Background:
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) we
hypothesize that a lower DEX dose would provide patients with adequate
anesthesia.
Aim: 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.
Methods: 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 patients 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.
Analysis: 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.
Significance: This study will help us
determine the ED50 of DEX used as an adjuvant in IVRA. Based on the
potency ratios of Clonidine vs. DEX we 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.
All eligible patients like you undergoing minor hand and forearm surgery under IVRA at AUB-MC
Convenient Non random Sampling
Patients 18 years of age or older, ASA physical status I-II, undergoing unilateral hand or forearm surgery under IVRA.
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.