Pain Intensity, Analgesic Requirement and Shivering. Patients and Methods After Approval of Medical Institution

Group D: patients will receive 3 mL volume of 0.5% hyperbaric bupivacaine and 4 µg dexmedetomidine in 0.5 mL of normal saline intrathecal (dexmedetomidine 100 µg/mL will be diluted in 12.5 ml preservative-free normal saline, 0.5 ml will be withdrawn)

Group F:patients will receive 3 mL volume of 0.5% hyperbaric bupivacaine with 25 µg fentanyl (0.5 mL) intrathecal.