ONSET OF ACTION OF MIVACURIUM CHLORIDE - A COMPARISON OF NEUROMUSCULAR BLOCKADE MONITORING AT THE ADDUCTOR POLLICIS AND THE ORBICULARIS OCULI

Background: The optimal site for monitoring neuromuscular blockade for intubations facilitated with mivacurium chloride has not been establi shed. The primary purpose of this evaluation was to determine the diff erence in onset of neuromuscular blockade between the orbicularis ocul i and adductor pollicis in patients administered mivacurium chloride. We also evaluated intubating conditions when intubation was timed to m aximal neuromuscular blockade at either the orbicularis oculi or the a dductor pollicis. The results for patients administered mivacurium chl oride were compared with those for a control group administered succin ylcholine. Methods: In a double-blind randomized design, the time to l oss of the compound muscle action potential at the orbicularis oculi a nd adductor pollicis was monitored in 20 patients administered mivacur ium chloride and ten patients administered succinylcholine. After admi nistration of mivacurium chloride (0.15 mg.kg(-1)), ten patients under went tracheal intubation at maximal depression of the orbicularis ocul i (group 2) and ten patients at maximal depression of the adductor pol licis (group 3). In an additional ten patients the trachea was intubat ed 60 s after administration of succinylcholine (1 mg.kg(-1)) (group 1 , control). Intubation and evaluation of conditions was performed by o ne investigator blinded to patient treatments. Results: Loss of compou nd muscle action potential at the orbicularis oculi and adductor polli cis was more rapid in group 1, and intubation was completed at 86 +/- 26 s. In the patients administered mivacurium chloride, the orbiculari s oculi compound muscle action potential was lost 3 min earlier than t he adductor pollicis compound muscle action potential. Subsequently, i ntubation was completed at 134 +/- 50 s in the orbicularis oculi group , whereas the time to intubation was 321 +/- 57 s in the adductor poll icis group. There was no significant differences in intubation conditi ons between the mivacurium chloride groups. Conclusions: When monitori ng 95% twitch height depression of the orbicularis oculi muscle, intub ation can be accomplished in approximately 2 min after administration of mivacurium chloride (0.15 mg.kg(-1)). Because intubating conditions were comparable to the patients administered succinylcholine or intub ated during monitoring of the twitch height depression of the adductor pollicis, we believe that optimal site for monitoring during intubati on using mivacurium chloride is the orbicularis oculi muscle.