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

This is a randomized controlled trial (RCT) that will include 99 patients for elective lower limb surgery. This study will be conducted in Mansoura university hospitals. 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 Exclusion criteria: 1. Patient refusal. 2. Hepatic or renal impairment. 3. Neuromuscular diseases. 4. History of opioid abuse. 5. History of allergy to anesthetic drugs. 6. Infection at the lumbar area. 7. Coagulopathies. 8. Increased intra cranial tension (ICP). 9. Cardiovascular & respiratory diseases Patient preparation: All patients will be visited a day prior to surgery. The general physical as well as systemic examination will be carried out. Basic demographic characters including age, sex, weight and height will be recorded. Routine investigations like haemoglobin, bleeding time, clotting time and complete urine examination, serum creatinine, blood sugar, chest X-ray, ECG and any other specific investigation wherever needed will be carried out. A linear visual analogue scale (VAS) on a scale of 0-100mm (where 0 for no pain and 100 for worst possible pain) will be explained to each patient and consent to participate in the study will be obtained. Anesthetic Considerations: On arrival to the operating theater, routine monitoring including: heart rate, electrocardiogram, non-invasive blood pressure, and peripheral oxygen saturationand baseline values will be recorded. All patients will receive an intravenous preload of10ml/kg ringer solution before the subarachnoid block. Randomization: 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 (25micro gram fentanyl) with 0.5 ml preservative free saline. 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. Group M + F (n=33): patient will receive a premixed solution of 3ml (0.5%) of hyperbaric bupivacaine, 0.5 mL (25 micro gram) fentanyl with0.5 mL of 10% MgSO4. Blinding will be achieved through the use of equal amounts of intrathecal drugs (4 mL) in identical syringes prepared by an anaesthetist not involved in the study. Spinal anesthesia will be conducted by an investigator who will be unaware of the identities of the drugs. Technique of the neuroaxial block: 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. Intraoperative Assessment: Patients will be monitored with continuous ECG and pulse oximeter. Heart rate, oxygen saturation (SPO2), systolic, diastolic and mean arterial blood pressures will be monitored non-invasively at the baseline, immediately after block and then every 5 min for the first 30 min, and every 15mints till the end of surgery. Bilateral sensory block to pinprick will be tested in a cephaladto caudal direction in the midclavicular line bilaterally, measurements included:the onset time to sensory block (time from intrathecal injection of drugs to reach T10 sensory level), the highest dermatomal level assessed by pin-prickexam, the time to two segments regression from the previous highest dermatomal level, and the duration of sensory block (time from the onset of sensory block till regression to S1). Motor blockade of the lower extremity muscles will be assessed using Bromage Score: (0= no motor block, ability to raise hips, knees,and ankles. 1 = unable to raise extended legs, able to move knees and feet. 2= unable to raise extended leg or move knee; able to move feet.3= unableto move any partof the lower limbs), measurements included the onset (time from induction of spinal anesthesia till Bromage = 3) and duration (time from complete block till Bromage =0). Degree of motor block at the onset of sensory block and at the time of highest dermatomal level block. Sensory and motor block will be evaluated.post oprative the time and amount of post-operative analgesic requirement and the incidence of side effects will be assesssed.