The effect of adding magnesium sulphate to fentanyl and bupivacaine for spinal anaesthesia in patients undergoing lower limb orthopedic surgery

INTERVENTION: Patients will be randomly allocated to one of three groups (33 patients in each group) using closed envelop method. Group F (n=33): patients will receive a premixed solution of 3 ml (0.5%) hyperbaric bupivacaine, 0.5 mL (25 microgram fentanyl) with 0.5 ml preservative free saline by spinal injection. Group M(n=33): patient will receive a premixed solution of 3ml (0.5%) of hyperbaric bupivacaine, 0.5 mLof 10% MgSO4 with 0.5 ml preservative free saline by spinal injection. Group M + F (n=33): patient will receive a premixed solution of 3ml (0.5%) of hyperbaric bupivacaine, 0.5 mL (25 microgram) fentanyl with 0.5 mL of 10% MgSO4 by spinal injection. Lumbar puncture for the patients in the sitting position will be performed under complete aseptic conditions at L3‐4 or L4‐5 interspaces with a 25‐ gauge spinal needle using a midline approach. After a successful dural puncture and ensuring free flow of cerebrospinal fluid, the premixed anesthetic solution will be injected. Immediately after intrathecal injection of the local anaesthetic, patients will be turned into the supine position. Oxygen 3 L/min was applied to all patients via nasal prongs. Surgery will be permitted after ensuring T8 sensory block to pin‐prick. CONDITION: duration of spinal anaesthesia in lower limb orthopedic surgery PRIMARY OUTCOME: duration of spinal anesthesia SECONDARY OUTCOME: The incidence of side effects. The time and amount of post‐operative analgesic requirement onset and duration of motor block. onset and time of sensory block . INCLUSION CRITERIA: 1. ASA statuses I or II patients. 2. Aged between 20 and 60 years old. 3. Patients scheduled for elective lower limb surgery. 4. Both sexes.