Comparison Between Epinephrine and Clonidine as Adjuvants to Lidocaine in Axillary Brachial Plexus Block.

Overview

Adjuncts to local anaesthetics for the peripheral nerve blocks such as epinephrine, clonidine and opioids have been widely used to enhance quality, duration of anaesthesia and postoperative analgesia. Clonidine, an α2-adrenergic agonist, when combined with local anaesthetics in axillary brachial plexus block has shown to decrease block onset time and prolong the duration of anaesthesia. We propose to compare the effects of combining both adjuvants to 20 mL of lidocaine 2% on the onset of ultrasound guided axillary brachial plexus block.

Using a 20 mL lidocaine 2% when combined with epinephrine 1:200 000 and clonidine 1 µg/kg will shorten the onset time of sensory block when compared to lidocaine 2% with epinephrine 1:200 000 alone in ultrasound guided axillary brachial plexus block for elective upper limb surgeries. It is a prospective, randomized, observer blinded study. With institutional ethical approval and having obtained written informed consent from each, 24 patients will be studied. Randomisation and blinding: Using a computer generated and sealed envelope technique, 24 patients will be randomized in to one of two groups to receive ultrasound guided axillary brachial plexus block. Group 1: Patients will receive 20 ml of lidocaine 2% with epinephrine and 2 ml of 0.9% normal saline. Group 2: Patients will receive 20 ml of lidocaine 2% with epinephrine and clonidine 1µg/kg in 2 ml of 0.9% normal saline. Sample size and Statistical analysis: Sample size will be based on onset of block. Kaabachi et al16 found a sensory onset of axillary brachial plexus block (with 30 ml of lidocaine 1.5%) of 9 (SD, 3) mins. The sample size required to have an 90% probability of detecting a decrease in the onset time by 40% (level of significance 0.05)) will be 12 patients per group using an unpaired student's t test. Anaesthetic procedure: Having established intravenous access, standard anaesthetic monitoring will be applied. Sedation with midazolam will be administered as clinically indicated (to a maximum of 3 mg). The operative arm will be abducted and externally rotated with elbow flexed at 90 degrees. Under strict aseptic condition, ultrasound guided axillary brachial plexus block will be performed. Having identified musculocutaneous, median, radial and ulnar nerves, a 50mm 22-gauge ultrauplex short bevel insulated needle will be used with in-plane approach to block each nerve. 20 mL of Lidocaine 2% with epinephrine and 2ml of 0.9% Nacl(group 1) or clonidine 1µg/kg in 2 ml of 0.9% Nacl(group 2) will be divided equally among the 4 nerves. All blocks will be performed by single operator experienced in the ultrasound peripheral nerve blocks. Block assessment: When the block procedure has been completed, a blinded observer will assess the onset of sensory and motor block in the innervation of each nerve every 2.5 mins until complete sensory and motor block is achieved or 30 mins have elapsed . Complete sensory block is defined as absent sensation to cold and pinprick and complete motor block is defined as motor score ≤2. Each nerve distribution will be individually assessed. Onset time will be measured from conclusion of the block (t=0) to attainment of (surgical anaesthesia) complete sensory and motor block. Block will be deemed failure if sensory and motor block has not been achieved at 30 mins in one or more of the four nerve distribution. In case of failure, an additional rescue block or conversion to general anaesthesia will be performed. DATA from these patients will be analysed separately. Intraoperative period: All patients will receive 1 g of paracetamol and diclofenac 75 mg iv during surgery. In case of patients discomfort rescue analgesia in the form of fentanyl 25 micrograms aliquots IV will be administered to a maximum of 100 micrograms. Postoperative period: Upon arrival to recovery room, sensory and motor function will be assessed every 15 mins by a blinded observer. Assessment will be performed for each nerve separately. Block regression is defined as a return of sensation to cold and pinprick with motor power score ≥3 in any nerve region. Time to first request for postoperative analgesia will be noted. Postoperative analgesia will be prescribed as paracetamol 1 g 6 hourly and diclofenac sodium 75 mg 12 hourly. Oxycodone 5-10 mg orally 4-6 hourly will be administered as rescue analgesia. Heart rate, arterial blood pressure, spo2 and sedation score (1=awake and alert, 2= sedated, responding to verbal stimulus, 3= sedated, responding to mild physical stimulus and 4=sedated, responding to moderate to severe physical stimulus) will be recorded intraoperatively every 5 mins and every 15 mins postoperatively for the first 4 hours. Hypotension and bradycardia, defined as 20% decrease in blood pressure and heart rate in relation to preblock value, will be recorded. Primary Outcome: The primary outcome will be onset of sensory block. Secondary Outcomes: 1. Onset of motor block. 2. Duration of sensory and motor block 3. The quality of block intra operatively 4. The incidence of side effects in both groups. : sedation, hypotension, nausea, dizziness, tinnitus, vomiting convulsions or arrthymia

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