A Sequential Allocation Study to Determine the ED50 of Dexmetedomidine as an Adjuvant to Lidocaine Intravenous Regional Anesthesia
A Sequential Allocation Study to Determine the ED50 of Dexmetedomidine as an Adjuvant to Lidocaine Intravenous Regional Anesthesia
Intravenous Regional Anesthesia (IVRA) is an easy and reliable anesthetic technique for hand and forearm surgery. Its use is however limited by the presence of tourniquet pain during the surgery and the absence of postoperative analgesia. Many adjuvants to local anesthetics have been studied in order to overcome these shortcomings, including α2 adrenergic agonists. Clonidine has been shown to be efficacious when used with IVRA at a dose of 1µg/kg. Dexmetedomidine (DEX) is a recent more selective α2 adrenergic agonist that has been used successfully during IVRA at a dose of 0.5µg/kg. However when comparing potency ratios of Clonidine and DEX (8 to 1), the investigators hypothesize that a lower DEX dose would provide patients with adequate anesthesia.
We will determine the population average dose of DEX (ED50) that provides 50 minutes of tolerance to the tourniquet during a Lidocaine IVRA by a sequential Dixon up-down allocation study.
Eligible patients will be enrolled after obtaining informed consent. Patients will receive a standardized IVRA with Lidocaine and DEX adjuvant following a sequential allocation scheme. The first patient will receive a dose of 0.5 µg/kg of DEX. The dose will be then adjusted in 0.1 µg/kg increments for the following patients dependent on the success of the previous patients block. If a patient experiences tourniquet pain prior to 50 minutes after inflation of the distal tourniquet the next patient will receive a higher dose, if he does not experience pain prior to 50 minutes after inflation of the distal tourniquet the dose for the following patient will be decreased.
Recruitment will continue until 6 independent crossovers are observed with a minimum of 20 patients. The mean and the standard deviation of the ED50 of DEX will be calculated using the modified up-down method.
This study will help determine the ED50 of DEX used as an adjuvant in IVRA. Based on the potency ratios of Clonidine vs. DEX, the investigators hypothesize that the dose of DEX needed to achieve 50 minutes of pain free tourniquet time will be closer to 0.125 µg/kg rather than 0.5 µg/kg, a 75% reduction in the dose studied.
Inclusion Criteria:
• Patients 18 to 70 years of age, ASA physical status I-II, undergoing unilateral hand or forearm surgery (that require 30 minutes or more) under IVRA.
Exclusion Criteria:
•Patients with Raynaud's disease, sickle cell anemia, heart block, allergy to any of the anesthetic drugs used, patients on α-adrenergic agonists, ASA III or IV, emergency surgery and pregnant patients., Weight greater than 100Kg.