Analgesic effect of adding dexmedetomidine and or nitroglycerin (NTG) to lidocaine for intravenous regional anesthesia: a randomized clinical trial.

The patients will be randomly allocated into four groups (20 patients in each group): group I (lidocaine group; the control group) will receive 3 mg/kg of Lidocaine alone. The other three groups will receive the same amount of Lidocaine plus 1 microgram/kg dexmedetomidine in group II (dexmedetomidine group), 200 microgram nitroglycrin (NTG) in group III (nitroglycerin group) and 1 microgram/kg dexmedetomidine + 200 microgram NTG in group IV (dexmedetomidine-nitroglycerin group). In all groups the study drugs will be diluted with 0.9% normal saline to a total volume of 40 ml and will be prepared in identical syringes by an anesthetist not involved in the study protocol.On arrival to operating room, the patients will be monitored for heart rate (using ECG), oxygen saturation (using pulse oximetry), arterial blood pressure (non -invasive measurement of systolic, diastolic and mean values every 5 minutes) and the baseline values will be recorded. For each patient two intravenous cannulae will be inserted; the first (22-guage or smaller) in a distal vein of the operative hand for slow injection of the study drugs for intravenous regional anesthesia (IVRA) and will be removed immediately after injection of the anesthetic solution, and the second cannula will be inserted in the hand of the contra-lateral side for intraoperative fluid transfusion. An Esmarch bandage will be used for exsanguination of the operative arm after its elevation for 5 minutes then, a double cuffed pneumatic tourniquet will be wrapped around the upper arm. The proximal cuff will be inflated between 30 and 90 minutes at the discretion of the treating anaesthetist to 100 mm Hg above the systolic pressure of the patient or at least 250 mm Hg. IVRA will be achieved with slow injection of the study solution according to the patient's group. After the onset of sensory and motor block, the distal cuff of the tourniquet will be inflated to 250 mm Hg, and the proximal cuff will be released. Tourniquet pain, will be assessed using visual analogue scale (VAS) score (where o= no pain and 10 = the most severe pain) will be measured and recorded before and 5, 10, 15, 20, 25 and 30 min after injection of anesthetic solution if the VAS more than 3 the patient will receive 50 microgram fentanyl intravenous bolus. After the end of surgery deflation of the cuff will done using a “deflation/re-inflation” technique for 3 cycles of deflation of the cuff for 5 seconds and then re-inflation for 1 minute.