Dexmédétomidine et dexaméthasone ajoutées comme bloc adjuvant du plexus brachial sous-claviculaire dans la chirurgie des membres supérieurs

Brachial plexus blocks are successfully applied for perioperative/postoperative analgesia in upper extremity surgical procedures. These blocks include infraclavicular, supraclavicular, interscalene, and axillary blocks. The reason why infraclavicular block is preferred is that it provides comprehensive anesthesia/analgesia of the upper extremity. While the axillary approach may fail to block the musculocutaneous nerve that causes tourniquet pain, the interscalene and supraclavicular approaches generally fail to provide anesthesia in the distribution of the ulnar nerve. Other advantages include the lower risk of lung and pleural puncture compared to interscalene and supraclavicular blocks and the lower probability of injury to neurovascular structures due to the location of the block, unlike the interscalene approach.

Local anesthetics are used to block conduction in nerve fibers during brachial plexus blocks. Studies have shown that the commonly used bupivacaine and ropivacaine 0.25% concentrations are not recommended for anesthesia. Bupivacaine 0.5% and ropivacaine 0.5% have been shown to be similar in terms of sensory and motor block onset time, total sensory and motor block duration, analgesia duration, anesthesia duration, paresis and paralysis incidence. The minimum dose of bupivacaine 0.5% required for complete sensory block was determined as 14mL, but the onset time of the block performed at this low dose was recorded as a late onset of 40 minutes (30-45 minutes). It was observed that the onset time decreased to as short as 15 minutes (min) after the application of 30mL bupivacaine 0.5%. In order to reduce the amount of local anesthetic used, to avoid local anesthetic toxicity, to shorten the block onset time and to extend the postoperative analgesia period, a different local anesthetic or adjuvants were used together with bupivacaine. Bupivacaine used with lidocaine has been observed to have a faster onset of action. Other adjuvants added to accelerate the onset of block and improve the quality of the block include alpha-2 agonists (clonidine and dexmedetomidine), opioids (fentanyl and tramadol), and steroids (dexamethasone). Dexmedetomidine is an adjuvant that is an alpha-2 adrenergic agonist and has been observed to have a synergistic effect with local anesthetics and to prolong their duration of activity. The addition of dexmedetomidine 50 µg and 75 µg has been associated with a decrease in the time to onset of sensory and motor block, a decrease in postoperative morphine consumption, and an increase in the duration of sensory block, motor block, and the time to first morphine request. Dexmedetomidine 75 µg has been associated with an increased incidence of preoperative and intraoperative hypotension episodes. Dexamethasone, a perineural adjuvant, has been shown in many studies to significantly shorten the onset of sensory and motor block and prolong the duration of analgesia. Perineural dexamethasone is more commonly used intravenously for block. Currently, many studies have compared the effects of various perineural dexamethasone doses, such as 1 mg, 2 mg, 4 mg, 5 mg and 8 mg, on block, but the results remain controversial. Studies have shown that there is no difference in safety and efficacy between 4 and 8 mg perineural dexamethasone. Another study reported that 4 mg perineural dexamethasone constitutes a ceiling dose for prolonging the duration of analgesia when used with local anesthetics for block.