Analgesic Efficacy of Two Doses of Dexmedetomidine as Adjuncts to Lidocaine for Intravenous Regional Anesthesia

Preoperative evaluation of the patients will be done including medical history, physical examination, and laboratory investigations. Patients should be in fasting state for at least 8 h before surgery, and the visual analog scale (VAS) (from 0 to 10: 0 = no pain up to 10 = severe pain) will be explained to the patients to express their pain.

On arriving at the operating room, routine intraoperative monitors will be applied, such as a noninvasive blood pressure monitor, a five-lead ECG, and a pulse oximeter. Two (20 G) venous cannulae will be inserted, one in the dorsum of the operative hand and one in the other hand, for fluid infusion during surgery and for any intravenous medications.

Patients will be premedicated with IV 0.05 mg/Kg of midazolam. After the patient is taken to the operating room, mean arterial blood pressure (MAP), peripheral oxygen saturation (SPO2) and heart rate (HR) will be monitored. The operative arm will be elevated for 2 minutes then exsanguinated with an esmarch bandage. A pneumatic double tourniquet will be placed a round upper arm, and the proximal cuff will be inflated to 250 mmHg. Circulatory isolation of the arm will be verified by inspection, absence of radial pulse, and loss of pulse oximetry tracing in the ipsilateral index finger. After the bandage is removed, 40 ml of the respective solutions will be injected over 20 seconds by an anesthesiologist.

The Sensory block will be assessed by pinprick performed with a 22-gauge needle every 30 seconds until the dermatomal sensory block of medial and antebrachial cutaneous, ulnar, median and radial nerves achieved. Motor function will be assessed by asking the patients to flex and extend his/her wrist and fingers and complete motor block will be noted when no voluntary movement is possible. Sensory block onset time will be noted as the time elapsed from drug injection to complete sensory block achieved in all dermatomes. Motor block onset time is the time elapsed from injection of study drug to complete motor block. After complete sensory and motor blocks is achieved, the distal tourniquet will be inflated to 250 mmHg, and the proximal tourniquet will be released and the surgery will be s started.

MAP, HR and SPO2 level will be recorded before application of tourniquet and after the application of tourniquet every five minute and were measured after release of the tourniquet, and postoperatively at 30 min, 1 hr, 2 hr, 3 hr, 4 hr, 6 hr and 24 hours. Pain due to the tourniquet will be ssessed with visual analogue scale (VAS) scores (0 = no pain and 10 = worst pain imaginable).

Levels of sedation will be assessed with the Ramsey sedation scale as follows: 1-patient is anxious and agitated or restless or both, 2-patients is cooperative, oriented and tranquil, 3-patient responds to command only, 4-patient exhibits brisk response to light glabellar tap or loud auditory stimulus, 5-patient exhibits a sluggish response to light glabellar tap or loud auditory stimulus, and 6-patients exhibits no response .

Both VAS and sedation levels will be recorded before and after the application of tourniquet and during the operation (10, 15, 20, 30, 40, 50 and 60 min). When pain due to tourniquet was > 3 on the VAS, patients will be given nalbuphine 5 mg intravenously increments up to 0.1 mg/kg and total administered dose will be noted.

Oxygen will be administered with face mask if SPO2 is lower than 91%.

At the end of the operation patients will be asked to qualify the operative conditions such as tourniquet pain or incisional pain.

The tourniquet will be not deflated before 30 min and was not inflated more than 1.5 hours. At the end of the operation, the tourniquet deflation will be performed by cyclic deflation technique (the tourniquet was deflated three times in a cyclic manner with 10 seconds period of deflation).

Sensory recovery time will be documented (time elapsed after tourniquet deflation up to recovery of pain in all innervated areas determined by pinprick test).

Motor block recovery time will be noted (the time elapsed after tourniquet deflation up to movement of fingers). Also, first analgesic requirement time will be noted (the time elapsed after tourniquet release to the first patient request of analgesic).

In the postoperative period if patients starts to complain (VAS > 3); rescue analgesia will be given in the form of paracetamol (Perfalgan®) 1gm IV drip and/or diclofenac sodium (Voltaren®) 75 mg IM, and/or nalbuphine 5 mg IV (with maximum daily dose of 2 mg/Kg/day) till VAS ≤ 3.And total amount of nalbuphine administered in first 24 hours to each group will be recorded.

During the first 2 hours in the post-anesthetic care unit and later in the surgical ward, patients will be questioned for circumoral numbness and tingling, nausea and vomiting, skin rash, tinnitus, gastric discomfort and other side effects are noted if encountered and MAP, HR and VAS scores will be assed every 2 hours postoperatively during the first 24 hours.

Inclusion criteria

• Patients aged 20-60 years with American society of anesthesiologists physical status I or II undergoing minor hand or forearm surgeries (duration of surgery 60 min or less, such as carpal tunnel release, ganglion excision, trigger finger, tendon or nerve repair, and fracture finger or metacarpal bone) .

Exclusion criteria

• Patients with Raynaud's disease,
• history of drug allergy, sickle cell anemia, Liver diseases and kidney diseases
• Patients who had a history of allergy to the drugs used, recent or chronic use of analgesics,
• uncontrolled hypertension, diabetic neuropathy, peripheral ischemia, , or any psychological disturbances