Analgesic Efficacy of Sequential Rapid Intrathecal Injection Of Dexmedetomidine Followed by Slow Injection of Hyperbaric Bupivacaine Versus Sequential Slow Injection of Both Drugs in Patients Undergoing Unilateral Inguinal Hernia Repair Surgery

Once enrolled in the study, patients will be randomly assigned into two groups; rapid sequential group (Group A: n= 25) and normal sequential group (Group B: n=25). Randomization will be done by computer generated numbers and concealed by serially numbered, opaque and sealed envelopes. Upon arrival to the operating room, Wide bore intravenous line will be inserted, premedications (ondansetron 4 mg and midazolam 0.05 mg/Kg) will be administered, and routine monitors (Electrocardiogram - non-invasive blood pressure monitor - pulse oximeter) will be applied. The patient will be assisted into the sitting position, and sterilized surgical drapes will be placed to their back. Spinal anesthesia will be administered at L4-L5 using a complete aseptic technique. Group (A): will receive spinal anesthesia by applying sequential rapid injection of dexmedetomidine (5 µg in 0.5 ml saline, in insulin syringe within 1 second) followed by slow injection of 17.5 mg (3.5 ml within 12

-15 seconds) of 0.5% of heavy bupivacaine with no time lag between these injections. Group (B): will receive spinal anesthesia by applying normal sequential injection of 0.5 mL of 5 µg dexmedetomidine (injected over 3-4 seconds using a 5 ml syringe and mixed with cerebrospinal fluid (via barbotage), followed by slow injection of 17.5 mg (3.5 ml within 12 -15 seconds) of 0.5% of heavy bupivacaine with no time lag between these injections. Then the patient will be asked to lie down. The sensory level will be assessed by the cold ice technique every minute for 10-minutes. Motor blockade will be assessed every 5 min by the Bromage scale (4). After the T6 level is reached, the surgeon will be asked to operate. In case of failed spinal anesthesia (defined as failure to reach T6 level within 10 mins), the patient will be excluded, and further management will be according to the attending anesthetist. After spinal anaesthesia noninvasive blood pressure will be measured for then every 3 mins for 30 mins then every 5 mins till the end of operation. The occurrence of hypotension (defined as mean blood pressure <65 mmHg) will be recorded, and an anesthesiologist will be allowed to manage it by giving ephedrine (5-10 mg, intravenous [IV]) and IV fluids. If bradycardia occurred (heart rate<55 bpm), it will be managed by intravenous 0.5 mg atropine. Postoperative pain management All patients will receive acetaminophen 1gm/6 hours. Visual analogue scale (VAS) will be assessed at 0.5-, 1-, 2-, 4-, 6-, 8-, 10-, 12-,18- and 24-hour post operatively. Rescue analgesia administered in the form of (0.5-1 mg/kg) of intramuscular pethidine will be given on if VAS score was >3 Measurement tools

Patients will be monitored using:

• ECG, non-invasive blood pressure monitor, pulse oximeter.
• VAS (Visual analogue scale) pain assessment.