Comparison of Pain Relief Duration With Dexmedetomidine Versus Fentanyl Added to Spinal Anesthesia in Patients Undergoing Lower Limb Orthopedic Surgery

The goal of this randomized clinical trial is to compare how long effective pain relief lasts when dexmedetomidine or fentanyl is added to hyperbaric bupivacaine during spinal anesthesia for lower limb orthopedic surgery. The main question the study aims to answer is: Does adding dexmedetomidine to hyperbaric bupivacaine provide longer-lasting effective pain relief after surgery than adding fentanyl? The study will include 60 adults aged 18-65 years who are classified as ASA Grade I or II and are undergoing lower limb orthopedic surgery under spinal anesthesia. Participants will be randomly assigned to one of two groups. Participants in the dexmedetomidine group will receive dexmedetomidine with hyperbaric bupivacaine. Participants in the fentanyl group will receive fentanyl with hyperbaric bupivacaine. After surgery, participants will be monitored for pain using a visual analogue scale (VAS), ranging from 0 (no pain) to 10 (severe pain). Pain will be assessed hourly during the first 12 hours and subsequently according to the study protocol. If the VAS pain score is greater than 3, nalbuphine will be given as rescue pain medicine. The study will measure the time from administration of spinal anesthesia until the participant first requires rescue pain medicine. The total amount of nalbuphine required after surgery will also be recorded. The study hypothesis is that adding dexmedetomidine to hyperbaric bupivacaine will provide a longer duration of effective pain relief than adding fentanyl.