The Analgesic Efficacy of Dexmedetomidine Versus Fentanyl as an Adjuvant to Bupivacaine in Ultrasound Guided Peripheral Nerve Blocks as a Solo Anesthetic Technique in High Risk Patients Undergoing Unilateral Above Knee Amputation .

Inclusion Criteria: * \- Age ≥18 years * Both sexes * ASA III-IV * Documented cardiac disease (e.g., EF \< 40%, NYHA II or higher) * Documented pulmonary disease (e.g., COPD with FEV1 \< 60%) * Scheduled for above-knee amputations Exclusion Criteria: * Neurological or intellectual disability * Drug abuse * Allergy to study drugs * Pregnancy * Contraindications to regional anesthesia (e.g., coagulopathy, local infection) * Significant renal or hepatic impairment( plts \<75000 or INR \>1.5) * Current anticoagulant therapy * severe haemodynamically unstability at the time of block performance, defined as map \> 65 mmhg but achieved by high-dose vasopressors (e.g., norepinephrine ≥ 0.1 mcg/kg/min) after fluid ressuscitation .